Maternal effects and maternal selection arising from variation in allocation of free amino acid to eggs.

Devi Newcombe,John Hunt,Christopher Mitchell,Allen J Moore

doi:10.1002/ece3.1524

Devi Newcombe, John Hunt + Show 2 more

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https://doi.org/10.1002/ece3.1524

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Abstract

Maternal provisioning can have profound effects on offspring phenotypes, or maternal effects, especially early in life. One ubiquitous form of provisioning is in the makeup of egg. However, only a few studies examine the role of specific egg constituents in maternal effects, especially as they relate to maternal selection (a standardized selection gradient reflecting the covariance between maternal traits and offspring fitness). Here, we report on the evolutionary consequences of differences in maternal acquisition and allocation of amino acids to eggs. We manipulated acquisition by varying maternal diet (milkweed or sunflower) in the large milkweed bug, Oncopeltus fasciatus. Variation in allocation was detected by examining two source populations with different evolutionary histories and life-history response to sunflower as food. We measured amino acids composition in eggs in this 2 × 2 design and found significant effects of source population and maternal diet on egg and nymph mass and of source population, maternal diet, and their interaction on amino acid composition of eggs. We measured significant linear and quadratic maternal selection on offspring mass associated with variation in amino acid allocation. Visualizing the performance surface along the major axes of nonlinear selection and plotting the mean amino acid profile of eggs from each treatment onto the surface revealed a saddle-shaped fitness surface. While maternal selection appears to have influenced how females allocate amino acids, this maternal effect did not evolve equally in the two populations. Furthermore, none of the population means coincided with peak performance. Thus, we found that the composition of free amino acids in eggs was due to variation in both acquisition and allocation, which had significant fitness effects and created selection. However, although there can be an evolutionary response to novel food resources, females may be constrained from reaching phenotypic optima with regard to allocation of free amino acids.

Highlights

Provisioned egg constituents determine the initial resources available to the offspring for embryonic development so that maternal allocation of the quantity and quality of resources to the eggs can have profound effects on early offspring size and development, subsequent life history, and evolution (Fox and Mousseau 1996; Mousseau and Fox 1998)
The Laboratory source population reared on milkweed was the closest to the performance peak, followed by the Kentucky source population reared on milkweed, the Laboratory source population reared on sunflower, and the Kentucky source population reared on sunflower (Fig. 4B). Both diet and source population influenced egg size and hatchling mass, and while there is overlap in these effects, there are differences. To understand whether these differences reflected allocation or acquisition, we examined how the free amino acid content of eggs varied in response to differences associated with different source populations and different maternal diets, and the importance of these differences by analyzing maternal selection and performance surfaces associated with variation in amino acid composition
We found that the maternal diet, or differences in acquisition, influenced these profiles

Summary

Introduction

Provisioned egg constituents determine the initial resources available to the offspring for embryonic development so that maternal allocation of the quantity and quality of resources to the eggs can have profound effects on early offspring size and development, subsequent life history, and evolution (Fox and Mousseau 1996; Mousseau and Fox 1998). If mothers vary and this variation results in fitness differences among offspring, the provisioning of eggs results in maternal selection (selection arising because offspring fitness is determined by the maternal phenotype; Kirkpatrick and Lande 1989). This suggests that understanding the sources and consequences of variation in egg constituents would help reveal mechanisms of maternal effects.

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