In Sperm Biology and Infertility, we aim to combine four related main fields: 1) Evolutionary Sperm Biology and Ecology, 2) Sperm Metabolism and Sperm Oxygen Radicals Production, 3) the Role of the Mitochondria in Insect Sperm, 4) Lipids in the Sperm Membrane
Evolutionary Sperm Biology and Ecology
THEORY. Our group, together with Jessica Abbott in Lund, has introduced Sperm Ecology as a novel framework to study sperm cells with three aims. First, we reviewed the variety of environmental effects on sperm. Clearly, evolutionary and ecological research should not neglect the overwhelming evidence that sperm function is altered by many environments. This concerns the male, female and immediate sperm environments and applies to both external and internal fertilizers in terrestrial and aquatic habitats. Second, we concluded that the evidence for phenotypic plasticity in sperm function is overwhelming. We believe this necessitates a re-appraisal of some evolutionary assumption in sperm competition theory, especially also in light of our empirical study showing zero heritability of sperm competition (Dobler & Reinhardt 2016). Third, genotype-by-environment interaction effects on sperm function exist but their general adaptive significance (e.g. local adaptation) awaits further research. Unresolved issues are whether sperm diversification occurs by natural selection acting on sperm function, or on male and female micro-environments that optimise plastic performance of sperm (which we called ‘sperm niches‘). Environmental effects on sperm reduce fitness predictability under sperm competition, but are powerful to predict altered species distributions under global change, explain adaptive behaviour, and highlight the role of natural selection in behavioral ecology and reproductive medicine.
Our ‘manifesto’ appeared in Annual Reviews of Ecology, Evolution and Systematics in 2016. Link
Dobler R, Reinhardt K. 2016. Heritability, evolvability, phenotypic plasticity and temporal variation in sperm-competition success of Drosophila melanogaster. Journal of evolutionary biology 29: 929-941. link
Otti O, Johnston PR, Horsburgh G, Galindo J, Reinhardt K. 2015. Female transcriptomic response to male genetic and nongenetic ejaculate variation. Behavioral Ecology, link
Contact Klaus for further information.
Sperm Metabolism and Sperm Oxygen Radicals Production
Currently, sperm are widely assumed to be propelled by oxidative phosphorylation, i.e. by the mitochondria. The exclusive maternal inheritance of mitochondria generates the interesting situation that mitochondria-related sperm traits that benefit the father cannot be inherited to the son. This is a theoretical challenge for models that assume that sperm competition drives evolutionary change. Other researchers see a primary role of glycolysis in sperm metabolism. We are using a number of advanced microscopy methods to try and address this issue of sperm metabolism, such as FLIM or a biophysical method to measure reactive oxygen species (ROS).
A second area where we look at the role of mitochondria in sperm function is via the interaction of mitochondria with the nucleus. Such mito-nuclear interactions influence fertility and mismatches can cause complete male sterility. In collaboration with Damian Dowling’s lab, Monash University, we address some questions around such mismatches using mitolines – where a certain genotype is combined with either of several mitochondrial haplotypes. This is largely the topic of Ruijian‘s thesis.
more to come. For the moment see:
Reinhardt K, Breunig HG, Uchugonova A, König K. 2015. Sperm metabolism is altered during storage by female insects: evidence from two-photon autofluorescence lifetime measurements in bedbugs. Journal of the Royal Society Interface link (open access)
Ribou A-C, Reinhardt K. 2012. Reduced metabolic rate and oxygen radicals production in stored insect sperm. Proceedings of the Royal Society of London B 279: 2196-2203.
Reinhardt K, Ribou A-C. 2013. Females become infertile as the stored sperm’s oxygen radicals increase. Scientific Reports 3:2888
The Role of the Mitochondria in Insect Sperm
Insects possess two sperm mitochondria, helically wrapped around and along the tail. In Drosophila, they have a role in the elongation of sperm but other than that, we don’t know much what the sperm mitochondria actually do. Oxphos may, maybe not. We would like to know and one possibility to start addressing this question is to monitor sperm metabolism in males and females, such as using autofluorescence lifetime imaging.
Lipids in the Sperm Membrane
Sperm naturally are rich in polyunsaturated fatty acids (PUFA). This is odd because PUFA are very susceptible to oxidation and lipoxidation is not quite what sperm need to function. We have recently found that Drosophila when fed plant-based sterols and PUFA produce sperm that emit fewer reactive oxygen species than males fed a yeast-based diet. That’s all so far, we have no idea whether these sterols end up in mitochondria, and of course, we have no really an idea what sperm mitochondria do (see previous point).
A second aspect, related to our project on speciation in bedbugs, is the question how the lipids in the blood of bats and humans end up in the sperm cells. We know that something is going on and we also know it has a relationship to sperm metabolism. Watch this space.
*Guo R, Reinhardt K. 2020. Dietary polyunsaturated fatty acids affect volume and metabolism of Drosophila melanogaster sperm. Journal of evolutionary biology 33: 544-550. pdf.