Abstract
Snakehead fishes of the family Channidae are predatory freshwater teleosts from Africa and Asia comprising 38 valid species. Snakeheads are important food fishes (aquaculture, live food trade) and have been introduced widely with several species becoming highly invasive. A channid barcode library was recently assembled by Serrao and co-workers to better detect and identify potential and established invasive snakehead species outside their native range. Comparing our own recent phylogenetic results of this taxonomically confusing group with those previously reported revealed several inconsistencies that prompted us to expand and improve on previous studies. By generating 343 novel snakehead coxI sequences and combining them with an additional 434 coxI sequences from GenBank we highlight several problems with previous efforts towards the assembly of a snakehead reference barcode library. We found that 16.3% of the channid coxI sequences deposited in GenBank are based on misidentifications. With the inclusion of our own data we were, however, able to solve these cases of perpetuated taxonomic confusion. Different species delimitation approaches we employed (BIN, GMYC, and PTP) were congruent in suggesting a potentially much higher species diversity within snakeheads than currently recognized. In total, 90 BINs were recovered and within a total of 15 currently recognized species multiple BINs were identified. This higher species diversity is mostly due to either the incorporation of undescribed, narrow range, endemics from the Eastern Himalaya biodiversity hotspot or the incorporation of several widespread species characterized by deep genetic splits between geographically well-defined lineages. In the latter case, over-lumping in the past has deflated the actual species numbers. Further integrative approaches are clearly needed for providing a better taxonomic understanding of snakehead diversity, new species descriptions and taxonomic revisions of the group.
Highlights
Species identification and delimitation play a vital role in our understanding of the diversity of life
The resulting 434 channid coxI sequences downloaded from GenBank we retained included: a) out of the sequences generated by [32]. b) 124 of the 129 channid coxI sequences downloaded from GenBank by [32]
Multiple Barcode Index Number (BIN) were assigned to several species in the study of [32] and we found several additional cases of underappreciated diversity mainly in the species C. bankanensis, C. gachua, C. marulius, C. striata (Table 1)
Summary
Species identification and delimitation play a vital role in our understanding of the diversity of life. [6,7,8,9,10,11]; but see [12] for a critical view on the utility of single-locus approaches These analytical approaches can be classified into three main groups [11]: clustering, tree-based and character-based methods, with the former two approaches clearly dominating the burgeoning field of molecular species delimitation. Among the most popular clustering methods are the Automatic Barcode Gap Discovery (ABGD, [13]) and the Refined Single Linkage (RESL) / Barcode Index Number (BIN), methods [14], hereafter referred to as BIN only They are consistent in identifying the presence of a ’barcoding gap’, the discontinuity between intra- and interspecific sequence divergences, but are prone to fail when these two classes of pairwise genetic distances overlap [15]. Several recent studies have looked at different aspects of species delimitation and their effect on inferred species diversity based on: the different methods used [6,11,14]; the phylogenetic reconstruction methods used [18,19]; the presence of singletons and various degrees of incomplete sampling in the data set [9,18,20,21]; the geographic scale of taxon sampling [22]; and dispersal ability and migration rates and their impact on the formation of discrete genetic clusters [12,23]
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