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…any factor within a lineage that prevents an anticipated course of evolution.

Evolutionary Constraints. …any factor within a lineage that prevents an anticipated course of evolution. [Source: McKitrick 1993, Ann. Rev. Ecol. & Syst. 24, 307-330]. Evolutionary Constraints. Genetic Functional Developmental. [Source: Arnold 1992, American Naturalist 140, S85-S107].

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…any factor within a lineage that prevents an anticipated course of evolution.

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  1. Evolutionary Constraints …any factor within a lineage that prevents an anticipated course of evolution. [Source: McKitrick 1993, Ann. Rev. Ecol. & Syst. 24, 307-330]

  2. Evolutionary Constraints Genetic Functional Developmental [Source: Arnold 1992, American Naturalist 140, S85-S107]

  3. Genetic Constraints where, response to selection selection differential heritability [Source: Falconer 1981, Introduction to Quantitative Genetics, Longman Press]

  4. response to selection selection gradient for traiti genetic variance for traiti genetic covariance between traitsi and j Genetic Correlations Ri Rj βi βj GiiGij GjiGjj * = where, [Based on Lande and Arnold 1983, Evolution 37, 1210-1226]

  5. What are genetic correlations made of? • Linkage • Traits linked physically or statistically • Pleiotropy • Genes that affact one trait also affect other traits [Source: Lynch and Walsch 1998, Genetics and Analysis of Quantitative Traits]

  6. Evolutionary Constraints Genetic Functional Developmental [Source: Arnold 1992, American Naturalist 140, S85-S107]

  7. Functional Constraints …result from limitation on the values of traits or combinations of traits. Usually, functional constraints involve tradeoffs. [Source: Arnold 1992, American Naturalist 140, S85-S107]

  8. Functional Constraints • Allocation tradeoffs • Acquisition tradeoffs • Specialist-generalist tradeoffs Angilletta et al. (2003), Trends Ecol. Evol.

  9. Tradeoffs in the Allocation of Resources Growth Reproduction Storage

  10. Egg weight (mg) Clutch Size Grasshoppers that produce large eggs have smaller clutches. Field Grasshopper (Chorthippus biguttulus) [Source: Stearns 1992, The Evolution of Life Histories, Oxford University Press]

  11. Tradeoffs between Acquisition and Survival SC NS [Sources: Billerbeck et al. 2001, Evolution 55: 1863-187; Lankford et al. 2001, Evolution 55: 1873-1881]

  12. Specialist-Generalist Tradeoffs:An Example An increment in growth rate at one temperature results in a decrement in growth rate at another. This tradeoff is caused by thermal adaptation of enzymatic structure.

  13. Specialist-Generalist Tradeoffs:Evidence Selection of E. coli for growth at 37C for 2000 generations. [Source: Cooper et al. 2001, Evolution 55: 889-896]

  14. Three Classes of Tradeoffs • Allocation tradeoffs –a decrement in the resources allocated to one or more functions resulting from an increment in resources allocated to another function. • Acquisition tradeoffs –an increase in the probability of being killed or parasitized resulting from an increase in the duration or intensity of foraging. • Specialist-generalist tradeoffs –a decrement in performance within one range of environmental conditions that results from an increment in performance within another range.

  15. Evolutionary Constraints Genetic Functional Developmental [Source: Arnold 1992, American Naturalist 140, S85-S107]

  16. Developmental Constraints …result from limitations on the set of possible developmental states and their morphological expressions. [Source: Arnold 1992, American Naturalist 140, S85-S107]

  17. Evolution of Limb Morphology • Modification of limb structure are some of the best examples of adaptation. • Mutations in limb structures are common (e.g., polydactyly occurs in 0.1-0.2% of humans). • Yet, limb bones in vertebrates are highly conserved in number. Mortality of mutants is high. [Source: Galis et al. 2001, TREE 16, 637-646]

  18. Mechanisms of Losing Digits Opossum A reduction in digits occurs through destruction of some digits after development.

  19. Mechanisms of Adding Digits European Mole Extra digit is a modified sesamoid bone! Similar structures occur in turtles, whale, and pandas [Source: Galis et al. 2001, TREE 16, 637-646]

  20. Development Constrained by Pleiotropy • Limb development occurs during a highly conserved stage of embryonic development • Interactions among somites, notochord, neural tube, lateral plate mesoderm, and limb buds is intense. • Changes in limb development seems to have a pleiotropic effect on other structures. Mostly, this effect is deleterious. [Source: Galis et al. 2001, TREE 16, 637-646]

  21. Summary • Evolution is constrained by a lack of genetic variation, functional relationships between traits, and developmental mechanisms. • These constraints can be incorporated into optimization theory. • Some of these constraints are temporary, meaning that natural selection, mutation, and genetic drift can modify constraints over time.

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