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Flashcards in Species Deck (58):

what are the three types of species concept?

1) biological species concept
2) morphological species concept
3) phylogenetic species concept


what is the biological species concept?

Ernst Mayr

there is a TON of variation among members of a species (look at dogs)

species are groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups

much of the intraspecific variation is geographically structured


can species be defined by morphological differences?

biological species concept

species cannot be defined by the degree of morphological difference --> morphology is important but it's not necessarily what differentiates species


what are species?

species are population(s) of variable individuals connected through gene flow

species are systems of populations; the gene exchange between these systems is limited or prevented in nature by a reproduction isolating mechanism or several such mechanisms


what observations led to the biological species concept?

- variation within populations -->genetic differences

- geographic variation between populations --> look different in different regions, but interbreed where populations meet

- sibling ("cryptic") species --> reproductively these are different species but the look alike


what is another name for sibling species? what are they?

cryptic species

reproductively different species, but they look alike


what are limits to the biological species concept?

1) emphasis on sexual reproduction makes it difficult to address organisms whose life history is not defined by that process (e.g. parthenogenic or asexual species)

2) interbreeding is not "all or nothing"
- ex. hybrid zones

3) extinct species


biological species concept and extinct species

there's limits in this concept when it comes to extinct species because if interbreeding is the key, how can we determine the species boundaries of animals about whom we have no data on reproductive habits and capabilities (this is relevant to extinct and extant species)

how can we determine if geographically separated populations can potentially interbreed


how do we know if populations have the potential to interbreed?



what is the morphological species concept?

species are defined on the basis of physical features (morphology)

ex. body size, shape, color


what is the phylogenetic species concept?

The concept of a species as an irreducible group whose members are descended from a common ancestor and who all possess a combination of certain defining, or derived, traits

"an irreducible (basal) cluster of organisms, diagnosably distinct from other such clusters, and within which there is a parental pattern of ancestry and descent"

"the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals"


what is synapomorphy?

shared, derived (homologous) features

a character or trait that is shared by two or more taxonomic groups and is derived through evolution from a common ancestral form.

may be transformed over time with a newly transformed "state" characterizing a less inclusive group

fins --> arms --> wings or flippers


what is monophyly?

groups of species or populations characterized by synapomorphy

a monophyletic group is group of organisms which forms a clade which consists of an ancestral species and all its descendants


what is a clade?

a monophyletic group that consists of a complete lineage: ALL the descendants of a common ancestors

fish --> tetrapods --> birds or mammals


what is a synapomorphies?

shared, derived features that group and differentiate each named species


what is a solenobiella?

a population cluster that is diagnosable by a unique combination of features

all populations of solenobiella share a common ancestor


what is a monophyletic group?

contains an ancestor and all of its descendants


what is a paraphyletic group?

contains an ancestor but only some of its descendants


what's a polyphyletic group?

contains various organisms with no recent common ancestor


how do you interpret a phylogenetic tree/clydogram?

trees specify relationships between terminal groups --> these do not change when the node flips


what are commonalities of all species concepts?

species are populations linked by history

characterized by shared, derived attributes

genetic and morphological continuity maintained by interbreeding


what is speciation?

the mechanisms by which populations attain reproductive isolation


what are isolating mechanisms?

phenomena that prevent gene flow between populations or members of the same population


what are prezygotic barriers?

they prevent mating between populations

may outright prevent or just decrease the frequency or incidence of mating


what is positive assortative mating? what kind of barrier is it?

non-random mating based on genotype or phenotype

like mates with like

prezygotic barrier


what is reproductive isolation?

all these species concept imply

physical barriers between populations are not enough

the physical barriers between populations could interbreed

biologically based reproductive barrier accompany speciation


what is temporal isolation?

incipient/cryptic/sibling species in the same place but they mate at different times of the year or day


effect of temporal isolation on spawners

for spawners this will effectively eliminate opportunity for gene flow if the offset in mating time is greater than gamete competence because gametes won't come into contact


effect of temporal isolation on copulators

for copulators, mate searching or aggregating at specific times of day or year


trout and temporal isolation example

brown trout and rainbow trout live in the same streams but brown trout breed in the fall and rainbow trout breed in the spring


what is habitat isolation?

spending your whole life in a single place or on a single host and so you don't get a chance to meet


examples of habitat isolation

ex. epilachna spend their whole life in a single kind of plant

the european mosquito consists of six morphologically indistinguishable species but they breed in different habitats: brackish water, running fresh water, stagnant water, etc.


lack of interest

may be most critical barrier in animals

when the males don't engage females or when females don't respond to males
- specific mate recognition system
- mating behavior or song
- pheromone responses


what is behavioral isolation? what's another name for it?

ethological isolation

an important evolutionary mechanism that helps members of the same species identify each other as proper mates

morphologically indistiguishable, but don’t reproduce as the don’t recognize the song…perform a duet…


what is a post-mating prezygotic barrier?

mating of gamete transfer occurs but zygotes are not formed


what are types of post-mating prezygotic barriers?

lack of fertilization

gametic isolation


what is lack of fertilization?

post-mating prezygotic barrier

- parts don't fit (no sperm transfer)
- eggs and sperm mechanically incompatible


what is gametic isolation?

important for many marine invertebrates and nearly all plants

egg may not recognize sperm due to incompatible receptors

nuclei may not fuse


what are postzygotic barriers?

fertilization takes place but may not result in a successful offspring

hybrid zygotes are formed but have reduced fitness


what are some examples of postzygotic barriers?

interaction of incompatible genes

disruption of meiosis

different number/structure of chromosomes


what is the outcome of reproductive isolation?



zygote or hybrid mortality if the embryo dies shortly after fertilization

embryo dies shortly after fertilization:
- may not successfully complete development
-embryos of hybrids often fail to undergo metamorphosis successfully


hybrid mortality if hybrid offspring develop but then die

hybrid viability may differ depending on environment

selection against hybrids in both parental habitats

asymmetry in hybrid succes


hybrid sterility

hybrids viable but not fertile:
-asymmetry between crosses --> heterogametic sex most often sterile

aneuploid gametes:
- chromosomes have different genes or morphologies, and so can't segregate properly


what is an example of hybrid sterility?

horse + donkey = mule


what are models of speciation?

speciation is not the purpose but a by-product of other processes and events


what are the three types of models of speciation?

1) allopatry
2) sympatry
3) parapatry


what is allopatry

"different fatherland"
*most important mode of speciation for animals*

non-overlapping distribution by vicariance or by dispersal (peripatry)

one island: island splits and now there's two populations of the same species on two different islands and they mutation

Allopatric speciation is speciation that results when a population is separated by a physical barrier. It is also referred to as geographic speciation

A population is subdivided; during the separation, mutations arise in each subset such that each subset changes from the original in terms of morphology, behavior, etc --> the differences that arise are sufficient to maintain distinctiveness even in the absence of physical barrier


what what is sympatry?

"same fatherland'

overlapping distributions

Sympatric speciation is speciation that occurs without physical separation of members of the population


what is parapatry?

"through fatherland"

geographically contiguous
"isolation by distance"

the relationship between organisms whose ranges do not significantly overlap but are immediately adjacent to each other; they do not occur together except in a narrow contact zone.

two islands: some organisms travel from one island to another --> that's peripatetic


allopatric speciation vs. peripatric speciation

allopatric speciation by vicariance
peripatric speciation by dispersal

allopatric speciation: when the physical barrier is removed or the new species disperses over it, it re-establishes sympatry

peripatric speciation: range expansion re-establishes sympatry


what is vicariance?

the geographical separation of a population, typically by a physical barrier such as a mountain range or river, resulting in a pair of closely related species

allopatry that arises because extrinsic factors act to subdivide population


what is dispersal?

allopatry that arises because a subset of the population disperses to a new, isolated place --> peripatetic speciation or founder effect

subsets differentiate while separated --> small size of founding population spurs change (genetic drift)


what is parapatric speciation?

Speciation that occurs when the groups that evolve to be separate species are geographic neighbors; they are in different areas, but the areas are next to each other and individuals can move between the areas (gene flow)

strong selection to counteract the effect of gene flow, usually strong difference in environment

widespread species undergo local differentiation that leads to isolation --> 2 instances of change independent of one another

physical distance acts are the initial barrier to gene flow: isolation by distance



what are secondary contact zones?

Areas of overlap in range AFTER speciation

Hybrids may form if isolation is incomplete.


what is sympatric speciation?

Speciation without physical or spatial barrier

Subsets each specialize on particular resource within ecosystem --> Niche partitioning and adaptive radiation


what is an example of sympatric speciation?

an entomologist discovers that the apple maggot was Rhagoletis pomonella, an insect normally found on wild hawthorn

a certain set of flies changes their host causing reproductive isolation


what is sympatric speciation in action?

adaptive radiation!

if niches are empty, subsets of a population can specialize to fill new niches

common on islands where "normal" niche inhabitants may be absent