Meeting Abstract
External fertilization exposes gametes to variation in environmental conditions, including temporal and spatial variation in seawater pH. Gametes may be especially vulnerable to changes in pH because they are small and lack homeostatic capacities. In addition, sperm of many organisms rely on a mechanism of suppression in the testes that is regulated by the presence of high CO2/low pH. As a result, sperm are naturally pre-disposed to be sensitive to low seawater pH, which can pose a risk to fertilization under acidified conditions by reducing sperm activity. Our work with sea urchins has demonstrated that near-future (50-100 y) predicted changes in seawater pH reduce sperm motility and fertilization success, and that these effects vary between populations. To address one mechanism that could underlie this effect, I examined the pH sensitivity of dynein, a microtubule-associated ATPase that regulates energy use by sea urchin sperm. Using a microassay of inorganic phosphate production, I tested kinetics and stability of dynein under a set of pH and temperature conditions, using sperm from two populations of the sea urchin Arbacia punctulata from different latitudes. Dynein was highly sensitive to pH within a range that included near-future predicted conditions and that showed negative effects on sperm motility and fertilization. Populations differed in the sensitivity of dynein to pH and temperature. Dynein is therefore one component of sperm physiology that appears susceptible to ocean acidification, providing a possible mechanism that connects effects at the molecular level to whole organism performance.
