Studies On Molecular Phylogeny And Historical Biogeography Of Mugilid Fishes (Teleostei:Mugiliformes)

The Mugiliformes (Actinopterygii:Teleostei:Euteleostei:Acanthopterygii) contains a single family Mugilidae. They are important commercial coastal fishes and widespread across tropical and temperate latitudes.The phylogenetic position of Mugiliformes and interrelationships among members of the Mugilidae has been extensively debated in ichthyological systematic studies. In this thesis, phylogeny of Ovalentaria, including Mugiliformes, as well as interrelationships among mugilid genera were reconstructed based on mitochondrial genomes and nuclear multi-loci. Furthermore, the classification of Mugilidae was revised based on phylogenetic results and morphological characters.In addition, there are two features of globally distributed mugilid fishes:ⅰ) most of the mugilid genera with limited distributions; ⅱ) differences in species richness among marine regions. As a result, mugilid fishes is the ideal modal taxon to reveal the speciation and underlying historical causes for distributional patterns of Mugiliformes. Time-calibrated phylogeny of Mugiliformes was reconstructed using molecular dating, and ancestral distributional areas and climatic habitat states were further reconstructed. Besides, paleogeology evidence and paleoclimate information were integrated to understand the underlying causes for distributional patterns of Mugiliformes.The major results are as follows:1. Phylogenetic position of MugiliformesPhylogeny of Ovalentaria, including Mugiliformes was reconstructed based on mitochondrial genomes, as well as multilocus evidence of concatenated nuclear and mitochondrial genes, respectively. The results show that ⅰ) the monophyly of Mugiliformes is strongly supported by mitochondrial genomes, as well as nuclear multiloci; ⅱ) Pseudochromidae is the sister-taxon of Mugilidae supported by mitochondrial genomes; ⅲ) Congrogadidae+Plesiopidae are the sister-taxon of Mugilidae supported by multilocus evidence of concatenated nuclear and mitochondrial genes.2. Phylogenetic relationships among the genera of MugilidaePhylogenetic relationships among mugilid genera were well reconstructed based on twelve nuclear loci and three mitochondrial genes. The results show that i) the Mugilidae can be devided into four clades:clade A occupies a basal position, clade B occupies a hypobasal position and represents the sister taxon of clade C+D; ii) clade A includes Myxus and Neomyxus; iii) within the Clade B, the Cestraeus genus occupies a basal position, Chaenomugil and Mugil form a sister lineage, and they together represent the sister lineage of Dajaus+Joturus+Agonostomus; iv) clade C can be further devided into four tribes:SCI consists of Trachystoma, Gracilimugil and Aldrichetta, SC2 consists of Sicamugil, Minimugil and Rhinomugil, SC3 consists of Squalomugil, Plicomugil and Ellochelon, and SC4 consists of Crenimugil and Osteomugil; v) within the Clade D, Neochelon occupies a basal position, Pseudomyxus occupies a hypobasal position, the lineage of Planiliza+Parachelon+ Chelon forms the sister group of Oedalechilus; vi) the findings laid the foundation of revision of Mugilidae classification.3. Revised classification of MugilidaeUsing the phylogenetic relationships among mugilid genera in chapter 6 as criterion and reinterpreting synapomorphic characters, the revised classification of Mugilidae is proposed. The results show that i) the Mugilidae can be reclassified into four subfamilies, including three new subfamilies (Myxinae, Rhinomugilinae, and Cheloninae) and a new recombined subfamily (Mugilinae); ii) Myxinae includes Myxus and Neomyxus; iii) Mugilinae includes Cestraeus, Chaenomugil, Agonostomus and Mugil; iv) Rhinomugilinae can be further devided into four tribes, i.e., Trachystomaini, Rhinomugilini, Squalomugilini and Crenimugilinae. Among the four new tribes, Trachystomaini consists of Trachystoma, Gracilimugil and Aldrichetta, Rhinomugilini consists of Sicamugil, Minimugil and Rhinomugil, Squalomugilini consists of Squalomugil, Plicomugil and Ellochelon, and Crenimugilini consists of Crenimugil and Osteomugil; v) Cheloninae includes Neochelon, Pseudomyxus, Oedalechilus and Chelon; vi) a key to the subfamilies and genera in Mugilidae is erected using re-defined synapomorphic characters.4. The underlying causes for distributional patterns of MugiliformesTime-calibrated phylogeny of Mugiliformes was reconstructed using molecular dating, and ancestral distributional areas and climatic habitat states were further reconstructed. Besides, paleogeology evidence and paleoclimate information were integrated to investigate the underlying causes for distributional patterns of Mugiliformes. The results show that i) the ancestors of mugilids originated and diversified in the West Pacific in the Early Oligocene; ii) Myxinae, Mugilinae, as well as the most recent common ancestors of Crenimugilinae and Cheloninae were originated and diversified mainly in the West Pacific from Oligocene to Miocene; iii) the ancestors of mugilids distributed in tropical regions, and most transitions from tropical to temperate environment occurred in late Miocene to Quaternary; iv) dispersal events have played an important role in the distributional patterns of Mugiliformes, and four vacariance events, i.e., the forming of Old World Land Barrier, New World Land Barrier, East Pacific Barrier and Mid-Atlantic Barrier in the Miocene to Pliocene, are the major causes of the regional distribution of mugilid fishes.In summary, on the basis of mitochondrial genomes and multilocus evidence of concatenated nuclear and mitochondrial genes, i) the monophyly of Mugiliformes is supported; ii) the phylogenetic relationships among mugilids genera have been well resolved; iii) the classification of Mugilidae is revised based on phylogenetic results and morphological evidence. Three new subfamilies and four new tribes have been erected and a key to the genera of Mugilidae is provided. Meanwhile, this thesis firstly reveals the underlying historical causes for distributional patterns of Mugiliformes. The ancestors of mugilids originated in the West Pacific in the Early Oligocene, and then experienced a few dispersal events to form the present globally distributional pattern. Besides, four vacariance events, i.e., the forming of Old World Land Barrier, New World Land Barrier, East Pacific Barrier and Mid-Atlantic Barrier in the Miocene to Pliocene, are the major causes of the regional distribution of mugilid fishes. The findings will not only contribute to the conservation of mugilid biodiversity, but also promote the studies of ichthyological systematics and underlying causes for distributional patterns of marine fishes.