Sexual dimorphism in the Drosophila melanogaster (Diptera: Drosophilidae) metabolome increases throughout development

The expression of sexually dimorphic phenotypes from a shared genome between males and females is a longstanding puzzle in evolutionary biology. Increasingly, research has made use of transcriptomic technology to examine the molecular basis of sexual dimorphism through gene expression studies, but even this level of detail misses the metabolic processes that ultimately link gene expression with the whole organism phenotype. We use metabolic profi ling in Drosophila melanogaster to complete this missing step, with a view to examining variation in male and female metabolic profi les, or metabolomes, throughout development. We show that the metabolome varies considerably throughout larval, pupal and adult stages. We also fi nd signifi cant sexual dimorphism in the metabolome, although only in pupae and adults, and the extent of dimorphism increases throughout development. We compare this to transcriptomic data from the same population and fi nd that the general pattern of increasing sex differences throughout development is mirrored in RNA expression. We discuss our results in terms of the usefulness of metabolic profi ling in linking genotype and phenotype to more fully understand the basis of sexually dimorphic phenotypes. * Corresponding author; e-mail: [email protected] INTRODUCTION Sexual dimorphism is common across a wide range of plant and animal species, and there is a longstanding fi eld of research examining how the sexes can differ so markedly when they share the majority of their genes (Darwin, 1871; Lande, 1980). Most recently, research has built on the premise that for sexually dimorphic phenotypes to develop from the same genes, there is likely to be sex differences at the molecular level (Ellegren & Parsch, 2007). As such, a proliferation of data on sex-biased gene expression has shed some light on the molecular basis for sex differences. Sex-biased gene expression has been found in a diverse range of species – but especially in model insect species where high-throughput -omic technologies are increasingly cheap and available – and the extent of sexual dimorphism at the level of the transcriptome can be large (reviewed by Ingleby et al., 2015). Some research has also examined how sex differences in gene expression progress throughout development. At a phenotypic level, it is generally the case that sexual dimorphism increases throughout development, ultimately resulting in highly dimorphic adult phenotypes that are adapted to sex-specifi c reproductive roles. Research has shown that this progression through development is often mirrored by transcriptomic sex differences. In Drosophila Eur. J. Entomol. 114: 249–256, 2017 doi: 10.14411/eje.2017.030