The role of sperm phenotypic plasticity in speciation

• Applicants: Dr. Oliver Otti; Professor Dr. Klaus Reinhardt
• Subject Area: Evolution, Anthropology ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391178378

Speciation, the emergence of new species, is the ultimate source of biodiversity. Its most important step is that populations become reproductively isolated, i.e. their interbreeding is reduced, or results in reduced fitness. Characters causing reproductive isolation before mating have been intensively studied but reproductive isolation occurs post mating, either before or after fertilisation, called gametic isolation (prezygotic) and hybrid disadvantage, respectively. Gametic isolation is heavily understudied and current models exclusively describe its genetic component. However, substantial evidence shows that all aspects of sperm functioning depend also on environmental factors. Here, we propose that environmental effects on sperm contribute to reproductive isolation, and test this idea for the first time. We will examine the relative contribution on reproductive isolation of environmental effects on sperm (which, by definition, are sperm phenotypic plasticity) and the genetic component of sperm. We will do so in a system that currently undergoes speciation: We will compare the fitness outcome of replicate population crosses between bedbug host races that live on human or on bat hosts (bat-associated lines BL and human-associated lines HL). This system is suitable because BL and HL are currently diverging genomically, their crosses show postmating isolation and they can be reared on the diet of the other host race, allowing us to separate environmental and genetic factors experimentally. Across five Czech and German labs, we capitalise on a unique combination of theory, lab and field expertise in rearing bedbugs, analysing proteomics and lipidomics, measuring sperm metabolism and employing artificial insemination to characterise the functioning of HL and BL sperm in different environmental combinations. We will measure fertility and sperm parameters (lipidome, ROS production, metabolic rate, and longevity) of sperm by BL males that are i) reared on BL or HL diet, ii) stored by BL or HL females which iii) were also reared on BL or HL diet. iv) Male and seminal fluid effects on sperm will be separated by measuring BL and HL sperm parameters in the presence of either HL or BL seminal fluid. This tight focus on sperm functioning in different environments allows the applicants to test sperm effects against other male and female effects and thereby tests specific mechanisms of reproductive isolation - the issue suggested to be most urgent in speciation research. The proposal represents the first examination of the ecological, i.e. phenotypic plastic, component of sperm in speciation. It will be supported by the first data of an insect sperm lipidome, and a large-scale ecologically-induced proteome of the seminal fluid. The expected results will answer a key question in speciation - the relative role of genetic and ecological divergence in reproductive isolation at the postmating level; and they will do so in a re-emerging human parasite.

• DFG Programme: Research Grants
• International Connection: Czech Republic
• Partner Organisation: Czech Science Foundation
• Cooperation Partner: Professor Dr. Andrej Shevchenko
• Co-Investigators: Dr. Ondrej Balvin; Dr. Tomas Bartonicka