Speciation Flashcards
(26 cards)
theoretical species definition
a single lineage of ancestor-descendent populations, which maintains its identity from other such lineages, and has its own evolutionary tendencies and historical fate
why is defining a species difficult?
species are constantly changing - the idea of defining a species describes something dynamic as though it was static/unchanging
operational species definitions
morphological, phylogenetic, biological
morphological species concept
distinct physical characteristics/morphology define a species - useful w/ fossils
biological species concept
species are groups of actually or potentially interbreeding individuals that are reproductively isolated from other groups
phylogenetic species concept
a species is an irreducible cluster of organisms, diagnosably different from other such clusters, with a parental pattern of ancestry and descent
focuses on the outcome of the evolutionary process
unified species concept
anyone who has a reason to delineate a group as a species is allowed to call it a species
who came up with biological species concept
Ernst Mayr in 1942
HWE/ Fst
measure genetic divergence between geographically separated species to compare to genetic divergence between known distinct species
reproductive isolation can be:
prezygotic (via structural barriers) either pre- or post-mating
postzygotic (whether hybrids are viable)
allopatric speciation
formed by vicariance (big old mountain, etc). or dispersal i.e. populations are physically unable to intermix
parapatric and sympatric speciation…
maintain gene flow
allopatric speciation of organisms with greater migration/dispersal needs requires…
bigger islands/habitat patches
how do sympatric and parapatric speciation occur
disruptive selection linked to assortative mating reinforces speciation despite gene flow
hybrid zones
genetically distinct populations meet and interbreed to a limited extent, but there are partial barriers to gene exchange
introgression
genes from the gene pool of one species are incorporated into the gene pool of another
ecological isolation
ecological differences, for example habitat preference, contribute to genetic barriers to reproduction
prezygotic
sexual isolation
prezygotic reproductive isolation - sympatric species frequently encounter each other but do not mate
ex. females cannot recognize mating calls of males from other species
gametic isolation
prezygotic reproductive isolation - gametes of different species fail to unite when mating
assortative mating
individuals with similar genotypes/phenotypes mate with each other more frequently than would be expected under random mating patterns
causes disruptive selection (extreme phenotypes favored)
Dobzhansky-Muller incompatabilities
new alleles arise in isolation and are incompatible upon hybridization -> incompatibility can arise in a population without harming fitness of extant lineages
post-zygotic reproductive barrier
post-zygotic barrier: genetic incompatibilities
a selfish gene such as a Medea element arises (benefits itself), an antidote arises (benefits the individual) -> individual is no longer compatible with individuals w/o the antidote
polyploidy due to genome duplication
results in hybrids with incredibly low fitness due to problems undergoing meiosis, but can survive within a cluster of polyploids
post-zygotic reproductive barrier
species radiation
a rapid, essentially concurrent burst of speciation events diverging from a common ancestor
