Effects of Pattem and Toxicity in the Dendrobatid Frog Oophaga pumilio on Avoidance by the Predatory Ant Paraponera clavata
Berg, Torsten B.
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Warning signals of prey organisms have fascinated biologists since Darwin and Wallace first debated the evolutionary advantages of conspicuous coloration accompanying secondary defenses. Studying these signals provides insight into complex predator-prey relationships, yet relatively little is known about how invertebrates respond to them. Herein we examine the hypothesis that the toxic frog Oaphaga pumilia is avoided by invertebrate predators. We attempt to determine if the avoidance mechanism is pattern or chemical based and whether other toxic anurans would experience similar avoidance. To address these questions, we used two distinct series of trials. The first measured predation of 0. pumilia and the non-toxic frog Craugaslar bramfardii by the predatory ant Parapanera clavala. Juveniles were used to examine the effect of size and in the case of 0. pumilia, reduced toxicity compared to adults. The second series of trials used (1) adult 0. pumilia with experimentally altered alkaloid levels to examine whether avoidance by ants varied with toxicity, independent of size and (2) the toxic toad Rhaebo haematiticus to determine if other anuran families would be similarly avoided. Ant bellavior was recorded during four minute predation trials along a main foraging trail. Rates of attack for 0. pumilia were less than half those for C. bramfardii. Juvenile 0. pumilia, but not C. bramfardii, were attacked more often than adults. This suggests that ants do not prefer smaller prey, but that quantity, not just presence, of alkaloid defenses is important. The secondary trials showed predation as dependent on alkaloid levels in 0.pumilia, but undeterred by toxins in R. haemaliliclis. From these trials we can infer not only that individual variation in toxicity plays a role in fitness, but also that alkaloids are the aposematic signal recognized by P. clavata and likely other invertebrate predators.