Coloration in the polymorphic frog Oophaga pumilio predicts aggressiveness and the outcome of intraspecific and interspecific interactions

Background/Question/Methods

Novel insights into mechanisms influencing community assembly can be gained by examining the influences of intraspecific phenotypic variation on species interactions. Intraspecific morphological variation may associate with behaviors that mediate the strength of species interactions, and may ultimately affect species distributions and abundances. The territorial frog Oophaga pumilio from Bocas del Toro Archipelago, Panama is one of the most phenotypically diverse amphibians, providing an excellent system to examine this association. O. pumilio from different islands exhibit either bright, aposematic (red, orange) or dull, cryptic colorations (green, brown), and marked body size variation. We aimed to understand how O. pumilio coloration and body size influenced aggressiveness and agonistic interactions with conspecific and heterospecific frogs of two sympatric species. We predicted that red frogs would exhibit more behaviors that could increase detection than green frogs (e.g. aggressiveness), influencing the outcome of agonistic interactions. We conducted a male-male resident/intruder encounter experiment pairing small red, large red, small green, or large green resident O. pumilio with: 1) one similarly-sized conspecific of same morph; 2) one heterospecific, 3) one surrogate clay model. We compared latency (first aggression time), Index of Aggression (ranked evaluation of energy expenditure), and Aggression Score (aggressive minus submissive behaviors) among treatments.

Results/Conclusions

O. pumilio coloration influenced aggressiveness and the strength of interactions with conspecifics and one heterospecific, independent of body size. Aggression between O. pumilio and a conspecific occurred in 96% of the trials, with O. pumilio residents from red populations exhibiting shorter latency, higher Indices of Aggression, and higher Aggression Scores, than residents from green populations. Aggression between O. pumilio and the sympatric Phyllobates lugubris occurred in 86% of the trials, with O. pumilio from red populations exhibiting marginally shorter latency, and higher Indices of Aggression than green populations. Aggression between O. pumilio and the sympatric Andinobates claudiae only occurred in 59% of the trials, and coloration did not influence the strength of the interactions. Aggressiveness did not differ between O. pumilio from large and small bodied populations of either color morph. Frogs were not aggressive towards surrogate controls. These results suggest that coloration in O. pumilio is a good indicator of aggressiveness that predicts the outcome of intraspecific and some interspecific male-male interaction, providing support to a positive association between the strength of antipredator coloration, aggressiveness, and dominance in interspecific, intraguild interactions.