BOIEE 1780 1st Edition Lecture 14Outline of previous lectureI. AnnouncementII. Opsthokonts& FungiA) Fungi lifestylesIII. Fungi typesA) MicrosporidiaB) DikayaC) ChytridsD) ArbuscularmycorrhizalIV. SummaryOutline of current lectureI. Darwin’s idea of natural selectionII. Darwin’s finches on DaphneA) 1977 droughtB) El NinoCurrent lecture*Natural selection is only one mechanism of evolution (evolution is defined as a genetic change in a population)I. Darwin’s idea of natural selection*Darwin’s logic: 1) populations would grow exponentially if all animals born survived and reproduced2) populations typically stay stable3) natural resources are limited and remain relatively constant*Darwin’s inference:1) there must be fierce competition over resources2) survival is not random, but it influenced by heritable traits*Add a few more facts: 1) no individuals are exactly the same (even identical twins have slight variations from mutations!) except among very simple bacteria 2) much of this variation is heritable*So, natural selection will happen when: 1) individuals are variable in some trait(s)2) at least some of this variation is heritable3) the variation causes differential survival and reproductionII. Darwin’s finches on Daphne*Peter and Rosemary Grant have been continuing to study these on Daphne Island in the Galapagos*What features of this study system makes it so convenient to study?-It’s an island, so there is little immigration/emigration-Limited natural resources-The island is small, so you can easily monitor every single finch-Finches reproduce relatively quickly, which means they evolve quickly-Only cacti, so you don’t need to search through a bunch of trees or rocks*MVP: Medium ground finch (Ge ospizafortis)*Individuals on this island vary in beak depth*We know that this trait is heritable [around 56% heritability] because the average depth of the parents’ beaks correlates to the average depth of the offsprings’ beak*When there are plenty of seeds, no natural selection occurs because large-beaked bird eat caltrop, small-beaked birds eat spurge, and medium-beaked birds can eat eitherA) 1977 drought*Seed abundance plummeted *Most of the seeds were large and hard*84% of finches on the island died*Result: by the next generation, average beak size had shifted upward by 0.5 mmB) El Nino*This is the weakening of normal trade winds… tends to raise rainfall in certain regions*Increased rainfall made the small seed plants more competitive*What effect could his have had on the finch population? Tune in next week to find
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