The effects of temperature and pH on the reproductive ecology of sand dollars and sea urchins: Impacts on sperm swimming and fertilization

Abstract

In an era of climate change, impacts on the marine environment include warming and ocean acidification. These effects can be amplified in shallow coastal regions where conditions often fluctuate widely. This type of environmental variation is potentially important for many nearshore species that are broadcast spawners, releasing eggs and sperm into the water column for fertilization. We conducted two experiments to investigate: 1) the impact of water temperature on sperm swimming characteristics and fertilization rate in sand dollars (Dendraster excentricus; temperatures 8-38°C) and sea urchins (Mesocentrotus franciscanus; temperatures 8-28°C) and; 2) the combined effects of multiple stressors (water temperature and pH) on these traits in sand dollars. We quantify thermal performance curves showing that sand dollar fertilization rates, sperm swimming velocities, and sperm motility display remarkably wide thermal breadths relative to red urchins, perhaps reflecting the wider range of water temperatures experienced by sand dollars at our field sites. For sand dollars, both temperature (8, 16, 24°C) and pH (7.1, 7.5, 7.9) affected fertilization but only temperature influenced sperm swimming velocity and motility. Although sperm velocities and fertilization were positively correlated, our fertilization kinetics model dramatically overestimated measured rates and this discrepancy was most pronounced under extreme temperature and pH conditions. Our results suggest that environmental stressors like temperature and pH likely impair aspects of the reproductive process beyond simple sperm swimming behavior.

Marine heatwave temperatures enhance larval performance but are meditated by paternal thermal history and inter-individual differences in the purple sea urchin, Strongylocentrotus purpuratus

“…Additionally, sperm plasticity may elicit adaptive effects via the activity and motility of sperm cells themselves within their environment (Chirgwin et al, 2020;Abdelgalil et al, 2022). Given the influence of temperature and other environmental factors on fertilization, both itself and via parental conditioning, diving deeper into sperm morphology and performance under extreme event scenarios could prove a rich area of future research (Sewell and Young, 1999;Leuchtenberger et al, 2022).…”

Characterization of a sperm motility signalling pathway in a gonochoric coral suggests conservation across cnidarian sexual systems

“…lack of monophyly for the stony corals), demonstrating a possibly ancient origin for sAC in this phylum, which supports a conserved role for sAC in foundational biological processes such as sexual reproduction. Given that the activation of the sAC-cAMP-PKA pathway is stimulated by alkalinization of the sperm cytosol, this result also has important implications for the reproduction of broadcast spawning marine invertebrates in the face of anthropogenic ocean acidification, which is already known to alter sperm motility in many species after exposure of either sperm or adult males prior to spawning [6,[54][55][56][57][58][59]. Future work should investigate the role of sAC-cAMP-PKA signalling in sperm from a broader diversity of species to clarify the mechanisms by which ocean acidification might impact reproduction across invertebrate phyla in future seas.…”