Speciation Process by which a daughter species evolves from a parent species Genetic Divergence- when 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 BARRIER Species A becomes distinct from species B; cannot mate with each other AB

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 Species A and B cannot mate A B

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 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 “…all animals share the same control switches for development…”

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 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 “Macroevolution is not goal-oriented” “…speciation, diversification, and extinction are common occurances…”

Darwin’s drawing in The Origin of Species