Copepod life history evolution under high and low food regimes

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.