Engystomops

Abstract: The vast majority of embryological research on amphibians focuses on just a single genus of frogs, Xenopus. To attain a more comprehensive understanding of amphibian development, experimentation on non-model frogs will be essential. Here, we report on the early development, rearing, and embryological analysis of tungara frogs (genus Engystomops, also called Physalaemus). The frogs Engystomops pustulosus, Engystomops coloradorum, and Engystomops randi construct floating foam-nests with small eggs. We define a table of 23 stages for the developmental period in the foam-nest. Embryos were immunostained against Lim1, neural, and somite-specific proteins and the expression pattern of RetinoBlastoma Binding Protein 6 (RBBP6) was analyzed by in situ hybridization. Due to their brief life-cycle, frogs belonging to the genus Engystomops are attractive for comparative and genetic studies of development. Developmental Dynamics 238:1444 -1454, 2009. © 2009 Wiley-Liss, Inc.

Abstract: Sexual selection plays an important role in mating signal divergence, but geographic variation in ecological factors can also contribute to divergent signal evolution. We tested the hypothesis that geographic heterogeneity in predation causes divergent selection on advertisement call complexity within the Engystomops petersi (previously Physalaemus petersi) frog species complex. We conducted predator phonotaxis experiments at two sites where female choice is consistent with call trait divergence. Engystomops at one site produces complex calls, whereas the closely related species at the other site produces simple calls. Bats approached complex calls more than simple calls at both sites, suggesting selection against complex calls. Moreover, bat predation pressure was greater at the site with simple calls, suggesting stronger selection against complex calls and potentially precluding evolution of complex calls at this site. Our results show that geographic variation in predation may play an important role in the evolution and maintenance of mating signal divergence.

Abstract: Sexual selection is responsible for the evolution of extreme and elaborate sexual dimorphisms. This is especially true for communication systems involved in mate attraction. Anurans, in general, and tungara frogs (Physalaemus pustulosus), in particular, have emerged as an ideal model for studies of sexual selection and communication. Male tungara frogs gather in choruses and vocally advertise for females with a long-distance advertisement call. The call consists of whine that can be followed by 0–7 chucks; only the sister taxa of the tungara frog are known to produce similarly variably complex calls. Male tungara frogs add chucks in response to the vocalizations of other males, and females are more attracted to calls with chucks than calls without chucks. Females move about the chorus and choose a mate with minimum interference from males. Females are more likely to choose larger males, and this preference results from their preference for the lower-frequency chucks produced by larger males. The preference for lower-frequency chucks, in turn, results from the relationship between the average tuning of the female’s inner ear and the average dominant frequency of the chuck. The female’s basilar papilla is more sensitive to chucks with lower-than-average compared to higher-than-average frequencies. The tuning of this inner ear organ did not evolve in tungara frogs but also characterizes most of its close relatives; this suggests that aspects of the chuck evolved to match preexisting sensory biases in females. The communication system of tungara frogs does not occur in a private channel. As do female tungara frogs, two eavesdroppers, frog-eating bats, Trachops cirrhosus, and blood-sucking flies, Corethrella spp., also use the mating call to localize males, but in these cases the eavesdroppers either eat them or suck their blood. Furthermore, as with the female frogs, the eavesdroppers are attracted preferentially to complex calls over simple calls. This exemplifies the conflict between natural selection and sexual selection highlighted by Darwin.