Sexual Selection and Signal Evolution: Diversification of Peacock Spiders (Genus: Maratus)

Field: Agricultural and Biological Sciences (Life Sciences)

Across taxa, sexual communication is fundamental to an organism’s reproductive fitness, and ultimately, its evolutionary success. Consequently, strong selection pressures often lead to extreme adaptations in male physiology, morphology, and behavior to increase the efficacy of signal transfer to females. Similarly, selection acts on females to detect, process, and respond to information emitted by males. By these processes, theory predicts sexual selection has the potential to drive vast and rapid diversification of some traits, and indeed empirical evidence has shown this to be the case. Of particular interest to biologists are the more extravagant radiations of sexual ornamentation, those characterized by an overwhelming amount of diversity in not just one or two sexually selected traits, but instead on whole suite of signals. While many animals use multi-modal (more than one sensory modality) displays during courtship, the majority of work on female choice has thus far focused on individual signaling elements individually, or species that produce relatively simple, quantifiable displays such as cricket calls, and house finch coloration. Comparable work on systems with extremely elaborate displays has lagged behind, and it remains unclear if the same forces driving the evolution of more basic unimodal signals are the same as those shaping complex displays. For my dissertation research, I have used Australian endemic peacock spiders of the Maratus genus (Family: Salticidae) to explore the role of complex signals in mating behavior and diversification of this group. Members of this genus are ideal study organisms for such research as males use both visual and vibratory displays to attract and secure a mate. The adaptive significance (if any) of complex signaling is poorly understood, as is how females evaluate males based on these signals. Thus, my research has focused on understanding the role of sexual selection in the evolution and maintenance of such elaborate male courtship displays. Specifically, my dissertation work has aimed to: (A) describe multi-modal signal structure in peacock spiders; (B) investigate female preferences for these signals; (C) uncover how different signaling modalities act together or in isolation to affect mating and (D) elucidate patterns of signal evolution and species diversification across the genus. In the first few chapters of this dissertation, I demonstrate that: peacock spider males produce complex multimodal courtship displays; male mating success in M. volans is predicted by suites of combinatorial elements; both vibrations and visual displays are important for male mating success, although visual displays seem to play a more crucial role. The latter part of this dissertation provides a molecular phylogenetic framework of Maratus spiders, and as such, informs our knowledge about the evolutionary history of peacock spider courtship signals. As communication underlies all social networks, this body of research is important because it enhances our understanding of broad scale links between sensory processing, decision-making, behavior, and evolution.