An Analysis of Predator Selection to Affect Aposematic Coloration in a Poison Frog Species

Abstract

Natural selection is widely noted to drive divergence of phenotypic traits. Predation pressure can facilitate morphological divergence, for example the evolution of both cryptic and conspicuous coloration in animals. In this context Dendrobatid frogs have been used to study evolutionary forces inducing diversity in protective coloration. The polytypic strawberry poison frog (Oophaga pumilio) shows strong divergence in aposematic coloration among populations. To investigate whether predation pressure is important for color divergence among populations of O. pumilio we selected four mainland populations and two island populations from Costa Rica and Panama. Spectrometric measurements of body coloration were used to calculate color and brightness contrasts of frogs as an indicator of conspicuousness for the visual systems of several potential predators (avian, crab and snake) and a conspecific observer. Additionally, we conducted experiments using clay model frogs of different coloration to investigate whether the local coloration of frogs is better protected than non-local color morphs, and if predator communities vary among populations. Overall predation risk differed strongly among populations and interestingly was higher on the two island populations. Imprints on clay models indicated that birds are the main predators while attacks of other predators were rare. Furthermore, clay models of local coloration were equally likely to be attacked as those of non-local coloration. Overall conspicuousness (and brightness contrast) of local frogs was positively correlated with attack rates by birds across populations. Together with results from earlier studies we conclude that conspicuousness honestly indicates toxicity to avian predators. The different coloration patterns among populations of strawberry poison frogs in combination with behavior and toxicity might integrate into equally efficient anti-predator strategies depending on local predation and other ecological factors.

Radiation of the polymorphic Little Devil poison frog (Oophaga sylvatica) in Ecuador

“…A wide range of putative predators such as birds, reptiles, or arthropods with distinct visual abilities and predatory strategies might act on color selection and diversity among O. sylvatica populations (Crothers & Cummings, 2013; Dreher et al., 2015). In addition, sexual selection through nonrandom courtship within color morphs has been reported in O. pumilio (Reynolds & Fitzpatrick, 2007) and Ranitomeya (Twomey et al., 2014) and can possibly promote diversification of color among populations, while decreasing the variation within.…”

“…Currently, the Oophaga genus is composed of nine species, which have extraordinary morphological and chemical diversity (Daly, 1995; Daly, Brown, Mensah‐Dwumah, & Myers, 1978; Daly & Myers, 1967; Saporito, Donnelly, et al., 2007). Research conducted in O. pumilio , including a number of studies in population genetics, phylogeography, behavior, diet specialization, and chemical defenses (Dreher, Cummings, & Pröhl, 2015; Gehara et al., 2013; Richards‐Zawacki, Wang, & Summers, 2012; Saporito, Donnelly, et al., 2007), suggests that this species might include at least two distinctive mitochondrial lineages, each of which contain one or more congenerics: O. speciosa , O. arborea , or O. vicentei (Hagemann & Pröhl, 2007; Hauswaldt, Ludewig, Vences, & Pröhl, 2011; Wang & Shaffer, 2008). Moreover, the phylogeographic patterns observed in O. pumilio suggest a series of dispersals and isolations leading to allopatric divergence and then subsequent admixture and introgression among Oophaga species (Hagemann & Pröhl, 2007; Hauswaldt et al., 2011; Wang & Shaffer, 2008).…”

Color Assortative Mating in a Mainland Population of the Poison Frog Oophaga pumilio

“…; Dreher et al. ), seem incapable of discriminating differences in the brightness among frogs within populations (Cummings & Crothers ). However, given that conspecifics (i.e., potential mating pairs) are capable of such discrimination (Dreher et al.…”

“…However, given that conspecifics (i.e., potential mating pairs) are capable of such discrimination (Dreher et al. ), it is possible that brightness and chroma are maintained mainly by sexual selection. In contrast, hue was found to be least important with respect to assortment, and therefore, hue may more strongly be influenced by natural selection, a conclusion consistent with a number of other studies (e.g., Noonan & Comeault ; Chouteau & Angers ; Amezquita et al.…”

Mating status correlates with dorsal brightness in some but not all poison frog populations

“…The mechanisms that facilitate and maintain intraspecific color divergence among aposematic organisms remain an unresolved issue (Hegna, Galarza, & Mappes, ; Schaefer, Vences, & Veith, ) despite several in‐depth studies (Kapan, ). Some studies examining phenotypic variation in the strawberry poison frog have suggested that sexual selection promotes color divergence (Maan & Cummings, ; Richards‐Zawacki et al., ; Summers et al., ; Tazzyman & Iwasa, ), but the role of natural selection has also been discussed to drive divergence in this trait (Dreher, Cummings, & Pröhl, ; Maan & Cummings, ; Pröhl & Ostrowski, ). The most plausible scenario involves both natural selection (e.g., for initiation of color divergence), and sexual selection acting at different stages of divergence, and affecting different populations to a different degree (Cummings & Crothers, ; Dreher & Pröhl, ).…”