The Origin of Species Chapter 24 BCOR 012 Jan. 31 and Feb. 2, 2011

Outline for January 31, Feb. 2, 2011: I. Introduction II. What is a species? The biological species concept Reproductive isolating mechanisms Alternative species concepts III. Modes of speciation Allopatric Sympatric the tempo of change

What is a species?

The Biological Species Concept The biological species concept defines a species as a population or a series of populations whose members have the potential to interbreed and which are reproductively isolated from other such populations.

Reproductive Isolation and Isolating Mechanisms

Biologists distinguish between prezygotic and postzygotic isolating mechanisms. ex. fireflies

ex:mule

Limitations of the BSC: Not applicable to asexually reproducing organisms Useless with respect to the fossil record

Alternative species concepts: Ecological species concept - defines a species in terms of its ecological niche Morphological species concept - emphasis is on unique structural features Phylogenetic species concept - emphasis is on ancestor-descendent relationships Pluralistic species concept - acknowledges that, where species concepts are concerned, one size may not fit all!

There are an awful lot of living things; how did there get to be so many?

Anagenesis is change within a lineage; cladogenesis is the divergence of one lineage into two.

Modes of Speciation

There are two general modes of speciation: Allopatric (other homeland)- speciation takes place in populations with geographically separate ranges Sympatric (same homeland) - speciation takes place in geographically overlapping populations

SN Ammospermophilus harrisiAmmospermophilus leucurus Allopatric speciation of antelope squirrels in the Grand Canyon

In allopatric speciation In allopatric speciation, a new species originates while geographically isolated from its ancestor. As the new species evolves by genetic drift and natural selection, reproductive isolation from the ancestral species may evolve as a by-product of genetic change.

Sympatric speciation - a mode in which a new species arises in the geographic midst of its progenitor species. Copper-tolerant Mimulus guttatus

In plants, sympatric species may arise by polyploidy a condition that results in extra sets of chromosomes in the derivative species. An example from the European holly ferns ….

P. aculeatum European holly ferns (Polystichum) P. lonchitis P. setiferum

The origin of European Polystichum aculeatum P. aculeatum P. setiferum P. lonchitis primary diploid hybrid (2X) (4X) (2X)

The origin of European Polystichum aculeatum P. aculeatum P. setiferum P. lonchitis primary diploid hybrid P. setiferum n=41

Sympatric speciation in animals - East African Cichlids (sick-lids)

Pundamilia pundamilia a) Normal light b) Monochromatic orange light sympatric speciation Non-random mating, in which females select mates having a preferred appearance, is the main reproductive barrier keeping these two species separate in nature. This is an example of sympatric speciation in response to sexual selection. Pundamilia nyererei

Sympatric speciation Sympatric speciation requires the emergence of some sort of reproductive barrier that isolates the gene pool of a population subset without geographic separation from the parent population.

Hybrid Zones

The Tempo of Evolution

Darwin’s original idea was that species diverge gradually. More recently, the idea that there are rapid speciation events interrupting periods of no change has become popular.

Punctuated equilibria vs. gradual divergence edu/evosite/evo101/VIIA1bPunctuated.shtml

edu/evosite/evo101/VIIA1bPunctuated.shtml Punctuated equilibria vs. gradual divergence

Possibly include spur story

Pollinator shifts drive increasingly long nectar spurs in columbine flowers. Whittall and Hodges, Nature 447:

Outline for January 31, Feb. 2, 2011: I. Introduction II. What is a species? The biological species concept Reproductive isolating mechanisms Alternative species concepts III. Modes of speciation Allopatric Sympatric the tempo of change