Behavioral ecology, ecophysiology, and social dynamics in miniaturized Puerto Rican geckos (Sphaerodactylus)
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The impact of body size on organismal biology continues to fascinate biologists, particularly when considering miniaturized animals at the smallest extremes. Geckos of the genus Sphaerodactylus are characterized by their diminutive size, species richness, and the diverse habitats they occupy across the Caribbean. First, I contextualized Sphaerodactylus within the squamate phylogeny, demonstrating the repeated evolution of miniaturization across 11 families, corroborating brain size as a limiting factor for body size (along with a relative increase in telencephalic volume), and revealing an ecological shift to terrestrial microhabitats [Chapter II]. These findings were used as a springboard to evaluate the potential consequences of miniaturization in Sphaerodactylus with respect to activity patterns [Chapter III], thermal physiology [Chapter IV], and social behavior [Chapter V]. Under natural conditions, I implemented a vibrational monitoring system to characterize activity patterns across leaf litter strata in S. grandisquamis and S. townsendi. Vibrational data revealed that Sphaerodactylus exploit their niche in a threedimensional manner, a pattern thus far underappreciated, and that behavior is used as a mechanism to buffer climatic changes in xeric habitats [Chapter III]. Physiological traits are expected to evolve to favor homeostasis under a species' preferred habitat conditions, regardless of body size, yet few studies have tested whether this pattern extends to miniaturized taxa. I measured standard metabolic rate (SMR) and evaporative water loss (EWL) via open-flow respirometry in five Sphaerodactylus species from three distinct habitat types. Physiological traits exhibited divergence mediated by habitat type -- xeric, mesic, and submontane -- and between sympatric species, indicating that the evolutionary potential of physiological traits was not limited by miniaturization in Sphaerodactylus [Chapter IV]. Lastly, I used S. grandisquamis to study social dynamics, further elucidating the behavioral ecology of a miniaturized leaf litter species. Specifically, I evaluated the possibility of social recognition and the effect of the social environment on individual behavior. Through behavioral assays, I introduced familiar individuals to their own groups and unfamiliar individuals to existing groups. Increased rates of exploratory and agonistic behaviors were performed by group members toward unfamiliar individuals, supporting recognition of familiarity. Furthermore, geckos from multi-male groups showed reduced rates of behaviors toward unfamiliar individuals, including agonistic behaviors, in concert with male-male agonism and potentially increased intersexual conflict within their groups. Social recognition and the effect of the social environment as a modifier of individual behavior are perhaps unexpected for a putatively solitary, miniaturized species. The cognitive processes underlying social behavior may be related to the ecology of Sphaerodactylus, particularly their high population densities, facilitated by miniaturized body size [Chapter V].
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Ph. D.