Molecular Systematics and Biogeography of the Family Sciaenidae (Teleostei: Perciformes)

The family Sciaenidae, also known as croakers or drums, contains approximately 292 species in 68 currently recognized genera and is one of the large perciform families. Members within this family mostly occur in marine and brackish waters of the Atlantic, Indian and Pacific Oceans; only a few inhabit freshwaters. As the worldwide-distributed groups of living animals always attract the attention of biogeographers to document the origins and patterns of diversification in time and space, the knowledge of historical biogeography worldwide within the non-coral marine species is still very limited, such as the Sciaenidae. In addition, most of the sciaenid species are ecologically, economically and recreationally important fish. Since the past decades near-shore fishing, commercial trawling and even by-catch in shrimp fisheries threaten the sciaenid species all over the world. The fishery production has been declining yearly. In order to create and implement effective conservative strategies, taxonomic knowledge of conservative targets and clear phylogenetic relationships within Sciaenidae are essential. The aims of this study are 1) to infer the phylogenetic relationships of the global Sciaenidae; 2) to reconstruct the historical biogeography of the global Sciaenidae to investigate the origin and to test the hypotheses explaining the present-day biogeographic patterns of the global Sciaenidae; 3) to further review and clarify the systematics of the species within the sciaenid genera that are endemic to the Indo-West Pacific (IWP). For the former two aims, a total of 93 globally sampled sciaenid species from 52 genera were used for reconstructing a molecular phylogeny of the global sciaenids based on two mitochondrial and four nuclear genes (i.e. mitochondrial COI and Cyt b plus nuclear RAG1, RH, EGR1, EGR2B gene; total 6619 bp). The partitioned maximum-likelihood analysis supports the monophyly of the family Sciaenidae. Within the inferred phylogenetic tree, fifteen main and well-supported lineages were identified; some of which have not been recognized previously. Eight genera for which two or more species were examined are monophyletic while eight others are not. The eight strictly freshwater sciaenid species (from five of six described genera) examined herein form three independent freshwater lineages/clades. In addition, the historical biogeographical analysis concomitant with fossil evidence indicates that the crown group sciaenids originated and diversified in the tropical America during the Oligocene to Early Miocene before undergoing two range expansions. Later eastward dispersal events, subsequent diversification via vicariates (EA vs. IWP), and within region (e.g., IWP) diversification are hypothesized to account for their current global distribution and species diversity patterns. For the third aim, the present study with the emphasis on the sciaenid genera endemic to the IWP (IWP clade). A total of 308 samples from 51 out of 91 recognized sciaenid morpho-species sampled from 96 different localities within the IWP clade were used in the conducting analyses. Species delimitation analyses conducted by using two different tools (ABGD and GMYC) based on COI gene dataset and other lines of evidence (genetic similarity, monophyly, geographic distribution and morphology) result in 60 OTUs (Operational Taxonomic Units) than expected. This indicates that possible cryptic and/or potential new species are present. The result from the phylogenetic analysis conducted with likelihood method confirms the monophyly of the IWP sciaenid clade. However, the genus Protonibea forms a monophyletic group with genus Megalonibea. This thus suggests that the Megalonibea is an invalid genus. In summary, I provide the most comprehensive molecular systematic study of the Sciaenidae, which will advantage the future work with the sciaenids, especially to resolve several issues in their systematics, as well as to reliably reconstruct their historical biogeography. Additionally, the advanced phylogenetic study of those IWP endemic sciaenids provides an important framework for the taxonomic study of the family Sciaenidae. Furthermore, the results on DNA-based species delimitation analyses have increased the pace and stringency of our biodiversity assessments that could be served as a guideline for the management and the conservation of the IWP sciaenid species.