Geography of Species

The geographic context that gives rise to speciation

Allopatric - species geographically isolated with no gene flow Parapatric - species close together limited gene flow Sympatric - free gene flow in a population in which divergence occurs

• Reproductive isolation involves many factors • New forms of a species are usually found in particular locations • Genes causing reproductive isolation are unlikely to spread within a population

Assumes that speciation occurs when a species is split into geographical sub-population and these subpopulations undergo selection and drift with limited gene flow so that they can no longer interbreed

Describes geographic isolation as happening due to dramatic geographical events and while these do occur, climate change (glaciation) has probably been more important

The study of patterns of geographic variation within closely-related species

Assumes that the most important changes occur in populations on the periphery of species ranges

Selection could be more intense and in a more unusual direction

• Genetic drift could change gene frequencies dramatically • Can fix unusual forms/deleterious genes • Weird sexual selection

• When there is differentiation along an ecotone - When there is secondary contact between forms that started to diverge in allopatry

• Metal tolerant and pasture ecotypes have developed flowering periods that are a week apart

When selection against hybridisation could exaggerate sexual differences so that species no longer interbreed

• Doubt on how genes causing unfitness could spread throughout a species • Muller proposed that genes could evolve independently and have negative interactions

• Investigating American apple maggot fly Rhagoletis pomonella which infects either apple plants or hawthorn plants • Argues that both pre and post-mating isolation would build up due to adaptation to alternative hosts • Some proof of genetic differences