Date of Award

May 2018

Degree Type

Thesis

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Gerlinde Höbel

Committee Members

Peter Dunn, Rafael Rodríguez

Keywords

Choosiness, Hyla versicolor, Light pollution, Lunar cycle, Mate Choice Behavior, Preference Function

Abstract

Chapter 1: While the influence of environmental variables, particularly temperature and rainfall, on the breeding behavior of amphibians is widely recognized, relatively few studies have addressed how the moon affects amphibian behavior. Yet, the lunar cycle provides several rhythmic temporal cues that animals could use to time important group events such as spawning, and the substantial changes in light levels associated with the different moon phases may also affect the behavior of nocturnal frogs. Using seven years of field observation data, we tested for lunar effects on the reproductive activity of male and female Eastern gray treefrogs (Hyla versicolor). We found that chorusing and breeding activity was statistically more likely to occur around the first quarter of the moon and during intermediately bright nights, but that reproductive activity also occurred during various other times during the lunar cycle. We discuss these findings in relation to the two main hypotheses of lunar effects on animals: predator avoidance and temporal synchronization of breeding.

Chapter 2: 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.

Chapter 3: Human activities are drastically changing the amount of artificial light entering natural habitats. Because light pollution alters the sensory environment, it may interfere with behaviors ranging from prey detection and vigilance to mate choice. Here we test the hypothesis that anthropogenic light pollution affects the mate choice behavior of female Eastern gray treefrogs (Hyla versicolor). We tested this hypothesis under two experimental light treatments that simulate the light pollution created by streetlights (i.e., expansion of lit areas and increased light intensity), and the light pollution created by headlights of passing vehicles (i.e., rapid fluctuations between bright and dark conditions). The hypothesis predicts that females tested under conditions simulating light pollution will show behavioral changes geared towards mitigating detection by predators, such as relaxed preferences, decreased choosiness for the normally preferred call, and differences in approach behavior (either more directional, faster, or stealthier movements, or no approach at all). Contrary to our prediction, we found that light pollution did not affect mate choice behavior in gray treefrogs, and should therefore neither interfere with population persistence nor affect the sexual selection regimes on male call traits of this species. However, we caution that this result does not imply that anthropogenic light pollution is of no concern for amphibian conservation, because behavioral responses to variation in nocturnal light levels (both in the natural as well as anthropogenically enhanced range) seem to be highly species-specific in anurans. We encourage additional studies to help gage the vulnerability of anurans to anthropogenic light pollution.

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