Phylogenomics and Evolution of Bonytongue Fishes (Teleostei, Osteoglossomorpha)
Open AccessBonytongues (Osteoglossomorpha) constitute an ancient clade of teleost fishes distributed in freshwater habitats throughout the world. This group includes well-known species such as arowanas, featherbacks, pirarucus, and the weakly electric fishes in the family Mormyridae. Their disjunct distribution, bizarre morphologies, and ability to produce electricity (Gymnarchidae and Mormyridae) have attracted much scientific interest, but a comprehensive phylogeny for comparative studies is missing, especially for the species-rich family Mormyridae. Firstly, I conducted a phylogenomic analysis based on 546 exons of 179 species (out of 260), 28 out of 29 genera, and all six families of extant bonytongues. Based on a recent reassessment of the fossil record of osteoglossomorphs, I inferred dates of divergence among trans-continental clades and the major groups to understand the process responsible for the global distribution of this freshwater clade. My results indicated that the current diversity of osteoglossomorphs is likely explained by trans-oceanic dispersal and that there is a pervasive misalignment between the phylogenomic results and mormyrid taxonomy, likely due to convergence of craniofacial morphologies. Next, I investigated how mormyrid biogeography relates to the evolution of craniofacial morphology and if the five craniofacial morphologies within mormyrids evolved multiple times. Significant results include that the tubesnout evolved four times independently, the chin-swelling evolved six times, the Schnauzenorgan evolved once, and the tubesnout with Schnauzenorgan evolved three times. The biogeographic analysis reveals species diversity is high in the Congo Basin due to range reductions of previously widespread ancestors. Combining the ancestral state estimation with biogeographical analyses suggests that the convergence of craniofacial morphologies may have evolved as a way of niche partitioning in the Congo Basin. Thirdly, I compared the anatomy of the soft-tissue craniofacial morphologies (chin-swelling, Schnauzenorgan following the tubesnout, and Schnauzenorgan), to assess if the independent gains of these morphologies are convergent at a histological level. I found that the independent gains of the chin-swelling and of the Schnauzenorgan are also convergent at a tissue level. Lastly, I propose based on the anatomy that these rostral appendages function as a fovea to enhance electrosensory abilities related to foraging. Finally, I assessed if convergent gains of the bony elongations (tubesnout and tubesnout with a Schnauzenorgan) share a common genetic mechanism. I sequenced and assembled 42 genomes spanning the craniofacial diversity of mormyrids and extracted 14 candidate genes to detect signals of positive selection and intensified/relaxed selection. I found three genes were under positive or intensified selection for all tubesnouted mormyrid lineages suggesting the elongation of convergent tubesnouts arises through common genetic mechanisms.
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Peterson_gwu_0075A_16116.pdf | 2022-10-04 | Open Access |
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