Frog and toad larvae become vegetarian when it is hot

Abstract

Temperature changes alter the relative quality of plant and animal diets for ectotherms. Omnivorous amphibian tadpoles avoid protein-rich diets at higher temperatures simulating heat waves, and two out of three species benefit from this diet shift. Tadpoles may optimize energetic intake by increasing herbivory at higher temperatures.Recent climate change has unfolded many ecological questions, and the influence of temperature on nutrient acquisition by ectothermic organisms became the focus of several studies, whose results suggest that increasing herbivory should allow ectotherms to cope with the greater nutritional demands of higher temperatures. 1 Indeed, under the current climatic projections, a better understanding of temperature and nutrient interactions across ecological organization levels is crucial to realistically predict responses to global change. 2 Since most experimental research neglected the importance of discrete weather events as components of climate change, the authors decided to study the effects of heat waves on nutrient acquisition by aquatic omnivorous ectotherms.Temperature has different scaling effects on the various components of ectotherm metabolism, which may result in a greater assimilation of plant material at higher temperatures through two distinct pathways. First, through a passive effect upon nutrient assimilation, as the imbalanced temperature effects on metabolic processes may positively discriminate plant diets (carbohydrate-rich) at higher temperatures. By promoting a greater increase in feeding and gut passage rates than in assimilation rates at the intestine wall, higher temperatures may hamper the assimilation of slow digestion nutrients such as proteins, and favor the assimilation of smaller and structurally less complex nutrients, thereby increasing the relative assimilation efficiency of carbohydrates. Second, through an active modulation of ectotherm feeding preferences that increases the consumption of plant diets at higher temperatures. Plant diets are rich in carbohydrates, which are fast energy sources that should allow ectotherms to compensate for the lower assimilation efficiency at higher temperatures. Furthermore, high temperatures promote a greater increase in respiration than in growth, increasing the demand for carbon over nitrogen, which could motivate ectotherms to feed selectively and increase the consumption of plant diets at higher temperatures.The relationship between ectotherm diet and temperature may be of particular relevance in freshwater communities, as these are mainly composed of ectotherm species. Therefore, rising water temperatures resulting from global warming and extreme climatic events such as heat waves may induce generalized shifts in the trophic position of omnivorous ectotherms. This is especially significant because global climatic models project more frequent, intense and longer lasting heat waves in the areas of the globe currently afflicted by these climatic anomalies, such as the basin of the Mediterranean. Under this new regim...

Revisiting “what do tadpoles really eat?” A 10‐year perspective

“…Diets of omnivorous tadpoles appear to shift with temperature fluctuations (Carreira, 2017;Carreira et al, 2016). Carreira et al (2016) investigated how different temperature regimes affected the trophic status of three common omnivorous tadpoles (Discoglossus galganoi, Hyla arborea, and Hyla meridionalis) inhabiting ponds in the Iberian Peninsula of Western Europe.…”