Biological Science 2/e

Biological Science 2/e

The Origin of Species Presented & supported two hypotheses: 1) Evolution as descent with modification

and 2) Natural selection as the mechanism for adaptation But Didnt really talk about the origin of species!

Speciation = the divergence of a single ancestral species into two descendent species. It is the process responsible for all biodiversity. What is a species? Do I know one when I see one? (Morphological species concept = looks different Biological species concept:

Reproductive isolation between species. Reproductive isolation = evolutionary independence. Willow and Alder Flycatchers Look identical! Dont interbreed.

Phylogenetic Species Concept The PSC looks for pattern of independent evolution. Monophyletic group =

group that contains all descendents of an ancestor. PSC= a species is the smallest monophyletic

group. Species concepts have conservation implications Dusky seaside

VERY RARE N=6 males in 1980 Species concepts have conservation implications

Conservation managers mated these subspecies to try to save the dusky seaside sparrow

The PSC recognizes two species. Matings should not be done between the two.

Biological Species Concept focuses on Reproductive Isolation. Reproductive Isolation could be pre-or post-zygotic

Examples of pre-zygotic RI include: Habitat differences Many examples! Behavioral differences Many examples! Examples of pre-zygotic RI include: Genetic differences among species

Bindin protein on urchin sperm is species-specific.

post-zygotic reproductive isolation, offspring hav her low fitness: example, stickleback with intermediate morphology.

Or low fertility: Horse 2N=64; Donkey 2N = 62. Mule has 2N = 63. Cant make balanced gametes.

How is reproductive isolation established? In Allopatric (different homeland) speciation, geographic isolation leads to reproductive isolation.

Drift and selection can cause divergence. Allopatric speciation can result from dispersal. Speciation on islands is famous

example. Allopatric speciation can also result from vicariance. Physical barrier divides species. Barrier could be due to geologic changes such

as continental drift and volcanism or to habitat changes due to climate change. tites are flightless birds.

ndwana 150 mya, gan to split up 140 mya. Summary of allopatric speciation.

Is sympatric (same homeland) speciation possible? Gene flow can prevent divergence, even when selection would favor different

adaptations. mpatric speciation may be occurring in soapberry bu mpatric speciation also thought to occur in fish: nthic and lotic forms of sticklebacks in Alaska

d in Rhagoletis flies that feed on apples instead o wthorne.

Polyploidy in plants also leads to sympatric speciation. Tetraploids are reproductively isolated from diploids. Their triploid progeny are sterile.

t happens when recently diverged species e into contact? etimes R.I. is not complete, and fertile hybrids fo wnsends warbler is overtaking the hermit warbler.

Some Townsends have mtDNA of hermits suggesting

repeated gene flow from Townsends to hermits.

Humans create hybridization opportunities. Lose distinct species through hybridization. Humans create hybridization opportunities.

Create new invasive species through hybridization. netic context, but still somewhat typological. Notice that the degree of resolution i ater for non-Africans, and also that Europe is placed farthest from the root of the tr tp://

Australia/New Guinea mt DNA Europe ~ 50,000 ybp

Asian/Native American African African

Ingman et al. (2000) Nature 408:708.

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