Zoology 445 Fall 2006Reading Sections 9.1 to 9.4 and 9.6Studying Adaptation: HandoutI. IntroductionWhy is the giraffe’s neck so long?II. Studying adaptationsA. ObservationB. HypothesisC. Analysis- Observational studies (Text section 9.3)- Comparative Method (Text section 9.4)- Experimental manipulations (Text section 9.2)Best work includes more than one of method of analysis when making a case for a trait being adaptive.AM Jarosz 1Zol 445 JaroszExample: Snail shell morphology along the coast of Maine.Species Littorina obtusata an intertidal marine snail found along the east coast of US.Observation: Temporal change of many populations in shell morphology along coast of Maine.Shell Morphology.When scaled for overall size, found that spire decreased in height and shell thickness increased through time.Fig 2A Seeley (1986) PNAS 83:6897-6901. Paper is postec on the course web page as an OPTIONAL reading.Temporal pattern: Spatial pattern:B. Hypothesis: Decrease in spire height and increase in shell thickness adaptive because they reduce predation by crabs.C. Analysis:1. Comparative method: Shell height also found to vary spatially among areas where crab densities differed.2Zol 445 Jarosz2. Experimental manipulation: Placed 18 pairs of tethered snails in water at three locations that differed in crab density.Location Crab densityGleason Point HighSipp Bay LowTimber Cove Absent (or very rare)Fig 3. - = snails with high spire- = snails with low spiresIII. Trade-offs and Constraints on adaptation (Section 9.6)Example of an evolutionary trade-off: Female flower size in the plant Begonia involucrate. (Pages 351 to 353)3Zol 445 JaroszWe have already talked a bit about evolutionary or historical constraints. At one level we are constrained by the number of limbs we have.Book examines two other constraints on pages 354 to 358.Take Home message:1. Must be cautious when stating that a trait is adaptive.2. Trade-offs and constraints may limit a traits ability to approach optimal adaptive state.\Evolution Zol 445\2006\Studying adaptation