Taking the heat: can mothers buffer global warming and still produce smart babies?

Global warming is a major threat to global biodiversity, particularly to reptiles because early developmental temperatures influence their life-history and survival. In fact, rising global temperatures have already caused widespread extinctions among lizards. Nonetheless, most research on climate change has focused on the impacts on species and population persistence while ignoring key behavioural and physiological responses. I investigated the ability of lizards to respond to changes in their early thermal environment in relation to their mode of reproduction and the impact of incubation temperatures on their learning ability and brain development. Global warming is changing how animals interact with their environment. The brain as the source of behavioural and physiological control will be prone to selection favouring animals that adapt to a rapidly changing environment. However, it is still unclear which brain regions/processes are vulnerable to changes in developmental temperature. Chapter I reviews the existing literature about the effect of elevated developmental temperatures on the ectotherm brain. I provide a perspective on the potential effects of rising temperatures due to global warming on the brain and a framework for future research in the field. Viviparous lizards are considered to be more vulnerable to global warming compared to oviparous lizards although this is not without debate. Nevertheless, this hypothesis has been rarely tested. Chapter II investigated whether the effect of high developmental temperatures on hatchling’s morphology and physiological performance differed between oviparous and viviparous populations of a lizard species (Saiphos equalis) with geographic variation in its reproductive mode. My results show that, regardless of their reproductive mode, global warming will likely have a negative impact on lizard phenotype. High developmental temperatures have a negative effect on morphology and performance in most species studied to date. However, less is known about the effect of high temperature on behavioural and cognitive traits. Chapter III investigates the effect of elevated developmental temperatures on hatchling behaviour and learning ability in viviparous and oviparous populations of S. equalis. Viviparous lizards were less impacted by elevated developmental temperatures suggesting that maternal behaviour and/or physiology may ameliorate some effects of global warming. Behavioural thermoregulation is perhaps the most important way in which female lizards control the developmental environment of their offspring. However, few studies have tested this premise in relation to global warming. In Chapter IV, I used viviparous S. equalis to test if female thermoregulatory behaviour could mitigate the negative effects of global warming on their offspring’s phenotype and if behavioural thermoregulation during pregnancy has a negative impact on females. My results suggest that although females can mitigate some negative effects of global warming on their offspring, this is not complete protection and females might incur in a cost. Elevated developmental temperatures affect the brain anatomy and cognitive ability of reptiles. However, it remains unclear if the effect of elevated temperatures on hatchlings’ and learning ability is transitory. Chapter V examined the effect of high incubation temperatures on the gecko Amalosia lesueurii to test: 1) if elevated temperatures affect hatchlings’ learning ability, 2) if this effect persists in juvenile lizards, and 3) if these differences in learning ability match changes in lizards’ brain anatomy. I found that elevated temperatures reduced the learning performance of hatchlings, but this effect disappeared once they were juveniles. Interestingly, we did not find an effect of elevated temperature on the brain anatomy of hatchlings and juveniles. In summary, this thesis provides novel information into the extent to which lizards with different reproductive mode can modify key life-history traits in response to global warming. It also provides experimental evidence supporting an increased vulnerability of viviparous species to global warming. Finally, my results suggest that the negative effect of high incubation temperatures on lizard’s cognitive ability might be transitory.