Austin Stanley Rand

Consistency of female choice in the tungara frog: a permissive preference for complex characters

Previous phonotaxis experiments in the túngara frog, Physalaemus pustulosus, indicated a permissiveness in female preference that allows sexually selected complex call characters to be replaced with various alternative characters. Although they prefer complex to simple calls, females as a group did not discriminate between several alternative complex characters appended to the simple conspecific call. However, these studies did not address the possibility that the apparent permissiveness in female preference occurred because of an averaging of population data. The observed patterns in female preference could result from all females finding a certain set of call variants equally attractive, or from a polymorphism in female call preference. To discriminate between these two alternatives, consistency of mate choice was determined for three pairs of calls that elicited no phonotactic bias in population studies. Individual females did not repeatedly choose one stimulus of a pair over the other, demonstrating that the patterns of permissiveness observed in the population are paralleled by similar patterns within females. A broad preference for complex calls in the P. pustulosus species group would permit the evolution of sexually selected call variation through sensory exploitation. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

Effects of inter-pond distance on the breeding ecology of tungara frogs

Abstract Habitat and resource distributions can influence the movement and aggregation of individuals and thus have important effects on breeding behavior and ecology. Though amphibians have been model systems for the study of breeding behavior and sexual selection, most studies have examined breeding behavior within a single pond. As a result, little is known about how inter-pond distance affects breeding amphibians. We studied the effects of inter-pond distance on the breeding ecology of the tungara frog, Physalaemus pustulosus, in replicated pond arrays in which distance was varied from 0 to 50 m. We predicted that male site fidelity and male aggregation within arrays would increase with inter-pond distance, and that the opportunity for mate choice and oviposition site selectivity by females would decrease with the distance between ponds. Male site fidelity did increase with inter-pond distance. However, male aggregation decreased with distance, such that males tended to be more evenly spaced among ponds when ponds were farther apart. The opportunity for mate choice by females, measured as the number of males within the phonotactic radius of females, also decreased with inter-pond distance. Each of these three responses was consistent with a threshold effect between 5 m and 10 m in inter-pond distance. This threshold corresponded to the maximum distance at which females in laboratory choice experiments exhibited phonotaxis toward the ”whine” call of a tungara male, suggesting that phonotactic limits may play an important role in tungara movements and spacing patterns. The distribution of egg masses among ponds, a potential correlate of oviposition site selectivity, did not vary with inter-pond distance. Multiple egg masses deposited on the same night were significantly overdispersed in all distance treatments, implying that females may select oviposition sites to avoid conspecific egg masses over distances of at least 50 m. Collectively, these results demonstrate that inter-pond distance may indeed affect amphibian breeding and movement behavior, and that consideration of multiple habitat patches and their spatial distributions can provide new insights into even the most well-understood mating systems.

Signal variation and call preferences for whine frequency in the tungara frog, Physalaemus pustulosus

Abstract Properties of sexual signals can differ in the amount of within-male variability. In several species of anurans, females exert stabilizing or weakly directional preferences on less variable call properties, and highly directional preferences on more variable ones. Preferences of female túngara frogs, Physalaemus pustulosus, were examined for two call characteristics: a less variable spectral character, dominant frequency of the whine, and a more variable temporal character, inter-call interval. Eight phonotaxis experiments using synthetic calls were conducted with gravid females. Stimuli presented for both characters were based on the mean and standard deviation (SD) of those characters in the study population. For each character, we used four intervals of variation (1, 2, 3, and 4 SD) between stimuli in four different experiments. As has been found in some other anuran species, preference was stronger for the more variable temporal character, increasing in proportion to the difference between stimuli. Preference for the less variable spectral character was not significant until the difference between stimuli was substantial. The strength of female preference, estimated as latency to choose, the number of speakers visited, and the number of females showing phonotaxis, increased in proportion to the increase in the difference between stimuli. All these measures of strength of preference were greater in response to the more variable temporal character compared to responses to the less variable spectral character.

Vestigial preference functions in neural networks and túngara frogs

Although there is a growing interest in understanding how perceptual mechanisms influence behavioral evolution, few studies have addressed how perception itself is shaped by evolutionary forces. We used a combination of artificial neural network models and behavioral experiments to investigate how evolutionary history influenced the perceptual processes used in mate choice by female túngara frogs. We manipulated the evolutionary history of artificial neural network models and observed an emergent bias toward calls resembling known ancestral states. We then probed female túngara frogs for similar preferences, finding strong biases toward stimuli that resemble a call hypothesized for a recent ancestor. The data strongly suggest that female túngara frogs exhibit vestigial preferences for ancestral calls, and provide a general strategy for exploring the role of historical contingency in perceptual biases.

Patterns of mating call preferences in túngara frogs, Physalaemus pustulosus

We examine acoustic mating preferences of a focal population at four different scales of divergence: within the population, between populations in the same genetic group, between populations in different genetic groups and between different species. At all scales there is substantial genetic divergence, variation in mating signals and preferences are influenced by signal variation. There is, however, no support for the hypothesis that mating preferences accumulate predictably with genetic distance. Females preferred the local conspecific call to the foreign conspecific call in about one‐third of the experiments, and preferred the local call to all of the heterospecific calls tested. But there was no significant relationship between the variation in the strength of preference and genetic distance either among conspecific populations, or among heterospecific species. Thus, in this study macroevolutionary patterns are not apparent at the microevolutionary scale.

RESPONSE TO VARIATION IN CHUCK FREQUENCY BY MALE AND FEMALE TÚNGARA FROGS

We examined how male and female túngara frogs, Physalaemus pustulosus, respond to variation in the frequency spectrum of the chuck component of the advertisement call. We varied chuck frequency in two different ways. In the fixed frequency series, the sequence of calls within each series had chucks of the same dominant frequency. Different fixed-frequency series had chucks of different dominant frequencies designated as high, high–medium, medium, medium–low, or low frequency relative to variation in the test population. In the second varying frequency series, the sequence of calls varied in the chucks dominant frequency such that the individual series had the same average frequencies as the high, high–medium, medium, medium–low, and low fixed-frequency experiments. Both males and females tended to respond more to lower-frequency chucks. The responses of both sexes to the same mean chuck frequency was similar to the fixed- and varying-frequency series of chucks.