DOI: 10.5061/dryad.37pvmcvf2
title: Data from: Ocean acidification during pre-fertilization chemical communication affects sperm success

description: Ocean acidification (OA) poses a major threat to marine organisms,
 particularly during reproduction when externally shed gametes are
 vulnerable to changes in seawater pH. Accordingly, several studies on OA
 have focused on how changes in seawater pH influence sperm behaviour
 and/or rates of in vitro fertilization. By contrast, few studies have
 examined how pH influences pre-fertilization gamete interactions, which
 are crucial during natural spawning events in most externally fertilizing
 taxa. One mechanism of gamete interaction that forms an important
 component of fertilization in most taxa is communication between sperm and
 egg-derived chemicals. These chemical signals, along with the
 physiological responses in sperm they elicit, are likely to be highly
 sensitive to changes in seawater chemistry. In this study, we
 experimentally tested this possibility using the blue mussel, Mytilus
 galloprovincialis, a species in which females have been shown to use
 egg-derived chemicals to promote the success of sperm from genetically
 compatible males. We conducted trials in which sperm were allowed to swim
 in gradients of egg-derived chemicals under different seawater CO2 (and
 therefore pH) treatments. We found that sperm had elevated fertilization
 rates after swimming in the presence of egg-derived chemicals in low pH
 (pH 7.6) compared to ambient (pH 8.0) seawater. This observed effect could
 have important implications for the reproductive fitness of external
 fertilizers, where gamete compatibility plays a critical role in
 modulating reproduction in many species. For example, elevated sperm
 fertilization rates might disrupt the eggs’ capacity to avoid
 fertilizations by genetically incompatible sperm. Our findings highlight
 the need to understand how OA affects the multiple stages of sperm-egg
 interactions, and to develop approaches that disentangle the implications
 of OA for female, male and population fitness.
description: These data contain fertilization success scores from gametes of
 the mussel <em>Mytilus galloprovincialis</em>, following sperm
 chemotaxis trials in two different seawater pH treatments (ambinet and
 experimentally lowered pH). They also contain seawater carbonate chemostry
 measurements (pH on the total scale and total alkalinity) from each batch
 of seawater at each treatment.
description: The first spreadsheet contains fertilization success scores
 following sperm chemotaxis trials at the two pH treatments. Columns
 included are experimental block number, focal male (sperm donor) ID, pH
 treatment in chemotaxis chamber, fertilization design (unstandardised or
 standardised pH conditions in the fertilization pools - see manuscript for
 full description), focal male fertilization success, focal male failures
 (eggs not fertilized), and total eggs counted. The second spreadsheet
 contains seawater carbonate chemistry measurements from the seawater
 batches in each experimental block. The columns include sample ID (block
 and pH treatment), temperature, salinity, pH on the total scale
 (measured potentiometrically via calibration against Tris buffers) and
 total alkalinity (measured via potentiometric titration).