Document Type

Article

Publication Title

The American Naturalist

Publication Date

Spring 4-2018

Keywords

dietary choicegeometric frameworkGryllodes sigillatusimmune functionreproductive efforttrade-offs

Abstract

Life-history theory assumes that traits compete for limited resources, resulting in trade-offs. The most commonly manipulated resource in empirical studies is the quantity or quality of diet. Recent studies using the geometric framework for nutrition, however, suggest that trade-offs are often regulated by the intake of specific nutrients, but a formal approach to identify and quantify the strength of such trade-offs is lacking. We posit that trade-offs occur whenever life-history traits are maximized in different regions of nutrient space, as evidenced by nonoverlapping 95% confidence regions of the global maximum for each trait and large angles (θ) between linear nutritional vectors and Euclidean distances (d) between global maxima. We then examined the effects of protein and carbohydrate intake on the trade-off between reproduction and aspects of immune function in male and female Gryllodes sigillatus. Female encapsulation ability and egg production increased with the intake of both nutrients, whereas male encapsulation ability increased with protein intake but calling effort increased with carbohydrate intake. The trade-offs between traits was therefore larger in males than in females, as demonstrated by significant negative correlations between the traits in males, nonoverlapping 95% confidence regions, and larger estimates of θ and d. Under dietary choice, the sexes had similar regulated intakes, but neither optimally regulated nutrient intake for maximal trait expression. We highlight the fact that greater consideration of specific nutrient intake is needed when examining nutrient space–based trade-offs.

Funding Source

S.K.S. was funded by the National Science Foundation (NSF; IOS-1118160 and IOS-1654028). C.M.H. was funded by a Leverhulme Early Career Fellowship. J.H. was funded by a Royal Society Fellowship (UF120087) and Equipment Grant (RG090854) and by the Natural Environment Research Council (NERC; NE/G00949X/1). J.R. was funded by a NERC studentship (awarded to J.H.). E.D.C. was partially funded by NSF grant CMII 1634878.

Comments

First published in The American Naturalist (2018): https://doi.org/10.1086/696147

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Supplemental: hhttp://dx.doi.org/10.5061/dryad.qv437

DOI

10.1086/696147

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Biology Commons

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