Lecture Topic : Speciation I. Importance What are species? How do they evolve? II. Levels of Variation ~ microevolution A) Variation within locally breeding populations (=demes) 1) Environmental variation 2) Genetic variation 3) Genetic x Environment interaction = Adaptation

Levels of Variation (cont.) B) Variation between populations or demes. 1) Environment 2) Genetic (common environment) a. Selection b) Drift Balance between selection and drift. c) Reciprocal exchange of individuals = migration Population differentiation --> No population differentiation -->

Levels of Variation (cont.) C) Variation among GROUPS of populations 1. races 2. sub-species 3. often geographically isolated ~ lack of migration between populations 4. incipient species??

Levels of Variation (cont.) D) Development of ecotypes (plants) and ecological races (animals) are produced by a G x E interaction ~ adaptation cline = trait exhibits gradual change along a gradient 1920s Turreson Defined term ecotype from plant work s Clausen, Keck, and Heisey: tested if ecotypic differentiation exists: 1) Reciprocal Transplant 2) Common Garden

Figure Clinal variation in a plant

Levels of Variation (cont.) E) Variation between species 1) individuals appear very different 2) often reproductively isolated 3) individuals of a species appear more similar to one another than to other species. III. A. History of Definition 1) Type Concept a. species is a special creation b. variation around true type "whether breed true"

III. History of Definition (cont.) John Ray First person who asked "what is a species?" He noted there exist individuals that produce similar looking offspring..... Linneaus –early 1700’s Species basic unit of organizing diversity with binomial nomenclature Genus species Thought elemental species from creator because often garden varieties need constant work to maintain (since artificially selected).

III. B. Modern Usage of term 1940 Biological Species Concept: Evolutionary biologist Ernst Mayr = A species is defined as groups of actively or potentially cross fertilizing individuals which are isolated from other such groups. Alternate Defn.: Individuals whose genes can recombine with one another. Alternate Defn.:Similar individuals which breed mostly among themselves and which change as a unit through time. Phenotype?Breeding Behavior? Evolutionary Unit?

Six Concepts of Species Compared

Figure Biological species concept is based on interfertility rather than physical similarity

Figure Galapagos tortoise

Figure Long-distance dispersal- Role of gene flow

Figure Long-distance dispersal

Problems with defining a species Are species reproductive units? Is a species a unit of evolution? V. Origin of Species Microevolution = Macroevolution is the SAME PROCESS: An issue of scale and time! 1) Anagenesis = Slow and directional changes that transform a species. 2) Cladogenesis = Splitting of species (divergence) to form a new species or many species. Clade = group of species derived from a single common ancestral species.

Figure Two patterns of speciation

Figure The biological species concept is based on interfertility rather than physical similarity

Modes of Speciation 1) Sympatric Speciation Evolution of reproductive isolation within a local population (=deme) Likely infrequent but can occur. Species A and Species B Scale: 10 m square population A B A B A B B A A B B A B A BA

Figure Two modes of speciation

Figure Sympatric speciation by polyploidy in plants: Allopolyploidy

Figure Sympatric speciation by polyploidy in plants: Autopolyploidy

Modes of Speciation 2) Allopatric Speciation~Geographic Speciation Evolution of reproductive isolation within a local population (=deme) Likely infrequent but can occur. Species A and Species B Scale: Mt. Range >1000 Km BB AA

Figure Two modes of speciation

Modes of Speciation 2) Allopatric Speciation (cont.) ~Geographic Speciation geographical separation differences in habitat  populations exposed to different selection pressures ->increasing divergence over time OR peripheral or splinter populations at the edges of the species range. Examples:

Figure Has speciation occurred during geographic isolation?

Figure Allopatric speciation of antelope squirrels in the Grand Canyon

Isolating Mechanisms or Reproductive Barriers Post-Zygotic Barriers (initial contact) 1)zygotes do not develop normally or die = reduced hybrid viability 2) if zygotes develop normally they are sterile = reduced hybrid fertility 3) Less fit or vigorous F1 progeny produced, AxB mating < fit then AxA or BxB = heterozygote disadvantage 4) Hybrid breakdown= F1 hybrids okay but F2 and F3 etc. hybrid progeny produced are less fit then AxA and BxB.

Isolating Mechanisms or Reproductive Barriers Pre-Zygotic Barriers (secondary contact) 1) Mechanisms a) Ecological Isolation = 2 potentially interbreeding species found in same area but different habitats. Ex., tiger and lion b) Temporal Isolation = 2 species mate at different times during the year. Ex., flowering time,

Isolating Mechanisms or Reproductive Barriers c) Behavioral Isolation = often species specific, courtship behaviors etc. Ex., Blue footed boobies d) Mechanical Isolation = structural differences between species prevent copulation Ex., orchid pollinators

Figure Courtship ritual as a behavioral barrier between species

The role of sexual selection in the radiation of Hawaiian Drosophila species

Figure A summary of reproductive barriers between closely related species

End for Fall 2008………