BIOL 201 1st Edition Lecture 12Outline of Previous LectureI. Phylogenetic analysis – a difficultya. Homoplasyi. Causes of homoplasyII. Comparative methoda. Order of evolutioni. Hypothetical exampleb. correlationIII. Implications of phylogenetic thoughta. Hierarchyb. classificationIV. Speciationa. Diversityb. Species conceptsOutline of Current LectureI. Isolating mechanismsa. Postzygoticb. Postmating, prezygoticc. PrematingII. Mechanisms of lower fertility in interspecific crossesIII. Geography of Speciationa. Allopatric Speciationb. Parapatric Speciationc. Sympatric SpeciationIV. ReinforcementV. Adaptive radiationCurrent LectureI. Isolating mechanismsa. Postzygotic- 2 individuals decide to mate, produce a zygote and something goes wrong with the zygote, after crossbreeding event has taken placei. Intrinsic: something wrong with the genes in the organism itself, don’t work together to produce a viable and fertileoffspring; have to survive AND be fertile to get genes to cross all the way into other species1. May get from underdominance but this doesn’t usually occur and is more likely when there is drift2. Another intrinsic is Dobzhansky-Muller: have interactions between genes at different loci [epistasis]3.ii. Extrinsic: depend on the environment and the fitness depends on if there’s a niche for organisms to survive in and there usually isn’t1. Ex: sticklebacks and carabid beetlesb.c. Postmating, prezygotici. Higher mortality between mating and producing offspringii. Lower fertilityiii. Ex: ligersd. Premating- maybe most effective; act before mating has even occurredi. Temporal isolation: when species are breeding at different timesii. Habitat choice is a spatial reason; individuals choose to breed in different micro-habitats1. Ex: pea aphid2. Have 2 races; one eats alfalfa and the other eats clover3. Phytophagus: plant eating class of insects in which speciation occurs very easily4. They stay on the plant they eat and they breed on it. 5. Don’t really encounter other types of insects and won’t really ever encounter them during breeding time because they aren’t on the same plantsiii. Mate choice is very important; can choose not to mate with another species because not attracted to them1. Ex: hummingbirds; males differ widely in plumage; usedin sexual selection and females won’t really try to mate with wrong type of maleII. Mechanisms of lower fertility in interspecific crossesa. Proteins or behaviors not stimulating ovulationb. Sperm surviving for less time in the femalec. Ineffective sperm transport, storage, passage through a femaled. Incompatibilities between sperm proteins and egg receptorse. Matching behaviors in fertilizationIII. Geography of Speciationa. Allopatric Speciation- have uncrossable geographic barrier between 2 species so don’t have the opportunity to cross at all; major driver of speciationi. Vicariance: a single large population splits into 2 because of a geographical barrier arises like mountain, river, etc.ii. Peripheral isolation (dispersal)- colonization of a brand new area that is isolated in the beginning allowing them to evolve tobe different and may come into contact later BUT wouldn’t interbreed because now 2 different species; Founder’s effect common when this happens1. Ex: Hawaiin Drosophila; have arisen as the new islands come to existenceb. Parapatric Speciation- 2 different adaptations happening in different areas; grow larger until they meet in the middle and the two species are incompatible [can’t breed]c. Sympatric Speciation- the least likely to happened and the most difficult to provei. Possible example: Lake Victoria cichlids1. Have diff. environmental adaptations and it doesn’t looklike there are any geographical barriers2. Also the lakes are young so it’s hard to believe there were ever any barriersIV. Reinforcement: the evolution of premating isolation after secondary contact to prevent the formation of unfit hybridsa. Secondary contact- when you have differentiation and maybe not complete speciation and they overlap with one another geographicallyb. Had some allopatry and then they come into contact physically afteri. Explanation for slide 41ii. Top left had white and blue fish while top right white and red fishiii. Hybrids between red and blue has lower fitness than parentals so females would have higher evolutionary fitness is blue females mated with blue males instead of red onesiv. As time progress, because you have low hybrid fitness, it benefits the females in the species to NOT cross breed v. Bottom left is now 2 blue fish and bottom right is 2 red fishV. Adaptive radiation- evolutionary divergence of members of a single phylogenetic line into a variety of different adaptive formsa. May be due to an ecological event like extinction of another speciesb. Often occur rapidlyc. Usually differ in the use of resources or habitatsd. Ex: eutherian mammals, hawaiian honeycreepers,