How to study natural selection 1: observations2: experimentsObservational Studies: Thermoregulation in ectotherms-Desert iguanas- thermal performance curves-Huey et al 1989- thermal preferences in garter snakes- Observational studies- Environmental monitoring - Habitat studies-Iguanas have a range of temperatures they could live in, and they would often choose about 40 C. They had the best “performance” (in endurance, burst speed, digestive efficiency, etc.) when they were in warmer temps -Garter Snakes appear to maintain a constant temperature in the field (not in a lab setting). Huey would capture garter snakes and then track them and get data on where they would spend their time. They would spend their day finding environments to keep them at optimal temperature. He measured their temps under different types of rocks and while out in the sun, etc. and showed that the snakes are betteroff under a medium sized rock and where they could be in the field and moving on their own. Snakes showed a preference under a medium rock so they supported his theory on ectotherms favorite environments to maintain optimal temperature. Mimicry and Predation: -Zonosemata vittigera- distinct wing patterns and wing-waving behavior-Greene et al. 1987- speculated this was due to mimicry of jumping spiders (thought they were mimicking their main predator, the jumping spider)-Experimental analysis- manipulation of wing pattern and behavior -He set up a series of experiments & had 3 main hypothesis: -1: Null hypothesis -2: Mimicry deters other predators-3: Mimicry deters jumping spiders **-The prediction of his hypothesis was confirmed Experimental Design:-Important to have controls-Experimental conditions should be consistent among treatments-Randomize experiment order -Carry out multiple trails for each treatment (gives you more variation)-Better estimates and statistical tests could be performedExperimental EvolutionLife Histories: Egg and Clutch Size (how big are the eggs, how many offspring)Reproductive Maturity (what age do they begin to reproduce)Energy Allocation: Reproduction vs Growth/Survival (how much time/energy to reproduce)Life History Traits:A flexible zygote: -when and how big should this zygote be before reproducing?-How much energy should it allocate to reproduction?-Should it produce many or few, large or small offspring-How should it live its life?-How long should it live?-How many offspring should be male or female?Egg & Clutch Size: The Lack Clutch-Lack clutch- intermediate clutch size produces the largest number of fledglings -“inherent tradeoff” between clutch size and offspring survival. So if you produce a lot of offspring, you’dhave to divide up your resources between each offspring, so the more offspring, the lower the survival probability Guppy Life History Evolution: David Reznick -Comparative analysis-Observational studies -Evolutionary experiments-Genetic analysesLife History Evolution: two major questions1: What proportion of resources should be devoted to reproduction as opposed to maintenance or growth (reproductive vs. somatic effort)? 2: How should resources be devoted to reproduction be divided between offspring- few lavishly fed and cared for offspring, or many poorly nourished and cared for offspring? :: Key concept: Tradeoffs between traitsGuppies: Life History and Predation-Guppies live in streams with different predator communities-Some predators can only consume juveniles -Some predators can eat adults as easily as juveniles -Guppy Predators: Crenicichla altil: predation on adults & Rivulus hartii: predation on juveniles -Highland pools: Rivulus only, low adult predation-Lowland pools: lots of Crenicichla, high adult predation-Predictions: - Lowland: early maturation, high reproductive rate, more and smaller offspring per brood- Highland: late maturation, low reproductive rate, fewer, larger offspring The Next Step: Experiments! -He took guppies from lowland (high predation) pools and put them in highland (low predation) pools (11 years)-They waited longer to reproduce, their clutch size was reduce, offspring size increased, etc. Was this an evolutionary change? -He had to prove this was a genetic change to show that it was evolutionary-“Common Garden” Experiment: -Raise guppies from each environment in an identical environment for several generations-Experiments supported his