Effects of diet quality on morphology and intraspecific competition ability during development: the case of fire salamander larvae

The environmental conditions of the habitats in which organisms live may induce a variety of plastic adaptive responses for numerous developmental, behavioural and morphological traits. One of the most relevant environmental features is the amount of available food occurring in a certain habitat. In this study, we wanted to assess whether, during development of vertebrates, diet quality may induce plastic responses at both behavioural and morphological levels. We tested whether diet may affect the rate of aggressive interactions between fire salamander larvae (Salamandra salamandra) and changes of head morphology during development. We collected 15 newborn larvae from five different localities, and we randomly assigned them to three diets (small nourishing prey, big scant prey, mixed prey). For each larva we recorded the number of snap attempts to a target larva 4 days after salamander collection, and after the 50 days of feeding treatment. We recorded and analysed head shape development using a geometric morphometrics approach. Analyses showed a significant relationship between diet and aggressiveness: larvae fed with small nourishing prey were significantly more aggressive. Diet had a significant effect in determining the quantity of head morphology changes during larval development, but did not affect the characteristics of the morphology; this means that all the larvae showed a similar shape modification, but those treated with the more nourishing prey showed a more pronounced change. These results indicate that diet features may induce both behavioural and morphological plastic responses. High-quality diets may be linked to competition for trophic resources, increasing development rates and determining higher competitive ability.