Abstract
Changing environments associated with rapid climate change can shape direct measures of fitness such as reproductive success by altering mating behavior, fecundity and offspring development. Using a polymorphic oceanic population of threespine stickleback (Gasterosteus aculeatus), we investigated whether a 4°C increase in sea surface temperature influenced clutch siring success, reproductive output, and offspring growth among lateral plate morphs. Since low plated morphs are thought to have a selective advantage in warmer environments, we predicted that low plated males should have higher clutch siring success in +4°C environments, and that thermal plasticity of traits (e.g., egg size, offspring growth) should reflect different trait optima in different environments among plate morphs. Parentage analysis of egg clutches revealed temperature-specific clutch siring success, in that low plated males sired more clutches in +4°C environments and completely plated males sired more clutches at ambient (seasonal) temperature. Both completely and low plated females laid larger eggs when acclimated to +4°C, but only completely plated females had smaller clutches at +4°C. Offspring of low and partially plated females grew much less at +4°C compared to those of completely plated females. Taken together, our results demonstrate that ocean warming could impact reproductive success at various levels, with differential effects depending on phenotype, in this case, lateral plate morph. Some traits (clutch siring success, egg size) showed better performance for low plated fish at +4°C, whereas others (e.g., growth) did not. Higher clutch siring success of low plated males at elevated temperature might indicate a future shift in plate morph composition for polymorphic stickleback populations, with potential implications for colonization ability during range shifts under climate change.
Highlights
Rapid warming of the world’s oceans is a major threat to population persistence and biodiversity of marine ecosystems (Intergovernmental Panel on Climate Change [IPCC], 2014)
Our study revealed that stickleback lateral plate morphs showed different plastic responses to simulated ocean warming for several traits related to reproductive success, a direct measure of fitness
Fecundity traits differed depending on female plate morph and acclimation temperature experienced during the last phases of oogenesis, and offspring growth varied depending on the interaction between parental plate morph and offspring thermal environment
Summary
Rapid warming of the world’s oceans is a major threat to population persistence and biodiversity of marine ecosystems (Intergovernmental Panel on Climate Change [IPCC], 2014). Organisms can respond to fast changing environmental conditions either by moving to where conditions better match their thermal optima, or by remaining in place and coping via genetic adaptation and/or phenotypic plasticity (Gienapp et al, 2007). Changing environmental conditions may influence reproductive success – a direct measure of fitness – and can affect different phenotypes at several levels: (1) changing environments can alter mating preferences (Candolin, 2019), which may lead to premating isolation, and reduce the frequency of certain phenotypes in the population, (2) change the fecundity of particular phenotypes (Barneche et al, 2018), with some having higher reproductive output in changed conditions than others, and (3) have developmental effects on offspring (Monaghan, 2008), such that some phenotypes produce offspring that outperform others. Ocean warming can influence how both natural selection and sexual selection shape phenotypes (Safran et al, 2013), with changes to reproductive success likely influenced by a combination of all of these factors
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