Final Exam Flashcards
(339 cards)
1
Q
Mating system isolation
A
Reduced gene flow between two taxa caused by a change in breeding system.
E.g., changes from outcrossing (pollen to pollen reach)to asexuality (apomixis) or selfing (autogamy) in plants
2
Q
Is mating system isolation an isolating barrier?
A
Not really isolating barriers or components of speciation. It can indirectly promote speciation if there is continued mating system isolation.
3
Q
Behavioural (ethological) isolation
A
All species differences that reduce attraction (will not recognize) – and therefore mating – between heterospecific individuals during the breeding period.
4
Q
Who does behavioural isolation apply to?
A
Animals
5
Q
What is they key feature of behavioural isolation?
A
Involve interaction between traits in different sexes. One sex (usually males) has a signal that stimulates preference in conspecifics but not heterospecifics of the opposite sex.
ex. western and eastern meadowlark males have different songs
6
Q
How to infer the existence of behavioural isolation?
A
If they live in sympatry, breed at the same time, encounter each other in the wild, but rarely or never hybridize.
7
Q
What part of behavioural isolation can you measure experimentally?
A
The strength.
8
Q
What type of experiments for behavioural isolation?
A
No choice (female with single male then conspecific), female-choice (two males), male-choice (two females), or multiple-choice (multiple individuals of opposite sex) experiments. It all depends on typical encounters in the wild.
9
Q
What is difficult in studying behavioural isolation?
A
Easy to demonstrate the isolation, but more difficult to determine the traits involved.
ex. hundred of studies in Drosophila, but traits involved are known for only a handful of cases
10
Q
What traits help in behavioural isolation for Drosophila?
A
Wing vibrations and contact pheromones.
11
Q
What not to assume in behavioural isolation?
A
That differing traits in males of two closely-related species cause behavioural isolation. Females might not differ in their preferences OR traits used in male-male competition may not influence female choice.
12
Q
Behavioural isolation in butterflies.
A
Pieris occidentalis and P. protodice butterflies are sympatric in western US. Male P. occendatlis
have darker forewings. Female P. occidentalis mate with
conspecific males and reject heterospecifics in experiments. Artificial darkening of male P. protodice
wings increased heterospecific matings. Clear evidence that the trait believed was included in behavioural isolation. Similar findings in sulfur butterflies Colias
eurytheme and C. philodice.
13
Q
Behavioural isolation in Darwin’s finches.
A
Work on Geospiza Darwin’s finches byRatcliffe and Grant (1983-1985). Morphology of cactus finch (Geopsiza
scandens) and medium ground finch (G. fortis). Used model presentation experiments to show that males preferentially court conspecific females. Song may also help distinguish between heterospecifics and conspecifics.
14
Q
Behavioural isolation in frogs.
A
Phonotaxis experiments (speakers on either side playing male songs) in tungara frogs (Ryan and Rand 1993). Females always prefer conspecific (own males) calls. Most heterospecific calls do not elicit phonotaxis.
15
Q
What is the relative importance of behavioural isolation compared to other mechanisms?
A
Because it acts early in the life cycle, probably an important current barrier to gene flow.
16
Q
What is the first line of evidence that behavioural isolation is important in initiating speciation?
A
In sympatric Drosophila taxa, behavioural isolation
much stronger than postzygotic isolation. Not as high in allopatric taxa.
17
Q
What is the second line of evidence that behavioural isolation is important in initiating speciation?
A
In Lake Victoria cichlids, females strongly prefer conspecifics in full spectrum light but preference breaks down under monochromatic light (one colour). This is because females can’t tell difference in colour.
18
Q
What suggests that cichlids can mate between species?
A
When there is monochromatic light, there are viable hybrids produced. Also, fewer species in turbid water, where you cannot see, most likely due to fusion of some species.
19
Q
What is the third line of evidence that behavioural isolation is important in initiating speciation?
A
Comparative studies of birds and insects show positive associations between sexual selection and speciation. Higher sexual selection have more species in them, as plummage colour and male colour are traits that can differentiate between species.
20
Q
What are the four evolutionary forces that cause behavioural isolation?
A
- Initial selection on preference
- Initial selection on trait
- Genetic drift
- Non-genetic mechanisms
21
Q
Direct selection on preference
A
Change in preference directly influences female fitness and leads to change in male trait to match preference.
ex. female have a preference for something because of benefical to them, then male develops a trait to match it
22
Q
Indirect selection on preference
A
Change in female preference through genetic correlations with male traits. They are not directly advantageous but can help her or the offspring’s survival. This include siring more offspring by mating with a male with good genes or runaway sexual selection (female “preference” becomes amplified in males).
23
Q
Direct selection on trait
A
Trait makes the bearer more attractive and the female will more likely mate with that individual.
24
Q
What are the traits direct selection can occur on?
A
- Selection from male-male competition
- Selection for species recognition –> adaptation to new environments by natural selection changes traits and preferences in both sexes, and reinforcement will prevent hybrid matings
25
What could genetic drift lead to in behavioural isolation?
Could lead to small, random neutral changes in female preference (ones not related to survival or reproductive advantage) and selection in males to keep up with female preference.
ex. start to prefer another mate
26
Why does genetic drift in behavioural isolation evolve slowly?
Because the changes occur very rarely and are a neutral (do not have an advantage tied to them).
27
What are non-genetic mechanisms in behavioural isolation?
Populations become productively isolated without genetic change through cultural evolution.
28
Cultural evolution
Behaviours that's passed down through learning in critical periods of life near early years. This is not inherited.
ex. dialects and local song preferences in white-crowned sparrows
29
Cultural evolution in brood parasites.
Host recognition in brood parasites. Females lay eggs in nests of other species. Males learn host songs (being raised) and females learn to recognize host songs, so they know where to lay the eggs.
ex. vidua indigobirds show 99% host fidelity (know the host due to vocals in early years)
30
How many genes needs to be involved in behavioural isolation?
Requires changes in more the one gene. At least one for the trait and one for the preference.
31
What did F1 hybrid females show in behavioural isolation? What does this mean?
F1 hybrid females between behaviourally isolated species show no strong preference, which suggests that preference is based on recessive alleles and hybrids show no preference.
32
Is the strength of behavioural isolation the same for ever species?
No, it's asymmetric where it's stronger in one direction of a species cross. One of the species is better in recognising conspecifics and heterospecifics.
33
Mechanical isolation
Inhibition of fertilization between two species due to incompatibility between their reproductive structures that prevents normal copulation (animals) or pollination (plants). Can be structural or tactile differences.
34
Structural isolation
Incompatibility between morphological features. Lock and key mechanism of reproductive parts.
35
What does the tactile isolation apply to?
Animals
36
Tactile isolation
Fertilization impaired because one sex (usually female) detects unusual morphology or inappropriate movement of partner prompting her to terminate copulation or expel sperm.
37
Structural isolation in beetles.
Two species of beetles with overlapping ranges, Carabus maiyasanus and C. iwakianus. Interspecfic mating occurs in the lab but females suffer high mortality or low fertility. Males have differently shaped
copulatory pieces. In mismatched species pair, leads to
low fertilization success, damage to female reproductive organs, or even kills female.
38
When is tactile isolation implied?
When interspecific matings fail to transfer sperm even if no misfit (fit properly) between males and females.
39
Tactile isolation in beetles and butterflies.
Found in Macrodactylus scarab beetles, Drosophila simulans and D. mauritiana, and Erebia nivalis and E. cassioides butterflies. In each example, male but not female structures differ among species. Females prevent or terminate interspecific matings based on abnormal feel of foreign genitalia.
40
Why is mechanical isolation considered rare?
Very hard to study, this is because it occurs at a very small scare involving interactions between male and female reproductive parts. In addition, it can only be studied if behavioural and temporal isolation are incomplete.
41
What could mechanical isolation result from?
Sexual selection acting on "cryptic" male traits.
42
What is the relative importance of mechanical isolation?
In many groups, male genital morphology is the most important trait for diagnosing species. In these species, male genitalia evolve faster than other sexually selected traits. If females can tell the difference between males within a species, can likely easily tell the difference between males between species.
43
How does mechanical isolation evolve (lock n key)?
Could evolve through reinforcement or character
displacement if hybrids are unfit or if interspecific
copulations are maladatpive (as in Carabus beetles).
44
How does mechanical isolation evolve (sexual selection)?
Runaway sexual selection, sensory bias (prefer certain sounds), antagonistic coevolution (males developing certain reproductive parts to force copulations - male ducks have long parts or water striders), and male-male competition to fertilize females.
45
What are the genetics of mechanical isolation?
Sexual selection yielding a gradual evolution of male trait and female preference will help to produce genitalic differences that are polygenic.
46
What did the drosphilia study for mechanical isolation reveal about genetics?
Genetic analysis revealed at least 14 chromosomal regions involved between D. simulans and D. mauritiana.
47
Gametic isolation (postmating prezygotic isolation)
All reproductive barriers acting between pollination and fertilization in plants and between spawning or copulation and fertilization in animals.
48
Noncompetitive gametic isolation
Occurs during single intraspecific pollinations or copulations (one species of pollen or sperm involved in reproductive event).
ex. failure of pollen to germinate on foreign stigma
49
Competitive gametic isolation
Requires simultaneous presence of conspecific and
heterospecific male gametes. It causes isolation that might not be predictable from results of single heterospecific matings. Reproductive barrier apparent only when gametes compete.
ex. heterospecific and conspecific placed on stigma at same time, and view which one grows a pollen tube quicker.
50
What are examples of noncompetitive gametic isolation?
1. Poor transfer or storage of sperm
2. Inviability of gametes in foreign reproductive tract
3. Inability of gametes to effect fertilization due to poor movement or cross-attraction
4. Failure of fertilization when gametes contact each other
5. Foreign ejaculate fails to stimulate oviposition/reduces rate.
NOTE: all heterospecific
51
What are examples of competitive gametic isolation
1. Conspecific sperm precedence
2. Conspecific pollen precedence
52
Poor storage or transfer of sperm example.
Matings between Drosophila simulans females and D. sechellia males results in very few or no sperm transferred. OR poor interspecific sperm storage in
ladybird beetles, which leads to poor success of fertilization.
53
Inviability of gametes in foreign reproductive tract example.
In crickets Allonemobius fasciatus and A. socius, stored sperm is less motile in storage organs of heterospecific females, leads to lower fertilization.
54
Poor movement or cross-attraction of gametes in animals.
In nine species of free-spawning starfish Macrophiothrix, ovarian extracts attract conspecific sperm more strongly than heterospecific sperm, lower liklihood of heterospecific fertilization.
55
Poor movement or cross-attraction of gametes in plants.
In Rhododendrons, pollen tubes from species with short styles often fail to reach ovules of long-styled species (pollen tube not long enough).
56
What is intrinsic gametic incompatibility?
Failure of biochemical recognition mechanisms for fusion of sperm and eggs.
57
Intrinsic gametic incompatibility in animals.
Abalones in genus Haliotis have species-specific sperm and egg surface proteins.
58
Intrinsic gametic incompatibility in plants.
Failure of pollen tubes to penetrate ovules due to recognition.
59
Failure of sperm to stimulate oviposition (egg-laying) example.
In crickets and Drosophila, if the female is fertilized with sperm from wrong species, she might not get the correct stimulation required to ovulate and lay eggs.
60
When does competitive gametic isolation occur?
When females are inseminated or pollinated by both conspecific and heterospecific males. Conspecific ones usually have an advantage.
ex. drosophilia simulans females mated with con have greater offspring then those with hetero. When both mated with con first then hetero, similar to con mating but fewer hetero babies. When hetero first, then con, only produces a great deal of con babies.
61
What is the relative importance of gametic isolation?
Reproductive proteins have been shown to evolve more quickly than other proteins, suggesting selection and species-specific. Safeguard if other isolating measures fail.
ex. male proteins in drosphilia; female proteins in mammals; and male proteins in primates
62
Evolution of gametic isolation via genetic drift.
Could cause divergence in the "preference" of female gametes through random mutations and chance followed by selection on male gametes to match preference.
63
Evolution of gametic isolation via natural selection.
Important in plants by favouring different style lengths, for ecological reasons, that have to be matched by pollen tubes.
64
Evolution of gametic isolation via reinforcement.
Promote the evolution by favouring the poor fitness of hybrids.
65
Evolution of gametic isolation via sexual selection.
Sexual selection on gametes or sexually antagonistic coevolution of male and female gametes resulting from male-male competition.
66
Postzygotic isolation
Reduced viability or sterility of hybrids.
67
What is the conundrum of postzygotic isolation?
Postzygotic isolation is caused through natural selection, so how could natural selection favour the evolution of unfit offspring.
68
What is the conundrum of postzygotic isolation called?
Darwin's dilemma.
69
Extrinsic postzygotic isolation
Deal with matters outside an animal.
70
Intrinsic postzygotic isolation
Deal with the physiological aspect of an animal.
71
Ecological Inviability
Hybrids undergo normal development but suffer decreased viability as they cannot find a suitable
ecological niche.
72
How do Heliconius butterflies exhibit ecological inviability?
Heliconius melpomene and H. cydno both mimic poisonous species that look very different. When they do hybridize, their hybrids are intermediate in colour, causing them to be eaten more often. This means the hybrids have a lower fitness.
73
What does the benthic morph feed on?
Small inverts
74
Where are the benthic morphs found?
In the littoral zone
75
What is the body shape of benthic morphs?
Broad body and broad jaw gape.
76
What does the limnetic morph feed on?
Plantkon
77
Where does the limnetic morph exist?
In open water
78
What is the body shape of a limnetic morph?
Tapered body and narrow jaw gape.
79
How do the threespine stickleback show ecological inviability?
The hybrid of the benthic and limentic morphs is intermediate in it's traits, causing it to poorly adapt to either habitat.
80
Explain ecological inviability in sagebrush species.
Basin, is a lower elevation species, and the mountain species is a higher elevation species. The sagebrush that is a hybrid does poorly in both habitats, but very well in a common garden.
81
What does the hybrid sagebrush doing well in a common garden suggest?
No developmental problems with the hybrid just poorly adapted in the original habitats.
82
Explain ecological inviability in the blackcaps of Sylvia atricapilla.
One population from Germany migrates southwest to Africa, whereas the Austrian population migrates southeast to Africa. The hybrids migrate south instead, ending up directly in the Alps, which isn't favourable; high mountains (many don't survive the journey.
83
Behavioural Sterility
Hybrids undergo normal gametogenesis but suffer
lowered fertility because they cannot obtain mates. Their intermediate courtship behaviour or phenotype makes them unattractive to the other sex.
84
How do wolf spiders show behavioural sterility?
Males of either Schizocosa ocreata and S. rovneri have very different courtship behaviour, but the hybrid males are intermediate in this, so they are rejected by either species of female.
85
How do warblers show behavioural sterility?
Golden-winged (yellow wing) and blue-winged warblers (full yellow, expect wing) hybridise in North America. The F1 hybrids are intermediate in appearance and song leading to reduce reproductive success.
86
Hybrid inviability
Hybrids suffer developmental defects causing full or partial inviability.
87
When does hybrid inviability occur?
At various stages of development like the embryo, or not surviving to adult stage.
88
What sex does hybrid inviability affect?
Both or one of the sexes in certain cases.
89
What does a cross of Drosophilia melangaster females and D. simulans males produce?
Only hybrid daughters are produced as the males die at the larval to pupal transition.
90
What does a cross of Drosophilia melangaster males and D. simulans females produce?
Only hybrid sons are produced as the females die as embryos.
91
Hybrid sterility
Hybrids suffer reduced fertility.
92
Physiological sterility
Hybrids suffer developmental defects in their
reproductive system causing full or partial sterility.
93
Physiological sterility example.
A cross between a female donkey and male horse produces a mule, which survives to adult age, but is sterile.
94
Behavioural sterility
Hybrids suffer a neurological or physiological defect that
renders them fully or partially incapable of courtship.
95
How does behavioural sterility differ from extrinsic behavioural sterility?
Rather than having an intermediate phenotype or behaviour, the hybrid loses one of the phenotypes or it's interfered with to function ill.
96
Behavioural sterility in lovebirds.
In Agapornis roseicollis and A. personata fischeri, the hybrid females respond very slowly to male courtship displays and they are poor at building nests. The females don't cut the proper pieces, don't tuck them in their wings properly (lose them). They also exhibit unnormal incubation behaviour, so eggs never hatch.
97
How did extrinsic postzygotic isolation evolve?
Adaptation to divergent ecological niches drives speciation, but the intermediate hybrids are unfit in either, decreasing their numbers. In addition, additive gene action gives heterozygote alleles to hybrids, leading to them not do well in the parental habitats.
98
How did intrinsic postzygotic isolation evolve?
Hybrids suffer lower fitness regardless of the environment (developmental problems). It's an inherent issue of the hybrid.
99
Darwin's dilemma
How can two populations separated by a “fitness valley”
evolve from a common ancestor without either lineage passing through the valley?
100
Explain: How can two populations separated by a “fitness valley” evolve from a common ancestor without either lineage passing through the valley?
How it is possible for two populations to evolve separately from a common ancestor without experiencing a period of low fitness (the fitness valley). Hybrids create this dilemma as they are usually unfit.
101
Do genes affect intrinsic postzygotic isolation?
Yes, something goes wrong in hybrids for them to become sterile and inviable. It has a genetic basis as it consistently occurs in hybrids, but not in pure species.
102
What are three possible genetic mechanisms for intrinsic postzygotic isolation?
1. Chromosomal rearrangements (polyploidy in plants)
2. Problematic allele combinations (genic)
3. Endosymbionts
103
Chromosomal rearrangement
Type of abnormality that involves a change in the structure of the chromosome, either being a deletion, duplication, inversion, and/or translocation.
104
Do chromosomal rearrangements play a role in speciation?
Some theoretical models suggest that it may play a role in speciation.
105
Chromosomal speciation theory
Differences in the number or structure of chromosomes between two populations can lead to reproductive isolation and eventually speciation (the formation of new species). This can happen because when two populations with different chromosomes try to interbreed, the mismatch in chromosome number or structure may make it difficult for the hybrid offspring to produce viable or fertile offspring.
106
When is the chromosomal speciation theory more common?
When the population size is small or in the face of meiotic drive.
107
How does a small population help the chromosomal speciation theory?
Small populations may allow for fixation of rearrangements, which would otherwise be selected against or disappear in a large population.
108
How does meiotic drive help the chromosomal speciation theory?
One gametic type if over-represented in the gametes formed during meiosis, and hence in the next generation.
109
What is the problem with the inviability of hybrids with chromosomal speciation in animals?
Cannot explain the inviability of F1 hybrids because
it is solely a theory of sterility. The statement points out that while both hybrid inviability and hybrid sterility may show similar patterns (such as the hybrids being unable to function properly), the reasons behind these two issues are different. Chromosomal differences between species can cause sterility because of problems in chromosome pairing during reproduction, but they don't directly explain why the hybrids die before reaching reproductive age (inviability).
110
What is the problem with the sterility of sexes with chromosomal speciation in animals?
Why are male hybrids sterile more often than female ones?
Typically patterns within species show that rearrangements usually cause female infertility.
111
What is the problem with the X chromosome pattern with chromosomal speciation in animals?
It cannot explain one of the most striking patterns that characterize the genetics of postzygotic isolation in animals. This is the fact that the X chromosome has a disproportionaly large effect on hybrid male sterility.
112
What is the problem with the research results of hybrid fitness with chromosomal speciation in animals?
Many studies have showed factors having a large effect on hybrid fitness have been mapped or molecularly characterized. In these studies, there was no obvious link to chromosomal rearrangement.
113
What animals do chromosomal speciation occur more often in?
Mammals
114
What chromosomal speciation type occur in mammals?
Centric fusion, where two chromsomes fuse together at a centromere during meoisis.
115
Why might chromosomal rearrangements cause speciation?
Some cause meiotic problems in hybrids without ever causing problems within species.
116
Why could centric fusion lead to poor hybrids but not within a species?
Members of a species typically having similar chromosomes that divide and rearrange during meiosis, but the formation of a hybrid, puts together different chromosomes that could face fusion problems during meiosis, leading to reducing fertility.
117
Do centric fusions occur often?
Yes, they arise spontaneously at relatively high rates.
118
What is the most common type of rearrangement fixed between closely related mammalian species?
Centric fusion
119
What did the European house mouse show for chromosomal speciation?
The predominant race has 40 chromosomes whereas the other 40 races have a lower chromosome number because of the accumulation of centric fusions. Centric fusions almost create reproductive isolation as hybrids heterozygous for many centric fusions suffer a reduced fertility.
120
How are chromosomal rearrangements in plant speciation?
When plants begin to change their polyploidy levels, they become reproductively isolated from the other groups.
121
What reproductive barriers result from genetic incompatibilities?
Hybrid sterility and inviability result from between locus incompatibilities.
122
What does evidence of Drosophila show for genetic incompatibilities?
Sterility or inviability between different species is caused by incompatibilities between chromosome regions.
123
What model explains the evolution of genic incompatibilites?
The Dobzhansky-Muller Model.
124
How does genes within a population work? Between?
Genes within a population are selected to work together, while genes from other populations might not work together as they have evolved separately.
125
Explain Dobzhansky-Muller Model.
Explains how hybrid incompatibility, leading to sterility or inviability, can arise due to negative epistatic interactions between alleles that evolved independently in different populations.
126
How does the Dobzhansky-Muller Model work? What does it solve?
It solves Darwin's dilemma as two alleles can evolve on their own, without ever mixing to create a hybrid. As the incompatible alleles arise, the two taxa are separated by an adaptive valley, where no genotype is intermediate, meaning future hybrids are most likely in viable or sterile.
127
Explain the model of genic incompatibilities.
- two allopatric populations are diverging over time
- substitutions of lower case alleles to upper case alleles occur
- newer alleles are possibly not compatible with ancestral alleles as they have evolved in different environments, not inherited together
- incompatibilities are asymmetric as they might not affect one population as much on the other depending on their genotype
- as the populations continue to evolve, more genes from hybrid inviability and sterility evolve leading to complex incompatibilities
128
What must occur in genes to cause incompatibilities?
Substitutions at both loci.
129
What is cytoplasmic incompatibility?
Intrinsic isolation (genetic) through cytoplasmically inherited endosymbionts (organisms that live within an organism).
130
What are cytoplasmic incompatibilities most often caused by?
Wolbachia which is a genus of bacteria that affects insects.
131
How does Wolbachia affect reproductive?
When uninfected females are crossed with infected males most or all of the progeny die as embryos, but vice versa they all survive.
132
What sex and infection level would have an advantage with Wolbachia?
Infected females have an advantage because they can produce offspring with any male, infected or not.
133
How does Wolbachia manipulate the host?
They mainpulate the host's reproductive system to encourage the endosymbiont's spread. In this process, Wolbachia causes eggs from infected females to be unable to develop if they are fertilized by sperm from an uninfected male, encouraging the spread of Wolbachia infection through the population.
134
How does Wolbachia solve Darwin's dilemma?
The inviability of hybrids in this case is due to the bacteria’s natural selection (its evolution to spread; better to spread even if it harms hybrid offspring), not because of genetic differences between the species themselves (fit or not).
135
When can Wolbachia cytoplasmic incompatibility reduce gene flow to 50%?
If one of the species is infected and the other is not.
136
When can Wolbachia cytoplasmic incompatibility reduce gene flow to 0%?
When a host is infected with a different variant of Wolbachia.
137
Why is Wolbachia not a common cause of speciation?
It does not explain some of the common patterns of postzygotic isolation like:
- complete hybrid sterility (not genetic differences, manipulation of host's reproductive system)
- sex-limited hybrid inviability of heterogametic sex (why hybrid males are more often sterile); effects both sexes without preference
- postzygotic isolation appears to evolve gradually but endosymbiont-based speciation is instantenous (two populations affected with different strains, no gene flow at all)
138
How does chromosomal speciation solve Darwin's dilemma?
Hybrid sterility might evolve from genetic drift (random changes can cause genetic incompatibilities) in opposition to natural selection.
139
Genic speciation
Reproductive isolation arises due to changes in specific genes rather than chromosomal changes or physical barriers. This is a form of speciation that results from genetic differences at multiple loci (specific locations on the chromosomes).
140
How does genic speciation solve Darwin's dilemma?
Involves epistatic cross-locus interactions unopposed by natural selection. There is no period of low fitness as these genes aren't actively selected for by natural selection rather epistasis creating random gene interactions.
141
What does chromosomal speciation play a large role in?Small?
Large role in plants and small role in animals, more speifically mammals.
142
What is the most widespread cause of postzygotic isolation?
Genetic incompatibilities that evolve over time in different genetic backgrounds. Since those genes haven't been tested, they can cause reduced survival.
143
What is reinforcement?
The enhancement of prezygotic isolation in sympatry by natural selection.
144
What is the only case where natural selection is directly promoting speciation?
Reinforcement
145
Who popularized reinforcement?
Dobzhansky
146
How did Dobzhansky describe reinforcement?
Two taxa will diverge in allopatry and upon secondary contact hybridization yields unfit hybrids. The less fit hybrids means that individuals will start mating within their own taxon for a fitness advantage. Natural selection will favour traits the prevent hybridization, enhancing prezygotic barriers.
147
When does reinforcement occur?
Occurs in taxa that have not yet fully diverged (not yet a good species), so gene flow is still occuring, but hybrids have a reduced fitness.
148
When does reproductive character displacement occur?
In true species with no gene flow when speciation is already complete.
149
Give an example of reproductive character displacement.
Tinkerbirds. The allopatric species have a similar frequency call whereas those in sympatry have completely different songs. This suggests that there is an evolutionary pressure that drives these differences. This is to prevent confusion between mates.
150
What are types of selection experiments for reinforcement?
Destroy-the-hybrid or disruptive selection experiments.
151
Who did the first destroy-the-hybrid experiment?
Koopman (1950).
152
What was the first destroy-the-hybrid experiment about?
Drosophila pseudoobscura and D. persimilis with eye colour mutation for easy sorting. He discarded all progeny from hybrids in each generation.
153
What were the findings of the first destroy-the-hybrid experiment?
50% offspring hybrids in the first generation and less than 5% hybrids in only six generation. This was for Drosophila.
154
What was the destroy-the-hybrid experiment in plants?
Used two strains of maize, Zea mays to examine prezygotic isolation. They scored the frequency of hybrid matings by each individual (more red). Only non-hybrid kernels from individuals with low rates of intercrossing were planted.
155
What were the results of the destroy-the-hybrid experiment in plants?
30-40% decrease in hybrids of the Zea mays in six generations.
156
What do destroy-the-hybrid experiments test?
Reproductive character displacement as you're getting rid of the unfit hybrids and none at all if you're completely getting rid of them, so speciation is complete.
157
Is there publication bias?
Maybe publication bias because of destroy-the-hybrid experiments with people trying to make their experiment match their hypothesis. Negative results might not get their results published that failed to find selection for prezygotic isolation (reinforcement).
158
What does a disruptive selection experiment test?
Does assortative mating evolve when intermediate hybrid phenotypes are selected against?
159
What did the Thoday and Gibson experiment measure?
Selected for bristle number in D. melanogaster.
160
Explain the Thoday and Gibson disruptive selection experiment.
High and low bristle females were allowed to mate freely, separated, and allowed to produce progeny.
161
What was the result of the Thoday and Gibson disruptive selection experiment?
Over 12 generations, high and low bristle females produced almost exclusively high and low bristle progeny. This suggests that they preferred to mate with individuals that matched their bristle count number, thus assortative mating.
162
What was the downfall of Thoday and Gibson disruptive selection experiment? Why is this important?
Couldn't ever be replicated but this is important because selection experiments should fail.
163
Why should selection experiments fail?
Reinforcement requires non-random associations (linkage) between alleles for disruptive character and alleles for assortative mating. However, recombination in hybrids destroys this linkage.
SIMPLE (RE-WORD): In short, selection experiments might fail because the genetic associations needed for reinforcement (e.g., traits favoring reproductive isolation) could be disrupted by recombination in hybrids, making it harder for natural selection to strengthen isolation between populations.
164
When do selection experiments work best?
Loosely connected to reinforcement.
165
When do selection experiments work least?
When closely connected to reinforcement.
166
What do the case studies that provide evidence for reinforcement look at?
They contrast the strength of prezygotic isolation in sympatry vs. allopatry.
167
What was the first case study from nature for evidence of reinforcement (fly)?
It studied Drosophila miranda (Puget Sound, WA) and D. pseudoobscura (Western US).
168
What did the first case study from nature find for evidence of reinforcement (flies)?
Sexual isolation increased in pseudoobscura populations when in sympatric with D. miranda. Mate preferences were stronger when overlap with similar species.
169
What was the second case study from nature for evidence of reinforcement (damselflies)?
Studied Calopteryx damselflies.
170
What did the second case study from nature for evidence of reinforcement find (damselflies)?
Females differed in wing colour in symaptry but not in allopatry. The males in areas of geographic overlap could tell the difference between females than the males in areas without overlap.
171
What was the third case study from nature for evidence of reinforcement (marine populations)?
Studies from Haliotis abalones, echinometra sea urchins, arbacia sea urchins, and mytilus mussels.
172
What did the third case study from nature for evidence of reinforcement (marine populations)?
Gametic isolation in marine organisms is greater in sympatric populations.
173
What was the fourth case study from nature for evidence of reinforcement (frogs)?
Studied behavioral isolation in frogs:
- Gastrophyne olivacea and G.
carolinensis
– Hyla erwingi and H. verreauxi
– H. gratiosa and H. cinerea
174
What did the fourth case study from nature for evidence of reinforcement find (frogs)?
Male calls attract females and females prefer conspecific (own species) calls. Several studies show that male calls differ more in sympatry than allopatry.
175
What was the fifth case study from nature for evidence of reinforcement (fish)?
Behavioural isolation in three-spined sticklebacks. looked at the benthic and limnetic forms.
176
What did the fifth case study from nature for evidence of reinforcement find (fish)?
Benthic females from the lakes that contain both forms of males discriminate against limnetic males; however, benthic females from lakes that do not contain limnetic males, they do not discriminate against them.
177
What was the sixth case study from nature for evidence of reinforcement (birds)?
Behavioral isolation in birds, specifically Darwin's finches: Geospiza fuliginosa and G. difficilis.
178
What did the sixth case study from nature for evidence of reinforcement (birds)?
The males prefer conspecific female models in sympatry but not allopatry.
179
What was the seventh case study from nature for evidence of reinforcement (flycatchers)?
Collared and pied flycatchers
180
What is the difference between populations of male collared and pie flycatchers?
The male flycatchers look very similar in allopatric populations (white chin and grey plummage), but in sympatric populations they look very diffferent: collared has white neck now (collar) and the pied one has brown plumage.
181
What did the seventh case study from nature for evidence of reinforcement find (flycatchers)?
When a female given a choice between collared and pie flycatcher males in sympatry, they always picked the conspecific mate. When in allopatry, they mated with both, meaning they couldn't discriminate between their conspecifics or heterospecifies. More times mated with con, but many still chose hetero.
182
What did some studies fail to find for reinforcement?
Failed to find a pattern of greater pre-zygotic isolation in sympatric versus allopatric populations. This means there is not a universal pattern.
183
What was the UWindsor case study from nature for evidence of reinforcement?
Looked at banded wrens and rufous-and-white wrens. More specifically the responses to male song in sympatry and allopatry.
184
What did the UWindsor case study from nature for evidence of reinforcement find?
No difference between responses to male song in sympatry and allopatry in banded wrens and rufous-and-white wrens. This means they always kinda preferred their conspecific even in sympatry and allopatry.
185
What do comparative studies do for reinforcement?
They are larger, more systematic studies that compare the strength of isolation in sympatry versus allopatry in large groups.
186
What do you get to control for comparative studies?
Age of taxa, how closely related they are, etc.
187
What was the comparative study from nature for evidence of reinforcement (flies)?
Had a large dataset of drosophila looking at sympatry versus allopatric populations, their genetic distance, and the strength of prezygotic and postzygotic isolation between many pairs of species.
188
What is genetic distance?
How long differ pairs of taxa had been isolated for, the greater the genetic distance, the more they have been isolated.
189
What did the comparative study from nature for evidence of reinforcement find for allopatric taxa (flies)?
Prezygotic isolation increases with genetic distance in allopatric taxa. These differences just accumulate over time because of separation.
190
What did the comparative study from nature for evidence of reinforcement find for sympatric taxa (flies)?
Prezygotic isolation is higher in sympatric taxa regardless of genetic distance.
191
What did the comparative study from nature for evidence of reinforcement find for postzygotic isolation (flies)?
Postzygotic isolation doesn't differ between sympatric and allopatric populations.
192
What was the second comparative study from nature for evidence of reinforcement (multiple animals)?
Large study by Howard that reviewed studies that tested for enhanced isolation in sympatry.
193
What did the second comparative study look at?
Insects, birds, mammals, amphibians, reptiles, fish, and plants.
194
What were the results of the second comparative study?
69% of the 48 studies showed enhanced isolation in sympatry, suggesting that the concept of reinforcement can be applied broadly.
195
What are the three stages of the theory of reinforcement?
1. Early enthusiam
2. Objections to reinforcement
3. Revival of reinforcement
196
Who began the early enthusiam period of reinforcement?
Ronald Fisher.
197
What was the model during the early enthusiam period of reinforcement?
Population genetic model considering a widely distributed species that adapts over an ecological gradient. A certain set of alleles if favoured at one end of the distribution and another set at the other end.
198
What did Fisher argue during the early enthusiam period of reinforcement?
That selection would favour limited dispersal, and the populations might split into two species.
199
Who also worked during the early enthusiam period of reinforcement?
Wilson and Bossert
200
What did Wilson and Bossert recoginze about reinforcement?
Need to enhance prezygotic isolation for reinforcement to work, so there isn't any fusion of populations.
201
How did Wilson and Bossert test their theories?
Used early computer simulations that showed that low hybrid fitness and low error rates in mate choice often lead to reinforcement.
202
What conditions would lead to fusion?
High hybrid fitness and high error rates in mate choice.
203
What was another study during the early enthusiam period of reinforcement (Sawyer and Hartl)?
A population genetic study that showed that prezygotic isolation increases when hybrids are completely sterile or inviable.
204
What was another study during the early enthusiam period of reinforcement (Sved)?
Quantitative genetic study showed that increase in prezygotic isolation is unproblematic when hybrid fitness is zero.
205
What could be argued about Sawyer and Hartl, and Sved's studies?
Studying character displacement rather than reinforcement because there is no gene flow at all between two populations is hybrid fitness is zero. Speciation process would be complete.
206
When did objections to reinforcement come abiut?
In the 1980s.
207
What was reinforcement considered in the 1980s?
Considered unlikely at best and wishful thinking at worst.
208
What were the objections to reinforcement?
1. Selection-recombination antagonism
2. Race between extinction and reinforcement
3. Swamping effect
4. Reinforcement is self-defeating
5. Pre- versus postzygotic isolation
209
Who studied selection-recombination antagonism?
Fenselstein and Barton & Hewitt.
210
What did Fenselstein show?
That selection builds up associations between mate choice and favourable loci while recombination tears them down. This means that there must be very strong selection required to overcome recombination during hybridization.
211
What did Barton and Hewitt show?
Selection-recombination problem is worse when many genes are involved.
212
What is the idea of the race between extinction and reinforcement?
Taxa that are coming into secondary contact are prone to extinction because the rare population meets the "wrong" type more often and produces unfit hybrids.
213
What did Spencer show about the race between extinction and reinforcement?
Computer simulations showed that extinction often occurs before reinforcement (this is of the less common species).
214
What is the swamping effect?
Selection for reinforcement in the zone of overlap between two species could be swamped by gene flow from allopatric populations.
215
Give an example of the swamping effect.
Chickadee range:
- black-capped in Can
- carolina in southern US
- the sheer magnitude of the range sizes of both populations swamps out the selection in the hybrid zone
216
What does it mean when reinforcement is self-defeating?
The strength of selection for increased prezygotic isolation is proportional to the frequency of hybridization. Any increase in prezygotic isolation automatically reduces the strength of selection for further reinforcement, as you are reducing the amount of unfit hybrids.
217
What isolation occurs an advantage when we increase it?
Prezygotic isolation
218
What isolation occurs an advantage when we decrease it?
Postzygotic isolation (increasing hybrid fitness).
219
How does isolation types relate to objections of reinforcement?
Why not eliminate the cost of hybridation by increasing the fitness of hybrids (known advantages) instead of reinforcement? = If hybrids were fit and able to survive and reproduce, the cost of hybridization would be eliminated, and there would be less selective pressure on populations to evolve mechanisms to avoid hybridization.
220
How did the revival of reinforcement come about?
A new burst of theoretical work triggered by studies showing that enhanced isolation in sympatry is relatively common in nature.
221
What did Liou and Price show for the revival of reinforcement?
Computer simulations showed that reinforcement occurs relatively often if hybrid fitness is low and populations already differ in female preference and male traits.
222
What did Liou and Price study?
The effects of sexual selection.
223
What did Liou and Price find about sexual selection?
That sexual selection boosts reinforcement because two forces drive female preference.
224
What two forces drive female preference?
1. Direct selection on females against hybridization
2. Indirect selection on females as a correlated response to sexual selection on males (produce sons that have an attractive trait and gain reproductive success)
225
What was the lesson from the revival of reinforcement?
Evolutionary theories do not tell us what is and isn't possible. It does this through a set of assumptions, which can be wrong.
226
How can natural selection play a role in speciation?
Through direct or indirect selection for isolating traits.
227
How can drift play a role in speciation?
Through founder events in small population.
228
Direct selection
Individuals with greater reproductive isolation are more fit (something is being favoured), so selection acts directly to increase isolation.
229
What is direct selection important in?
Sympatric speciation (opportunity for individuals to mate with the wrong species as they overlap geographically) and reinforcement.
230
Why is direct selection not ubiquitous?
1. Most speciation seems to occur in allopatry
2. It is almost impossible for selection to act directly on intrinsic postzygotic isolation (genetic mechanisms not driven by direct selection)
3. Many species share several incompatibilities, each of which causes complete hybrid inviability or sterility
---> Such overkill impossible under direct selection (one isolating mechanism only needed)
231
Indirect selection
Isolating barriers evolve as a byproduct of selection for something else that isn't speciation.
232
What is more common: direct or indirect selection?
Indirect just because in many cases selection doesn't normally result in speciation.
233
What are the forms of indirect selection?
1. Primary
2. Secondary
3. Tertiary
234
Primary indirect selection
Selection on a character that ultimately causes reproductive isolation (not caused by the need to reduce hybridization).
235
Example of primary indirect selection.
Natural or sexual selection on plumage colour in birds acting differently in two populations; causes reproductive isolation in secondary contact. Those in small islands, monarch flycatchers have darker plummage, but mainland ones have lighter ones.
236
Secondary indirect selection.
Selection acts on a character and underlying genes have a pleiotropic effect on another character that causes isolation.
237
Example of secondary indirect selection.
Selection on a character that gives rise to an intrinsic compatibility.
238
Tertiary indirect selection
Selection acts on a character and linked genes that hitchhike along with those under selection ultimately cause isolation.
239
Example of tertiary indirect selection.
Hybrid inviability between certain Mimulus (monkeyflower) populations.
240
What are the two mechanisms of speciation by drift?
1. Neutral divergence
2. Genetic drift must overcome selection (peak-shifts)
241
Explain neutral divergence.
Reproductive isolation results from genes whose divergence was strictly or nearly neutral (chance).
242
Explain how genetic drift must overcome selection (peak-shifts).
Reproductive isolation involves a period of maladaptive evolution due to founder effect. Go through valleys of low fitness.
243
When is neutral divergence more likely to occur?
In small populations or during the founder effect.
244
What is more important in speciation: natural selection or drift?
Natural selection.
245
Why is natural selection more important in speciation than drift?
It's very easy to see how isolation could evolve as a byproduct of natural selection. Mate preferences might evolve as correlated responses to selection on morphology or physiology, leading to prezygotic isolation.
ex. beak size from food resources can affect songs and lead to non-recognition of mates
246
How could natural selection lead to hybrid incompatibility?
Natural selection may have selected for certain substitutions in the genome that provide individuals with some sort of advantage. These genetic differences could lead to hybrid incompatibility leading to intrinsic postzygotic isolation.
247
What traits normally evolve by natural selection? What would this lead to?
Phenotypic divergence in ecologically important traits (those that help them survive in their environments). This would lead to extrinsic postzygotic isolation because of intermediate hybrid phenotypes.
ex. three-spined sticklebacks
248
How can sexual selection be important in speciation?
Sexual selection acting in allopatric populations could lead to prezygotic isolation and even postzygotic isolation via behavioural or hybrid sterility.
249
What types of models exist for speciation by selection?
Mathematical theories.
250
What are mathematical theories of speciation by selection?
- Quantitative genetics of sexual selection
– Population genetics of intrinsic postzygotic isolation
– Speciation by selection in allopatry is conceptually straightforward so models are not required
251
What type of speciation by selection has few theoretical models?
Speciation by indirect selection.
252
What types of models exist for speciation by drift?
Neutral models and peak shift models.
253
What do the neutral models for speciation by drift show? By who?
Models by Nei (1976) and Nei et al. (1983) show that neutral evolution can cause reproductive isolation between allopatric populations.
254
What is problematic with the neutral models?
– Reproductive isolation evolves very slowly (waiting for chance in time)
– Even more slowly in large populations
– Fitness schemes are artificial and more realistic schemes would probably lead to even less reproductive isolation
255
What is meant by peak shift models?
Population must travel downhill on an adaptive landscape (in an area of low fitness) – in opposition to natural selection – before travelling up new fitness peak.
256
What are the axis for the peak shift models?
w = fitness
p1/p2 = allele frequencies at two loci
257
What does the separation of the two adapative peaks?
They are reproductively isolated.
258
What do the peak shift models emphasize?
A founder event, where a new population is established by one or a few individuals, which can trigger founder effects, rapid evolution of reproductive isolation due to sudden shift to a new fitness peak.
259
Founder effects.
Rapid evolution of reproductive isolation due to sudden shift to a new fitness peak.
260
What are three peak shift models?
1. Mayr: genetic revolution
2. Carson: founder-flush-crash
3. Templeton: transilience
261
Who came up with the genetic revolution peak shift model?
Mayr
262
Who came up with the founder-flush-crash peak shift model?
Carson
263
Who came up with the transilience peak shift model?
Templeton
264
What did Mayr based the genetic revolution peak shift model off of?
Observations that small isolated populations often appear distinct. This is most common in island populations such as the New Guinea kingfisher Tanysiptera galatea.
265
What was the observations of the Mayr genetic revolution peak shift model?
The phenotypic uniformity over large geographic regions results from gene flow, but divergence in this phenotype results from a break in gene flow.
266
What can strain change in large populations?
Epistasis also places restraint on genetic and phenotypic change in large populations. Change can reduce fitness and be selected against very quickly.
267
How do populations overcome areas of low fitness to develop new phenotypic variations in the Mayr genetic revolution peak shift model?
Population bottleneck coinciding with the founding of a new population.
ex. colonization of an island
268
Explain Mayr genetic revolution peak shift model.
1. High level of genetic variation
2. Founder event (birds blown away to nearby island), so genetic variation drops drastically
3. Genetic variation drops further at beginning due to inbreeding with the small population
4. As the population increases and you mate with more distantly-related individuals, the genetic variation will recover
269
How did the term genetic revolution come about?
When you get this break in gene flow, allele frequencies may shift, which may cause changes at other loci, and so on, producing a genetic chain reaction, or "genetic revolution."
270
What was Carson's flounder-flush-crash peak shift model based on?
His work on Hawaiian Drosophila suggesting that many species originated from founder events (older islands colonized new islands with different gene pools).
271
How many phases in Carson's flounder-flush-crash peak shift model?
Three
272
What is the first phase in Carson's flounder-flush-crash peak shift model?
Founder event, often a single inseminated foundress (a female that has a fertilized embryo).
273
What is the second phase in Carson's flounder-flush-crash peak shift model?
Flush phase with a rapid increase in population due to low intraspecific competition (single species); many new mutations appear, and selection is relaxed due to low competition.
274
What is the third phase in Carson's flounder-flush-crash peak shift model?
Crash in population due to increased intraspecific competition and population exceeding carrying capacity.
275
Explain Templeton's transilience peak shift model.
Genetic transilience occurs when a founder event
triggers a rapid adaptive shift in a previously stable genetic system due to fixation at some loci and a rapid increase in inbreeding levels.
276
What does inbreeding do in Templeton's transilience peak shift model?
It increases homozygosity, which allows some alleles too experience novel selection pressures (those like recessive ones). This triggers epistatic changes at other loci because of a change in genetic background.
277
How does Templeton's transilience differ from Mayr's genetic revolution peak shift model?
Because changes concentrated at few loci rather than whole genome.
278
When will Templeton's transilience model occur in Drosophila?
– Many offspring per parent
– Overlapping generations
– Assortative mating
– Many chromosomes
– Few crossover suppressors
279
What is the problem with the peak shift models in terms of the founder effect?
- Founder effect theories are not necessary: adaptive
radiation can explain most patterns attributed to
genetic drift (because environments are most likely different that will have extreme selective pressures)
- No clear evidence that speciation requires small
populations
- Although founder events can cause the loss of rare
alleles, those that do make it into the population
begin at intermediate frequencies
280
What is the problem with the peak shift models in terms of chance?
Chance of peak shifts is very small and should yield
only trivial reproductive isolation:
– In adaptive landscape, the shallower the valley, the greater the chance of peak shift
– But the deeper the valley, the greater the reproductive
isolation (harder to cross): THEREFORE,
Peak shifts can only occur if genetic variation is large enough that it spills into the valleys, but if it is too large.
281
What is the problem with the peak shift models in terms of the founder-flush-crash?
The repeated occurrence of founder-flush-crash cycles is questionable:
– Populations approaching carrying capacity usually
stabilize, not crash
282
How did the new peak shift model fix criticisms?
Gavrilets and Haistings (1996) model proposes that
evolution might move along a ridge of intermediate
phenotypes with fairly high fitness (won't have to move through the worst genotype; not too shallow or deep).
283
What do all the theoretical peak shift models of speciation by drift suggest?
That speciation by drift is possible but not very likely.
284
What do most laboratory evidence for speciation by selection involve?
Subjecting replicate lines to divergent selection (e.g., positive and negative geotaxis). This is indirect selection.
285
What would the laboratory evidence for speciation by selection lead to?
Prezygotic isolation would evolve.
286
What did Dodd study for laboratory evidence for speciation by selection?
Studied eight lines of Drosophila pseudoobscura derived from a single natural population.
287
What did Dodd do for laboratory evidence for speciation by selection?
Out of the Drosophila pseudoobscura lines, half the lines reared on stressful starch medium and half on stressful maltose medium (not preffered food source for either, but could create high selective pressure).
288
What were the results of Dodd's laboratory evidence for speciation by selection?
After one year, sexual isolation evolved between all lines
reared on different media, but not those reared on the
same medium.
289
What did Dodd's laboratory evidence for speciation by selection conclude?
1. Showed that reproductive isolation evolved as a byproduct of selection, not by drift
2. Showed that adaptation to different environments
yields more reproductive isolation than adaptation
to similar environments
290
What species are studied for laboratory evidence for speciation by drift?
Drosophilia
291
What were the results of laboratory evidence for speciation by drift?
Sporadic, weak, and transient effects on drift on reproductive isolation. NOT STRONG EVIDENCE.
292
What was one example of laboratory evidence for speciation by drift?
Looked at studies for assortative mating across number of lines of Drosophilia and created an assortaive mating index.
293
What was the results of the study for laboratory evidence for speciation by drift?
Most generally assortative mating index was 0, so effects were random, and that genetic drift did not seem to increase or decrease speciation in a lab setting.
294
What is evidence from nature for speciation by drift through chromosomes?
Chromosomal rearrangements may have been facilitated by genetic drift in small founding populations, but there has been no evidence so far in animals besides mammals or plants.
295
How to use molecular data from nature to study speciation by drift?
Can look at levels of genetic polymorphisms in species that allegedly arose by founder effects.
296
What would you assume for molecular data from nature to show to support speciation by drift?
The island population created by the founder event would most likely show lower genetic variation.
297
What are the observations of molecular data from nature for speciation by drift?
Most studies show similar or higher genetic variation in those populations, usually island ones, that are formed by a founder event.
298
What do Hawaiian Drosphilia show in molecular data from nature for speciation by drift?
Generally highly variable genetic variation despite the numerous colonization events.
299
What do Darwin's finches show in molecular data from nature for speciation by drift?
Extensive variation at the MHC complex, which suggests at least 30 founders colonized the islands rather than a single founder event.
300
What do levels of pre- and postzygotic isolation in Drosophila correlate with?
More closely with coding regions than silent DNA divergence.
301
What does the coding regions of Drosophilia suggest?
Selection is more important because the coding regions are those that are under selection having more differences than neutral areas (under drift).
302
What does the genes show a strong positive selection in Drosophila and free-spawning marine organisms?
Reproductive isolation.
303
What does comparative studies show for speciation by drift or selection?
1. Studies showing an association between plant-feeding
(phytophagy) and species richness in insects
2. Many studies showing an association between sexually selected traits and species richness in birds and insects
THIS IMPLICATES SELECTION IN SPECIATION.
304
What is a case study for a plant for speciation by natural selection?
Pollinator isolation in Mimulus monkeyflowers.
305
What did the monkeyflower case study show?
Isolation caused by adaptation to different types of pollinators with different floral and nectar trait
preferences, thus displaying speciation by natural selection (was done to increase foraging efficiency and pollination widespread by lead to reproductive isolation).
pink, landing strip, and short corolla = bee
red, long corolla = hummingbirds
306
What is a case study for a fish for speciation by natural selection?
Different morphs of the threespine stickleback
307
What did the three-spine stickleback case study show?
Isolation caused by morphological adaptations to different parts of the lake and female preference for those traits, thus displaying speciation by natural selection.
308
What is a case study for an insect for speciation by natural selection?
Heliconius butterflies
309
What did the Heliconius butterflies case study show?
Isolation caused by selection for aposematic colouration (warning) used in predator deterrence with female preference for conspecific colouration, thus displaying speciation by natural selection.
310
What are the two case studies for speciation by drift?
1. Chromosomal speciation in plants and mice
2. Coiling direction in snails (coiling in same direction allows mating; a mutation in a small population immediately creates reproductive isolation)
311
What are key factors that affect speciation rates?
1. Properties of organisms that facilitate speciation
2. Properties of organisms that prevent extinction
3. Properties of organisms that open new adaptive zones
4. Species-level traits that affect speciation or extinction rates
312
What is a test for speciation rates?
Comparative analysis
313
What do comparative analyse test?
Diversification rates (speciation - extinction).
314
What do comparative analyses compare?
Species richness of sister clades whose ancestors differ in the presence or state of a potential key factor.
315
What is the age of sister clades?
Same age as they descended from a common ancestor.
316
What are single comparisons?
Groups containing many more species than their sister groups.
ex. angiosperms (250,000 species) vs sister group containing conifers, Gnetales, ginkgos, and cyads (770 species)
317
What is the problem with single comparisons?
1. Difficult to know which feature
affects speciation rate; multiple
differences between clades
2. Clades chosen for analysis are
likely non-random since biologists
may pay more attention to species-
rich clades due to size
3. Use of null models in analyses
may underrepresent real degree of
asymmetry between clades
4. Lack of replication due to single
clade
318
What is an important pollinator isolation factor for speciation process in angiosperms?
Evolution of flowers and closed carpals.
319
What are multiple comparisons?
Comparing many evolutionarily independent pairs of sister taxa differing in trait of interest
320
What must multiple comparisons contain?
Clades can be at any taxonomic level (families,genera, species, etc) as long as each group is monophyletic (common ancestor) and clades are true sister groups
321
How do we distinguish speciation from extinction?
Examine traits where effect on speciation and extinction are likely to be in the same direction.
322
What may sexual selection increase?
1. Behavioural isolation
2. Extinction if male traits reduce survival or females become too choosy
323
What did the mutiple comparison study show for diversification rates?
A significant association with diversification rates from 23 features including individual traits (nectar spurs in plants) to species traits (range size and
degree of fragmentation in birds).
324
What were strong patterns of sexual selection (important in driving diversification)?
1. Polyandry in insects
2. Longer testes in hoverflies
3. Promiscuity in birds
4. Sexual dichromatism in passerine birds
5. Feather ornaments in birds
325
How may sexual selection increase extinction rates?
1. Extreme polygamy or polygyny could reduce effective population size
2. Evolution of male traits that reduce viability or increase susceptibility to predators or parasites
326
Where is evidence for sexual selection increasing extinction rates?
Birds
327
If sexual selection is associated with species diversity and extinction, what does this mean for speciation?
This suggests a net positive effect on speciation.
328
What other traits can increase rates of speciation and extinction?
1. Nectar spurs in flowers (animal pollination and speciation rates = specialization of species)
2. Biotic pollination in angiosperms
329
What are examples of traits that could increase speciation but decrease extinction rates?
1. Resin canals in plants could accelerate speciation by increasing range size and reduce extinction by repelling herbivores
2. Nondioecious plants could be more speciose because hermaphrodites can colonize with fewer individuals, but this may also reduce extinction rates
330
What is species richness associated with low body mass apparent in?
Insectivores, bats, rodents, and carnivores.
NOTE: small body size may reduce extinction rates
331
How could dispersal increase extinction rates?
Making populations susceptible to stochastic changes.
332
How could dispersal decrease extinction rates?
Allowing isolated populations to escape predation, parasitism, or disease.
333
What did mutiple comparison show about dispersal rates?
Unpredictable but all could increase speciation by abiotic dispersal in herbs, increase dispersal in birds, and range fragmentation in birds.
334
What is the effect of biogeographic region on diversification rates?
1. Temperate-zone clades are less species rich than clades living close to the equator in birds and swallowtail butterflies
2. But extinction rates may be lower in the tropics due to larger populations
335
What studies showed an association between phytophagy (plant-eating by insects) and species richness?
1. Phytophagy in insects (higher species than non-plant eating); co-diversification
2. Angiosperm (higher species) vs conifer feeding by phytophagous beetles
336
Why was there increased speciation in phytophagy studies?
1. Invasion of new adaptive zones
2. Reflect increased availability of allopatric food sources or disruptive
selection for divergent resource use in sympatry
BUT this expansion into new niches can decrease extinction rates
337
What are puzzling findings of multiple comparison?
1. Species richness associated with herbaceous growth (non-woody stems like grasses and stems) forms in angiosperms; maybe shorter generation time
2. Species richness associated with branch length in phylogenies; measure of molecular time
3. Species richness associated with rates of molecular evolution (faster ones like shorter generation times)
338
What did studies find no association between species richness?
– Small body size in birds
– Ecological diversity in tiger beetles
– Parasitism in carnivorous insects
– Body size in several groups of mammals
– The presence of image-forming eyes
– Host specificity in fish ectoparasites
– Self-compatibility in plants
339
What are two key factors that are important in promoting speciation?
1. Traits increasing sexual selection in animals
2. Traits relating to animal pollination in plants
