Variation in nocturnal light levels does not alter mate choice behavior in female eastern gray treefrogs (Hyla versicolor)

Abstract

Nocturnal light levels vary throughout the course of the lunar cycle, being darkest during the new moon and brightest during the full moon. Many nocturnal animals change their behavior in response to this natural variation in moonlight intensity. Frequently, these behavioral changes can be attributed to the way in which moonlight affects the ability of predators to spot potential prey. Mate sampling females may expose themselves to predators, making mate choice a behavior likely influenced by moonlight. Because mate choice is an important cause of sexual selection, understanding the causes of variation in mate choice decisions can yield a better understanding of the strength and direction of sexual selection under natural conditions. We predicted that female eastern gray treefrogs (Hyla versicolor) would prefer longer calls (i.e., more attractive males) and/or be choosier, under darker conditions, because cover of darkness may aid in predator evasion. However, light treatment did not affect how females responded to variation in call duration, nor did it affect female choosiness or aspects of their approach behavior. This suggests that in gray treefrogs, variation in light levels associated with the changing phases of the moon does not alter the sexual selection regime on male call traits. Looking for the perfect mate can be very dangerous, especially when environmental conditions make it more likely to be spotted by potential predators. Changes in mate choice behavior associated with predator exposure is quite common in nature, yet have rarely been examined in connection with the drastic variation in nocturnal illumination associated with the changing phases of the moon. We investigated whether females of a nocturnal treefrog change their behavior depending on whether they look for mates under simulated new moon or full moon conditions. We found that females preferred longer calls under both conditions, and that they also did not move more stealthily during bright compared to dark conditions. Our results suggest that males with long calls always have a mating advantage, and that sexual selection by female choice is uniformly strong across the lunar cycle.