Diversity and Evolution of Frog Visual Opsins: Spectral Tuning and Adaptation to Distinct Light Environments.

Visual systems adapt to different light environments through several avenues including optical changes to the eye and neurological changes in how light signals are processed and interpreted. Spectral sensitivity can evolve via changes to visual pigments housed in the retinal photoreceptors through gene duplication and loss, differential and coexpression, and sequence evolution. Frogs provide an excellent, yet understudied, system for visual evolution research due to their diversity of ecologies (including biphasic aquatic-terrestrial life cycles) that we hypothesize imposed different selective pressures leading to adaptive evolution of the visual system, notably the opsins that encode the protein component of the visual pigments responsible for the first step in visual perception. Here, we analyze the diversity and evolution of visual opsin genes from 93 new eye transcriptomes plus published data for a combined dataset spanning 122 frog species and 34 families. We find that most species express the four visual opsins previously identified in frogs but show evidence for gene loss in two lineages. Further, we present evidence of positive selection in three opsins and shifts in selective pressures associated with differences in habitat and life history, but not activity pattern. We identify substantial novel variation in the visual opsins and, using microspectrophotometry, find highly variable spectral sensitivities, expanding known ranges for all frog visual pigments. Mutations at spectral-tuning sites only partially account for this variation, suggesting that frogs have used tuning pathways that are unique among vertebrates. These results support the hypothesis of adaptive evolution in photoreceptor physiology across the frog tree of life in response to varying environmental and ecological factors and further our growing understanding of vertebrate visual evolution.

Linking microbiome and stress hormone responses in wild tropical treefrogs across continuous and fragmented forests.

The amphibian skin microbiome is an important component of anti-pathogen defense, but the impact of environmental change on the link between microbiome composition and host stress remains unclear. In this study, we used radiotelemetry and host translocation to track microbiome composition and function, pathogen infection, and host stress over time across natural movement paths for the forest-associated treefrog, Boana faber. We found a negative correlation between cortisol levels and putative microbiome function for frogs translocated to forest fragments, indicating strong integration of host stress response and anti-pathogen potential of the microbiome. Additionally, we observed a capacity for resilience (resistance to structural change and functional loss) in the amphibian skin microbiome, with maintenance of putative pathogen-inhibitory function despite major temporal shifts in microbiome composition. Although microbiome community composition did not return to baseline during the study period, the rate of microbiome change indicated that forest fragmentation had more pronounced effects on microbiome composition than translocation alone. Our findings reveal associations between stress hormones and host microbiome defenses, with implications for resilience of amphibians and their associated microbes facing accelerated tropical deforestation.

Habitat split as a driver of disease in amphibians.

Anthropogenic habitat disturbance is fundamentally altering patterns of disease transmission and immunity across the vertebrate tree of life. Most studies linking anthropogenic habitat change and disease focus on habitat loss and fragmentation, but these processes often lead to a third process that is equally important: habitat split. Defined as spatial separation between the multiple classes of natural habitat that many vertebrate species require to complete their life cycles, habitat split has been linked to population declines in vertebrates, e.g. amphibians breeding in lowland aquatic habitats and overwintering in fragments of upland terrestrial vegetation. Here, we link habitat split to enhanced disease risk in amphibians (i) by reviewing the biotic and abiotic forces shaping elements of immunity and (ii) through a spatially oriented field study focused on tropical frogs. We propose a framework to investigate mechanisms by which habitat split influences disease risk in amphibians, focusing on three broad host factors linked to immunity: (i) composition of symbiotic microbial communities, (ii) immunogenetic variation, and (iii) stress hormone levels. Our review highlights the potential for habitat split to contribute to host-associated microbiome dysbiosis, reductions in immunogenetic repertoire, and chronic stress, that often facilitate pathogenic infections and disease in amphibians and other classes of vertebrates. We highlight that targeted habitat-restoration strategies aiming to connect multiple classes of natural habitats (e.g. terrestrial-freshwater, terrestrial-marine, marine-freshwater) could enhance priming of the vertebrate immune system through repeated low-load exposure to enzootic pathogens and reduced stress-induced immunosuppression.

Low microbiome diversity in threatened amphibians from two biodiversity hotspots.

Microbial diversity positively influences community resilience of the host microbiome. However, extinction risk factors such as habitat specialization, narrow environmental tolerances, and exposure to anthropogenic disturbance may homogenize host-associated microbial communities critical for stress responses including disease defense. In a dataset containing 43 threatened and 90 non-threatened amphibian species across two biodiversity hotspots (Brazil's Atlantic Forest and Madagascar), we found that threatened host species carried lower skin bacterial diversity, after accounting for key environmental and host factors. The consistency of our findings across continents suggests the broad scale at which low bacteriome diversity may compromise pathogen defenses in species already burdened with the threat of extinction.

Signatures of functional bacteriome structure in a tropical direct-developing amphibian species.

BACKGROUND: Host microbiomes may differ under the same environmental conditions and these differences may influence susceptibility to infection. Amphibians are ideal for comparing microbiomes in the context of disease defense because hundreds of species face infection with the skin-invading microbe Batrachochytrium dendrobatidis (Bd), and species richness of host communities, including their skin bacteria (bacteriome), may be exceptionally high. We conducted a landscape-scale Bd survey of six co-occurring amphibian species in Brazil's Atlantic Forest. To test the bacteriome as a driver of differential Bd prevalence, we compared bacteriome composition and co-occurrence network structure among the six focal host species. RESULTS: Intensive sampling yielded divergent Bd prevalence in two ecologically similar terrestrial-breeding species, a group with historically low Bd resistance. Specifically, we detected the highest Bd prevalence in Ischnocnema henselii but no Bd detections in Haddadus binotatus. Haddadus binotatus carried the highest bacteriome alpha and common core diversity, and a modular network partitioned by negative co-occurrences, characteristics associated with community stability and competitive interactions that could inhibit Bd colonization. CONCLUSIONS: Our findings suggest that community structure of the bacteriome might drive Bd resistance in H. binotatus, which could guide microbiome manipulation as a conservation strategy to protect diverse radiations of direct-developing species from Bd-induced population collapses.

Biomonitoring of mutagenicity and cytotoxicity in patients undergoing fixed orthodontic therapy.

INTRODUCTION: The aim of the present study was to evaluate DNA damage (micronucleus) and cellular death (pyknosis, karyolysis, and karyorrhexis) in exfoliated buccal mucosa cells from adults after fixed orthodontic therapy. MATERIAL AND METHODS: A total of 23 healthy adults (10 men and 13 women) undergoing orthodontic therapy were included in this setting. RESULTS: The results pointed out no significant statistically differences (P >0.05) of micronucleated oral mucosa cells. In the same way, orthodontic therapy was not able to increase other nuclear alterations closely related to cytotoxicity such as karyorrhexis, pyknosis and karyolysis (P >0.05). CONCLUSION: In summary, these data indicate that orthodontic therapy may not be a factor that induces chromosomal damage, nor it is able to promote cytotoxicity. Since DNA damage and cellular death are important events during carcinogenic processes, especially in early phases, this study represents a correct evaluation with respect to real health risks induced by orthodontic devices.

Chromosome damage and cytotoxicity in oral mucosa cells after 2 months of exposure to anabolic steroids (decadurabolin and winstrol) in weight lifting.

The aim of the present study was to evaluate DNA damage (micronucleus) and cellular death (pyknosis, karyolysis and karyorrhexis) in exfoliated buccal mucosa cells from anabolic steroid users after 2 months of exposure. Two experimental groups consisting of 15 adult males who practise weight lifting and are anabolic steroid users or 15 adult males who practise weight lifting, but are non-anabolic steroid users, were recruited. In addition, 20 sedentary males, who do not practise any physical activity regularly, were matched by age with experimental groups. No significant statistical differences (p>0.05) were noticed in individuals who practise physical activity only. On the other hand, an increase of micronucleated cells (MNCs) in anabolic steroid (decadurabulin and Winstrol) users was observed. Regarding cytotoxic parameters, the same observation has occurred, that is, significant statistical differences (p<0.05) were noticed in the group exposed to anabolic steroids when compared with other controls, as depicted by high frequencies of pyknosis, karyolysis and karyorrhexis. Taken together, our results suggest that genomic instability and cytotoxicity are induced by anabolic steroid administration in oral mucosa cells as assessed by the micronucleus test.

Biomonitoring of oral epithelial cells in petrol station attendants: comparison between buccal mucosa and lateral border of the tongue.

Owing to the influence of geno- and cytotoxicity on chemical carcinogenesis, studies have demonstrated that petroleum derivatives are able to induce genetic damage and cellular death with conflicting results so far. The aim of the present study was to comparatively evaluate DNA damage (micronucleus) and cellular death (pyknosis, karyolysis and karyorrhexis) in exfoliated oral mucosa cells from gas petrol attendants using two different anatomic buccal sites: cheek mucosa and lateral border of the tongue. A total of 23 gas petrol attendants and 23 health controls (non-exposed individuals) were included in this setting. Individuals had epithelial cells from cheek and lateral border of the tongue mechanically exfoliated, placed in fixative and dropped in clean slides which were checked for the above nuclear phenotypes. The results pointed out significant statistical differences (p<0.05) of micronucleated oral mucosa cells from gas petrol attendants for both oral sites evaluated. In the same way, petroleum derivate exposure was able to increase other nuclear alterations closely related to cytotoxicity such as karyorrhexis, pyknosis and karyolysis, being the most pronunciated effects as those found in the lateral border of the tongue. No interaction was observed between smoking and petroleum exposure. In summary, these data indicate that gas petrol attendants comprise a high risk group for DNA damage and cellular death. It seems that the lateral border of the tongue is a more sensitive site to geno- and cytotoxic insult induced by petroleum derivates.