Faithful fathers and crooked cannibals: the adaptive significance of parental care in the bush frog Raorchestes chalazodes, Western Ghats, India

Reed bamboos drive skull shape evolution in bush frogs of the Western Ghats, Peninsular India

Reed bamboo is a major ecological and economic resource for many animals, including humans. Nonetheless, the influence of this plant's evolutionary role on the morphology of animal species remains unexplored. Here, we investigated the significance of bamboo habitats as ecological opportunities in shaping the skull morphology of bush frogs (Raorchestes) from the Western Ghats, Peninsular India. We applied a three-dimensional (3D) geometric morphometric approach to capture the skull shape of 55 species of bush frogs. We visualized the skull shape variables in phylomorphospace with principal component analysis and performed phylogenetic generalized least-squares analysis to assess the impact of cranial size (evolutionary allometry) and habitat (bamboo or non-bamboo) on cranial shape. We quantified the morphological disparity between bamboo and non-bamboo bush frogs' skull shape, and employed RRphylo, a phylogenetic ridge regression method, to access the evolutionary rate and rate shifts of skull shape change. The phylomorphospace delineated bamboo and non-bamboo bush frogs. While cranial shape exhibited a significant but smaller association with size, its association with habitat type was non-significant. We detected, however, significant differences in skull shape between the two frog groups, with bamboo frogs showing higher morphological disparity and a remarkable shift in the evolutionary rate of skull shape diversification. These findings underscore the role of reed bamboo in the evolution of skull shape in the radiation of frogs, endemic to the Western Ghats. We demonstrate that the association between the members of two distinct endemic clades (bamboo reeds and bamboo frogs) is the outcome of a deep-time ecological opportunity that dates back to the Miocene.

Correlated evolution of parental care with dichromatism, colors, and patterns in anurans

Parental care is widespread and has fitness benefits. But caregiving parents incur costs including higher predation, and this may lead to selection for body colors or patterns that help mitigate the risks of caring. The evolution of coloration, including sexual dichromatism, however, can be driven by other factors, such as sexual selection. Therefore, examining the associations between parental care and color patterns may provide key insights into evolutionary patterns and selection pressures for parental care. Our comparative analysis of 988 anuran species reveals that dichromatic species are less likely to provide parental care, irrespective of the caregiving sex, and are more likely to breed in aquatic habitats. We then examined whether dorsal colors and patterns that enhance crypticity or function as aposematic signals are associated with the caregiving sex, and the modality of care (transport or stationary). Only caregiving males are more likely to have dorsal Stripes, but none of the colors (Green-Brown, Red, Yellow, Blue-Black) and other patterns (Plain, Bands, Spots, Mottled-Patches) were associated with caregiving females or the modality of care. Overall, sexual dichromatism, breeding ecology, and parental care are associated, but the evolution of caregiving behavior does not appear to influence the myriad colors and patterns characteristic of anurans globally.

Females prefer the calls of better fathers in a Neotropical frog with biparental care

Male secondary sexual traits potentially function as indicators of direct or indirect fitness benefits to females. Direct benefits, such as paternal care, may be especially important to females in species with biparental care. In an experimental field study of the golden rocket frog (Anomaloglossus beebei), a Neotropical species with biparental care, we tested predictions from four hypotheses proposed to explain the evolutionary relationship between male secondary sexual traits and paternal care quality (the “good parent,” “differential allocation,” “trade-off,” and “essential male care” hypotheses). We examined: 1) the influence of paternal care on offspring survival, 2) the relationships between male calls and paternal care, maternal care, and opportunities for males to acquire multiple mates, and 3) female preferences for three acoustic properties of male advertisement calls. Our results reveal that paternal care positively impacts offspring survival, that males producing longer calls also provide higher-quality paternal care in the form of greater egg attendance and territory defense, and that females prefer longer calls. Females did not discriminate among potential mates based on differences in dominant frequency or call rate. These findings, which suggest male advertisement calls are indicators of potential direct benefits to females in the form of paternal care, are consistent with the good parent hypothesis and inconsistent with the trade-off, differential allocation, and essential male care hypotheses.