Dung Beetles Eat Acorns to Increase Their Ovarian Development and Thermal Tolerance

José R Verdú,Catherine Numa,José L Casas,Jorge M Lobo,Ryan L Earley

doi:10.1371/journal.pone.0010114

José R Verdú, Catherine Numa + Show 3 more

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https://doi.org/10.1371/journal.pone.0010114

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Abstract

Animals eat different foods in proportions that yield a more favorable balance of nutrients. Despite known examples of these behaviors across different taxa, their ecological and physiological benefits remain unclear. We identified a surprising dietary shift that confers ecophysiological advantages in a dung beetle species. Thorectes lusitanicus, a Mediterranean ecosystem species adapted to eat semi-dry and dry dung (dung-fiber consumers) is also actively attracted to oak acorns, consuming and burying them. Acorn consumption appears to confer potential advantages over beetles that do not eat acorns: acorn-fed beetles showed important improvements in the fat body mass, hemolymph composition, and ovary development. During the reproductive period (October-December) beetles incorporating acorns into their diets should have greatly improved resistance to low-temperature conditions and improved ovarian development. In addition to enhancing the understanding of the relevance of dietary plasticity to the evolutionary biology of dung beetles, these results open the way to a more general understanding of the ecophysiological implications of differential dietary selection on the ecology and biogeography of these insects.

Highlights

The main reason animals eat is to acquire the mixture of nutrients required to fuel growth, development, and reproduction
Given the high content in polyunsaturated fatty acids, triglycerides, and sterols present in the acorns [25], we demonstrate that this diet expansion significantly affects fat body development, hemolymph composition, cold resistance and ovary development under laboratory conditions
Beetles fed with acorns developed a fat body 4.6-fold heavier than those fed with cow dung (Table 1)

Summary

Introduction

The main reason animals eat is to acquire the mixture of nutrients required to fuel growth, development, and reproduction. A high-quality diet for insects permits the storage of different compounds (e.g., lipids, carbohydrates, or proteins) in the fat body, the most important organ for nutrient metabolism and storage in insects [1]. Freeze-avoiding insects may adopt one or both of these main mechanisms to decrease the SCP: (a) the production of AFPs that inhibit the growth of ice, modify the thermal hysteresis (the difference between the freezing point and the melting point of a solution) and stabilize supercooled hemolymph and other fluids [7], [8], [9], [10], and (b) the adjust concentration of multi-component cryoprotectant compounds that depress the SCP [11]

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