Skull diversity and evolution in miniaturized amphibians, genus Brachycephalus (Anura: Brachycephalidae)

Abstract

Miniaturized amphibians of the genus Brachycephalus are phenotypically diverse. The species of Brachycephalus have bufoniform or leptodactyliform Baupläne and any of three skeletal states: nonhyperossified, hyperossified without dorsal shield, and hyperossified with dorsal shield. We integrate highresolution microcomputed tomography, geometric morphometrics, and an estimate of molecular phylogenetic relationships to investigate skull diversity in shape and size-shape space in selected species of Brachycephalus. Skull diversity amongst species of Brachycephalus can be partitioned into shape and size-shape space according to the four conditions of skeletal states-Baupläne, namely, nonhyperossified leptodactyliform, nonhyperossified bufoniform, hyperossified bufoniform without dorsal shield, and hyperossified bufoniform with dorsal shield. Skull diversity in shape and size-shape space in nonhyperossified leptodactyliform species of Brachycephalus is markedly larger, when compared to skull diversity in species of the three other conditions of skeletal states-Baupläne. Variation in skull shape scales with size across Brachycephalus and, therefore, can be explained by allometry. Skull diversity, Baupläne, and skeletal states covary to a large extent with monophyletic lineages of Brachycephalus, as revealed by a mitochondrial DNA species tree. Nonhyperossified bufoniform species and hyperossified bufoniform species with or without dorsal shield are monophyletic lineages, as inferred from a mitochondrial DNA species tree. Nonhyperossified leptodactyliform species of Brachycephalus do not share, however, a most recent common ancestor. The nonhyperossified leptodactyliform species of Brachycephalus, due to their marked skull diversity and lack of monophyly, emerge as evolutionarily complex. Therefore, further sampling of the nonhyperossified leptodactyliform condition of skeletal states-Baupläne will be necessary to further understand the evolutionary history of Brachycephalus.

Overview of special issue on current advances in Brazilian biomedical and anatomical sciences

“…The next paper “Skull Diversity and Evolution in Miniaturized Amphibians, Genus Brachycephalus (Anura: Brachycephalidae; dos Reis et al, 2021) is also an international effort by authors from the State University of Campinas, in São Paulo; the Federal University of Rio de Janeiro, in Rio de Janeiro; the Queen's University, in Ontario, Canada; and the School and Museum of Natural Sciences, in La Plata, Argentina. The manuscript explores the phenotypical diversity of the miniaturized amphibians of the genus Brachycephalus.…”

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

“…Species in this genus are essentially diurnal, leaf-litter inhabitants, miniaturized, and characterized by direct development [18,19]. Brachycephalus species are divided into two groups according to their body plans, popularly known as pumpkin-toadlets (34 species) and flea-toads (4 species) [20]. All pumpkin-toadlets are characterized by a "bufoniform" appearance, with a robust body and pectoral girdle, head as wide as long and short snout; the flea-toads instead have a "leptodactyliform" appearance with slender body and pectoral girdle, head longer than wide and long snout (Supplementary Figure S1).…”

“…All pumpkin-toadlets are characterized by a "bufoniform" appearance, with a robust body and pectoral girdle, head as wide as long and short snout; the flea-toads instead have a "leptodactyliform" appearance with slender body and pectoral girdle, head longer than wide and long snout (Supplementary Figure S1). The relatively more elongated skull of the flea-toads is also reflected in a skeletal multivariate morphospace [20]. The coloration of pumpkin-toadlets is usually bright, orange/yellow but sometimes greenish/brownish dorsally, and always with some orange components at least on the hands and feet and/or on the ventral surface.…”

“…Several pumpkin-toadlets are also known to contain toxins: TTX has been reported in B. ephippium, B. nodoterga, B. pernix, B. pitanga, and B. rotenbergae (as B. ephippium) [15,21,22] and bradykinin-potentiating peptides (BPP) have been reported in B. rotenbergae ([23]-as B. ephippium). On the contrary, flea-toads have an inconspicuous brown coloration [19,20] and their putative toxicity has so far not been assessed. These characteristics make Brachycephalus an excellent model for studying the evolution of anti-predator defense mechanisms associated with toxins.…”

“…Surprisingly, early molecular phylogenetic evidence (Figure 2A) suggested that these two morphological groups are not reciprocally monophyletic within Brachycephalus [18]. Based on DNA sequences of few mitochondrial and two nuclear-encoded genes (tyrosinase and recombination activating gene 1), two major clades of pumpkin-toadlets were recovered: the B. ephippium group (with 15 species), characterized by a gradient of increased mineralization in the skull [20,[24][25][26][27], and the B. pernix group (with 19 species), which is not hyperossified [18][19][20]. The B. ephippium group is distributed across the Serra do Mar and Serra da Mantiqueira mountain ranges whereas the B. pernix group is distributed across the Serra do Mar, respectively at the north and south of the Guapiara Lineament [19] (Figure 1).…”