The conditional benefits of cannibalism for wood frog tadpoles (lithobates sylvaticus)

Wood frog tadpoles have an incredible ability to rapidly adapt to changing conditions, and when population densities become high tadpoles often become cannibalistic. Cannibalism potentially represents an ideal diet by composition, and should be beneficial to the growth and development of cannibalistic individuals. To test the relative efficacy of cannibalism to growth and development we conducted multiple feeding experiments. Results indicate that cannibalism represents a better alternative to starvation and provides some benefit to development and survival of tadpoles over low quality diets. However, cannibalism can be detrimental to tadpole growth and/or develop­ment relative to diets of similar protein content. Additionally, tadpoles raised individually appear to initially avoid consuming the cannibalistic diet, and may continue to do so until they face the risk of starvation. Conversely, when tadpoles were raised in groups providing them with compe­tition, they immediately fed upon the cannibal diet. Our results suggest that competition, rather than dietary quality is likely the driving force behind cannibalistic behaviour unless tadpoles oth­erwise face the risk of starvation

Data from: Locomotor endurance predicts differences in realized dispersal between sympatric sexual and unisexual salamanders

Dispersal is the central mechanism that determines connectivity between populations yet few studies connect the mechanisms of movement with realized dispersal in natural populations. To make such a link, we assessed how physiological variation among individuals predicted dispersal in natural populations of unisexual (all-female) and sexual Ambystoma salamanders on the same fragmented landscape in Ohio. Specifically, we assessed variation in a trait that influences long-distance animal movement (locomotor endurance) and determined whether variation in endurance matched patterns of realized dispersal assessed using genetic assignment tests. A possible mechanism for why unisexuals would have lower locomotor endurance than a sympatric sexual species (Ambystoma texanum) is the potential energetic cost of evolutionarily mismatched mitochondrial and nuclear genomes within polyploid unisexuals. We found that sexuals walked four times farther than unisexuals during treadmill endurance trials that mimic the locomotor endurance required for dispersal. We then applied landscape genetic methods to identify dispersed adults and quantify realized dispersal. We show that the differences in locomotor endurance between unisexual and sexual salamanders scale to realized dispersal: dispersing sexual individuals travelled approximately twice the distance between presumed natal wetlands and the site of capture compared to dispersing unisexuals. This study links variation in individual performance in terms of endurance with realized dispersal in the field and suggests a potential mechanism (physiological limitation due to mitonuclear mismatch) for the reduced endurance of unisexual individuals relative to sexual individuals although we discuss other possible explanations. The differences in dispersal between these two types of salamanders also informs our understanding of sexual/unisexual coexistence by suggesting that unisexuals are at a competitive disadvantage in terms of colonization ability under a extinction-colonization model of coexistence