Genomics of incipient speciation in a highly vagile marine mammal: genome-wide analysis of demographic history, population structure and local adaptation in the endangered Galápagos sea lion

• Applicant: Professor Dr. Joseph Hoffman
• Subject Area: Evolution, Anthropology ; Evolutionary Cell and Developmental Biology (Zoology) ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 255821879

One hundred and fifty years after Charles Darwins seminal work On the Origin of Species, the mechanisms by which animals speciate in the wild are still unresolved. However, the genomic revolution is now providing us with the necessary tools to investigate the genomic architecture of speciation. Among the most promising systems to reveal the evolutionary processes that control adaptation and govern the early steps of speciation are evolutionary young lineages diverging along strong environmental gradients. In particular, marine species provide ideal systems in which to test whether ecologically divergent selection in the absence of physical barriers to gene flow can lead to heterogeneous genomic divergence.The Galapagos sea lion (Zalophus wollebaeki) provides just such a system, occupying a remote, depauperate environment that has been a fertile ground for speciation research ever since the time of Charles Darwin. This species diverged from its Californian sister (Zalophus californianus) over one million years ago and has remained isolated ever since. Its range is tiny relative to the dispersal capability of the species but is characterized by a steep environmental cline between the nutrient rich grounds around the young western islands and the islands on the shallow central shelf of the archipelago. These environmental contrasts translate into marked differences in morphology, diet and the underlying genetics, as documented in a pilot study using 22 microsatellites and mitochondrial DNA. This challenges the view that geographic barriers to gene flow are required for genetic divergence and also makes the Galapagos sea lion a prime candidate for examining micro evolutionary processes that have facilitated local adaptation and localized genetic differentiation in the face of unrestricted dispersal potential.Our proposal will be among the first to harness the possibilities of the post genomic era in a unique ecological setting in the wild. We propose conducting genome-scale population genetic analyses across the entire species range, using the closely related Antarctic fur seal genome as a reference. The resulting data will allow us determine the primary mechanism underlying ecological incipient speciation, to identify speciation islands (i.e. candidate genomic regions carrying signatures of divergent selection) and to link these to divergent environmental parameters. These data will also provide an ideal opportunity to test the theoretical predication that the sex chromosomes speciate faster than the remainder of the genome. The combination of genome-scale population genetic approaches and coalescent modeling in this unique setting will yield fundamental insights into the evolutionary processes governing adaption and speciation in natural populations.

• DFG Programme: Research Grants
• International Connection: Sweden
• Participating Persons: Professor Dr. Alexander Goesmann; Professor Dr. Oliver Krüger; Professor Dr. Jochen B. W. Wolf