Ch17 Evolution of Species Interactions5.pdf

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University of Toronto St. George
University College Courses
Spencer Barrett

BIO120H © Li| Page 5011  on Floreana and San Cristobal, the 2 species Geospiza fuliginosa and G. fortis have diff. beak sizes  on Daphne Island where G. fortis occurs alone, its beak is intermediate in size b/w those of the two species on Florana and San Cristobal  on Los Hermanos Island, G. fuliginosa occurs alone w/ intermediate-sized beak COEVOLUTION INVOLVES MUTUAL EVOLUTIONARY RESPONSES BY INTERACTING POPULATIONS  coevolution can also result in suites of traits forming mutualism b/w species ex. flowers and pollinators  difficult to discern the order in which adaptations occurred (sometimes not even due to interactions)  ants protect aphids and leafhoppers from predators for excreted nutritious honeydew in return  most insects that suck plant juices produce large amounts of excreta from which they can’t extract all the nutrients  thus, honeydew production may not have evolved to encourage protection by ants  ants are voracious generalists and are likely to attack any insect they encounter  they may not need special adaptations to deter the predators of aphids  ants don’t attack aphids or leafhoppers  evolved trait that facilitates the ant- homopteran mutualism  or due to their behaviour of defending plant structures that produce nectar Plant Defenses and Herbivore Responses  bruchid beetle larvae vs. legume seeds  adult bruchids lay eggs on developing seedpods of legumes  seeds release secondary compounds which inhibit digestive enzymes of most insects  bruchids have metabolic pathways that bypass or are insensitive to the toxins  among legume species,
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