66 research outputs found

    Effects of Variable Oceanographic Conditions on Forage Fish Lipid Content and Fatty Acid Composition in the Northern California Current

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    Lipids and fatty acids (FA) were investigated in 4 species of forage fish: northern anchovy Engraulis mordax, Pacific sardine Sardinops sagax, Pacific herring Clupea pallasi, and whitebait smelt Allosmerus elongatus, for their ability to serve as biological indicators of ocean conditions in the California Current large marine ecosystem (CCLME). Samples were collected during the oceanographically contrasting years of 2005 and 2006. Upwelling was severely curtailed in the spring and early summer of 2005, leading to delayed biological productivity, whereas upwelling was relatively normal in spring 2006. Principal components analysis described 78% of the variance within the lipid and FA dataset using the first 2 principal components. We found significant intra- and interspecific, interannual, and seasonal differences in lipid and FA profiles using univariate and permutation- based multivariate analysis of variance. Indicator species analysis showed distinct lipid and FA properties associated with each fish species. Using the ratio of docosahexaenoic acid (C22:6n-3) to eicosapentaeonic acid (C20:5n-3), we detected a transition from a diet composed primarily of dinoflagellate origin in early 2005 to a diet resulting from diatom-based productivity by late summer 2006. This shift was due to interannual differences in primary production, which was confirmed through phytoplankton sampling. Our study demonstrates that lipid and FA biomarkers in the forage fish community can provide information on ocean conditions and productivity that affect food web structure in the CCLME

    The relationship between maternal phenotype and offspring quality: Do older mothers really produce the best offspring?

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    Maternal effects are increasingly recognized as important drivers of population dynamics and determinants of evolutionary trajectories. Recently, there has been a proliferation of studies finding or citing a positive relationship between maternal size/age and offspring size or offspring quality. The relationship between maternal phenotype and offspring size is intriguing in that it is unclear why young mothers should produce offspring of inferior quality or fitness. Here we evaluate the underlying evolutionary pressures that may lead to a maternal size/age-offspring size correlation and consider the likelihood that such a correlation results in a positive relationship between the age or size of mothers and the fitness of their offspring. We find that, while there are a number of reasons why selection may favor the production of larger offspring by larger mothers, this change in size is more likely due to associated changes in the maternal phenotype that affect the offspring size-performance relationship. We did not find evidence that the offspring of older females should have intrinsically higher fitness. When we explored this issue theoretically, the only instance in which smaller mothers produce suboptimal offspring sizes is when a (largely unsupported) constraint on maximum offspring size is introduced into the model. It is clear that larger offspring fare better than smaller offspring when reared in the same environment, but this misses a critical point: different environments elicit selection for different optimal sizes of young. We suggest that caution should be exercised when interpreting the outcome of offspring-size experiments when offspring from different mothers are reared in a common environment, because this approach may remove the source of selection (e.g., reproducing in different context) that induced a shift in offspring size in the first place. It has been suggested that fish stocks should be managed to preserve these older age classes because larger mothers produce offspring with a greater chance of survival and subsequent recruitment. Overall, we suggest that, while there are clear and compelling reasons for preserving older females in exploited populations, there is little theoretical justification or evidence that older mothers produce offspring with higher per capita fitness than do younger mothers
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