BIOL 446 Notes (got 95% on Final)

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BIOL 446
James Marden

Course goals: 1. Learn to think and analyze from genes to ecosystems 2. Learn to recognize features of habitats that present functional challenges to organisms 3. Learn the diversity of solutions to problems of temperature, osmolarity, energy, etc.. 4. Begin to understand how and why organisms work the way they do Topic 1: Adaptation What is an adaptation? 1. Used as a noun to describe a trait or character: 1 A trait that enhances fitness and that arose historically as a result of natural selection for its current biological role (Lauder 1996) fitness: relative contribution of offspring to next generation(s) historically: fitness effect must have been working in the past natural selection: the process that determines fitness; not a random process like genetic drift 2. Used to describe an evolutionary process Over evolutionary time, organisms become adapted to their environment - infers increasingly good fit between organism and environment brought about by the process of natural selection acting on hertitable genetic variation that causes evolutionary change 3. Used to describe a process of phenotypic adjustment within individuals Over the summer, trout become adapted to higher water temperatures - describes a non-heritable change (although the ability to make such a change is usually heritable!!!) - in order to avoid confusion, I will try to use the word acclimate to refer to phenotypic changes within individuals 2 How do we know an adaptation when we see one? In the old days (pre-1980’s) - observe a trait - measure or speculate on its adaptive features - voila: it’s an adaptation! Problem: progress in the field of population genetics showed us that not all traits are expected to be adaptive (because of things like genetic drift, linkage, selection on correlated traits [i.e. shared developmental pathway]) Also: With advent of gel electrophoresis came the discovery of unexpectedly large degree of heterozygosity in metabolic enzymes. Many polymorphisms began to look as if they are selectively neutral. An important paper: Gould and Lewontin (1979) The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme 3 Richard Lewontin: a population geneticist who was one of the first to discover high levels of polymorphism in metabolic enzymes; these came to be interpreted in terms of genetic drift and neutral evolution Steven J. Gould: a paleontologist who studied primarily the history and architecture of snail shells. He interpreted shell morphology in terms of geometrical constraints rather than functional attributes, and he observed many sudden shifts in shell morphology in the fossil record. He thought that many things in evolution are the result of chance events that leave lasting impacts. The message from Gould & Lewontin: not all of organismal features are likely to be adaptations, AND there has been an enormous amount of sloppy science surrounding the identification of traits that are supposedly adaptive. How can we best study adaptation? 1) Clinal variation: when traits or allele frequencies are repeatedly correlated with latitude or other spatial change in an environmental variable (examples in readings and some more later in this packet) 2) Functional effects of variants: show how genetic variation or heritable phenotypic variation affects fitness, and why the allele is not fixed (i.e. context- dependent selection; see coral example later in this lecture packet). 4 3) Mapping traits onto a phylogeny: show that multiple species have independently evolved similar trait-environment relationships (example: leg length in Caribbean lizards) 5 4) Reciprocal transplant experiments: determine if local variants perform best in the habitat in which they are found (classical approach with plants; example: Mimulus at different elevations) 6 5) Determine how genetic variation changes with an environmental change - Heliconius erato and H. melpomene have co- evolved their patterns of wing coloration. This is an example of Mullerian mimicry. - Genetic distance in hybridizing races of H. melpomene butterflies at chromosomal regions flanking genes responsible for wing color. Note the low genetic distance at loci not involved in wing color spots whereas there is much higher divergence (F stat the color loci, presumably maintained by avian predators responding to local Mullerian mimicry complexes. 7 6) Transgene experiments: determine if presence/absence of an allele affects fitness (Nature 423: 74-77 [2003]) 8 Some additional case studies 1. Case stu
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