Abstract
The geographic mosaic theory of coevolution predicts 1) spatial variation in predatory structures as well as prey defensive traits, and 2) trait matching in some areas and trait mismatching in others mediated by gene flow. We examined gene flow and documented spatial variation in crushing resistance in the freshwater snails Mexipyrgus churinceanus, Mexithauma quadripaludium, Nymphophilus minckleyi, and its relationship to the relative frequency of the crushing morphotype in the trophically polymorphic fish Herichthys minckleyi. Crushing resistance and the frequency of the crushing morphotype did show spatial variation among 11 naturally replicated communities in the Cuatro Ciénegas valley in Mexico where these species are all endemic. The variation in crushing resistance among populations was not explained by geographic proximity or by genetic similarity in any species. We detected clear phylogeographic patterns and limited gene flow for the snails but not for the fish. Gene flow among snail populations in Cuatro Ciénegas could explain the mosaic of local divergence in shell strength and be preventing the fixation of the crushing morphotype in Herichthys minckleyi. Finally, consistent with trait matching across the mosaic, the frequency of the fish morphotype was negatively correlated with shell crushing resistance likely reflecting the relative disadvantage of the crushing morphotype in communities where the snails exhibit relatively high crushing resistance.
Highlights
IntroductionPredators can show variability in predatory structures
Prey often vary in defenses that reduce their susceptibility to predators [1,2,3]
Crushing resistance varied among populations when adjusted by shell length in the former two species (ANCOVA: F10,214 = 14.8, P,0.0001 for Mexipyrgus churinceanus; F10,209 = 4.9, P,0.0001 for Nymphophilus minckleyi)
Summary
Predators can show variability in predatory structures This phenotypic variation provides the substrate for reciprocal evolution between predator and prey at the population level. Spatial variation in predatory structures and prey defensive traits should exist. Matching of these traits between predators and prey in populations where reciprocal selection is strong, and trait mismatching in populations where selection is weak [6,10,11,12]. We document spatial variation in traits that potentially mediate antagonistic interactions in an aquatic predator-prey network and test whether this system exhibits patterns consistent with the geographic mosaic theory of coevolution at a spatial scale that encompasses the entire geographic range of all interacting species
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