Copepod life history evolution under high and low food regimes

Abstract

Copepods play a critical role in the carbon cycle of the planet - they mediate the sequestration of carbon into the deep ocean, and are the trophic link between phytoplankton and marine foodwebs. Global change stressors that decrease copepod productivity create the potential for catastrophic positive feedback loops. Accordingly, a growing list of studies examine the evolutionary capacity of copepods to adapt to the two primary stressors associated with global change: warmer temperatures and lower pH. But the evolutionary capacity of copepods to adapt to changing food regimes, the third major stressor associated with global change, remains unknown. We used experimental evolution to explore how a 10-fold difference in food availability affects life history evolution in the copepod, Tisbe sp. over two years, and spanning 30+ generations. Different food regimes evoked evolutionary responses across the entire copepod life history: we observed evolution in body size, size-fecundity relationships and offspring investment strategies. Our results suggest that changes to food regimes reshape life histories and that cryptic evolution in traits such as body size is likely. We demonstrate that evolution in response to changes in ocean productivity will alter consumer life histories, and may distort trophic links in marine foodchains. Evolution in response to changing phytoplankton productivity may alter the efficacy of the global carbon pump in ways that have not been anticipated until now.

Evolving to stay the same: life history evolution and tradeoffs in response to high and low total food

“…For example, restoration ecology was used in Daphnia to show shifts from 'thrifty' higher growth efficiency and flatter reaction norms in ancient low phosphorus (P) environments to 'opportunistic' lower growth efficiency modern genotypes with greater plasticity to P supply (Frisch et al 2014). High-food regimes can select for either larger (in mosquitofish) or smaller (in copepods and guppies) offspring relative to low-food regimes (Hulthén et al 2021, Blake and Marshall 2023. In copepods, egg size-fecundity tradeoffs are hidden by countergradient variation, while in guppies they are not (Felmy et al 2022).…”

“…However, our understanding of what drives 'fast' and 'slow' life histories remains incomplete (Del Giudice 2020), and without a clear role for food. Overall, while experimental evolution studies (Hulthén et al 2021, Blake and Marshall 2023 do show life history evolution under different levels of total food -reiterating that the focus on relative (per capita) food in classic r/K theory is insufficient -generalising remains a challenge.…”

“…IPMs can also identify such nuances, for example by perturbing trait values and evaluating which life history components show the highest sensitivities of fitness (Coulson et al 2022). Using these tools, we dig deeper into previous work in copepods (Blake and Marshall 2023) to obtain a fuller picture of life history tradeoffs under different food regimes across the whole life cycle.…”

“…And higher temperatures reduce the efficiency of energy transfer from phytoplankton to copepod grazers (Barneche et al 2021). As model organisms, marine copepods have been used in previous experimental evolution studies (Kelly et al 2012, Blake andMarshall 2023), but the indirect effects of changing food regimes, for example due to climate change, have remained largely unexplored. Copepods are highly suitable for parameterising IPMs due to their short life cycles (for measuring lifetime reproductive output) and established protocols for vital-rate measurement (Coulson 2012).…”

“…Copepods are highly suitable for parameterising IPMs due to their short life cycles (for measuring lifetime reproductive output) and established protocols for vital-rate measurement (Coulson 2012). In this study we built on work by Blake and Marshall (2023) and evaluated how the total amount of food influenced life history evolution in a marine copepod. We did so by investigating the joint life history and ecological effects of food regime, including tradeoffs, using IPMs and an experimental evolution approach.…”