Mimicry, an adaptation to deceive, fascinated early naturalist and has been proof of evolution by natural selection since proposed by Henry W. Bates 150 years ago. Yet, despite the abundant theoretical and empirical work that it has inspired, little is known of effects in intra and interspecific communication that might result from resembling phenotypic traits of sympatric species. In this dissertation research I studied sexual behavior and communication in Heliconius, a genus of diverse toxic butterflies with extraordinary convergence in wing coloration, habitat preferences and flight characteristics. Well-known ecological interactions and evolutionary history of Heliconius contrast with a poor understanding of key elements of their sexual behavior and intraspecific communication, which are central for the evolution of mimicry in this genus of butterflies. This thesis starts with an introduction that, expanding on the ideas above, explains the motivation behind studying sexual communication and behavior in Heliconius. In the subsequent four chapters I report on two aspects of sexual behavior that are presumably connected in these butterflies with the occurrence of mimicry: Pupal mating behavior and antiaphrodisiac pheromones. Pupal mating is a mate-searching strategy wherein males find females when still immature and guard them with the goal of mating at female eclosion. This mating behavior might have influenced the evolution of mimicry as males rely less on commonly used species recognition traits that in mimetic Heliconius are shared with coexisting species. I identified cues males use to find and recognize conspecific immatures, which not only come from the animal themselves but also from the host plant where they are located. Chemical and visual cues are involved in the process of finding partners, but only sex-specific pheromones allow males to identify females before their eclosion. The second aspect of sexual behavior studied in Heliconius involved the identification of a pheromone that, after being transferred to females at mating, renders them unattractive to courting males. Variation in the chemical composition of such antiaphrodisiacs across eleven species in this genus showed that, contrary to my expectations, there is no evidence that mimicry has affected the evolution of this signal. Instead, I found that clade-specific mating systems in these butterflies adequately explain the observed patterns of interspecific variation. / text

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Male-typical copulatory behaviors such as mounting and intromission are dependent on testicular androgens in most vertebrates, being eliminated by castration and re-instated by administration of exogenous testosterone. Testosterone implants in the preoptic area (POA) can re-instate behavior as effectively as systemic testosterone replacement, implicating this area as a critical locus of hormonal gating. The cellular mechanisms underlying this gating phenomenon are not well understood, but according to one model, testosterone induces an up-regulation of nitric oxide synthase (NOS) in the POA, increasing nitric oxide synthesis following exposure to a sexual stimulus. Nitric oxide in turn, possibly through its effect on catecholamine turnover, influences the way the stimulus is processed and enables the appropriate copulatory behavioral response. The experiments described in this Dissertation were designed to test this model as it pertains to hormonal gating in Cnemidophorus lizards. Specifically, experiments were conducted to test the predictions that nitric oxide synthesis inhibition would suppress the expression of behavior; that preoptic nitric oxide synthesis would be greater in animals expressing copulatory behavior; and that preoptic NOS expression, at both the mRNA and the protein levels, would be greater in animals exposed to testosterone than in animals deprived of hormone. All three of these predictions were upheld, offering support to the model as described. / text

In animal communication, individuals within a species often vary widely in their behavioral responses to species-typical signals. These variations in behavior may be due to differences in the sensory processing of communication signals. Sensory processing of behaviorally relevant stimuli is likely to be influenced by reproductive hormones. Here I report investigations on the influence of sex and reproductive condition on auditory processing in the green treefrog, Hyla cinerea. I conducted electrophysiological experiments that tested how sex and reproductive condition influence the neural representation of sounds in the auditory midbrain, the torus semicircularis. I found differences between and within the sexes that were both frequency-dependent (low vs. high frequency) and stimulus-dependent (tones vs. calls). For sex differences at auditory threshold, females were less sensitive to frequencies outside the spectral range of the male advertisement call and were not different from males inside the range. Sex differences were also stimulus-dependent with females more sensitive to the advertisement call than males. For stimuli consistent with close-range communication, I tested whether or not sex differences in response strengths to advertisement call and noise stimuli depended on the reproductive state of the female. I found that in response to low frequency stimuli postmated females had significantly reduced response strengths compared to males and unmated females. Additionally, I tested whether circulating reproductive hormones influenced auditory processing by manipulating androgen levels and assessing neural thresholds and response strengths to auditory stimuli. Elevated androgen levels in females resulted in increased thresholds and reduced response strengths but only in response to stimuli that are consistent with species-typical communication. Together the evidence from these studies suggest that sex and reproductive hormones influence auditory processing in a way that shapes the filtering properties of the auditory system for the detection of communication signals.

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This study investigates the colonization of Barbados, the seasonality of breeding, and the function of breeding plumes in the cattle egret Bubulcus ibis ibis. Colonization occurred around 1956, and the island now has 4 colonies. Numbers of birds at each colony are still increasing. Colonies are evenly spaced around the island. Plumage scores varied seasonally, and males had higher scores than females. Breeding activity peaked in July-August and November-March. Conspecific interference may force poorly plumed birds to breed when environmental conditions are poor. Chick mortality was primarily from starvation during periods of low breeding activity, and primarily from conspecific attack during high breeding activity. Fledging success did not increase with breeding activity. Plumage scores correlated positively in breeding pairs. Well-plumed males fed chicks more often than poorly plumed males and had the higher fledging success. Males contributed more to nest and nestling attendance when their mates were well plumed. Plumes appear to indicate the potential paternal care and the genetic quality of a mate.

A survey of a natural population of Aquarius remigis, a stream dwelling water strider, living in East Turkey Creek, Arizona, USA, revealed that they were mostly found in either pairs consisting of one male and one female, or in small female biased groups. Chi-squared analysis confirmed that this finding was not due to random chance. The sex ratios were manipulated to further test this observation, that is, that the water striders would return to the most commonly observed sex ratio combinations even after being deliberately rearranged. Pairs of water striders or female biased sex ratios were observed in the experimental pools after a 24 hour period. Behavioural experiments conducted in the laboratory were performed to investigate the possible behavioural interactions that could influence the sex ratios observed in the field. Artificial pools with three water striders, in four sex ratio combinations, and four water striders, in five sex ratio combinations, were used. (Abstract shortened by UMI.)

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Thesis (Ph. D.)--Oregon State University, 1989. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.