Evolutionary divergence in behavioural traits related to mating may represent the initial stage of speciation. Direct selective forces are usually invoked to explain divergence in mate-recognition traits, often neglecting a role for neutral processes or concomitant differentiation in ecological traits. We adopted a multi-trait approach to obtain a deeper understanding of the mechanisms behind allopatric divergence in the Amazonian frog, Allobates femoralis. We tested the null hypothesis that geographic distance between populations correlates with genetic and phenotypic divergence, and compared divergence between mate-recognition (acoustic) and ecological (coloration, body-shape) traits. We quantified geographic variation in 39 phenotypic traits and a mitochondrial DNA marker among 125 individuals representing eight populations. Geographic variation in acoustic traits was pronounced and tracked the spatial genetic variation, which appeared to be neutral. Thus, the evolution of acoustic traits tracked the shared history of the populations, which is unexpected for pan-Amazonian taxa or for mate-recognition traits. Divergence in coloration appeared uncorrelated with genetic distance, and might be partly attributed to local selective pressures, and perhaps to Batesian mimicry. Divergence in body-shape traits was low. The results obtained depict a complex evolutionary scenario and emphasize the importance of considering multiple traits when disentangling the forces behind allopatric divergence.

Predation risk is allegedly reduced in Batesian and Müllerian mimics, because their coloration resembles the conspicuous coloration of unpalatable prey. The efficacy of mimicry is thought to be affected by variation in the unpalatability of prey, the conspicuousness of the signals, and the visual system of predators that see them. Many frog species exhibit small colorful patches contrasting against an otherwise dark body. By measuring toxicity and color reflectance in a geographically variable frog species and the syntopic toxic species, we tested whether unpalatability was correlated with between-species color resemblance and whether resemblance was highest for the most conspicuous components of coloration pattern. Heterospecific resemblance in colorful patches was highest between species at the same locality, but unrelated to concomitant variation in toxicity. Surprisingly, resemblance was lower for the conspicuous femoral patches compared to the inconspicuous dorsum. By building visual models, we further tested whether resemblance was affected by the visual system of model predators. As predicted, mimic-model resemblance was higher under the visual system of simulated predators compared to no visual system at all. Our results indicate that femoral patches are aposematic signals and support a role of mimicry in driving phenotypic divergence or mimetic radiation between localities.

We estimated interactions among and within three species of predator in their effects on prey survival using short-term predation experiments. The prey were Rana temporaria tadpoles, and the predators were dragonfly larvae (Anax imperator), newts (Triturus alpestris), and backswimmers (Notonecta glauca). Mortality rate per predator imposed by Triturus and Notonecta did not decline with predator density, whereas the predation rate of Anax was strongly reduced when the number of predator individuals increased. Impacts of all three predators were not altered by the presence of other species in pairwise combinations. This system is therefore characterized by interference between individual dragonflies but relatively independent effects of predator species. These results were largely predictable based on the natural history of the predators, and are encouraging for attempts to model communities as assemblages of interacting species. Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland Abstract We estimated interactions among and within three species of predator in their effects on prey survival using short-term predation experiments. The prey were Rana temporaria tadpoles, and the predators were dragonfly larvae (Anax imperator), newts (Triturus alpestris), and backswimmers (Notonecta glauca). Mortality rate per predator imposed by Triturus and Notonecta did not decline with predator density, whereas the predation rate of Anax was strongly reduced when the number of predator individuals increased. Impacts of all three predators were not altered by the presence of other species in pairwise combinations. This system is therefore characterized by interference between individual dragonflies but relatively independent effects of predator species. These results were largely predictable based on the natural history of the predators, and are encouraging for attempts to model communities as assemblages of interacting species. Institute of Evolutionary Biology and Environmental Studies, University of