Evolution: Biogeography and Speciation

speciation

evolution of a new species through splitting from an ancestral lineage

extiction

termination of a species

outcomes that could arise if the populations are the same as the existing population

1. decreased likelihood of inbreeding and inheriting a deleterious allele

2. introduction of advantageous alleles 

   • an increase in genetic diversity among the individual

outcomes that could arise if the populations are the different as the existing population

1. could create sterile offspring

2. hybrids

mechanisms of evolution

1. gene flow (limited)

2. mutations

3. genetic drift

4. natural selection

factors that may cause a population to separate

1. geographic or physical barriers (moutains)

2. different courtship behaviors (different mating rituals)

3. different breeding seasons (summer vs winter)

4. different periods of activity (diurnal vs nocturnal)

isolated populations rarely interbreed due to lack of gene flow

yes

limiting gene flow is a prequisiste for speciation

yes

species concepts

1. morphological species concepts

2. biological species concept

3. phylogenetic species concept

morphological species concept

two populations that have distinguishable phenotypic characteristics are classified as different species

limitations of morphological species concept

1. oldest species concept

   1. sorting organisms by their appearance is outdated

2. other things that could phenotypically look like other species but actually are not

   1. genetic polymorphs

   2. phenotypic plasticity

   3. sexual dimorphism

artificial selection

the process by which humans choose individual organisms with certain phenotypic trait values for breeding

biological species concept

defines a species as a member of populations that actually or potentially interbreed in nature and produce fertile offspring that can also reproduce

limitations in biological species concept

1. assumes sexual reproduction

2. should we test hte ability to mate between every pair of species

3. can be impractical/ unethical to test if species breed in captivity

phylogenetic species concept

species are groups of individuals that share a unique common ancestor

allopatric speciation

population is divided into geographically isolated subpopulations

parapatric speciation

part of a population enters a new habitat bordering the range of the original

sympatric speciation

diverging populations live in the same geographic area

vicariance

geographical seperation of a population

dispersal

changing location in space after reaching reproductive maturity, usually involving movement from one habitat to another

requirements for parapatry to occur

1. no geographic barrier to dispersal

2. cline

   • spatial gradient in the frequency of genotypes or phenotypes

3. narrow hybrid zone

ring species

a single species becomes geographically distributed in a circular pattern over a large area

species who are ring species we don’t question parapatry

yes

sympatric speciation

diverging populations live in the same geographic area

pre-zygotic isolation

pre mating isolation that occurs before fertilization

post zygotic isolation

post mating isolation occurs after ferilization

pre zygotic reproductive isolation =

no zygotes are formed

pre mating barriers =

impede transfer of gametes to members of other species

ecological isolation

potential mates do not breed

temporal isolation

species breed at different seasons or times of day

habitat isolation

species mate and breed in different habitats

sexual isolation in animals

individuals prefer mating with their own species

pollinator isolation in plants

pollinators do not transfer pollen between species

post mating barriers =

mating occurs but zygotes are not formed

mechanical isolation

reproductive structures of the sexes are not compatible

copulatory (sex) isolation

female is not stimulated by males of the other species

gametric isolation

failure of fertilization

post zygotic reproductive isolation =

hybrids are formed but have reduced fitness

extrinsic

hybrids have low fitness fro environmental reasons

ecological inviability

hybrids are poorly adapted to both of the parental habitats

behavioral sterility

hybrids are less successful in obtaining mates

intrinsic

low hybrid fitness is independent of enviornmental context

hybrid inviabilty

reduced survival is due to genetic incompatibility

hybrid sterility

reduced production of viable gametes

changes to hybrid zone over time

1. reinforcement

2. fusion

3. stability

reinforcement

hybrids are less fit than either purebred species. species continue to diverge until hybridization can no longer occur

fusion

reproductive barriers weaken until the species become one

stability

fit hybrids continue to be produced

phylogeny

the evolutionary history of a group of organisms, usually represented graphically by a phylogenetic tree

character

a phentypic feature (flower petal color)

character state

two or more forms of a character (red vs white petal color)

homology

similarities in a trait between two or more species that result from inheritance of a trait from their most recent common evolutionary ancestor

synapomorphy

shared character state or a homology that evolved in the most recent common ancestor of a group of species

autopomorphy

distincitive feature, known as a derived trait, that is unqiue to a given taxon

homoplasy

similarity between two or more species that results from convergent evolution or evolutionary reversal

convergent evolution

distantly related organisms independently evolve similar adaptive traits to similar selective pressures

evolutionary reversal

a lineage evolves towards one of its more ancesteral traits, effectivilty losing a more recently evolved trait

which type of taxonomic grouping would indicate a homoplasy

polyphyletic grouping

principle of parsimony

choose the simplest scientific explanation to explain the evolutionary changes

SNP

single nucleotide polymorphism

maximum likelihood

tree construction and assignment of branched lengths are performed using evolutionary probilities of nodal connections

transitions

interchanages of two ring purines (A G), or of one ring pyrimidines (C T)

transversion

interchanges of purine for pyrimidine bases

evolutionary biogeography

the present and past distribution patterns of biological diversity and their underlying environmental and historical causes

island biogeography

field within biogeography that examines the factors that affect the species richness and diversifification of isolated natural communities

species diversity =

Richness + Evenness

Evenness

the number of species but also considers the abundance of each species

Richness

simply a count of unique species

adaptive radiation

when a single or small group of ancestral species rapidly diversifies into a large number of descendant species

species number equilibrium

when immigration rate is equal to extinction rate

eco-evolutionary feedback loop

populations alter their environment and those changes in the environment feed back to influence subsequent evolution of the polution