Abstract
The diversity of gymnotid electric fishes has been intensely studied over the past 25 years, with 35 species named since 1994, compared to 11 species in the previous 236 years. Substantial effort has also been applied in recent years to documenting gymnotid interrelationships, with seven systematic studies published using morphological and molecular datasets. Nevertheless, until now, all gymnotids have been assigned to one of just two supraspecific taxa, the subfamily Electrophorinae with one genus Electrophorus and three valid species and the subfamily Gymnotine also with one genus Gymnotus and 43 valid species. This simple classification has obscured the substantial phenotypic and lineage diversity within the subfamily Gymnotine and hampered ecological and evolutionary studies of gymnotid biology. Here we present the most well-resolved and taxon-complete phylogeny of the Gymnotidae to date, including materials from all but one of the valid species. This phylogeny was constructed using a five-gene molecular dataset and a 115-character morphological dataset, enabling the inclusion of several species for which molecular data are still lacking. This phylogeny was time-calibrated using biogeographical priors in the absence of a fossil record. The tree topology is similar to those of previous studies, recovering all the major clades previously recognized with informal names. We propose a new gymnotid classification including two subfamilies (Electrophorinae and Gymnotinae) and six subgenera within the genus Gymnotus. Each subgenus exhibits a distinctive biogeographic distribution, within which most species have allopatric distributions and the subgenera are diverged from one another by an estimated 5–35 million years. We further provide robust taxonomic diagnoses, descriptions and identification keys to all gymnotid subgenera and all but four species. This new taxonomy more equitably partitions species diversity among supra-specific taxa, employing the previously vacant subgenus and subfamily ranks. This new taxonomy renders known gymnotid diversity more accessible to study by highlighting the deep divergences (chronological, geographical, genetic and morphological) among its several clades.
Highlights
The family Gymnotidae Rafinesque is represented by 46 valid species and seven valid subspecies [1], with at least two additional species currently known and being described elsewhere (Table 1)
We propose a new classification of the family Gymnotidae that includes two subfamilies (Electrophorinae and Gymnotinae, following [14]), two genera (Electrophorus, Gymnotus) and six subgenera within the genus Gymnotus
The Bayesian analysis recovered the G. anguillaris clade as sister to the G. coatesi clade with a node support of 100%, whereas the total evidence ML phylogeny recovered G. anguillaris clade as sister to a clade comprised of the G. carapo clade, the G. cylindricus clade and the G. tigre clade, with the G. coatesi clade as the sister all four of these clades
Summary
The family Gymnotidae Rafinesque is represented by 46 valid species and seven valid subspecies [1], with at least two additional species currently known and being described elsewhere (Table 1). Despite its relative species richness, the family Gymnotidae is currently divided into only two supraspecific (higher) taxa, one of which is the subfamily Electrophorinae with a single genus (Electrophorus) and three valid species and the other the subfamily Gymnotinae with a single genus (Gymnotus) and 43 valid species. Knowledge of Gymnotus species diversity has expanded rapidly in the past 20 years [5,6,7] (Fig 1), with the descriptions of 34 species or 77% of the currently-known diversity of this clade. This expansion of knowledge at the species level has been accompanied by seven major efforts to create a systematic classification of the genus. Concurrent with a rapid increase in our understanding of Gymnotus as a species-rich genus, an informal but widely-accepted taxonomy was developed for use below the genus level
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