Evolutionary transitions from camouflage to aposematism: Hidden signals play a pivotal role

The initial evolution of warning signals in unprofitable prey, termed aposematism, is often seen as a paradox because any new conspicuous mutant would be easier to detect than its cryptic conspecifics and not readily recognized by naïve predators as defended. One possibility is that permanent aposematism first evolved through species using hidden warning signals, which are only exposed to would-be predators on encounter. Here, we present a large-scale analysis of evolutionary transitions in amphibian antipredation coloration and demonstrate that the evolutionary transition from camouflage to aposematism is rarely direct but tends to involve an intermediary stage, namely cryptic species that facultatively reveal conspicuous coloration. Accounting for this intermediate step can resolve the paradox and thereby advance our understanding of the evolution of aposematism.

Larval morphology of Amazonia foam-nesting frogs of the genus Engystomops (Anura: Leptodactylidae: Leiuperinae)

The highly differentiated anuran larvae make them an interesting and complementary source of information to understand anuran evolution. Among neotropical foam-nesting frogs, the available information on tadpole morphology for the subfamily Leiuperinae remains largely incomplete and variably reported among genera; in the monophyletic genus Engystomops it is still incipient. Herein, we summarize available information on larval morphology for five of the nine known species of Engystomops, three of them for the first time, reporting external morphology, buccopharyngeal cavity, and skeleton. The tadpoles of the genus have an overall generalized morphology and many traits are conserved across species. Nevertheless, many characters are systematically informative and some are diagnostic for some species, as the paravertebral gland in E. petersi and the dorsally directed spiracle in E. puyango. Other characters provide support for some subclades within the genus. Moreover, some traits, such as the direction of the vent tube, supports the close relationship between Engystomops and Physalaemus, whereas other support the existence of these two as distinct genera, such as the overall shape of the lateral ridge papillae and the presence of a processus pseudopterygoideus. This article is protected by copyright. All rights reserved.

Combined phylogenetic analysis of Pleurodema (Anura: Leptodactylidae: Leiuperinae)

The genus Pleurodema comprises 15 species distributed through the Neotropical region, from sea level up to 5000 m.a.s.l. A total-evidence analysis of Pleurodema is provided based on the parsimony criterion. The combined dataset included morphometric, phenotypic, and DNA evidence (34 taxa, 4441 characters). The parsimony analysis yielded one most-parsimonious tree. Pleurodema was recovered as a well-supported clade composed of two major subclades. One subclade has an identical topology to that of previous analyses, the P. brachyops Clade (P. alium, P. borellii, P. brachyops, P. cinereum, P. diplolister, and P. tucumanum). The other subclade includes the remaining nine species of the genus, exhibiting a topology different from that of previous studies. According to the present phylogeny, this second lineage is formed by the P. nebulosum Clade (P. guayapae + P. nebulosum), P. marmoratum, the re-defined P. thaul Clade (P. bufoninum, P. somuncurense, P. thaul) and the P. bibroni Clade (P. bibroni, P. cordobae, P. kriegi). The reproductive modes of Pleurodema represent a unique combination of features within Leiuperinae, including three egg-clutch structures, two types of amplexus, and lack of vocalization. Also, some species of Pleurodema have been considered fossorial, because they are capable of digging with their hind-limbs and remaining in self-made burrows during dry seasons. The evolution of characters associated with reproductive biology and fossoriality is discussed in light of the obtained results.