Speciation & Macroevolution Packet #30

Reproductive Isolating Mechanisms Restriction of gene flow between species.

Reproductive Isolating Mechanisms Prezygotic Barriers Reproductive isolating mechanisms that prevent fertilization from taking place Temporal Isolation Two species reproducing at different times of the day, season or year Habitat Isolation Two closely related species that live and breed in different habitats in the same geographic area

Prezygotic Barriers II Behavioral Isolation Distinctive courtship behaviors prevent mating between species Mechanical Isolation Incompatible structural differences in reproductive organs of similar species Gametic Isolation Gametes of different species are incompatible Due to molecular and chemical differences

Postzygotic Barriers Definition Hybrid Inviability Hybrid Sterility Reproductive isolating mechanisms that prevent gene flow after fertilization has taken place Hybrid Inviability Death of interspecific embryos during development. Hybrid Sterility Prevents interspecific hybrids that survive adulthood from reproducing successfully Hybrid Breakdown Prevents offspring of hybrids that survive to adulthood and successfully reproduce, from reproducing beyond one or a few generations.

Speciation The evolution of a new species from an ancestral population More likely to occur when the population is small.

Allopatric Speciation One population becoming geographically isolated from the rest of the species Eventually leading to divergent evolution Death valley pupfish Kaibab squirrels Porto Santo rabbits

Sympatric Speciation Animals The genetic divergence of multiple populations (from a single parent species) inhabiting the same geographic region Plants Results from allopolyploidy Polyploid individual (one with more than two sets of chromosomes) is a hybrid derived from two species Kew primroses and hemp nettles Animals How it occurs remain to be determined Fruit maggot flies and cichlids

Pace of Evolution Punctuated Equilibrium Gradualism Evolution of species that occur in spurts Short periods of active speciation are interspread with long periods of stasis. Gradualism Populations diverge slowly from one another by the accumulation of adaptive characteristics within a population.

Macroevolution Definition Large-scale phenotypic changes in populations that warrant their placement (species) in taxonomic groups at the species level and higher. (new taxons)

Macroevolution II Appearance of evolutionary novelties may be due to changes that occurred during development Changes in regulatory genes could cause structural changes in the organism. Novelties may originate from preadaptation. Structures that originally fulfilled one role but changed in a way that was adaptive for a different role. Feathers Allometric Growth Varied different rates of growth for different parts of the body Result in a change in the overall shape of an organism Paedomorphosis Retention of juvenile characteristics in the adult Occurs to changes in the timing of development Adult axolotl salamanders with external gills and tail fins

Macroevolution III Adaptive Radiation Extinction Process of diversification of an ancestral species into many new species. Extinction Death of a species Adaptive zones become vacant Background extinction Continuous low level extinction of species Mass extinction Extinction of numerous and higher taxonomic groups in both terrestrial and marine environments