To determine the effects of dispersal ability and diet breadth on population-genetic structure, we reviewed the allozyme literature and estimated genetic isolation by distance (IBD) for 43 species/host races of phytophagous insects. Subsequently, we tested two opposing hypotheses regarding the influence of dispersal ability on IBD: that IBD slopes do not vary with mobility, but that intercepts increase with mobility, and, alternatively, that IBD slopes vary with dispersal ability. We found that from tens of kilometers to more than 1,000 km, IBD is weak in sedentary and highly mobile species but pronounced in moderately mobile species. We attribute the weak IBD in strong dispersers to the homogenizing effects of gene flow, whereas in sedentary species, limited gene flow allows nearly all populations to diverge. In intermediate dispersers, genetic homogeneity is achieved at small spatial scales, but limited dispersal promotes genetic divergence over long distances. We also tested the hypothesis that IBD increases with decreasing diet breadth. We discovered no such pattern, casting doubt on the supposition that specialization promotes speciation by influencing population-genetic subdivision. Finally, we found that the number of populations is a more important consideration than the number of polymorphic loci in studies of IBD.

We present a model to test Osgood's ( 1978 ) proposition that viviparous snakes have optimal reaction norms for temperature-sensitive meristic traits, such as scale counts. Our model predicts that traits that are subject to temperature effects during development will evolve a flat or [Formula: see text]-shaped reaction norm (average scale count as a function of developmental temperature). We tested this prediction by maintaining 67 female garter snakes (Thamnophis elegans) at eight different constant temperatures (21 degrees -33 degrees C) during pregnancy and making a series of scale counts on their newborn offspring (n = 491). To insure that the experimental temperatures were ecologically relevant, we used automated radiotelemetry to record the body temperature of pregnant, free-ranging females. The resulting temperature data allowed us to test the prediction that the inflection points of reaction norms would correspond to the average temperature experienced by embryos in the field. In line with predictions of the Osgood model, reaction norms were flat or U-shaped. In the case of U-shaped reaction norms, the inflection point of the curves corresponded to the average temperature imposed on embryos by free-ranging females. In contrast to some past studies, none of the standard scale scores (ones commonly used in systematics) showed significant temperature effects in either sex. Reaction norms were flat. In contrast, incidences of various abnormalities showed U-shaped reaction norms. Temperature effects were more pronounced in males than in females. The results have implications for systematics and for the evolution of canalization and phenotypic plasticity.

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1Exceptionally high rates of tooth fracture in large Pleistocene carnivorans imply intensified 2 interspecific competition, given that tooth fracture rises with increased bone consumption, a 3 behavior that likely occurs when prey are difficult to acquire. To assess the link between prey 4 availability and dental attrition, we documented dental fracture rates over decades among three 5 well-studied populations of extant gray wolves that differed in prey:predator ratio and levels of 6 carcass utilization. When prey:predator ratios declined, kills were more fully consumed, and rates 7 of tooth fracture more than doubled. This supports tooth fracture frequency as a relative measure 8 of the difficulty of acquiring prey, and reveals a rapid response to diminished food levels in large 9 carnivores despite risks of infection and reduced fitness due to dental injuries. More broadly, large 10 carnivore tooth fracture frequency likely reflects energetic stress, an aspect of predator success 11 that is challenging to quantify in wild populations. 12 13 14

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