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Exam 4 Flashcards

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1
Q

What is prezygotic isolating mechanism?

A

Live in the same place, but do not encounter each other

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2
Q

What are the prezygotic mechanism?

A

Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic incompatability

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3
Q

What are the postzygotic mechanism?

A

Zygote mortality
Hybrid inviability
Hybrid infertility

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4
Q

What is reinforcement?

A

The process by which two populations begin to diverge in allopatry but complete the process of species in sympatry when matings between individuals in these populations produce hybrids with reduced fitness

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5
Q

What is postzygotic mechanism?

A

prevent the hybrid zygote from developing into healthy and fertile adults. There are three likely cases that will occur to ensure that the hybrid does not reproduce.

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6
Q

What could happen is secondary contact occurs when two formerly
allopatric populations meet?

A

Three outcomes are possible:
1. No interbreeding occurs
• isolating mechanisms in place – speciation
=completed.
2. Introgression (complete inbreeding)
• no isolating mechanisms in place – populations merge completely
3. Partial interbreeding occurs:
Some isolating mechanisms in place – a
hybrid zone forms (but hybrids are less fit).
reinforcement should occur to “complete”
the process by the evolution of additional prezygotic barriers

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7
Q

Can postzygotic isolation be possible?

A

Yes it reduced viability or fertility of interspecific hybrids

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8
Q

What are some patterns of partial postzygotic isolation?

A

In some species, male hybrid offspring can be
produced, but females cannot.
• In other species, female hybrid offspring can
be produced by males cannot.
• Haldane summarized this pattern due to the
mode of sex determination: If among hybrid offspring “one sex is absent, rare, or sterile, that sex is the [heterogametic] one

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9
Q

What are the sympatric speciation mechanism?

A

Host shifts
Polyploid speciation

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10
Q

What is speciation without physical isolation?

A

Sympatric speciation

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11
Q

Why is sympatric speciation difficult to understand?

A

because gene flow should be higher under such conditions compared to, for
instance, geographically isolated species or across a geographic cline.

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12
Q

What is an example of sympatric speciation? (Host shift)

A

Parasitic apple maggot flies would inject eggs in hawthorn tree (fruit) but have shifted to apples in the past 150 years.

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13
Q

What are consequences of host shift? (Using apple maggot flies)

A

Reproductive isolation resulting from host specificity:
Flies emerging from hawthorn fruits are attracted to hawthorn
during mating. Those emerging from apples are attracted to apples
Reproductive isolation resulting from “allochronic” mating periods:
Apples ripen 3-4 weeks earlier than hawthorns.
Selection favors incompatible genotypes in the two races:
- Hawthorn fly larvae must develop rapidly so that they can pupate and reach diapause before the onset of winter.
- Apple fly larvae must sustain a longer diapause period before
emerging in the spring.
- This leads to different optimal developmental processes

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14
Q

What are the two types of reproduction?

A

Asexual and sexual

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15
Q

What are the three common components of sex?

A

–Crossing over (recombination)
–Independent orientation and Reduction division (meiosis)
–Fusion of gametes (syngamy)

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16
Q

Did sex evolve to facilitate reproduction?

A

No

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17
Q

What does sexual reproduction increase?

A

Genetic variation by:
1. Recombination that produces new chromosomes variant
2. Haploid gametes are produced by meiosis
3. Gametes fuse, and diploid is restored in zygote.

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18
Q

What is cost of sex?

A

Twofold cost of sex: it takes two individuals to produce the same number of progenyin sexual reproduction as opposed to asexual reproduction.

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19
Q

Cost of sex also impact what part of reproduction?

A

Meiosis: twofold cost of meiosis
Asexuality is twice eas efficient at transmitting genes and should be strongly favored by selection. Sexual only transmits 50% of their alleles to their offspring.

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20
Q

Cost of sex: whats another point of meiosis?

A

Meiosis is more complicated than mitosis
– Requires more energy (more stages)
– More error-prone

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21
Q

Cost of sex: what does sit say about mating?

A

Sex incurs the difficulties of finding a mate
– Asexual organisms don’t have to find a mate
– For sexual individuals, finding a mate is costly
(encounter, energy, predation, mate recognition)

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22
Q

Cost of sex: what about gene complexes?

A

Sex splits up gene complexes
- In asexual lineages, linked groups of coadapted
gene complexes remain linked within the genome
- With sex, linked groups of gene complexes can be
split apart

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23
Q

Cost of sex: what about fitness variation?

A

Sex can generate fitness-reducing variation
-In a diploid sexual lineage, 50% of the offspring produced
by a pair of heterozygotes will be homozygous
(and hence, less fit)

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24
Q

Cost of sex: another downside to sex? (Think bacteria/virus)

A

Sex can lead to sexually transmitted diseases

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25
How common is sex?
42,000 vertebrate species described: 0.01% asexual (22 species of fish, 23 amphibians, 29 reptiles, NO ASEXUAL birds or mammals. Almost no taxa composed of entirely species that reproduce asexually. On a phylogeny, asexual species are rare and short lived
26
Why is sex so common?
Theory for evolution of sex 1. Long-term advantages - Fisher-Muller Hypothesis - Muller’s Ratchet 2. Short-term advantages - Lottery model - Red Queen hypothesis
27
What is the fisher-mullee hypothesis?
Response to natural selection is proportional to existing variation • Sexual reproduction produces more variation than asexual reproduction Therefore, sexual populations can evolve faster if and when selection pressures change
28
What is fisher Muller model?
Muller’s example: Fisher-Muller Model - Population with 2 loci: a and b - All individuals start with genotype ‘ab’ but AB is more fit - Favorable mutations: a → A b → B Asexual: takes twice as long to mutate twice Sexual: gets to population quickly by mating
29
What are the conditions in which fisher-mullee hypothesis doesn't work?
Small population size or low mutation rate – Either A or B will spread through the population to fixation before the other allele mutates – Therefore populations will result in either aB or Ab (depending on which mutated first) - The chances of mutating to AB are then the same as for asexual populations
30
What is Muller's ratchet?
Purging deleterious alleles through sex In an asexual population: • Mildly deleterious mutations accumulate over time. • The more mutations in an individual, the less fit it is. • If there is only a small number of individuals with no mutations, there is a good chance these individuals might not reproduce because of chance (drift). Long-term Advantages of Sex This results in everyone in the population having at least one mutation. The “Ratchet” has clicked! Mean fitness has decreased
31
How does sex reverse Muller's ratchet?
Recombination gets rid of deleterious alleles through sex. Thus, in a sexual population: • Two individuals with mutations could mate to produce offspring with NO mutations • Each generation, new mutation-free individuals would be produced • Therefore the ratchet cannot operate
32
What are some cons to Muller's ratchet theory?
It seems to act too slowly to prevent asexual populations from out-competing sexual rivals before themselves going extinct. - It would require greater mutation rates than are generally observed, and/or that mutations have a synergistic effect. That is, the deleterious effects of a pair of mutations would have to be multiplicative, rather than additive.
33
What are the short term advantages of sex?
Lottery model Red queen hypothesis
34
What is the lottery model of evolution of sex?
If the environment is patchy (i.e. heterogeneous) then different genotypes do well in different patches - By producing genetically diverse offspring, the chances are better that at least some offspring will match some patches (assuming offspring disperse) - Sibling competition: If two siblings are identical they compete for identical resources. This is less likely to happen if offspring are diverse. Lottery: Better to buy 100 different numbers than 100 of the same numbers than 100 of the same number.
35
Can species switch between asexual and sexual reproduction?
Yes, Many species have the capacity to switch between sex and asex. In such species, sex usually occurs as a response to a change in the environment.
36
Why is asexual most common in harsh environment? (Deserts and alpine regions)
Less energy required , don't have to worry about a mate
37
What kind of reproduction is factored by abiotic features?
Asexual reproduction because they can track changes
38
Biotic features favors which type of reproduction?
Sexual reproduction When one species adapts to its competitors, etc., the environment for the competitors changes, thus imposing new selection pressures on the competitors. This in turn changes the environment for the first species, imposing new selection pressures on it.
39
What type of organism play importance in Red-Queen hypothesis? (Pro sexual reproduction)
Parasites pose one of the most important selective forces Why? - Parasite loads are costly - Most parasites are host specific - high degree of coevolution - Parasites have very short generation times in relation to host; this allows them to evolve more quickly than the host Therefore, one way to escape parasitism is to make offspring as different from parents as possible
40
What is polygyny? Ex of animal
1 males + more than 1 female Elephant seal
41
What is polyandry?
1 female with more than one male
42
What is polygynandry? Ex of animal
More than one male more than one female Frogs or sea urchins
43
What are the polygamous mating system?
A polygyny or polygynandry Defined as a mating system in which either males or female have more than one mate during a given breeding season or cycle.
44
What is anisogamy?
Asymmetrical gamete investment. Females produce larger but fewer gametes (eggs) • invest lots of energy per gamete (15% bird body mass) – Males produce more small, mobile gametes (sperm) • invest little energy per gamete (8 billion in bird testes)
45
Why use the two strategies of anisogamy?
Maximize either fertilization or developmental ability
46
How does anisogamy impact parental investment?
When there is 1) Anisogamy, leads to: – 2) differences in parental investment • Females generally expend more time and energy – Gestation and lactation in mammals
47
Anisogamy+ difference in parental investment leads to what?
Differences in potential reproductive rate • Males can fertilize eggs at faster rate than females can produce them (Male RS limited by access to females) • Female RS limited by resources (egg production, time, food, etc.)
48
What's the difference of reproduction rate in males vs females?
Variance in reproductive success is much higher in males than in females
49
Why are females generally the choosier sex?
When there is 1) Anisogamy, 2) differences in parental investment, 3) differences in potential reproductive rate, leads to: – 4) Differences in operational sex ratio – Ratio of sexually receptive males to receptive females (usually male-biased) – Females generally are limiting resource – Typically: Males compete for access to females, females are choos
50
What is sexual selection? How does it relate to natural selection?
Differential reproduction due to competition over access to mates (SS is a subset of natural selection)
51
What are the types of sexual selection?
Intrasexual selection and intersexual selection
52
What is intersexual selection?
–Members of one sex choose the other (advertising competition) »Usually female choice
53
What is intrasexual selection?
–Members of one sex compete for access to the other sex (contest competition) »Usually male-male contests
54
Intersexual selection: how do they choose?
Assessment through signals » Visual (e.g., bowerbirds) » Acoustic (e.g., frogs) » Chemical (e.g., moths)
55
Why be choosy for intersexual selection?
Direct benefits = non-genetic resources from mate • Examples of direct benefits – 1) Food provisioning for offspring – 2) Protection of female/offspring from predators – 3) Territory use – 4) Nuptial gifts given at mating –5) Avoid males with parasites/STDs
56
Why do females choose?
In many cases, males do not provide females with direct resources such as food and shelter or assisting in parental care.
57
What if the indirect benefits of females choosing?
Fisher's "runaway selection" Once a female preference for an arbitrary trait evolves, a positive feedback loop leads to a “runaway” process:
58
How do you demonstrate Fisherman process?
one must show: a) genetic variation for both male trait and female preference b) genes for trait and preference covary (they are linked) c) the male trait does not affect male viability thus, demonstration of runaway requires a negative result!
59
What another indirect benefits of females choosing?
Good genes for viable offspring: Zahavis "handicap" model
60
What is good genes theory?
If they can signal their parasite-free state, males should've more desirable (Ham and Zuk)
61
What is sensory bias for intersexual selection?
Females prefer certain male traits because they “exploit” some benefit outside of mate choice • Evolution of preference should predate the appearance of the evolution of the trait • Lots of fun examples: tungara frog “chucks”, swordtail “swords” and, my favorite, the “net stance behavior of water mites.
62
What are the models for intrasexual selection?
Pre-copulatory and mate guarding/sperm competition
63
What does pre-copulatory mean? Ex animal?
"“King of the Hill” (usually male-male competition) – Intimidate or attack rivals so that only you get to mate with females Elephant seals
64
Pre-copulatory why how? What type of behavior?
Competition over resources – Agonistic behavior: contests involving threats – Dominance hierarchies: rankings within a group – Territoriality: defense of particular area • Aggression (elephant seals, etc) • Scent-marking (cheetahs) • Visual/Vocal displays (songbirds)
65
Pre-copulatory give an animal what?
Badge of status • Signal dominance between competitors • Cost of fighting can be experienced by both individuals (not just by loser) • Thus, if one individual is likely to win, then it is beneficial for both to signal and avoid a fight.
66
What is sperm competition? (Postcopulatory)
Sperm competition: competition between the sperm from two or more males to fertilize the eggs of a single female during one reproductive cycle
67
What does sperm competition require?
1) Temporal uncoupling between copulation & fertilization (delayed fertilization, with or without sperm storage) (2) Females must mate with multiple males
68
What is speciation without physical isolation?
Sympatric speciation
69
Why is sympatric speciation hardest to understand?
Gene flow should be higher under sympatric conditions compared to geographic cline.
70
What is zygote mortality? Pre or post zygotic?
Result of chromosomal incompatability Post
71
What is hybrid inviability?
When the embryo does develop but the hybrid experiences reduced fitness and often an early death.
72
What is hybrid infertility?
Occurs when a hybrid develops into a mature adult but is unable to undergo successful meiotic division, and is unable to produce offspring (donkey)
73
What is temporal isolation?
Seasonality is just one way you can partition time (Mating only at certain times)
74
What two prezygotic isolating mechanisms allow for species to live in same place but not encounter each other?
Habitat isolation and temporal isolation
75
What is polyploidy?
Polyploidy is the heritable condition of possessing more than two complete sets of chromosomes. Polyploids are common among plants, as well as among certain groups of fish and amphibians.
76
What is the evolutionary species concept?
a species is “a lineage of populations which maintains its identity from other lineages and which has its own evolutionary tendencies and historical fate”
77
What are three tools to to identify species?
- Phenetic Species Concept - Biological Species Concept - Phylogenetic Species Concept
78
What is phenetic (morphological) species concept?
Commonly used in classification of plants and microorganisms. Paleontologists (only have fossils), often use this method when analyzing their data.
79
What's a disadvantage of morphological (phenetic ) species concept?
Even morphologically different individuals may well be members of the same species • Sex differences • Polymorphism within populations • Variation among populations
80
What's another disadvantage of morphological species concept?
morphologically similar individuals may be reproductively isolated • Cryptic species – Many species may look identical to you and I, but will not interbreed.
81
What is biological species concept?
A species comprises actually or potentially interbreeding natural populations that are reproductively isolated from other such groups
82
What's the most important criterion for biological species concept?
reproductive isolation - By definition, “good species” cannot successfully hybridize: there is no gene flow between species
83
What are problems with biological species concept?
The BSC is not based on attributes of individuals but delineates species based on properties possessed by populations Often very difficult to apply since many sister species are geographically isolated (are they also reproductively isolated??) - Cannot be tested in fossil specimens - Does not apply to asexual, parthenogenic and selfing populations - Difficult to apply in definitions of plant species, as so many can hybridize - Occasional hybridization events can occur between individuals in populations that are, for all practical purposes, reproductively isolated
84
What is phylogenetic species concept?
A species is a monophyletic group composed of the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent - Species reflect independent evolutionary units - Requires an understanding of phylogenetic relationships - Species can be determined statistically based on differences in diagnostic traits
85
What is the most import criterion for phylogenetic species concept?
Monophyletic Group: A taxon that contains all known descendents of a single common ancestor Relies on shared derived traits of monophyletic groups
86
What are the problems with phylogenetic species concept?
Few “good” phylogenies exist - Are seemingly trivial diagnostic traits (e.g. single base-pair substitutions) biologically meaningful? - If PSC is applied, the number of extant species described would more than double
87
What are the two reproductive isolating mechanisms that defines a species?
Prezygotic isolation and postzygotic isolation
88
What are the three stages in speciation?
1. Geographic isolation of populations (usually) 2. Divergence between populations (certainly) 3. Reproductive isolation of populations (certainly)
89
Genetic drift increases or decrease variation within a population? Between populations?
Within: decrease Between: increases
90
Migration increases or decrease variation within population? Between population?
Within: increases Between: decreases
91
Natural selection increases or decreases variation within population? Between populations?
Within: decrease Between: increase if condition differ Decrease if conditions are the same
92
Mutation increase or decrease variation within pop? Between pop?
Increase both
93
What are the major ecological speciation models?
Allopatric ( dumbel/vicariance and peripheral/peripatric), parapatric, and sympatric
94
What happens in vicariance allopatric speciation?
splitting of a population into two or more isolated ranges and reduction (or prevention) of gene flow between them
95
What happens in peripatric allopatric speciation?
Colonization of a disjunct space such that gene flow is interrupted
96
What is a cline?
A cline is the gradual change in the phenotypes and genotypes of a species across a geographical gradient.
97
What happens in parapatric speciation?
Unlike Allopatric models – no geographic barrier exists! • Key idea: a cline in selective conditions generates a cline in phenotypes or genotypes
98
What is sympatric speciation?
Speciation without physical isolation.

evolution (3 decks)

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