Date of Award
Ph.D. in Biological Science
Brice P. Noonan
John M. Rimoldi
Aposematic signaling is a common defensive strategy whereby prey species use conspicuous signals (i.e., bright coloration) to warn predators of the risks of predation due to a secondary defense. Theoretical, lab, and field experiments have demonstrated that individuals who project novel conspicuous signals should experience disproportionately high predation pressure as predators will not associate novel signals with a secondary defense. Thus, aposematic signaling should be subject to strong positive frequency-dependent selection (FDS). Numerous species show considerable intrapopulation variation (polymorphism) in direct conflict with the expectations of FDS. Interpopulation variation (polytypism) can adhere to expectations of FDS, but as its origins likely involve polymorphism, FDS likely plays a role in the establishment of such populations. Both the Dyeing Poison Frog (Dendrobates tinctorius) and the Australian Brood Frogs (Pseudophryne) exhibit considerable inter- and intrapopulation variation making them excellent candidates to investigate how aposematic signaling can evolve and under what circumstances of FDS can be relaxed. Consequently, I approach this question by systematically investigating how predators perceive conspicuous colors, how secondary defense influences predator response, how predators respond to known and novel colors, and the role that gene flow plays in promoting or limiting phenotypic divergence. By using model, naïve predators for learning experiments, I found that the hue color component influences predators’ abilities to learn to avoid an aposematic signal. I provide the first among-population characterization of alkaloid toxins in D. tinctorius and, when using a model avian predator to examine unpalatability of alkaloid toxins, found that a subset of these alkaloids is driving the predator response. In examining how predators respond to known and novel phenotypes, I elucidate the function of conspicuous signals in Pseudophryne and how predators may generalize to novel signals. Finally, I find that despite field and lab experiments that indicate a selective disadvantage of a weak aposematic signal, it can persist when isolated with limited gene flow. Together, these studies provide evidence for the evolution of aposematic signals and propose mechanisms that can allow the relaxation of FDS and thus allow for phenotypic polymorphism in aposematic species.
Lawrence, Justin Philip, "Impacts And Implications Of Polytypism On The Evolution Of Aposematic Coloration" (2018). Electronic Theses and Dissertations. 382.