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Towards a complete classification of the Neotropical thorny catfishes (Siluriformes: Doradidae)
FIGURE 4 | Phylogenetic relationships among all genera and subfamilies of Doradidae inferred from Maximum Parsimony analysis of rag1, 16s and co1 DNA sequence data (strict consensus of 144 most parsimonious trees, each with 9235 steps).
Abstract
We propose a revised classification of Doradidae based on phylogenetic analyses of sequence data for one nuclear (rag1) and two mitochondrial (co1, 16s) genes, and corroborated by caudal-fin morphology. The molecular dataset comprises 174 doradid specimens representing all 31 valid genera, 83 of the 96 valid extant species and 17 species-level taxa that remain undescribed or nominally unassigned. Parsimony and Bayesian analyses of molecular data support six major lineages of doradids assigned here to three nominal subfamilies (Astrodoradinae, Doradinae, Wertheimerinae) and three new ones (Acanthodoradinae, Agamyxinae, Rhinodoradinae). The maximum parsimony topology of Doradidae was sensitive to ingroup density and outgroup age. With the exceptions of Astrodoradinae and Doradinae, each subfamily is diagnosed by caudal-fin characteristics. The highest degree of fusion among skeletal elements supporting the caudal fin is observed in Acanthodoradinae and Aspredinidae, lineages that are sister to the remaining doradids and aspredinoids (i.e., Auchenipteridae + Doradidae), respectively. Fusion among caudal-fin elements tends to be higher in taxa with rounded, truncate or emarginate tails and such taxa typically occupy shallow, lentic habitats with ample structure. Caudal-fin elements are more separated in taxa with moderately to deeply forked tails that occupy lotic habitats in medium to large river channels.
RESULTS
Molecular Analyses. In our final analyses, 180 of the 218 specimens were represented by complete molecular data (all genes: rag1, co1, 16s; Tab. 1). Seven specimens were represented only by rag1 and co1 sequences, nine specimens were represented only by rag1 and 16s sequences, and 22 specimens were represented only by co1 and 16s sequences. The Maximum Parsimony (MP) analysis produced 144 most parsimonious trees of 9235 steps each. Under MP, the rag1 dataset consisted of 1861 total and 716 parsimony-informative base pairs for 196 specimens, the 16s dataset consisted of 583 total and 188 parsimony-informative base pairs for 211 specimens, and the co1 dataset consisted of 593 total and 246 parsimony-informative base pairs for 209 specimens. The combined dataset included 3037 total base pairs of which 1150 were parsimony informative for 218 terminals.
Trees produced by the Maximum Parsimony (MP) and Bayesian (BI) analyses were highly resolved and agreed on most intergeneric relationships (Figs. 4, S1, S2, S3) with a few notable exceptions. The largest disagreement between the MP and BI topologies involved the base of Doradidae. In the MP analysis, Acanthodoradinae was the first subfamily to diverge from the rest of Doradidae and Astrodoradinae was the second. BI reversed this topology with Astrodoradinae diverging first, followed by Acanthodoradinae. Relationships within Astrodoradinae also differed between the two analyses. Both identified AnadorasEigenmann, 1925 as the first genus to diverge in Astrodoradinae. MP supported Physopyxis Cope, 1871 sister to Astrodoras + Hypodoras and Amblydoras Bleeker, 1862 sister to ScorpiodorasEigenmann, 1925. BI placed Physopyxis sister to a clade composed of Scorpiodoras and Amblydoras (Astrodoras + Hypodoras).
Within the subfamily Doradinae, MP and BI differed in four major respects. In the parsimony analysis, Doraops + Pterodoras was the first group to diverge within Doradinae, followed by Oxydoras Kner, 1855. BI weakly supported (0.5 posterior probability) the reverse with Oxydoras as the first genus to split from the rest of Doradinae, followed by Doraops + Pterodoras. A second difference between MP and BI was placement of the clade Centrodoras (Lithodoras + Megalodoras). In the parsimony analysis, Centrodoras (Lithodoras + Megalodoras) was sister to the fimbriate-barbel doradids. Alternatively, BI supported a sister group relationship between Centrodoras (Lithodoras + Megalodoras) and Centrochir + Platydoras, and that clade was sister to the fimbriate-barbel doradids. Thirdly, MP supported the monophyly of Doras inclusive of Doras punctatusKner, 1855 a species formerly assigned to Ossancora (Birindelli, Sabaj Pérez, 2011), and placed Doras sister to all other fimbriate-barbel doradids. In the BI analysis, Doras carinatus (Linnaeus, 1766; type species), D. micropoeus (Eigenmann, 1912), and D. higuchii Sabaj Pérez & Birindelli, 2008 formed a clade sister to all other fimbriate barbel taxa except D. phlyzakion Sabaj Pérez & Birindelli, 2008 and D. punctatus. Those two species, respectively, were successive sister taxa to the remaining fimbriate-barbel taxa. Finally, near the crown of the doradid tree, MP and BI disagreed on relationships within a clade composed of Hassar Eigenmann & Eigenmann, 1888, Nemadoras Eigenmann, 1925, TennellusBirindelli, 2014 and Hemidoras + Ossancora. MP weakly supported two monophyletic clades, Nemadoras + Tennellus and Hassar (Hemidoras + Ossancora), each with a Godman-Bremer support value of 1 (Fig. S2). In the BI analysis, Nemadoras was the first genus to diverge and Tennellus + Hassar and Hemidoras + Ossancora formed reciprocally monophyletic clades