Multiple sexual signals: calls over colors for mate attraction in an aposematic, color-diverse poison frog

Abstract

Sexual signals indicate species identity and mate quality, and their importance for mate attraction is largely recognized. Recently, research in animal communication has started to integrate multiple signal modalities and evaluate their interactions. However, mate choice experiments across animal taxa have been limited to laboratory conditions, and assessments of multiple sexual signals under field conditions are still lacking. We take advantage of the divergence in visual and acoustic signals among populations of the Neotropical poison frog Oophaga pumilio to evaluate the importance of male advertisement calls and color patterns in female mate selection. Previous mate choice experiments in this species suggested color-assortative female mate preferences across many populations. Nevertheless, acoustic signals are crucial for sexual selection in frogs, and males of O. pumilio use advertisement calls to attract females. We hypothesize that both advertisement calls and coloration affect female mate selection in O.pumilio. To test this hypothesis we tested 452 receptive females from six populations in Costa Rica and Panama in their natural home ranges for preferences regarding local vs. non-local advertisement calls and color patterns. Overall, the calls overrode the effect of coloration, whereby most females preferred local over non-local calls. We found a tendency to prefer brighter (but not necessarily local) males in two populations. Furthermore, the strength of preferences varied geographically, and thus might be involved in prezygotic isolation among populations. The stronger effect of calls on mate attraction is associated with acoustic divergence between genetic groups in the species, while color pattern diversity is mostly located within one genetic group, i.e., not linked to large-scale population structure. Finally our data highlights the importance to consider an array of signal modalities in multiple wild populations in studies of behavioral isolation.

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“…This occurs in the form of female choice on call frequency where spectral call characteristics such as dominant frequency are important to frog evolution (Ryan 1986). Female frogs or toads recognize male of their own species in mating through male mating calls which play an important role in prezygotic isolating mechanism (Dreher & Prohl 2014). Failure to mate might result in offspring reduction that eventually leads to local extinction.…”

Magic or Not? Sounds vs. Colors in Sexual Selection and Genetic Divergence of Strawberry Frogs

“…Previous studies revealed color-assortative mate preferences Cummings, 2008, 2009) but disregarded the potential relevance of acoustic signals. Dreher and Pröhl (2014) found that acoustic signals, that is, male advertisement calls, were more important in female choice than color patterns. Across populations, females preferred local to non-local advertisement calls, largely unaffected by the simultaneous presentation of local and non-local color morphs of the calling males.…”

“…Most strikingly, Dreher and Pröhl (2014) observed that differences in advertisement calls were associated with genetic divergence, whereas color patterns varied within genetic groups. The strength of acoustic preference for local calls varied among populations, which might indicate different stages of prezygotic behavioral isolation, from loose to almost complete.…”

“…In two out of six populations, females going for local calls also displayed a preference for color brightness, which likely correlates with the males' health status and/or toxicity for predators. The findings by Dreher and Pröhl (2014) imply that strawberry frogs use acoustic and visual cues in a sequential (hierarchical) order, with advertisement calls used to attract potential mates from the distance and visual cues gaining importance in close-range mate assessment (Pröhl and Berke, 2001;Pröhl and Ostrowski, 2011). The distance between calling males is probably simply too large, and their view often obstructed by habitat features, to allow females visually choosing between males based on coloration.…”

“…Sexually relevant traits that both evolve in response to divergent natural selection and contribute to non-random mating, ultimately leading to genetic divergence, are called magic traits (Servedio et al, 2011;Merot et al, 2015). Dreher and Pröhl (2014) assessed the relative importance of visual and acoustic signals in female choice in six populations of two genetic groups, Northern and Southern, of the Neotropical poisonous strawberry frog Oophaga pumilio in their natural home ranges in Costa Rica and Panama. Geographically separated populations of this species are highly variable in both body color patterns (Daly and Myers, 1967) and acoustic signals (Pröhl et al, 2007).…”