Effect of elevated incubation temperatures on learning and brain anatomy of hatchling and juvenile lizards

Global warming is a major threat to reptiles because temperature strongly affects their development. High incubation temperatures reduce hatchling body size and physiological performance; however, its effects on brain development and learning abilities are less well understood. In particular, it remains unclear if the effects of elevated temperatures on learning are restricted to hatchlings or instead will persist later in life. To address this gap, we examined the effect of 'current' and 'future' (end-of-century, + 4 °C) incubation temperatures on hatchling and juvenile geckos Amalosia lesueurii, to test: (1) if elevated temperatures affect hatchling learning ability; (2) if the effects on learning persist in juvenile lizards, and (3) if and how elevated temperatures affect hatchling and juvenile brain anatomy and neuronal count. We found that fewer future-incubated hatchlings succeeded in the learning tasks. Nonetheless, the successful ones needed fewer trials to learn compared to current-incubated hatchlings, possibly due to a higher motivation. Reduced learning ability was still observed at the juvenile stage, but it did not differ between treatments due to a reduced cognitive performance of current-incubated juveniles. Future-incubated hatchlings had a smaller telencephalon, but this pattern was not found in juveniles. Neuron number and density in hatchlings or juveniles from both treatments were not different. Our results suggest that global warming will affect hatchling survival in the wild but it remains unclear if future-incubated lizards could compensate for the harmful effects of elevated temperatures. Further testing beyond the laboratory is required to understand whether phenotypic plasticity in lizards is sufficient to track global warming.