Bio 3400 1nd Edition Lecture 19 Outline of Last Lecture I The Comparative Method II Testes size in bats III Speciation and History of Life IV Biological Species Concept V Phylogenetic Species Concept VI Speciation Outline of Current Lecture I Mechanisms of speciation II Signatures of sympatric speciation III Secondary contact IV Reinforcement V Isolating mechanisms VI Adaptive radiations Current Lecture I II III IV Mechanisms of Speciation a Model of sympatric speciation via shifts to new host food b EX population uses ancestral host 1 new population founded via shift to derived host 2 populations on two hosts become reproductively isolated Goldenrod gallmaker an example of speciation via host plant shift Signatures of sympatric speciation via host habitat shift a Sympatric overlap of host patches b Mating on the host causes reproductive isolation between races c Host phenology differs d Divergent selection on different hosts habitats i Example sources of mortality differ wasp beetle bird early larval death unknown insect Speciation via Sexual Selection a Females in ancestral populations prefer blue males populations becomes reproductively isolated allopatry or sympatry female preference for male trait diverges due to genetic shift upon recontact populations reproductively isolated due only to female preference b Signatures of speciation via sexual selection These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute V VI VII VIII IX X XI i Populations or species vary in sexually selected traits and associated preferences resulting in partial or full pre mating isolation ii Differ in few other traits besides those involved in mate choice iii Little genetic differentiation suggesting rapid divergence iv Sexual selection promotes divergence because it affects gene flow directly Incipit speciation in Vogelkop bowerbirds a The populations differ strongly in male signals and female preferences 1 b Genetic divergence between the populations is very low African Cichlids a Explosive speciation in African lakes e g 1000 in Lake Malawi b Rapid last few million years c Vary widely in feeding habits FOOD d Females select mates based on color and pattern SEX Divergent sexual selection may explain sympatric speciation in African cichilds Secondary contact what happens when incipit species come back into contact a Do not interbreed too different different species b Hybridize infertile offspring different species c Hybridize fertile unfit offspring reinforcement d Hybridize fertile fit offspring i Homogenize the divergent populations prevent speciation event ii Stable hybrid zone iii Third new species Reinforcement a Selection against hybrids b How does selection against hybrid offspring impact the fitness of the parents i Should favor the evolution of pre zygotic isolating mechanisms ii Explain Isolating mechanisms a Evolve via reinforcement OR occur as a by product of genetic differentiation b Prezygotic i Habitat choice ii Timing of reproduction iii Mate choice iv Mechanics v Gamete incompatibility c Post zygotic i Non viable zygote ii Hybrid sterility Outcomes of secondary contact and hybridization Fitness of hybrids Hybrid zone Eventual outcome Lower than parental Relatively narrow and Reinforcement forms short lived differentiation between I II Equal to parental forms Relatively wide and long lived Higher than parental forms Depends on whether fitness advantage occurs in ecotone or new habitat parental populations increases Parental populations merge differentiation between parental populations decreases Stable hybrid zone or formation of new species Speciation in a nutshell a Reproductive isolation i Allopatric geographical ii Sympatric FOOD or SEX b Genetic divergence i Genetic drift ii Natural selection c Permanent isolation i Prezygotic or postzygotic isolation Adaptive Radiations a The diversification of members of a single phylogenetic line into a variety of different forms under the action of natural selection b A major theme in the history of life c Triggers i Ecological opportunity ii Morphological innovation