Perspectives on the Effect of Incubation Temperature on Pine Snake Hatchlings

ABSTRACT The effects of incubation temperature on sex in sea turtles and other reptiles have long been known, but behavioral and morphological effects were unknown. I summarize and synthesize experiments in Northern pine snakes ( Pituophis melanoleucus ) nesting in the New Jersey Pine Barrens that show that incubation temperature directly alters the risks pine snakes face upon hatching, emerging, avoiding predators, and searching for prey. NJ pine snakes are unique among most snakes in North America because females dig their own nests in pine barrens sand and can partly control temperature conditions in the nest. Experimental incubation temperatures included the range of temperatures that occur in natural nests. Incubation temperature affected every morphological and behavioral test that could be devised, and the snakes that were incubated at the lowest temperatures (21°C–23°C) were the most severely affected; there were some adverse effects at 33°C. Incubation period decreased with increasing temperature, while the percentage that hatched was highest at 30°C (98%), but decreased at 32°C. Body length increased to 30°C but decreased thereafter. At the optimal temperature (26°C–28°C): (1) there were fewer morphological abnormalities, (2) they required less time to emerge from the nest and shed, and less time to emerge once their head was exposed, (3) they made more underground tunnels from the nest (e.g., avoiding predators), (4) righting response was lowest and they required less time to move a 3 m course, (5) they fell less often from an incline, could bridge a longer gap and climb a tree faster, and (6) they ate a mouse quicker and avoided predators faster than other incubation groups. The experiments indicate an optimal temperature bounded by adverse outcomes in pine snakes at both low and high temperatures. Implications for offspring survival given temporal patterns of reproductive activities, female options, and climate change are discussed.