Teleost fishes are a highly diverse group that includes about half of vertebrate species living today. Many phylogenetic relationships within teleosts remain disputed, including the placement of three early-branching teleost clades that diverged about 250 million years ago: Elopomorpha (including tarpon and eels), Osteoglossomorpha (including arapaima and elephantnose fishes) and Clupeocephala (all the remaining living teleosts). Writing in Science, Parey et al. use a combination of established and novel phylogenetic approaches to solve the relationships of these early-diverging groups. The authors assembled high-quality genomes of 7 Elopomorpha species, which they use in combination with 18 publicly available genome assemblies, including 4 Osteoglossomorpha species, 10 Clupeocephala species and 4 vertebrate outgroups. They first used traditional phylogenetic methods based on a large dataset of 955 genes and recovered Osteoglossomorpha and Elopomorpha as sister clades, forming a group that they named Eloposteoglossocephala. The authors then use an innovative approach based on conservation of genome structures, including phylogenetic reconstructions using gene adjacencies and shared chromosomal breakpoints. This analysis, together with the identification of a single chromosomal fusion exclusively shared between Osteoglossomorpha and Elopomorpha species, confirmed the Eloposteoglossocephala scenario. This is an unexpected scenario given the absence of a morphological character that is exclusively shared by Elopomorpha and Osteoglossomorpha. Nevertheless, the authors proposed that the fusion of two jaw bones is unique to Eloposteoglossocephala but was secondarily lost in some Osteoglossomorpha. This study opens prospects of using the conservation of genome structures to solve other challenging phylogenetic relationships.
Original reference: Science 379, 572–575 (2023)
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