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Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

The causes and consequences of variation in aposematic signals during immature stages are not clearly understood. This thesis explores the effects of early environment on the expression of aposematic signals in the green and black poison frog (Dendrobates auratus), and the consequences of variation in such components in the wild. It also explores how aposematic expression relates to levels of chemical defences in immature froglets. Embryos and larvae of poison frogs in the genus Dendrobates are known to be darkly pigmented. This thesis reports for the first time polymorphism in egg pigmentation in D. auratus and ontogenetic colour change through development reverting to a normally pigmented phenotype; however whether this pigmentation results from constraints or has adaptive consequences remains unclear. Evidence on how immature individuals allocate resources to growth and warning signalling is scarce. Experimental results in this thesis show that food supply during early environment affected body size and signal luminance in post-metamorphic froglets. Therefore the relative importance of these traits in relation to predation risk was further tested, using artificial prey in a field experiment. The results indicated that rates of attack by birds correlated negatively with body size, and on the contrary survival of artificial prey was independent of signal luminance. I therefore tested the hypothesis that in the wild larger, relatively well-nourished juvenile frogs are chemically better defended. I found that in fact larger juveniles are at a selective advantage conferred by their greater foraging efficiency and their superior levels of chemical defences. Overall, these results shows plasticity in aposematic traits in relation to early environmental nutrition in D. auratus; and suggests that acquiring large body size and similar integument colour as to adults are key determinants for survival during the early stages of their terrestrial life.

The worldwide amphibian diversity is severely threatened, mainly due to deforestation. Lack of sufficient knowledge for species conservation is common. This is the first detailed study of the poison dart frog Excidobates mysteriosus including habitat requirements, occupancy patterns and behaviours. It is known only from one location in north-western Peru, living in Bromeliaceae plant species. The frogs and tadpoles were found in two unidentified Bromeliaceae species; Bromeliad Species 1 and Bromeliad Species 2. Bromeliad quality variables were evaluated for habitat requirements, behavioural recordings were performed ad libitum and catching-and-release with photographingof frogs for monitoring dispersals. Results show that for Bromeliad Species 1 significantly more frogs were present in bromeliads that were wider, received less sun exposure, had deeper water cavities and in bromeliads growing on lower altitudes. For Bromeliad Species 2 deeper water cavities had a significant effect on presence of frogs. In both bromeliad species higher presence of tadpoles were found in plants that were wider and had deeper water cavities. The density of bromeliads had no effect on frog or tadpole occupancy for neither bromeliad species. The dispersal, feeding and tadpole release behaviours are reported. Individual frogs were found to disperse 0-113m. The total number of encountered frogs was 1006 and 86 tadpoles, most of them found in three core areas. These areas should be targeted for conservation management and monitoring, diminishing the high deforestation pressure which saves old-growth forests and thereby as well the preferred wider bromeliads containing deeper water cavities and the biggest frog populations.

The home range encompasses an animal’s movements as it goes about its normal activity, and several home range estimators have been developed. I evaluated the performance of the Minimum Convex Polygon, Bivariate Normal, and several kernel home range estimators in a geographical information system environment using simulations and a large database of O. pumilio mark-recapture locations. A fixed 90% kernel estimator using Least-Square Cross-Validation (to select the bandwidth) outperformed other methods of estimating home range size and was effective with relatively few capture points. Home range size, core area size, intrasexual overlap, and movement rates among coordinates were higher in female frogs than in male frogs. These measures likely reflect behavioral differences related to territoriality (males only) and parental care (both sexes). The simple Biological Index of Vagility (BIV) generated movement values that scaled well with home range size while revealing more information than home range estimates alone.

Evolutionary transitions between the two major predator avoidance strategies aposematism and crypsis are expected to be associated with changes in many important traits of animals. However, empirical studies on populations experiencing ongoing or recent transitions between these strategies are rare. This thesis investigates the co-evolution of traits among populations of the Strawberry poison frog D.pumilio in Bocas del Toro, Panama. I found that all investigated populations were genetically distinct but that colour and pattern did not correlate with genetic or geographic distance, which suggests that selection needs to be invoked to explain the observed variation. Based on the chromatic contrast between frog dorsal colour and the natural habitat substrates used by the frogs, the populations were defined as bright or dull coloured. I found that frogs from bright coloured populations were larger. This is expected if aposematism is enhanced by large signals while crypsis is enhanced by small size. Further, individuals from bright coloured populations had a coarser black dorsal pattern, which is expected if crypsis is impaired by a bold pattern. The importance of pattern coarseness was confirmed by an avian detection experiment showing that coarse patterned dark green prey were more easily detected than dark green prey without pattern or with fine pattern. I put forward the hypothesis that enhanced protection, gained by aposematism, may affect behaviours that influence dispersal and pairing patterns. Indeed, males from bright coloured populations displayed at more exposed sites and showed a tendency to be more explorative and aggressive. In summary, my results show that the bright and dull coloured populations most likely represent an aposematic and a cryptic strategy, respectively. Furthermore, I show that evolutionary changes between aposematism and crypsis can be associated with coevolution of both morphology and behaviour. I argue that this coevolution may increase the likelihood of both pre- and post-zygotic reproductive isolation. This is because greater phenotypic differences between populations increase the likelihood of selection against badly adapted migrants and hybrids with intermediate traits.

Flamboyant colors are widespread throughout the animal kingdom. While many of these traits arise through sexual selection, bright coloration can also evolve through natural selection. Many aposematic species, for example, use conspicuous warning coloration to communicate their noxiousness to predators. Recent research suggests these signals can also function in the context of mate choice. Studies of warning color evolution can therefore provide new insights into how the interplay of natural and sexual selection impact the trajectory of conspicuous signal evolution. For my dissertation, I investigated the potential for male-male competition to impact the warning color evolution of a species of poison frog. I focused my work on an exceptionally bright and toxic population of the strawberry poison frog (Oophaga pumilio) where males are brighter than females, a classic signature of sexual selection. In Chapter 1, I used theoretical models of predator and frog visual systems to determine which can see the variation in bright warning coloration within this population. I found that birds, the presumed major predator, likely cannot see this variation, indicating that sexual selection can work under the radar of predators in this species. In Chapter 2, I tested the aggressive responses of males using a two-way choice paradigm that manipulated the perceived brightness of stimulus males. I found that males directed more of their behaviors to bright stimulus frogs, and brighter focal frogs more readily approached stimuli and directed more of their attention to the brighter rival. In Chapter 3, I tested the outcomes of dyadic interactions between males of varying brightness and observed male reactions to simulated intruders in their territories. I found that brighter males initiated aggressive interactions with rivals more readily, and brightness asymmetries between males settled interactions in a way that is consistent with classic hypotheses about male sexual signals. In Chapter 4 I sought to describe physiological correlates of male warning color brightness. While male brightness did not co-vary with classic measures of body condition (circulating testosterone and skin carotenoids), it did correlate with toxins sequestered from the diet and thus appears to be a reliable signal of toxicity in this population. / text