Even fewer males were robust to far-future acidification scenarios (ΔpH −0.5). If this robustness to near-future conditions is heritable, it could act as a base for adaptation to far-future conditions ( Sunday et al., 2011), provided that adaptation can occur within the relatively short time frame of predicted future ocean acidification. The inter-male variability we observed was not unexpected: G. caespitosa naturally exhibit high intra-specific variation in sperm swimming behavior ( Kupriyanova and Havenhand, 2002, Fig. 1A). The extent to which this variability depends on seasonal changes in reproductive condition and temperature is unknown. Further, the substantial range in sperm responses among individuals to ocean acidification

observed here – from highly positive to negative ( Fig. 1B) – suggests that these responses are not reaction BKM120 concentration norms. Such large variation in responses increases the scope for selection of rare sperm phenotypes robust to future acidification ( Pistevos et al., 2011, Sunday et al., 2011, Foo et al., 2012 and Schlegel et al., 2012), which may contribute disproportionately more to subsequent generations. This selection

may thus ameliorate ocean acidification effects on a species, if traits associated with acidification resistance are heritable. In this context, it is important to stress the need for adequately replicated studies on climate change impacts in order to accurately estimate the extent of inter-individual learn more variation ( Havenhand et al., 2010). Resilience to near-future climate change observed in the sperm of some males could act as a stepping stone for adaptation to far-future conditions, if gathering of advantageous alleles through not recombination in subsequent generations can outrun the rapidity of predicted ocean acidification.

Consequently, simultaneous selection against susceptible phenotypes could quickly reduce genetic diversity, with flow-on consequences for species fitness and competitive ability ( Reed and Frankham, 2003 and Frankham, 2005). Changes in sperm swimming behavior affect fertilization success (Vogel et al., 1982, Styan and Butler, 2000 and Styan et al., 2008). Positive relationships between fertilization success and sperm concentration – influenced by percent motility – as well as sperm swimming speeds have been reported for this species (Kupriyanova and Havenhand, 2002 and Kupriyanova, 2006). Sperm swimming speeds are reported to be enhanced under increased water temperatures (Kupriyanova and Havenhand, 2005), and therefore future ocean warming could ameliorate acidification-related reductions in sperm swimming speeds, particularly during warmer summer temperatures (Hobday and Lough, 2011). For the majority of G. caespitosa, however, potential positive effects of ocean warming on sperm swimming speeds would likely be swamped by the substantial negative effects of ocean acidification on percent motility that we observed ( Fig. 1).