Abstract
The determinants of intraspecific stoichiometric variation remain difficult to elucidate due to their multiple origins (e.g. genetic vs. environmental) and potential interactive effects. We evaluated whether two size-selected lines of medaka (Oryzias latipes) with contrasted life-history strategies (small- and large-breeder lines with slow growth and early maturity vs. fast growth and late maturity) differed in their organismal stoichiometry (percentage and ratios of carbon [C], nitrogen [N] and phosphorus [P]) in a mesocosm experiment. We also tested how size-selection interacted with environmental conditions (i.e. two levels of fish density and light intensity), body condition and sex. Results showed that large-breeder fish were significantly N-enriched compared to small-breeders, while the two size-selected lines did not differ in body P composition. Size-selection interacted with density – high density only affected small-breeders leading to decreasing %C and C: N – and with sex – large-breeder females had higher %C and C:N values than large-breeder males. Finally, C:P and N:P ratios increased with body condition due to decreasing %P. Overall, our results show that the ecological consequences of size-selective mortality extend to organismal stoichiometry and may, from there, change nutrient cycling and ecosystem functioning.
Highlights
Environmental changes have long been recognized to affect evolutionary processes, while the effects of evolution on ecosystem functioning – evo-to-eco pathways – have been until now little explored empirically (Brunner et al, 2019)
We evaluated whether two size-selected lines of medaka (Oryzias latipes) with contrasted life-history strategies differed in their organismal stoichiometry in a mesocosm experiment
From other factors, selection line did not affect %C and %P, and density and light intensity had no significant effect on organismal stoichiometry (Table 1; Fig. 1)
Summary
Environmental changes have long been recognized to affect evolutionary processes, while the effects of evolution on ecosystem functioning – evo-to-eco pathways – have been until now little explored empirically (Brunner et al, 2019). Size-selective mortality due to harvest often leads to a rapid evolution towards reduced body size (Sharpe and Hendry, 2009), which may reduce the top-down control on lower trophic levels through changes in the assemblage of top consumer (Shackell et al, 2009). This is likely because small-bodied top consumers have lower per-capita consumption rates and reduced ranges of prey body size (DeLong et al, 2015; Renneville et al, 2016). Such body size-dependent consequences of size-selective mortality are being investigated, a full understanding of its ecological effects requires considering how other traits such as organismal stoichiometry (i.e. elemental composition and elemental ratios in a consumer's body) respond to size selection
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