Genus-level supertree of Cyprinidae (Actinopterygii: Cypriniformes), partitioned qualitative clade support and test of macro-evolutionary scenarios.
Résumé
We used the supertree approach of matrix representation with parsimony to reconstruct to date the most exhaustive (genus-level) phylogeny of Cyprinidae. The supertree of Cyprinidae, representing 397 taxa (237 nominal genera) and 990 pseudocharacters, was well resolved (96%) through extended consensus majority rule, although 36 nodes (9.4%) were unsupported. The proportion of shared taxa among source trees was very low after calculation of the taxonomic coverage index (TCI = 0.059), which is proposed here as a more accurate alternative to the usual ratios calculated from the number of pseudo-characters or source trees per taxon. We define a new index for the calculation of partitioned qualitative clade support, the partitioned rQS ((p)rQS), which offers a straightforward visualization of the relative supports of source tree partitions at supertree nodes.The use of (p)rQS showed that the molecular source tree partition contributed to most node supports within the supertree of Cyprinidae (73%, contra 21% for the morphological partition) and evidenced a fair proportion of conflict at nodes between the two partitions (21%), notably reflecting (i) the greater number and resolution of molecular source trees, and (ii) potential morphological convergences. Most of the higher-level relationships within Cyprinidae were supported by both morphological and molecular source tree partitions. Our supertree showed a well-supported dichotomy between a clade consisting of a 'barbine' + 'rasborine' lineage, sister group to (Barbinae [paraphyletic], (Cyprininae, Labeoninae)), and a clade consisting of other rasborines (large polytomy) and the two monophyletic groups ((Tincinae, Tanichthys), (Ecocarpia, (Acheilognathinae, (Gobioninae, Leuciscinae)))) and (Squaliobarbinae, (Xenocyprinae, Cultrinae)). Through the non-monophyly of almost all the traditional subfamilies of Cyprinidae and 34 genera, our supertree exemplified the taxonomic chaos that reigns in the classification of the family. It also highlighted that further efforts should aim at increasing taxonomic sampling and generating alternative phylogenetic signals, notably for the still poorly apprehended Tincinae, Squaliobarbinae, Acheilognathinae, Gobioninae, and Rasborinae, the latter representing a key taxon for the understanding of early cyprinid evolution. Our supertree also proved useful for testing macro-evolutionary scenarios at a wide taxonomic scale. Ancestral reconstructions using linear parsimony confirmed that the Oriental tropical region was the centre of origin of Cyprinidae, and identified three Oriental-to-Palaearctic, two Palaearctic-to-Nearctic, and one Oriental-to-Afrotropical major migration events. On the other hand, we almost completely rejected the hypothesis of presence of barbels as a plesiomorphic condition within Cyprinidae (although ambiguous for maxillary barbels of the Barbinae-Cyprininae type). The supertree of Cyprinidae serves as a basis to discuss the applications and bias of the newly proposed (p)rQS, to provide future guidelines for a better achievement of cyprinid phylogeny, and to elaborate further on inter-continental migrations and the adaptive value of barbels.