Speciation

Know the evolutionary definition of “species”

Mutation, migration, selection, and drift occur in each species separately. Species form a boundary for the spread of alleles.

Define Biological Species Concept

reproductive isolation – lack of potential gene flow

difficult to apply to populations do not overlap, fossil species, asexual species, plants which hybridize

Define Phylogenetic Species Concept

species are the smallest diagnosable monophyletic (all descendents of a single common ancestor) group

populations must have been evolutionarily independent for long enough for diagnostic traits to occur that allow us to separate them

As yet, no standard of appropriate diagnostic traits

Define Morphospecies Concept

Species are distinguished by morphological differences between groups.

Potentially arbitrary and idiosyncratic.

There is some evidence that experienced systematists can use morphological features to distinguish biological species

Describe the three steps leading to speciation

Separation (little or no gene flow between populations), divergence, evolution of reproductive isolation

Describe examples of allopatric speciation

Physical separation of populations

Hawaiian Drosophila

Shrimp around the isthmus of Panama

Describe examples of sympatric speciation

Can happen if pressure for divergence is great and assortative mating occurs.

Apple maggot flies (Rhagoletis pomonella).

Chromosome doubling in plants

Describe the processes which cause “separated” populations to diverge

Genetic drift

Hawaiian Drosophila

Galapagos finches

Natural selection

Galapagos finches

Sexual selection

Hammer head Drosophila

Know the hypotheses about the evolution of reproduction isolation

The Reinforcement Hypothesis:

Because producing hybrid offspring reduces a parents fitness, there should be strong natural selection favoring assortative mating. (premating isolation)

The Speciation Gene Hypothesis

Hybrid inviability/sterility is often a result of separation (postmating isolation). One to two loci on the X chromosome in Drosophila responsible for the degree of hybrid inviability.

Describe the hypotheses about why speciation rates differ markedly among taxa.

may be due to differences in environmental heterogeneity experienced or by whether taxa are primarily generalists (slow evolving) or specialists (faster)