title: Ocean acidification impacts on sperm mitochondrial membrane potential bring sperm swimming behaviour near its tipping point.
abstract: Broadcast spawning marine invertebrates are susceptible to environmental stressors such as climate change, as their reproduction depends on the successful meeting and fertilization of gametes in the water column. Under near-future scenarios of ocean acidification, the swimming behaviour of marine invertebrate sperm is altered. We tested whether this was due to changes in sperm mitochondrial activity by investigating the effects of ocean acidification on sperm metabolism and swimming behaviour in the sea urchin Centrostephanus rodgersii. We used a fluorescent molecular probe (JC-1) and flow cytometry to visualize mitochondrial activity (measured as change in mitochondrial membrane potential, MMP). Sperm MMP was significantly reduced in ΔpH -0.3 (35% reduction) and ΔpH -0.5 (48% reduction) treatments, whereas sperm swimming behaviour was less sensitive with only slight changes (up to 11% decrease) observed overall. There was significant inter-individual variability in responses of sperm swimming behaviour and MMP to acidified seawater. We suggest it is likely that sperm exposed to these changes in pH are close to their tipping point in terms of physiological tolerance to acidity. Importantly, substantial inter-individual variation in responses of sperm swimming to ocean acidification may increase the scope for selection of resilient phenotypes, which, if heritable, could provide a basis for adaptation to future ocean acidification.
authors.affiliation: Marine Ecology Group, Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: Schlegel
authors.affiliation: Centre for Environmental Contaminants Research, CSIRO, Locked Bag 2007, Kirrawee, Sydney, NSW 2232, Australia Monique.binet@csiro.au.
authors.forename: Monique T
authors.initials: MT
authors.lastname: Binet
authors.affiliation: Department of Biological & Environmental Sciences - Tjärnö, University of Gothenburg, Strömstad 45296, Sweden.
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Havenhand
authors.affiliation: Ecotox Services Australasia, 27/2 Chaplin Drive, Lane Cove, NSW 2066, Australia.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Doyle
authors.affiliation: Marine Ecology Group, Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia.
authors.forename: Jane E
authors.initials: JE
authors.lastname: Williamson
mesh_terms: D000818:Animals; D001562:Benzimidazoles; D002232:Carbocyanines; D057231:Climate Change; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D008297:Male; D053078:Membrane Potential, Mitochondrial; D009792:Oceans and Seas; D012617:Sea Urchins / Q000502:physiology*; D012623:Seawater / Q000737:chemistry*; D013081:Sperm Motility; D013094:Spermatozoa / Q000502:physiology
chemical_list: D001562:Benzimidazoles; D002232:Carbocyanines; D005456:Fluorescent Dyes; C068624:5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolocarbocyanine
keywords: CO2; Fertilization kinetics; Reproduction; Resilience; Sperm metabolism