Raul Costa-Pereira, Benjamin Toscano, Franco L. Souza, Travis Ingram and Márcio S. Araújo
Animals must consume food and convert this food to energy to maintain bodily functions, grow and produce offspring. Recent research suggests that otherwise similar individuals within a population may differ in their food choices over time. For example, some individuals may consume a single type of food (“specialists”) while others may consume all available types of food (“generalists”). Because food types differ in the energy they provide, these choices could influence the maintenance, growth and reproductive output of individuals, and therefore their genetic contributions to the next generation (i.e. fitness). In particular, many animals build up energy reserves prior to reproducing because reproduction is energetically costly. Therefore, the degree to which individuals change their diet over this reproductive period could determine their fitness.
- Leptodactylus podicipinus and L. chaquensis, two common species of Thin-toed frogs in the Pantanal wetlands, Brazil (Photo: Matheus Moroti)
We measured individual diet change in thin-toed frogs over their reproductive period and tested how diet change affected frog body condition, the number of parasites they had, and the size of their gonads (i.e. reproductive investment). Thin-toed frogs are useful for such a project because they consume a variety of food types and have a distinct breeding period that occurs when their habitat, the Pantanal wetland, is flooded during the rainy season. We used stable isotopes to measure the way the frogs’ diet changes over time. Stable isotopes provide an integrated record of the food consumed by an individual. For example, muscle tissue integrates all the food consumed over a week. Our study took this idea a step further by measuring for each frog the isotopes of two tissues, liver and muscle, which reflect long and short snapshots of diet, respectively. Thus taking these measurements allowed us to track diet change over time.
We found that within populations some individual frogs have very consistent diets, while other individuals vary substantially in their menus over time. Importantly, within this natural range of individual diet flexibility, frogs that change their diet more during the time period preceding reproduction had better body condition, fewer parasites and larger gonads than individuals that remained more consistent in their diets. Our study shows that the ability to explore alternative food types over time (rather than stick with a specific diet) may be an important one for organisms, shaping how much they grow and their reproductive success.
Functional Ecology: Plain Language Summaries 