Laura and Craig have just had a paper accepted at Marine Environmental Research in which they outline a new method for measuring sperm motility – which we hope has promise as a quick and easily measured endpoint for future ecotoxicology studies.

We noticed that motile sperm from broadcasting spawning organisms a) swim downwards and b) often get caught (via surface tension forces) against clean surfaces of  glass slides and plastic well plates.  Combined, this means that active sperm accumulate against lower surfaces over time, whereas dead (or inactive) sperm sink only very slowly and do not really accumulate much at all. Consequently, for a given sperm concentration the rate of of accumulation of sperm over time in a well plate can potentially be used as a measure of the motility of sperm samples exposed to different levels of toxicants.  While there are other ways of measuring the impacts of toxicants on sperm motility (like computer aided sperm motion analysis), our measurements are extremely simple to make – needing only minimal hard/software (just a simple inverted microscope with phase contrast and a camera) and can be completed within minutes.  The measurements we make (number of sperm colliding per mm2 per sec) can also be more directly related to likely impacts on fertilisation success (via models of fertilisation kinetics that Craig developed in the last century).

One of the other things we are most excited about is that the method can be developed quickly for just about any broadcast spawning organism. In the paper we applied our new method with three very different organisms (oysters, a freshwater fish and an intertidal polychaete), but we’ve also seen the same effect (sperm sticking against surfaces) for a range of other organisms, including urchins, gastropods and algae. As part of his PhD, Antony Lockyer is hoping to develop these new methods across a range of species, for a variety of monitoring scenarios.