A mechanism for diversity in warning signals: Conspicuousness versus toxicity in poison frogs

Abstract

Many animals advertise their chemical defense to predators with conspicuous coloration and unpalatability, but little is known about the information in these signal elements. To effectively avoid predation, is it more advantageous to invest in increased conspicuousness or greater noxiousness, or to allocate equally to both signal modalities? Using natural variation among poison frog species measured with spectral reflectance and toxicity assays, we tested the relative importance of warning signal components with predator-learning and avoidance experiments. We demonstrate that closely related species use alternative strategies: increasing either conspicuousness or toxicity affords equivalent avoidance by predators and provides protection to nontoxic mimic species. These equally effective predator avoidance tactics demonstrate different aposematic solutions for two potentially costly signal components, providing a mechanism for natural diversity in warning signals.aposematism ͉ chemical defense ͉ predation

Not all colors are equal: predation and color polytypism in the aposematic poison frog Oophaga pumilio

“…Our findings differ from those of Noonan and Honest signaling within aposematic species remains a highly debated topic (Blount et al 2009). For instance, Darst et al (2006) showed signal strength in some members of the poison frog genus Epipedobates (Myers) to be inversely related to their toxicity. Wang (2011) also showed that conspicuous coloration and toxicity were inversely related in Oophaga granulifera (Taylor), a dendrobatid closely related to O. pumilio.…”

Does spatial variation in predation pressure modulate selection for aposematism?

“…These cardenolide compounds act as defensive chemicals in butterflies against their predators (Mebs, Zehner, & Schneider, 2000; Petschenka & Agrawal, 2015; Petschenka et al., 2013; Seiber, Lee, & Benson, 1983). Toxicity level has been used as a measure of noxiousness in aposematic studies combining warning signals and toxicity (Arenas et al., 2014; Blount, Speed, Ruxton, & Stephens, 2009; Darst et al., 2006). Birds use bitterness to estimate the level of toxicity (Skelhorn & Rowe, 2010), and cardenolides are bitter in taste (Malcolm, 1994).…”

“…This is because such highly conspicuous colors convey a clear signal, as they are very different from concealed, cryptic colorations (Sherratt & Beatty, 2003) and stand out against heterogeneous environment with varying light conditions (Osorio & Vorobyev, 2005). However, contrary to these expectations, there is increasing evidence that aposematic signals are diverse and conspicuousness among aposematic species varies from highly conspicuous to near cryptic (Darst, Cummings, & Cannatella, 2006; Endler & Mappes, 2004; Merilaita & Ruxton, 2007). …”

“…In other situations, there appears to be a trade‐off between the costs of accumulating toxin and the costs of signaling. As a result, highly toxic species may be intermediately conspicuous, while moderately toxic species can be highly conspicuous to gain similar protection (Darst et al., 2006). Also, when the production costs of toxins are low and the costs of signaling are high, some toxic species may remain inconspicuous (Lindstedt, Huttunen, Kakko, & Mappes, 2011).…”

Effects of Experimental Egg Composition on Rejection by Village Weavers (Ploceus Cucullatus)

“…Therefore, second, we used the contrasts to evaluate total egg conspicuousness (E N ). Following Endler and Mielke (2005) and Darst et al (2010), we calculated the Euclidean distance between pairs of contrasts using E N ¼ (DS 2 þ DL 2 ) 0.5 . As both contrasts were expressed relative to the same backgrounds, this produced a vector in 'perceptual space' (Darst et al 2010), with increasing values indicating greater conspicuousness.…”