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- Fouquet, Antoine, et al.
(author)
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Integrative species delimitation and biogeography of the Rhinella margaritifera species group (Amphibia, Anura, Bufonidae) suggest an intense diversification throughout Amazonia during the last 10 million years
- 2024
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In: Systematics and Biodiversity. - 1477-2000. ; 22:1
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Journal article (peer-reviewed)abstract
- The accumulation of studies delimiting species in Amazonia has not only shed light on the patterns of its outstanding species richness but also allowed a better understanding of the processes of diversification within this immense region. Nevertheless, vast knowledge gaps remain even for prominent anuran species complexes, such as the Rhinella margaritifera species group. This clade of toads comprises 23 valid species-level taxa, mainly distributed in Amazonia but also in South America’s Dry Diagonal and Atlantic and trans-Andean rainforests. Species boundaries and taxonomy in this group are notoriously complex, with studies suggesting the existence of several unnamed species. Available phylogenetic information suggests an Andean-western Amazonian origin of the group with subsequent diversification within Amazonian lowlands during the last 10 Myr and secondary dispersals into other Neotropical regions. To further test this biogeographic scenario and improve knowledge on species diversity, we used an unprecedentedly large mtDNA sampling (>800 16S sequences) across the clade’s distribution and comprising all but one described species. We delimited 54 Molecular Operational Taxonomic Units, which we tested further based on patterns of variation of a nuclear locus and acoustic and morphological data. This approach confirmed the existence of at least 25 candidate species, 19 of which correspond to currently recognized taxa whereas 30 remained ‘unconfirmed’. Our results clarify the taxonomic status of some species but also suggest multiple introgression events that blur some mtDNA-based species boundaries. Lastly, to provide a temporal framework for the clade’s diversification, we generated a time-calibrated phylogenetic tree based on a mitogenomic matrix, which confirmed a Miocene (∼9 Ma) western Amazonian origin and six major clades in the group, each having initially diversified in different regions within Amazonia. Most of these clades have later dispersed throughout Amazonia during the establishment of the modern Amazonian hydrographic system, i.e., in the last 6 Myr.
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| 2. |
- Schott, Ryan K., et al.
(author)
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Diversity and Evolution of Frog Visual Opsins : Spectral Tuning and Adaptation to Distinct Light Environments
- 2024
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In: Molecular biology and evolution. - 0737-4038. ; 41:4
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Journal article (peer-reviewed)abstract
- 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.
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