Evo. Biology Chapter 14: Species and Speciation

who developed the evolutionary species concept?

george gaylord simpson and E.O. wiley

what does the evolutionary species concept define a species as?

a group of organisms that forms a lineage that has distinct evolutionary fate from other lineages

what does the phenetic species concept define a species as?

a group of phenotypically similar individuals or populations

which speciation concept was used historically by numerical taxonomists?

phenetic species concept

what are numerical taxonomists?

scientists that use statistical analyses of multiple traits to classify organisms; examine large data sets and use algorithms to delineate species boundaries

within the phenetic species concept, are all characters considered equal?

no, they are now weighed

who developed the biological species concept?

ernst mayr

what does the biological species concept define a species as?

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

is the concept of gene flow important in the biological species concept? why?

yes, it delineates species by properties possessed by populations

what are the two major problems with the biological species concept?

1. difficult to apply it to extinct species

2. hybridization events occurring between individuals of non-interbreeding populations

how does the biological species concept view asexual species and their clones?

as reproductively isolated from one another

what does the phylogenetic species concept use to distinguish species?

character differences, shared derived characters that are unique to one monophyletic group and absent from all other populations in the phylogeny

what does the phylogenetic species concept define a species as?

the smallest monophyletic group distinguished by a shared derived character

do polymorphic characters within a population form monophyletic clades?

no

what are the two main problems with the phylogenetic species concept?

1. may account for more species than there actually are

2. allows for the possibility of gene flow; two species would be able to fuse back together, doesn’t ensure that unique species remain as such

what is the species boundary agreed upon by all three species concepts?

that most defined species will show large phenotypic differences, and absence of gene flow, and shared derived traits

when do these concepts disagree with one another?

when populations have had time to diverge in characters but not in gene flow

what are the three main models of speciation?

1. allopatric

2. parapatric

3. sympatric

what are the differences between each type of speciation?

allopatric: speciation between populations that are geographically isolated

parapatric: speciation of incipient species without a geographic barrier

sympatric: speciation within same location

what are incipient species?

diverging populations that are on the path to speciation

what three things allow for speciation in the allopatric speciation model?

1. genetic drift

2. mutation

3. natural selection

what are the two submodels of allopatric speciation?

1. dumbbell model

2. peripheral model

describe the differences between the dumbbell model and the peripheral model

dumbbell: large subdivided into large; genetic drift is not a major influence

peripheral: large into one or more smaller; genetic drift is a major influence

what are the two necessary components of parapatric speciation?

1. cline

2. hybrid zone

what is a cline?

a gradient in the frequency of pheno/genotypes

what two models are used to describe hybrdization?

1. ecologically neutral dynamic equilibrium

2. ecologically dependent bounded hybrid superiority

what is the difference between the two models?

ecologically neutral: hybrids are always inferior to nonhybrids

ecologically dependent: in hybrid zones, hybrids may have superior fitness to nonhybrids

what are the two possible candidates that allow for sympatric speciation?

1. resource competition

2. reproductive isolation

what are the two types of reproductive isolating mechanisms?

1. prezygotic

2. postzygotic

who established the reproductive isolating mechanisms?

dobzhansky

how do different pollinators effect speciation/gene flow in plants?

• certain pollinators are suited to different floral tube structures

• minimizes gene flow between species with different tube structures

can a mutation in a single gene result in reproductive isolation?

yes; EX: coils of snail shells

is dextral or sinistral coiling dominant?

dextral; sinistral is recessive

how can changes in ploidy lead to speciation?

when ploidy changes and is viable, there is also often instant reproductive isolation

why are most animal offspring infertile when experiencing changes in ploidy?

because embryos cannot undergo meiosis properly

why are changes in ploidy so commonly seen in plants?

1. minor affects on fitness

2. self-fertilization is common, so no need to find a mate with the same ploidy mutation

what traits is polyploidy in plants often associated with?

increased cell volume, larger pollen grains, seeds, and plant size

has speciation by change in ploidy been seen in animals?

yes

what four types of chromosomal rearrangements may initiate reproductive isolation?

1. fusion

2. fission

3. inversions

4. translocations

what are the two reasons as to why chromosomal rearrangements can cause reproductive isolation?

1. offspring often produces nonfunctional gametes leading to fewer or no offspring

2. reduced rates of genetic recombination cause an increase in linkage disequilibrium; if these traits are involved with mating behaviors, differences may increase

what does haldane’s rule state?

if among hybrid offspring, one sex is absent, rare, or sterile, that it is the heterogametic sex

in mammals and flies, what are the gametes for each sex?

males: XY, hetero

females: XX, homo

in birds and butterflies, what are the gametes for each sex?

males: XX, homo

females: XY, hetero

with haldane’s rule, what creates the basis for reproductive isolation?

decreased fitness of the heterogametic hybrids

what theory explains why the heterogametic sex is at a disadvantage?

the dominance theory

what does the dominance theory state?

for a recessive gene, there is a backup of the gene in the homogametic sex that is not present in the heterogametic sex