Molecular divergence in a marine animal-microbial symbiosis since the closure of the isthmus of panamá
Recently it has become clear that host-associated microbes play a major role in host adaptive responses to environmental change. To predict future responses, we can explore the past and use geological events, which provide valuable insights into adaptive mechanisms because these events were major drivers of evolution. The formation of the Isthmus of Panamá separated a previous, ancient ocean and all of its marine life into the Pacific Ocean and the Caribbean Sea. These two oceans have developed into very different habitats. Closely related animal populations that were separated by the Isthmus had to adapt to diverging environmental conditions. Today we find closely related species pairs, i.e., geminate species, that are genetically very similar but live in highly divergent habitats. This provides a powerful study system to explore drivers and processes of speciation, diversification, and adaptation. In this project, I am integrating this knowledge to study the evolution of an animal-microbial symbiosis that was divided into several geminate species pairs by the Isthmus of Panamá. I am going to compare lucinid clam populations (Lucinidae) and their endosymbiotic bacterial chemosymbionts (Candidatus Thiodiazotropha) at the genomic and transcriptomic level. Lucinid clams are an excellent model system in this context because their shells are preserved as fossils and we know that they have existed before the Isthmus closed. Hence, I can calibrate the rates of molecular evolution with the closure of the Isthmus. By studying several populations of hosts and bacterial symbionts, I will be able to use population genetic theory to inform how this symbiosis evolves in response to changing environmental conditions.