THE ANTIPREDATOR BEHAVIORS OF CRYPTIC AND APOSEMATIC ANURANS AND VARIABILITY IN ALKALOIDS, CONSPICUOUSNESS, AND PATTERN WITHIN DENDROBATES AURATUS (DENDROBATIDAE)

Crypsis and aposematism are common antipredator strategies that have evolved as defensive mechanisms to prevent predation. Prey that employ these defensive strategies also exhibit antipredator behaviors meant to avoid or deter predation. These behaviors include: (1) escape or immobility in the presence of an immediate predator or (2) exhibiting bold behavior by accepting the risk of potential predation in a novel environment in exchange for the benefits of foraging and mating opportunities. In this study, the escape and bold behaviors of cryptic members of Craugastor and the aposematic dendrobatid Dendrobates auratus were tested to compare these alternative antipredator strategies. Craugastor behaved more cryptically and was less bold than D. auratus in response to simulated predators and when emerging from a cover object. Further, a human and bird model were used as simulated predators to compare the escape behaviors exhibited by Craugastor and D. auratus in response to each. The results of this study support previous findings that cryptic anurans commonly rely on immobility to maximize camouflage, whereas aposematic anurans exhibit movement that enhance their warning signals. Also, movements exhibited by D. auratus were distinctive based on the identity of the approaching predator, suggesting that predator type is important when studying the escape behavior of an aposematic species. Furthermore, although crypsis and aposematism are thought to be alternative strategies, a continuum ranging from cryptic to aposematic may exist within aposematic species. The color/pattern and alkaloid chemical defense of individual D. auratus were measured and compared to their antipredator behavior to establish a potential spectrum of antipredator strategies. Two populations of D. auratus were found to exhibit alternative antipredator strategies – the Atlantic population was more bold, conspicuous, and chemically defended than the Pacific population. The two populations of D. auratus support the possibility that crypsis and aposematism are not mutually exclusive. Instead, populations of D. auratus, in response to unique selective pressures, can utilize a combination of antipredator strategies including morphology and behavior

Weak warning signals can persist in the absence of gene flow

Aposematic organisms couple conspicuous warning signals with a secondary defense to deter predators from attacking. Novel signals of aposematic prey are expected to be selected against due to positive frequency-dependent selection. How, then, can novel phenotypes persist after they arise, and why do so many aposematic species exhibit intrapopulation signal variability? Using a polytypic poison frog (Dendrobates tinctorius), we explored the forces of selection on variable aposematic signals using 2 phenotypically distinct (white, yellow) populations. Contrary to expectations, local phenotype was not always better protected compared to novel phenotypes in either population; in the white population, the novel phenotype evoked greater avoidance in natural predators. Despite having a lower quantity of alkaloids, the skin extracts from yellow frogs provoked higher aversive reactions by birds than white frogs in the laboratory, although both populations differed from controls. Similarly, predators learned to avoid the yellow signal faster than the white signal, and generalized their learned avoidance of yellow but not white. We propose that signals that are easily learned and broadly generalized can protect rare, novel signals, and weak warning signals (i.e., signals with poor efficacy and/or poor defense) can persist when gene flow among populations, as in this case, is limited. This provides a mechanism for the persistence of intrapopulation aposematic variation, a likely precursor to polytypism and driver of speciation

Linking Predator Responses to Alkaloid Variability in Poison Frogs

Many chemically-defended/aposematic species rely on diet for sequestering the toxins with which they defend themselves. This dietary acquisition can lead to variable chemical defenses across space, as the community composition of chemical sources is likely to vary across the range of (an aposematic) species. We characterized the alkaloid content of two populations of the Dyeing Poison Frog (Dendrobates tinctorius) in northeastern French Guiana. Additionally, we conducted unpalatability experiments with naive predators, Blue Tits (Cyanistes caeruleus), using whole-skin secretion cocktails to assess how a model predator would respond to the defense of individuals from each population. While there was some overlap between the two D. tinctorius populations in terms of alkaloid content, our analysis revealed that these two populations are markedly distinct in terms of overall alkaloid profiles. Predator responses to skin secretions differed between the populations. We identified 15 candidate alkaloids (including three previously undescribed) in seven classes that are correlated with predator response in one frog population. We describe alkaloid profile differences between populations for D. tinctorius and provide a novel method for assessing unpalatability of skin secretions and identifying which toxins may contribute to the predator response. In one population, our results suggest 15 alkaloids that are implicated in predator aversive response. This method is the first step in identifying the causal link between alkaloids and behavioral responses of predators, and thus makes sense of how varying alkaloid combinations are capable of eliciting consistent behavioral responses, and eventually driving evolutionary change in aposematic characters (or characteristics).Peer reviewe

Original data for article: Weak warning signals can persist in the absence of gene flow

Aposematic organisms couple conspicuous warning signals with a secondary defense to deter predators from attacking. Novel signals of aposematic prey are expected to be selected against due to positive frequency-dependent selection. How, then, can novel phenotypes persist after they arise, and why do so many aposematic species exhibit intrapopulation signal variability? Using a polytypic poison frog (Dendrobates tinctorius), we explored the forces of selection on variable aposematic signals using two phenotypically distinct (white, yellow) populations. Contrary to expectations, local phenotype was not always better protected compared to novel phenotypes in either population; in the white population, the novel phenotype evoked greater avoidance in natural predators. Despite having a lower quantity of alkaloids, the skin extracts from yellow frogs provoked higher aversive reactions by birds than white frogs in the laboratory, though both populations differed from controls. Likewise, predators learned to avoid the yellow signal faster than the white signal, and generalized their learned avoidance of yellow but not white. We propose that signals that are easily learned and broadly generalized can protect rare, novel signals, and weak warning signals (i.e., signals with poor efficacy and/or poor defense) can persist when gene flow among populations, as in this case, is limited. This provides a mechanism for the persistence of intrapopulation aposematic variation, a likely precursor to polytypism and driver of speciation