Preferred Session: Natural History of Amphibians 

Abstract:

Thigmothermy – the thermoregulatory behavior by which an organism seeks out contact with a warm substrate or object to affect body temperature – is a behavior present in most amphibians with limited access to solar radiation. It is often (correctly) assumed but poorly documented, It typically involves making exaggerated body contact with a warmer than ambient substrate. Thigmothermy has been shown in the Andean Toad (Rhinella spinulosa) during rainfall when its body temperature corresponded to warmer substrate temperatures and not to cooler air temperatures. However, for amphibians, substrate contact may serve a dual purpose: heat absorption by conductivity (thigmothermy) and water absorption through the skin (not thigmothermy). Determination of which is the driving force of the behavior may not always be possible. My observations provide examples of thigmothermy in endangered Arroyo Toads (Anaxyrus californicus). Rather than “casual” thigmothermy – that is, deriving a thermoregulatory benefit by being active and in substrate contact above a critical thermal minimum – my observations evidence the seeking out of warmer-than-ambient substrates by gravid females disproportionately to adult male, non-gravid female, and juvenile Arroyo Toads, which I hypothesize may facilitate egg maturation. Substrates used by some gravid females eliminate the dilemma of purpose.

The chance to study Plethodon cinereus for Ernest Williams at Harvard's Museum of Comparative Zoology – involving extensive field work throughout New England - was Bill's introduction to the amphibian world. His consequent (decades later) interest in the Arroyo Toad was heightened when he serendipitously found scores of these toads out and about on a wet San Diego winter night. Based on all the literature to that date, they should not have been. As with his upcoming presentation, he believes that if you watch an animal long enough, it will most likely contradict something that you thought you knew was true.