Comparisons of behavioural and TRPA1 heat sensitivities in three sympatric Cuban Anolis lizards.

Thermal tolerances of organisms play a role in defining geographic ranges and occurrence of species. In Cuba, three sympatric species of Anolis lizards (Anolis allogus, Anolis homolechis and Anolis sagrei) inhabit different thermal microhabitats. A previous study found that these species showed distinct gene expression patterns in response to temperature stimuli, suggesting the genetically distinct thermal physiology among species. To investigate whether the Anolis species inhabiting locally distinct thermal habitats diverge their thermal tolerances, we first conducted behavioural experiments to analyse the temperatures at which the three Anolis species escape from heat source. Then, for each of the three species, we isolated cDNA encoding a putative molecular heat sensor, transient receptor potential ion channel ankyrin 1 (TRPA1), which has been suggested to play a role on eliciting behavioural responses to heat stimuli. We performed electrophysiological analysis to quantify activation temperature of Anolis TRPA1 to see whether the pattern of divergence in TRPA1 responses is congruent with that of divergence in behavioural responses. We found that temperatures triggering behavioural and TRPA1 responses were significantly lower for shade-dwelling species (A. allogus) than for sun-dwelling species (A. homolechis and A. sagrei). The ambient temperature of shade habitats where A. allogus occurs stays relatively cool compared to that of open habitats where A. homolechis and A. sagrei occur and bask. The high temperature thresholds of A. homolechis and A. sagrei may reflect their heat tolerances that would benefit these species to inhabit the open habitats.

Differentially expressed genes associated with adaptation to different thermal environments in three sympatric Cuban Anolis lizards.

How animals achieve evolutionary adaptation to different thermal environments is an important issue for evolutionary biology as well as for biodiversity conservation in the context of recent global warming. In Cuba, three sympatric species of Anolis lizards (Anolis allogus, A. homolechis and A. sagrei) inhabit different thermal microhabitats, thereby providing an excellent opportunity to examine how they have adapted to different environmental temperatures. Here, we performed RNA-seq on the brain, liver and skin tissues from these three species to analyse their transcriptional responses at two different temperatures. In total, we identified 400, 816 and 781 differentially expressed genes (DEGs) between the two temperatures in A. allogus, A. homolechis and A. sagrei, respectively. Only 62 of these DEGs were shared across the three species, indicating that global transcriptional responses have diverged among these species. Gene ontology (GO) analysis showed that large numbers of ribosomal protein genes were DEGs in the warm-adapted A. homolechis, suggesting that the upregulation of protein synthesis is an important physiological mechanism in the adaptation of this species to hotter environments. GO analysis also showed that GO terms associated with circadian regulation were enriched in all three species. A gene associated with circadian regulation, Nr1d1, was detected as a DEG with opposite expression patterns between the cool-adapted A. allogus and the hot-adapted A. sagrei. Because the environmental temperature fluctuates more widely in open habitats than in forests throughout the day, the circadian thermoregulation could also be important for adaptation to distinct thermal habitats.