Sexual behavior, intraspecific signaling and the evolution of mimicry among closely related species
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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.