Transcript Speciation
Speciation • Process by which a daughter species evolves from a parent species Genetic Divergencewhen populations become reproductively isolated Species-population of individuals who can interbreed under natural conditions producing fertile offspring • Does evolution always result in a new species? 2 Concepts on Speciation • Evolutionary species concept every species has its own evolutionary history, part of which is in the fossil record, and diagnostic traits • Biological species concept reproductive isolation rather than trait differences define a species Reproductive Isolating Mechanisms • Any heritable feature of body form, functioning or behavior that prevents interbreeding between species • Pre-zygotic and Post-zygotic Pre-Zygotic Mechanisms • • • • • Behavioral Temporal Mechanical Habitat isolation Gametic mortality Post-Zygotic Mechanisms • Hybrid mortality lower in fitness, early death • Hybrid sterility • Would natural selection favor pre- or post-zygotic mechanisms? Types of Speciation Processes • Allopatric Speciation-species form due to physical barriers that prevents gene flow; mountain range, river, island A BARRIER B Species A becomes distinct from species B; cannot mate with each other Allopatric Speciation • Salamanders in Central California • Washington Sockeye salmon in lakes vs rivers Allopatric Speciation: Adaptive Radiation • A single ancestral species gives rise to a variety of species, each adapted to a specific environment • Hawaiian honeycreepers • Occurred after dinosaur extinction mammals diversified in only 10 million yrs! Types of Speciation Processes • Sympatric speciation-species forms within the home range of an existing species in absence of physical barrier Species A-blue Species B-purple A B Species A and B cannot mate Sympatric Speciation • Polypoidy in plants • Autopoidy diploid plant produces diploid gametes • Alloploidy hybrid plant doubles it chromosome # Models of Macroevolution • Gradual Model-new species formed through gradual changes in traits over time; most consistent with fossil record Models of Macroevolution • Punctual Model-new species formed in a short amount of time; occurs through bottlenecks/founder effects, mutations, directional selection (natural selection) Developmental Genes and Macroevolution “…all animals share the same control switches for development…” • Development of eyes is controlled by Pax6 gene – It did not matter if it was a lens or compound eye • Loss of gene results in failure of eye to develop in mice, humans Developmental Genes and Macroevolution • Development of overall shape is controlled by Hox genes – Control number and appearance of repeated structures • Differential expression in chickens vs snakes “…animal diversity is due to variation in the expression of ancient genes…” Evolution of the Modern Day Horse “Macroevolution is not goal-oriented” • Does not fit a gradual model perfectly • Trends observed – Increase in size – Toe reduction – Change in tooth size/shape • Modern horse evolved 4 mya adapted for living in open plains “…speciation, diversification, and extinction are common occurances…” Darwin’s drawing in The Origin of Species