Character displacement - Specific characters of the plant...

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Character displacement also provides and example of a pattern we might interpret as the result of coevolution. Mud snails show pattern of character displacement in sympatry due presumably to competition for food items (don't confuse this with reinforcement; the selective agent here is not reduced hybrid fitness). We might call this co evolution because both species show a shift when compared to allopatric samples of each species (mean of both ~ 3.2 in allopatry vs. ~ 4.0 and ~ 2.8 in sympatry). If only one species exhibited character displacement and you were a really picky evolutionist you might not be convinced of areciprocal response. Another strong case is the Ant - Acacia mutualism. Here specific traits in each species appear to have evolved in response to the interaction. The ant (Pseudomyrmex species) depends on the Acacia plant for food and housing ; acacia depends on ant for protection from potential herbivores (species that eat plant tissue).
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Unformatted text preview: Specific characters of the plant appear to have evolved for the maintenance of this mutualism : 1) swollen, ~ hollow thorns (= ant home), 2) extra-floral nectaries (source of nectaroutside the flower [i.e., the usual location] providing ants with food), 3) leaflet tips = Beltian bodies (= 99% of solid food for larval/adult ants). Specific characters in the ant that have evolved for the maintenance of this mutualism : 1) defense against herbivores 2) removal of fungal spores from Beltian body break-point (prevents fungal pathogens from invading plant tissues). The main point is that there are traits in both the ant and the acacia that are traits not normally found in close relatives of each that are not involved in similar mutualisms: mutualistic traits have evolved for the interaction in reciprocal fashion. See another example : fig. 22.1 & table 22.1, pg. 611....
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