Biology 1001A Lecture : Lec 19 species speciation post.pptx
6 Sep 2013
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Parent-offspring conflict before birth: fetus selected to demand more resources from mother than mother selected to give. Fetal tissue in placenta secretes allocrine hormones to manipulate maternal blood pressure and blood sugar; maternal sensitivity to these signals drops. Conflict of interest endangers both parties (gestational diabetes, pre-eclampsia) Biological species concept: species: interbreeding (or potentially interbreeding) group of individuals, reproductively isolated from other such groups. Secondary contact, if it occurs, may either reinforce reproductive isolation or re-establish gene flow. Populations may come back into (secondary) contact: if little divergence has happened, resume interbreeding (hybrid swarm, but, populations may have become reproductively isolated. Unfit hybrids: direct selection favouring prezygotic isolating mechanisms (reinforcement, uncertain whether postzygotic or prezygotic isolation usually happens first. Speciation without allopatry: polyploidy instant sympatric speciation. Speciation without allopatry: adaptations to a new food type can sympatric speciation, hawthorn maggot introduced to north. America: subset of maggots began feeding (and mating) only on apples.
