Initial Phylotranscriptomic Confirmation of Homoplastic Evolution of the Conspicuous Coloration and Bufoniform Morphology of Pumpkin-Toadlets in the Genus Brachycephalus

Abstract

The genus Brachycephalus is a fascinating group of miniaturized anurans from the Brazilian Atlantic Forest, comprising the conspicuous, brightly colored pumpkin-toadlets and the cryptic flea-toads. Pumpkin-toadlets are known to contain tetrodotoxins and therefore, their bright colors may perform an aposematic function. Previous studies based on a limited number of mitochondrial and nuclear-encoded markers supported the existence of two clades containing species of pumpkin-toadlet phenotype, but deep nodes remained largely unresolved or conflicting between data sets. We use new RNAseq data of 17 individuals from nine Brachycephalus species to infer their evolutionary relationships from a phylogenomic perspective. Analyses of almost 5300 nuclear-encoded ortholog protein-coding genes and full mitochondrial genomes confirmed the existence of two separate pumpkin-toadlet clades, suggesting the convergent evolution (or multiple reversals) of the bufoniform morphology, conspicuous coloration, and probably toxicity. In addition, the study of the mitochondrial gene order revealed that three species (B. hermogenesi, B. pitanga, and B. rotenbergae) display translocations of different tRNAs (NCY and CYA) from the WANCY tRNA cluster to a position between the genes ATP6 and COIII, showing a new mitochondrial gene order arrangement for vertebrates. The newly clarified phylogeny suggests that Brachycephalus has the potential to become a promising model taxon to understand the evolution of coloration, body plan and toxicity. Given that toxicity information is available for only few species of Brachycephalus, without data for any flea-toad species, we also emphasize the need for a wider screening of toxicity across species, together with more in-depth functional and ecological study of their phenotypes.

From genes to ecosystems: a synthesis of amphibian biodiversity research in Brazil

“…We are also using these sequences as an additional line of evidence to describe and revalidate species (e.g., de Sá et al 2015, Gazoni et al 2021, to flag groups of species where species diversity could be underestimated (Walker, et al 2018, Sabbag et al 2018, or even identifying invasive species (Melo et al 2014). In addition to COI and 16S reference sequences, we have also been adding information on the 12S gene fragment to our databases, including data from environmental DNA studies of monitoring endangered species (e.g., Lopes et al 2021a, Lopes et al 2021b, see below), and complete mitogenome sequences from studies of systematics and evolution (e.g., Lyra et al 2021). Besides supporting this variety of studies, DNA barcoding is also being used as an important tool for identifying mislabeled tissues in biological collections (Lyra et al 2017), serving as support for the selection of specimens for multilocus phylogenies and genomic studies.…”