Warm vegetarians? Heat waves and diet shifts in tadpoles

Abstract

Temperature can play an important role in determining the feeding preferences of ectotherms. In light of the warmer temperatures arising with the current climatic changes, omnivorous ectotherms may perform diet shifts toward higher herbivory to optimize energetic intake. Such diet shifts may also occur during heat waves, which are projected to become more frequent, intense, and longer lasting in the future. Here, we investigated how heat waves of different duration affect feeding preferences in omnivorous anuran tadpoles and how these choices affect larval life history. In laboratory experiments, we fed tadpoles of three species on animal, plant, or mixed diet and exposed them to short heat waves (similar to the heat waves these species experience currently) or long heat waves (predicted to increase under climate change). We estimated the dietary choices of tadpoles fed on the mixed diet using stable isotopes and recorded tadpole survival and growth, larval period, and mass at metamorphosis. Tadpole feeding preferences were associated with their thermal background, with herbivory increasing with breeding temperature in nature. Patterns in survival, growth, and development generally support decreased efficiency of carnivorous diets and increased efficiency or higher relative quality of herbivorous diets at higher temperatures. All three species increased herbivory in at least one of the heat wave treatments, but the responses varied among species. Diet shifts toward higher herbivory were maladaptive in one species, but beneficial in the other two. Higher herbivory in omnivorous ectotherms under warmer temperatures may impact species differently and further contribute to changes in the structure and function of freshwater environments.

Nutrient‐specific compensation for seasonal cold stress in a free‐ranging temperate colobine monkey

“…Likewise, grasshoppers that could perceive the presence of a predator (spider) selected an intake target higher in carbohydrates than did controls (Hawlena & Schmitz, 2010). Other studies have shown that omnivorous invertebrates increase the relative intake of plant over animal tissue at higher temperatures Carreira, Segurado, Laurila, & Rebelo, 2017;Carreira et al, 2016;Malzahn, Doerfler, & Boersma, 2016), presum-ably to obtain extra carbon to meet the increased metabolic costs for ectotherms at higher temperatures . Studies using chemically defined diets specifically showed that mealworms (Tenebrio molitor L.) (Rho & Lee, 2017) and Spodoptera litura caterpillars (Lee, Jang, Ravzanaadii, & Rho, 2015) increased their preference for carbohydrate relative to protein at higher temperatures.…”

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

“…Therefore, a better understanding of the relationship between tadpole diets and temperature becomes increasingly relevant in predicting the future structure and function of freshwater communities, which are predominantly composed of ectothermic species. Omnivorous tadpoles may adapt to increasing temperatures through the optimisation of energetic intake via a relative increase in plant matter consumption (Carreira et al, 2016). Although similar adaptations have been observed in omnivorous invertebrates (Boersma et al, 2016;Clissold, Coggan, & Simpson, 2013;Lee, Jang, Ravzanaadii, & Rho, 2015); it is less clear whether this response is likely to occur in other ectothermic omnivorous vertebrates as temperatures continue to increase.…”

“…Furthermore, Arribas et al (2015) observed both P. cultripes and Pelophylax perezi feeding at a higher ratios showed support for omnivory and suggested that some degree of diet specialisation in these tadpoles was probably influenced by temperature changes. Omnivorous tadpoles may adapt to increasing temperatures through the optimisation of energetic intake via a relative increase in plant matter consumption (Carreira et al, 2016). Discoglossus galganoi, which is primarily carnivorous, became more herbivorous and assimilated a higher proportion of plant material in the spring temperature treatment of 17-21°C (which simulated temperature rising during spring).…”

“…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. Results based on δ 15 N isotopic ratios showed support for omnivory and suggested that some degree of diet specialisation in these tadpoles was probably influenced by temperature changes.…”

Frog and toad larvae become vegetarian when it is hot

“…1B). 1 The proportions of animal and plant material assimilated by tadpoles offered both diets simultaneously were estimated using stable isotopes ( 13 C/ 12 C, 15 N/ 14 N), which allow reliable and time-integrated estimates of their diets, despite not directly quantifying consumption.…”