Abstract
Cryptobenthic clingfish of the genus Gouania are Mediterranean endemics. The genus currently includes five species that primarily separate along an axis of body elongation, with slender and stout morphotypes that independently evolved in the Adriatic Sea and the eastern Mediterranean basin. This makes Gouania an ideal model to study parallel evolution driven by strong natural selective forces on different levels such as genes, genomes, morphology or ecology. My PhD project builds upon promising and intriguing findings of my Bachelor's and Master's theses. As an important first step, I fixed the taxonomy of the genus Gouania, which also led to the first published chapter of my PhD thesis and forms the basis for further in depth investigation of this system. The second chapter of my PhD investigates the role of diverging microhabitat choices in sympatric Adriatic species of Gouania and the third illuminates the phylogenetic context of the Gouania radiation based on whole genomic data. Even though these previous chapters investigated crucial ecological and (macro)evolutionary factors that explain the diversity observed in Gouania, understanding and comparing the speciation potential of organisms unfolds best at a level of distinct populations within a species. This brings me to the host-group in Antwerp (Prof. Svardal) who is highly specialised in population genomic analyses. Therefore, for my final PhD chapter, which will be the major focus during my BOF funded stay in Antwerp, I aim to illuminate the drivers of local population structure of sympatric Gouania species, G. pigra and G. orientalis, from the island of Crete and an island closer to the mainland. Crete is interesting in this context, because it flanks two major marine biogeographic regions and is embedded in complex oceanographic circulation systems that show high seasonal fluctuations, which can drive population connectivity of marine animals. Gouania have a rather sedentary lifestyle as adults and dispersion can only happen during a short pelagic larval phase. Therefore, similar patterns of high geographic population structure would be expected in the investigated species. However, preliminary COI barcoding data suggests divergent population genetic patterns within the two species, whereby populations of G. orientalis from Crete seem to be more strongly isolated than G. pigra populations. By analysing whole genome population data from several sites, I aim to investigate microevolutionary processes in these two species such as population structuring, demographic history as well as recent events of hybridization and introgression (incl. their potential direction), to identify reasons for the contrasting patterns of geographic structure observed between the two species. My stay at the University of Antwerp will be crucial for this endeavour, because, having studied similar questions in other systems, Prof. Svardal and his group will provide essential expertise. Additionally, I will run Lagrangian simulations to model passive larval migration patterns, which will help to explain geographical structure observed in the dataset. Altogether, the results of this project will contribute to the general understanding of speciation and population dynamics of low-dispersing organisms in the marine realm, a group often neglected in the design and management of marine (protected) areas.
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