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Transcript
Biology 360: January 24, 2007 Development of behavior 2 I. What causes individuals of the same species to exhibit distinctly different behaviors? This is where we can discuss the extent to which differences seen are the result of genetic differences vs. environmental differences, and also the nature of those environmental differences. My approach is to explore the different experimental methods used to address this question. NOTE: Make sure you know/understand the basics of the experiment, including the basis experimental manipulations or observations, any controls if described and/or comparisons made, and what the researchers actually measured)) to the level presented in class/text (whichever is more detailed, if included in the text). You should also be able to summarize the key results, and explain whether the key results suggest a primarily genetic basis or a primarily environmental basis (or a mix of both for the differences seen among individuals of a species. A. B. C. Hybridization 1. What are hybrids? 2. How are hybrids used to determine whether behavioral differences have a genetic basis? a) General prediction: If there is a strong genetic basis for a behavioral difference, then hybridization should produce a stereotypical result with minimal variation among experiments. 3. Example 1: Cricket song (Hoy and Paul) [Fig. in PowerPoint only] 4. Example 2: rover vs. sitter Drosophila [Fig. 3.19] Artificial selection 1. What is artificial selection? 2. How can artificial selection techniques be used to determine whether behavioral differences have a genetic basis? a) General prediction: If the behavioral differences have a strong genetic basis, you can create strains that reliably display the behavioral characteristic you were attempting to select. 3. Example 1: Selection for mice that collect either a particular large amount or a particularly small amount of cotton for their nests [Fig. 3.24] 4. Example 2: Selection for crickets with short vs. long calling times over four generations [Fig. in PowerPoint only] Inbred strains 1. What are inbred strains? a) Closely-related individuals are bred over several generations. 2. How are inbred strains used to determine whether a behavior is largely genetically based? a) Compare inbred strains to each other, and to the population as a whole. Strain-specific behavior patterns, specifically less variability in behavior for strains compared to the population suggest a genetic component for behavioral differences seen. Page 1 of 3 3. II. III. Example 1: Anti-predator response of two different strains of paradise fish exposed to a model predator with eyes ([Fig. in PowerPoint, 1st pair of bars] 4. Example 2: garter snake food preferences [Fig. 3.21] 5. How are inbred strains used to determine the role of environment? a) Examine inbred strain(s) (or artificially-selected strains) in different environmental conditions. Similarity in responses of the different strains to particular environmental stimuli suggests an environmental basis for the differences seen. 6. Example 1: Anti-predator response of two different strains of paradise fish [Fig. in PowerPoint, 2nd pair of bars] D. Family relatedness studies (focused on twins) 1. How are studies of twins used to determine the relative genetic and environmental components of a behavior? a) If behavioral differences are primarily genetically based… The correlation between identical twins (MZ) should be??? The correlation between fraternal twins (DZ) should be??? The correlation between parents and offspring (P-O) should be??? The correlation between unrelated siblings (i.e. adopted sibs) should be??? b) If behavioral differences are primarily environmental, the level of relatedness should not show any pattern. Rather, there should be strong correlations between individuals brought up in the same environment. 2. Examples: Verbal ability in humans [Fig. 3.16] E. Creation/manipulation of mutant strains 1. Prediction: If a single gene alteration can significantly alter a behavior, behavioral differences are likely to have strong genetic basis. 2. Example: oxytocin and male memory of females [Fig. 3.18] Developmental Homeostasis A. Defined: The ability of individuals with genetic defects or with only minimal exposure to appropriate environmental stimuli to develop nearly normally. B. Classic experiments: Harlow’s experiments with isolated rhesus monkeys, called “social isolation experiments” [Fig. 3.27] C. Potential causal factors 1. Redundancy (i.e. similar genes that overlap in function) 2. Default programming 3. NOTE: We won’t go into this more, since they really don’t get into much more than the fact that it does occur. I think the examples about symmetry really don’t say anything about developmental homeostasis. Developmental switch mechanisms A. Overview: Phenotype that develops depends upon environmental conditions (polyphenism = multiple phenotypes are possible) B. Example 1: tiger salamander larvae [Fig. 3.33] 1. Two types (described) 2. Under what conditions do Type 2 larvae develop? Page 2 of 3 C. 3. Advantages to environmentally-determined cannibal development Example 2: Dung beetle males (not in text—I wasn’t impressed with the cichlid example that was similar) 1. “Resident” male appearance and behavior 2. Sneaker male behavior 3. Female behavior 4. What determines whether a male will have horns or be a sneaker? a) External environmental factors b) Internal environmental factors c) Advantages to remaining hornless Page 3 of 3