Commensalism at climate extremes: Investigating the biogeography of large-bodied Australian ectotherms

Ectotherms depend on the environment for thermoregulation and thus may rely on habitat features, such as the presence of thermal refuges, to persist during otherwise environmentally unfavourable periods. This issue is particularly acute for large-bodied oviparous reptiles, such as monitor lizards, which have long incubation periods during which eggs can experience extreme seasonal/environmental fluctuations without any parental care. Despite this, monitor lizards have a wide distribution in Australia with some species ranging from the tropics to cool temperate regions. How do these large reptiles persist in such a wide range of environments given that long incubation periods risk exposing their eggs to extremely variable environmental conditions?
Using the lace monitor (Varanus varius) as a model organism, I will examine how changes in reproductive behaviour might facilitate range expansion into more extreme environments. Specifically, I will test the hypothesis that termite mounds provide a warm, stable nesting environment that enable lace monitors to penetrate and persist in seasonally cool environments in Australia. To do this, I will survey termitaria across the latitudinal range of the species to quantify the frequency of termite mound nesting, anticipating that the frequency of this nesting behaviour will increase in cooler climates at higher latitudes. I will assess the importance of termite mound nesting by deploying thermal and hydric data loggers in live termitaria, dead termitaria, and nearby alternative nest sites such as burrows to compare how the nesting environment differs between potential nest sites along the latitudinal gradient. I will then perform incubation experiments to determine how the observed environmental differences between nest sites impacts lace monitor hatching success. I hypothesize that termite mounds will provide increasingly more favourable sites for lace monitor nesting and hatching success at higher latitudes, thereby enabling the penetration and persistence of monitor species in cold climates.