Ecology and evolution of a parasitic lifestyle, a multidimensional synthesis

Of all the lifestyles organisms follow, parasitism is one of the most complex and impactful on the global biota, directly on their infected hosts and with chain reactions in ecosystems and economies worldwide. In contrast to the tremendous investments in preventing and mitigating their impacts, we still lack fundamental understanding of their evolutionary mechanisms – the repeated origin and patchy persistence of parasitism across the tree of life are both mysterious. Such understanding can be instrumental not just to a deeper understanding of how biodiversity forms, but to more proactive approaches in disease management, wildlife conservation and public health, and is only possible to establish through a data-driven, comparative synthesis. Many organismal groups in nature contain both parasitic and free-living species, but rarely can we find a system with a balanced combination of research potential and feasibility. Here, we propose to investigate the ecology and evolution of parasitism in a group of marine invertebrates which presents exciting opportunities as a model system, the bivalve order Galeommatida. This group comprises a number of parasitic species, scattered among the free-living relatives on their phylogeny and living on or inside a variety of ecologically and economically significant taxa like crabs, shrimps, lobsters, sea urchins and sea cucumbers. There is rising interest in the dramatic diversity, global distribution, and fascinating morphological disparity in Galeommatida, leveraging the status of the larger Class Bivalvia as a classic model system across fields like ecology, biogeography and evolutionary biology. Multi-dimensional knowledge awaits to be synthesized. We have assembled a world-class team of taxonomists, systematists, malacologists, biogeographers and evolutionary biologists to mine an existing wealth of underutilised resources including the rich literature and bivalve collections at major natural history museums, supplemented with a targeted field survey by team members expert in targeted regions. Our short-term aim is to build an multidimensional database for galeommatid bivalves from the global marine biodiversity hotspot, the tropical western Pacific, and its adjacent temperate coastlines, and conduct the first large-scale comparative synthesis of the underlying eco-evolutionary mechanisms associated with parasitism. We propose two hypotheses to be tested, both potentially leading to higher extinction risk for parasitic species: 1) parasitism limits the ability of (and evolutionary investment in) long-distance dispersal and thus restricts the geographic range of species occurrences; 2) close interactions with hosts promote morphological innovation, leading to the proliferation of new species and further break-up of geographic ranges. Our novel, multidimensional investigation will build fundamental theories of why parasitism has evolved, and what costs have prevented parasitism from pervading whole clades. This project will build a powerful research basis for capturing larger grants. We have a clear, longer-term vision for extending this research to a full range of symbioses (i.e. from parasitic to mutually beneficial) and expanding the spatial coverage to the global scale to ask related, broader questions. The more ambitious goal, viable given our interdisciplinary expertise, is to strengthen the temporal perspective using fossil data – a direct window to the origin and evolution of parasitism. Many more extensions will be developed by this global partnership, which will inevitably grow through involving early-career researchers in our labs as well as inviting new partners through our existing research network, the proposed symposium in the Natural History Museum, London (in Year 2), and engagement with stakeholders backed by empirical evidence from this project.