The Origin of Species Presented & supported two hypotheses:

1) Evolution as modification with descent, and 2) Natural selection as the mechanism for adaptation But Didn’t 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 populations. Reproductive isolation = evolutionary independence. Willow and Alder Flycatchers Look identical! Don’t interbreed.

Phylogenetic Species Concept The PSC looks for pattern of independent evolution. PSC= a species is the smallest monophyletic group. Monophyletic group = group that contains all descendents of an ancestor.

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

Species concepts have conservation implications Conservation managers mated these two species 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.

In post-zygotic reproductive isolation, offspring have Either low fitness: for example, stickleback with intermediate morphology. Or low fertility: Horse 2N=64; Donkey 2N = 62. Mule has 2N = 63. Can’t 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.

Ratites are flightless birds. Gondwana 150 mya, Began 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.

Sympatric speciation may be occurring in soapberry bugs.

Sympatric speciation also thought to occur in fish: Benthic and lotic forms of sticklebacks in Alaska And in Rhagoletis flies that feed on apples instead of hawthorne.

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

What happens when recently diverged species come into contact? Sometimes R.I. is not complete, and fertile hybrids form.

Townsend’s warbler is overtaking the hermit warbler. Some Townsend’s have mtDNA of hermits suggesting repeated gene flow from Townsend’s to hermits.

Humans create hybridization opportunities. Lose distinct species through hybridization.

Humans create hybridization opportunities. Create new invasive species through hybridization.

Phylogenetic context, but still somewhat typological. Notice that the degree of resolution is far greater for non-Africans, and also that Europe is placed farthest from the root of the tree.

Australia/New Guinea Europe Asian/Native American African Ingman et al. (2000) Nature 408:708. ~ 50,000 ybp mt DNA