Morphological divergences of snake retinal structure point to complex evolutionary processes and adaptations. The Colubridae family has a remarkable variety of retinal structure that can range from all-cone and all-rod to duplex (cone/rod) retinas. To explore whether nocturnal versus diurnal activity is responsible for constraints on molecular evolution and plays a role in visual opsin spectral tuning of colubrids, we carried out molecular evolution analyses of the visual opsin genes LWS, RH1, and SWS1 from 17 species and performed morphological analyses. Phylogenetic reconstructions of the RH1 and LWS recovered major clades characterized by primarily diurnal or primarily nocturnal activity patterns, in contrast with the topology for SWS1, which is very similar to the species tree. We found stronger signals of purifying selection along diurnal and nocturnal lineages for RH1 and SWS1, respectively. A blue-shift of the RH1 spectral peak is associated with diurnal habits. Spectral tuning of cone opsins did not differ among diurnal and nocturnal species. Retinas of nocturnal colubrids had many rows of photoreceptor nuclei, with large numbers of rods, labeled by wheat germ agglutinin (WGA), and two types of cones: large cones sensitive to long/medium wavelengths (L/M) and small cones sensitive to ultra-violet/violet wavelengths (UV/VS). In contrast, retinas of diurnal species had only one row of photoreceptor nuclei, with four types of cones: large and double L/M cones, small UV/VS cones, and a second group of small cones, labeled by WGA. For LWS gene, selection tests did not confirm different constraints related to activity pattern. For SWS1, stronger purifying selection in nocturnal lineages indicates divergent evolutionary pressures related to the activity pattern, and the importance of the short wavelength sensitivity at low light condition. Activity pattern has a clear influence on the signatures of selection and spectral tuning of RH1, with stronger purifying selection in diurnal lineages, which indicates selective pressure to preserve rhodopsin structure and function in pure-cone retinas. We suggest that the presence of four cone types in primarily diurnal colubrids might be related to the gain of color discrimination capacity.

Endemic to South America, octodontid rodents are remarkable by being the only mammal taxa where allotetraploidy has been documented. The taxon's extensive morpho-physiological radiation associated to niche shifts has allowed testing phylogeographic hypotheses. Using maximum likelihood and Bayesian inference analyses, applied to all nominal species of octodontids, phylogenetic reconstructions based on sequences of 12S rRNA and growth hormone receptor gene are presented. Species boundaries were determined by coalescent analyses and divergence times among taxa were estimated based on mutation rates. Two main clades associated to the Andean orogenesis were recognized. The essentially western clade comprises genera Aconaemys, Octodon, Spalacopus, and Octodontomys whereas the eastern one included genera Octomys, Pipanacoctomys, Salinoctomys, and Tympanoctomys. Genetic relationships, coalescent analyses, and genetic distance supported the specific status given to Octodon pacificus and that given to Pipanacoctomys aureus as a species of Tympanoctomys. However, these analyses failed to recognize Salinoctomys loschalchalerosorum as a valid taxon considering its position within the diversity of Tympanoctomys barrerae. Although the origin of genome duplication remains contentious, the coincidence of the basal clade split with distinctive modes of karyotypic evolution across the Andes emphasizes the role of physiographic barriers and westerlies in shaping different edaphological conditions, selective grounds, and concomitantly distinct adaptations within the octodontids.

Red-nosed mice (genus Wiedomys) are restricted to the Brazilian Cerrado and Caatinga biomes, distributed along the São Francisco River (SFR). Until recently, Wiedomys was considered monotypic, but 2 species with poorly defined geographic and morphological limits have been recognized: W. cerradensis and W. pyrrhorhinos. Our study used morphological, phylogenetic, and cytogenetic analyses to review and detail species limits within the genus and test whether the SFR could be associated with divergence between lineages. This integrative approach indicated that the SFR delineates the geographic boundaries between species, with W. pyrrhorhinos on the right bank and W. cerradensis on the left bank. The species are reciprocally monophyletic and diverge in cranial size, nasal morphology, and facial pelage color pattern. Karyotypic differences between and within W. pyrrhorhinos and W. cerradensis were also detected, and new chromosome complements (2n = 62, FN = 96 and 2n = 62, FN = 88, respectively) were found. Divergence time (0.339 to 0.025 Ma) is concordant with the timing of diversification of other co-distributed vertebrate taxa, and close to a younger estimate for the formation of SFR’s recent lower course to the east coast. Therefore, our study considerably expands knowledge of the geographic range of the genus, diagnoses of species, karyotypic variability between and within species, and reinforces the role of SFR as an important vicariant barrier in northeastern Brazil.

Unlike the X chromosome, the mammalian Y chromosome undergoes evolutionary decay resulting in small size. This sex chromosomal heteromorphism, observed in most species of the fossorial rodent Ctenomys, contrasts with the medium-sized, homomorphic acrocentric sex chromosomes of closely related C. maulinus and C. sp. To characterize the sequence composition of these chromosomes, fluorescent banding, self-genomic in situ hybridization, and fluorescent in situ hybridization with an X painting probe were performed on mitotic and meiotic plates. High molecular homology between the sex chromosomes was detected on mitotic material as well as on meiotic plates immunodetected with anti-SYCP3 and anti-γH2AX. The Y chromosome is euchromatic, poor in repetitive sequences and differs from the X by the loss of a block of pericentromeric chromatin. Inferred from the G-banding pattern, an inversion and the concomitant prevention of recombination in a large asynaptic region seems to be crucial for meiotic X chromosome inactivation. These peculiar findings together with the homomorphism of Ctenomys sex chromosomes are discussed in the light of the regular purge that counteracts Muller's ratchet and the probable mechanisms accounting for their origin and molecular homology.

We report the sequencing and compare the mitochondrial genomes of the South American ground frogs Eupsophus vertebralis and E. emiliopugini and reconstruct phylogenetic relationships among Eupsophus species. These genomes consist of 16,156 and 16,711 bp in length, respectively and contain 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes (tRNA), and partial non-coding D-loop region. Both genomes share 94.5% identity with 879 variable sites. A phylogenetic analysis with other available mitogenomes recovered both species as the sister clade of Alsodes gargola. Sequences from D-loop, CO1, and Cyt b, amplified and sequenced with primers developed from the mitochondrial genomes, allowed us to reconstruct phylogenetic relationships among Eupsophus species. Since our report represents the first mitogenomes for the genus Eupsophus, we expect these data will be valuable for further studies on conservation genetics and on the evolution of Patagonian amphibians.

Some skin secretions with adhesive properties allow frogs to distract predators and escape; their nature is poorly studied. Here, we report the sticky skin secretion released by the Patagonian frog Eupsophus vertebralis when stressed. This secretion contained ~ 50% proteins spanning 25–250 kDa and required a fast setting time to turn into strong adhesive, which worked well on synthetic and biological materials. Lap-shear assays with Eupsophus glue secretion showed average shear strength of 3.34 MPa, comparable to cyanoacrylate (5.47 MPa). These properties suggest its biotechnological value for practical applications in industrial and medical sectors.