The effect of food availability on phenotypic plasticity and phenotypic integration in the hylid frog Hypsiboas pulchellus

Abstract

Background: Changes in food availability usually have an effect on the fitness-related traits of anuran larvae, such as body shape, developmental rate, and body size. Organism: Hypsiboas pulchellus, the South American common tree frog. Aim: Analyse the effect of food availability on larval survival, developmental rate (Gosner stage at the end of the experiment), body size (body mass and total length), body shape (the ratio between body length and total length), and intestine size (gut dry mass and gut length). Methods: We exposed tadpoles of H. pulchellus, all from a single clutch, to different levels of food availability. We set up eight food availability groups of five individuals each. After 39 days, we measured all phenotypic variables studied. We used linear and logistic regressions to analyse the data. We also used a structural equation modelling approach to evaluate the likelihood of ten causal models of covariation among the phenotypic traits (derived from four major biological hypotheses). Results: Three traits were observed to vary positively with food availability: developmental stage, body size, and gut size. Tadpole survival did not change with food availability. The results of structural equation modelling indicate that: (1) food availability acts directly on body size and gut size, (2) body size directly affects developmental rate, and (3) developmental rate acts directly on body shape. Conclusions: The present study supports the idea that anuran larvae are strongly affected by food availability. It also illustrates how structural equation modelling can increase our understanding of phenotypic integration among several traits that respond to changes in food availability.