One of the most spectacular examples of evolution is the existence of the bright, conspicuous colors that are widespread throughout the animal kingdom. Aposematic species, for example, use conspicuous ?warning? signals to advertize their toxicity to predators. The aposematic poison-dart frog, Dendrobates pumilio, has undergone a recent, rapid diversification in warning coloration. Though warning coloration evolves to deter predators, recent research suggests that it can also function in the context of within species communication. For example, the investigators have recently shown that male warning color brightness can predict the outcomes of D. pumilio male-male territorial interactions. Following from this, this study investigates the conditional correlates and fitness consequences of warning color variation in these males. Laboratory assays and behavioral observations will delineate the hormonal and dietary correlates and the social consequences of male color and brightness variation in natural populations of this species.

Because warning coloration can communicate to a triad of viewers (predators, males, and females), this research will provide insights into how the interplay between natural and sexual selection drives conspicuous signal evolution. Results will also yield information on what environmental and physiological factors are correlated with warning color, an ecologically important trait. This species has proven to be a charismatic animal for educational outreach: the investigators? research has been featured in public outreach talks in Panama and the US and on internationally broadcasted television specials. The proposed work will provide research experience for undergraduates, opportunities for collaboration with Panamanian scientists, and its findings will be shared with the public through publically available databases, blogs, and ongoing outreach work by the co-PI at the Texas Natural Science Center.

Project Report

Humans have admired and puzzled over conspicuous animal color patterns for millennia. While many of these traits arise through female mate preferences or male competition (collectively referred to as sexual selection), bright coloration can also evolve through natural selection. Many poison frog species, for example, use bright warning coloration to communicate their toxicity to predators. We focused our research on an exceptionally bright and toxic population of the strawberry poison frog (Oophaga [Dendrobates] pumilio), a species that is known for exhibiting incredible color pattern diversity. Our research integrated behavioral observations, chemical ecology, sensory ecology, and physiological measures to investigate how males, females, and predators might collectively impact the trajectory of warning color evolution in this species. Intellectual Impact: First, we used theoretical models of predator and frog visual systems to determine which can see the variation in bright warning coloration within this population. We found that birds, the presumed major predator, likely cannot see this variation, indicating that sexual communication systems can work under the radar of predators in this species. Our past research indicated that brighter males might be more aggressive, and that males pay attention to the brightness of rivals during territorial disputes. To follow up on these laboratory results, we tested the outcomes of contests between males of varying brightness and observed male reactions to simulated intruders in their territories. We 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. Finally, we sought to describe physiological correlates of male warning color brightness. While male brightness did not correlate with classic measures of body condition (circulating testosterone and total carotenoid pigments in the skin), it did correlate with toxins sequestered from the diet and thus appears to be a reliable signal of toxicity in this population. This project provides several significant contributions to the study of aposematic diversification in poison frogs, and to the study of signal evolution in general. First, this research presents evidence that conspicuous warning signals may be selected upon by both forms of conspecific "eavesdroppers" (conspecific competitors and potential mates). Therefore, the phenotypic diversity identified across a wide swath of aposematic taxa could be driven just as much by sexual selection as it is by patterns of natural selection. Second, we find that a conspicuous signal that has arisen through natural selection can evolve to function as an agonistic indicator trait, used by males to assess rivals before participating in costly fights. Finally, we find that warning signal brightness evidently exhibits physiological correlates different from those of classic sexual signals. While it does not appear to correlate with circulating testosterone or total skin carotenoids in the population we studied, we did observe a negative relationship between male brightness and two aspects of chemical defense: alkaloid diversity and aggregate pumiliotoxins in the skin (considered the major toxic alkaloid in these frogs). Broader Impacts: This research has received national and regional attention through a Smithsonian Magazine article ("Color" in the September 2013 issue), a "National Geographic Weekend" interview podcast (March 10th, 2013), a radio interview on a local radio station (KUT, "Eklektikos", Nov 21st, 2013), and a large public outreach lecture (Hot Science, Cool Talks, University of Texas, Nov. 22, 2013). This project has contributed to the training of several women in the STEM field, including the co-PI, who was trained in a variety of laboratory methods and statistical techniques during the project. Five young women (including one Latino and one student recruited through a University of Texas program focused on enhancing the diversity of UT students) were trained in behavioral analysis and fieldwork through the project. Both the PI and co-PI presented this project’s research at multiple scientific conferences and at many public outreach events, including talks to the Austin community (Darwin Day events; school STEM outreach talks; UT Forum series; Hot Science Cool Talks series) and to several Panamanian communities (Smithsonian Tropical Research Institute Biodiversity Fair, Bocas Town talk series, Valle de Aguas school outreach visit). All of these outreach events served as venues to address important conservation information about these poison frogs, which are a major focus of ecotourism and conservation efforts in the Bocas del Toro region of Panama.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Michelle M. Elekonich
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University of Texas Austin
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