Life-history theory assumes that resources are finite and that there may be trade-offs between traits competing for this common resource pool. The limiting resource most commonly studied is food and studies typically manipulate resource acquisition by varying diet quantity or quality without considering the specific nutrients involved. Recent studies using the Geometric Framework (GF) however, suggest that life-history trade-offs are often regulated by the intake of specific nutrients. Despite this, we lack a robust framework identifying and quantifying the strength of nutritionally based trade-offs using the GF. Here, we provide a conceptual framework showing that such trade-offs occur when life-history traits are maximised in different regions of nutrient space and that this divergence can be quantified by the overlap in the 95% confidence region (CR) of the global maxima, the angle (θ) between the linear nutritional vectors, and the Euclidean distance (d) between the global maximum for each trait. We then empirically test this framework by examining the effects of protein (P) and carbohydrate (C) intake on the trade-off between reproduction and immune function in male and female decorated crickets (Gryllodes sigillatus). Encapsulation ability and egg production in females increased with the intake of both nutrients, being maximised at a P:C ratio of 1.04:1 and 1:1.17, respectively. In contrast, encapsulation ability in males only increased with the intake of P being maximised at a P:C ratio of 5.14:1, whereas calling effort increased with C intake but decreased with P intake and was maximized at a P:C ratio of 1:7.08. Consequently, the trade-off between reproduction and encapsulation ability is much larger in males than females, a view supported by the non-overlapping 95% CRs on the global maxima for these traits in males but not females and the larger estimates of θ and d. When given dietary choice, the sexes regulated their nutrient intake in a similar way, at a P:C ratio of 1:2 and 1:1.84 in males and females, respectively. Although this ratio was more closely aligned with the optima for immune function and reproduction in females than males, neither sex optimally regulated their nutrient intake to maximise the expression of reproductive effort or immune function or, in the case of males, allow for moderate expression of both traits. Collectively, our study highlights that greater consideration should be given to the intake of specific nutrients when examining nutritionally based life-history trade-offs and how this varies between the sexes.
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The geometry of nutritionally based life-history trade-offs: sex differences in the effect of macronutrient intake on the trade-off between immune function and reproductive effort in decorated crickets
Life history theory is based on the assumption that resources are finite so that traits competing for this common pool of resources will experience a trade-off. The shared resource most commonly studied is food and studies typically manipulate resource acquisition by varying diet quantity or quality without considering the specific nutrients involved. Recent studies using the Geometric Framework (GF), however, suggest that life-history trade-offs are often regulated by the intake of specific nutrients. Despite this, a robust framework documenting the existence and quantifying the strength of nutritionally based trade-offs currently does not exist for studies using the GF. Here, we provide a conceptual framework showing that such trade-offs occur when life-history traits are maximised in different regions of nutrient space and that this divergence can be quantified by the overlap in the 95% confidence region (CR) of the global maxima, the angle (θ) between the linear nutritional vectors and the Euclidean distance (d) between the global maxima for each trait. We then empirically tested this framework by examining the effects of protein (P) and carbohydrate (C) intake on the trade-off between reproduction and immune function in male and female decorated crickets (Gryllodes sigillatus). Encapsulation ability and egg production in females increased with the intake of both nutrients, being maximised at a P:C ratio of 1.04:1 and 1:1.17, respectively. In contrast, encapsulation ability in males only increased with the intake of P being maximised at a P:C ratio of 5.14:1, whereas calling effort increased with the intake of C but decreased with the intake of P and was maximized at a P:C ratio of 1:7.08. Consequently, the trade-off between reproduction and encapsulation ability is much larger in males than females, a view supported by the non-overlapping 95% CRs on the global maxima for these traits in males and the larger estimates of θ and d. The sexes regulated their intake of nutrients in a similar way under dietary choice, at a P:C ratio of 1:2 and 1:1.84 in males and females, respectively. Although this ratio was more closely aligned with the optima for immune function and reproduction in females than males, neither sex optimally regulated their nutrient intake. Collectively, our study highlights that greater consideration should be given to the intake of specific nutrients when examining nutritionally based life-history trade-offs and how this varies across the sexes.
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- Award ID(s):
- 1634878
- NSF-PAR ID:
- 10029307
- Date Published:
- Journal Name:
- The American naturalist
- Volume:
- 191
- Issue:
- 4
- ISSN:
- 0003-0147
- Page Range / eLocation ID:
- 452-474
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Our findings show that intralocus sexual conflict over the optimal intake of nutrients is likely to be an important process generating sex differences in life span and reproduction and may help explain why females age faster and live shorter than males in
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Plain Language Summary can be found within the Supporting Information of this article. -
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