The Origin of Species

Presented & supportedtwo hypotheses:

1) Evolution as modificationwith descent,

and

2) Natural selection as the mechanism for adaptation

But

Didn’t really talk about theorigin of species!

Speciation = the divergence of a single ancestralspecies into two descendent species.

It is the process responsible for all biodiversity.

http://orgs.unca.edu/tulula/images/biodiversity.jpg

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 FlycatchersLook identical! Don’t interbreed.

Phylogenetic Species ConceptThe PSC looks for pattern of independent evolution.

PSC= a species is thesmallest monophyleticgroup.

Monophyletic group =group that containsall descendents of an ancestor.

Species concepts have conservation implications

Dusky seasideVERY RAREN=6 malesin 1980

Species concepts have conservation implications

Conservationmanagers matedthese two speciesto try to save the dusky seasidesparrow

The PSC recognizes twospecies.

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 differencesMany examples!

Behavioral differencesMany examples!

http://www.ebertfest.com/two/grave_fireflies_bluebat.jpg

Examples of pre-zygotic RI include:

Genetic differences among species

http://www.luc.edu/depts/biology/dev/spersem.jpg

Bindin protein onurchin sperm isspecies-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 ofhawthorne.

www.msu.edu/~jimsmith/research.html

Polyploidy in plants also leads to sympatric speciation.

Tetraploids are reproductively isolated from diploids.Their triploid progeny are sterile.

What happens when recently diverged speciescome into contact?

Sometimes R.I. is not complete, and fertile hybrids form.

Townsend’s warbler is overtaking the hermit warbler.

SomeTownsend’shavemtDNA ofhermits suggestingrepeatedgene flowfrom Townsend’s to hermits.

Humans create hybridization opportunities.

Lose distinct species through hybridization.

Humans create hybridization opportunities.

Create new invasive species through hybridization.

http://www.mcdonald.cam.ac.uk/genetics/images/MtDNA_DistributionMap.gif

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

African

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

~ 50,000 ybp

mt DNA