Frogs with denser group-spawning mature later and live longer

DNA methylation clocks for clawed frogs reveal evolutionary conservation of epigenetic aging

To address how conserved DNA methylation-based epigenetic aging is in diverse branches of the tree of life, we generated DNA methylation data from African clawed frogs (Xenopus laevis) and Western clawed frogs (Xenopus tropicalis) and built multiple epigenetic clocks. Dual species clocks were developed that apply to both humans and frogs (human-clawed frog clocks), supporting that epigenetic aging processes are evolutionary conserved outside mammals. Highly conserved positively age-related CpGs are located in neural-developmental genes such as uncx, tfap2d as well as nr4a2 implicated in age-associated disease. We conclude that signatures of epigenetic aging are evolutionary conserved between frogs and mammals and that the associated genes relate to neural processes, altogether opening opportunities to employ Xenopus as a model organism to study aging.

Flocking in birds increases annual adult survival in a global analysis

Adaptive hypotheses for the evolution of group foraging in animals typically invoke enhanced foraging efficiency and reduced predation risk. Net benefits of group foraging in different species should translate into a survival advantage for group members. Despite numerous interspecific studies in birds and mammals, few have documented a survival advantage for group foraging species. Using a large dataset in birds (> 1100 species worldwide), I investigated whether annual adult apparent survival was higher in species that forage in flocks than in solitary species. Using a phylogenetic framework to account for relatedness among species and controlling for known correlates of adult survival in birds such as body size, clutch size, latitude, and diet, I documented a positive effect of flocking on annual adult apparent survival. The increase in survival was less pronounced in occasionally flocking species suggesting that the benefits of group foraging can depend on the frequency of its use. The results highlight how group foraging can increase fitness in animals.

Relative Brain Size Is Predicted by the Intensity of Intrasexual Competition in Frogs

Competition over mates is a powerful force shaping trait evolution. For instance, better cognitive abilities may be beneficial in male-male competition and thus be selected for by intrasexual selection. Alternatively, investment in physical attributes favoring male performance in competition for mates may lower the resources available for brain development, and more intense male mate competition would coincide with smaller brains. To date, only indirect evidence for such relationships exists, and most studies are heavily biased toward primates and other homoeothermic vertebrates. We tested the association between male brain size (relative to body size) and male-male competition across N=30 species of Chinese anurans. Three indicators of the intensity of male mate competition-operational sex ratio (OSR), spawning-site density, and male forelimb muscle mass-were positively associated with relative brain size, whereas the absolute spawning group size was not. The relationship with the OSR and male forelimb muscle mass was stronger for the male than for the female brains. Taken together, our findings suggest that the increased cognitive abilities of larger brains are beneficial in male-male competition. This study adds taxonomic breadth to the mounting evidence for a prominent role of sexual selection in vertebrate brain evolution.