Sperm motility of oysters from distinct populations differs in response to ocean acidification and freshening

Laura J Falkenberg,Jon N Havenhand,Craig A Styan

doi:10.1038/s41598-019-44321-0

Abstract

Species’ responses to climate change will reflect variability in the effects of physiological selection that future conditions impose. Here, we considered the effects of ocean acidification (increases in pCO2; 606, 925, 1250 µatm) and freshening (reductions in salinity; 33, 23, 13 PSU) on sperm motility in oysters (Crassostrea gigas) from two populations (one recently invaded, one established for 60+ years). Freshening reduced sperm motility in the established population, but this was offset by a positive effect of acidification. Freshening also reduced sperm motility in the recently invaded population, but acidification had no effect. Response direction, strength, and variance differed among individuals within each population. For the established population, freshening increased variance in sperm motility, and exposure to both acidification and freshening modified the performance rank of males (i.e. rank motility of sperm). In contrast, for the recently invaded population, freshening caused a smaller change in variance, and male performance rank was broadly consistent across treatments. That inter-population differences in response may be related to environmental history (recently invaded, or established), indicates this could influence scope for selection and adaptation. These results highlight the need to consider variation within and among population responses to forecast effects of multiple environmental change drivers.

Highlights

Species’ responses to climate change vary among levels of organisation
Our finding that different populations, and individuals, of oysters showed distinctly different responses to ocean acidification and freshening could have pervasive implications for this species under marine climate change
The large changes in motility we observed under acidification and freshening imply that these drivers could cause correspondingly large shifts in fertilisation success for individuals[33]

Summary

Introduction

Species’ responses to climate change vary among levels of organisation. For example, differences have been found among Phyla[1], among populations of the same species[2,3,4], and among individuals of the same populations[5,6,7]. Sperm selection plays a key role in shaping the subsequent generation in many broadcast-spawning marine organisms[12,13]. Ongoing ocean acidification will likely generate significant novel selection pressures. While many studies have indicated that ocean acidification could lead to reduced sperm motility[8,17,18,19], others have found it can remain unchanged[20], or even increase[21]. Ocean acidification does not operate in isolation, and many studies show that multiple simultaneous drivers can have very different effects to those of drivers operating alone[22]. The combined effects of freshening and ocean acidification on sperm motility remain unassessed

Methods

Results

Conclusion