A lizard bathes in the afternoon sun on a rock in Uttarakhand, northern India. Photo: Sujayadhar / Wikimedia Commons

By Tim Radford
16 June 2015 LONDON (Climate News Network) – Scientists in California have identified a cold-blooded killer as global warming brings new hazards for ectotherms − creatures that cannot regulate their own body heat. The suggestion may seem counter-intuitive, as vipers, lizards, fish and frogs all depend on ambient warmth to keep their metabolisms busy. But while endotherms – among them mammals − have ways of keeping themselves cool on hot days, lizards and their like might not be so flexible and could overheat. Alex Gunderson and Jonathon Stillman, biologists at the Romberg Tiburon Centre for Environmental Studies at San Francisco State University, report in the Proceedings of the Royal Society B that they tested their suspicions about overheating risks by combing through 112 published studies that delivered 394 estimates of potential temperature tolerance in 232 species of ectotherm − laboratory species that had been tested in extremes of hot and cold. Their sample of the cold-blooded living things included amphibians, reptiles, crustaceans and insects, land-dwellers and water-dwellers. They found evidence that all had some ability to acclimate – that is, adapt to different temperatures – and some, such as fish, crab, lobster and shrimp, had more tolerance to acclimation than others. But, overall, many of them proved less likely to tolerate increasingly extreme climate swings. “Because animals have some ability to acclimate to higher temperatures, scientists hoped that they might be able to adjust their physiology to keep up with global warming,” Dr Gunderson says. “We found by compiling these data in the first large-scale study of hundreds of different animals that the amount they can actually adjust is pretty low. They don‘t have the flexibility in heat tolerance to keep up with global warming.” Global warming and attendant climate change is believed to threaten one species in six with extinction. It can do this by amplifying and adding to a range of existing hazards, threats and pressures such as habitat destruction, or over-hunting, or by changing in a few decades a whole climatic regime to which species have adapted over tens of thousands of years. […] “Our results suggest that their ability to acclimate to increasing temperatures will not buffer them from the changes that are occurring, and that they are going to have to depend on behavioural or evolutionary change to persist,” Dr Gunderson says. [more]

Temperatures soar to danger point for sun-loving creatures

ABSTRACT: Global warming is increasing the overheating risk for many organisms, though the potential for plasticity in thermal tolerance to mitigate this risk is largely unknown. In part, this shortcoming stems from a lack of knowledge about global and taxonomic patterns of variation in tolerance plasticity. To address this critical issue, we test leading hypotheses for broad-scale variation in ectotherm tolerance plasticity using a dataset that includes vertebrate and invertebrate taxa from terrestrial, freshwater, and marine habitats. Contrary to expectation, plasticity in heat tolerance was unrelated to latitude or thermal seasonality. However, plasticity in cold tolerance is associated with thermal seasonality in some habitat types. In addition, aquatic taxa have approximately twice the plasticity of terrestrial taxa. Based on the observed patterns of variation in tolerance plasticity, we propose that limited potential for behavioural plasticity (i.e., behavioural thermoregulation) favours the evolution of greater plasticity in physiological traits, consistent with the ‘Bogert effect’. Finally, we find that all ectotherms have relatively low acclimation in thermal tolerance and demonstrate that overheating risk will be minimally reduced by acclimation in even the most plastic groups. Our analysis indicates that behavioural and evolutionary mechanisms will be critical in allowing ectotherms to buffer themselves from extreme temperatures.

Plasticity in thermal tolerance has limited potential to buffer ectotherms from global warming