Phylogeography of the flathead mullet Mugil cephalus species complex – Using Next-Generation RAD-Sequencing to highlight a worldwide marine dispersion

• Applicant: Dr. Philipp Thieme
• Subject Area: Evolution, Anthropology
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 492963418

Of the high number of aquatic vertebrates, only a small percentage is represented by cosmopolitan fish species. This is hardly surprising as it seems difficult to achieve a global distribution and at the same time maintain a sufficient gene flow to prevent speciation. Recent genetic analyses propose that for some of these species it is indeed not possible to maintain gene flow between populations and that supposedly single species rather represent species complexes. Such species present the opportunity to study speciation events in aquatic habitats. While for terrestrial species, vicariance due to physical barriers are frequently proposed, these may also apply to aquatic species, but in apparent open environments like oceans other explanations, such as environmental or historical barriers, need to be considered as well. The Mugil cephalus species complex comprise up to 14 genetic lineages and is a promising model organism to study speciation in aquatic habitats. In the proposed research project, the phylogenetic relationships of Mugil cephalus lineages will be analysed and their evolutionary biogeography will be studied to find potential events and barriers that led to the speciation of genetic lineages. The project will be divided into four objectives. At first, nuclear data will be analysed using ddRADseq and Next-Generation-Sequencing. The combination of these methods can retrieve large numbers of mutations which will result in a well resolved phylogenetic tree. The reconstructed phylogeny will be used to discuss the phylogenetic relationships of the genetic lineages. The second objective of this project is the distinction of the distribution boundaries on the genetic lineages of Mugil cephalus. Based on a time-calibrated phylogeny, potential migration routes used by Mugil cephalus spp. ancestors will be evaluated and their evolutionary dispersal will be reconstructed. The third objective is to study potential distribution and interbreeding barriers. Previously suggested hypotheses on the separation of the genetic lineages will be reviewed and correlated to their distribution areas. Furthermore, historical and geographical barriers will be considered depending on estimated divergence times and the according distribution regions. Environmental influences will also be assessed to find potential barriers preventing interbreeding of genetic lineages today. The fourth objective is a taxonomic revision, in which previously described and later synonymized Mugil species will be matched with the genetic lineages based on morphological and distribution data. Additionally, morphological characters useful for discrimination of the genetic lineages will be examined.

• DFG Programme: WBP Fellowship
• International Connection: France
• Host: Dr. Jean-Dominique Durand