The adaptive significance and rapid evolutionary dynamics of seminal fluid proteins

• Applicant: Dr. Steven Ramm
• Subject Area: Evolution, Anthropology ; Sensory and Behavioural Biology ; Reproductive Medicine, Urology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448589387

Seminal fluid is widely believed to be a key mediator of post-mating sexual selection and sexual conflict. However, the complexity, rapid evolution and functional redundancy of this secretion means that identifying specific seminal fluid components responsible for influencing the post-mating behaviour, physiology and ultimately sperm utilization of mating partners - and the mechanisms through which this is achieved - is challenging. To date, detailed functional and evolutionary dissection of seminal fluid-mediated effects is therefore limited to just a few, primarily insect, model organisms. In this project, I will capitalize on our recent insights establishing the free-living flatworm Macrostomum lignano as a new and phylogenetically distinct model organism for studying seminal fluid. The project has two broad aims, to first elucidate the mechanisms of action of, and then second test for intra- and inter-specific diversification in, key seminal fluid proteins that modify post-mating behaviour of mating partners. We have identified two such SFPs that inhibit the so-called ‘suck behaviour’ often exhibited in response to ejaculate receipt in M. lignano, and which is hypothesized to remove ejaculate components. By contrast, a third SFP appears to act as a cue to stimulate such suck behaviour, potentially indicating that it has some as yet uncharacterized functional significance from the sperm donor perspective. Taking full advantage of M. lignano’s features including the transparency of the worm, a GFP-transformed line enabling in vivo observation of sperm and efficient gene knockdown through RNAi, I propose a series of experiments to test key predictions about the adaptive significance of these proteins and their mechanism of action. I will then test for rapid diversification in SFP expression and function by characterizing seminal-fluid mediated effects across multiple natural populations of M. lignano and in con- and hetero-specific matings involving M. lignano and its recently described sister species M. janickei. I thereby expect to expand and generalize our understanding of how sexual selection and sexual conflict shapes seminal fluid function and evolution.

• DFG Programme: Research Grants