Evolution of sperm conjugates: does sperm competition drive the cooperative behaviour of sperm?

forthcoming

Sperm conjugates, where multiple sperm cells attach to each other and move as a group, have been described in a wide range of taxa and could have significant impacts on the fertilization process, but understanding of their function is limited. Effective sperm cooperation through these conjugates could have evolved as an adaptation to sperm competition between multiple males, but this hypothesis has not been tested in insects, which have some of the largest reported sperm conjugates in animals. Bushcrickets have been well studied regarding species-specific variation in the level of polyandry and sperm competition. Large sperm conjugates (‘spermatodesms’) are also a common feature of this taxon, making it an ideal system to test the link between sperm conjugates and sperm competition. I will investigate this connection using within-species approaches, with controlled mating trials and sperm staining, as well as phylogenetic controlled studies, testing the link between the level of polyandry and spermatodesm traits between species. Finally, guided by the insight from these results I will construct a theoretical model to gain understanding into selection pressures that may have led to the evolution of conjugated sperm. The results will significantly improve our understanding of the evolutionary importance of collaborative behaviour of sperm, which has been largely unstudied until now. My supervisor, Dr Jussi Lehtonen, is an internationally renowned researcher who is experienced in developing mathematical models on sexual selection and sperm competition. The project includes a secondment hosted by Prof. Leigh W. Simmons, a leading expert in insect sperm biology. I, the candidate, am an expert on behavioural ecology, experienced in conducting mating trials in bushcrickets and phylogenetic analysis on insects. The project will strengthen my scientific skills and the future career prospects, as well as expand and complement the research of the host institution.