Differential gene expression is not required for facultative sex allocation: a transcriptome analysis of brain tissue in the parasitoid wasp Nasonia vitripennis.

Nicola Cook,David M Shuker,Rebecca A Boulton,Eran Tauber,Michael G Ritchie,Bart A Pannebakker,Urmi Trivedi,Jade Green

doi:10.1098/rsos.171718

Abstract

Whole-transcriptome technologies have been widely used in behavioural genetics to identify genes associated with the performance of a behaviour and provide clues to its mechanistic basis. Here, we consider the genetic basis of sex allocation behaviour in the parasitoid wasp Nasonia vitripennis. Female Nasonia facultatively vary their offspring sex ratio in line with Hamilton's theory of local mate competition (LMC). A single female or ‘foundress’ laying eggs on a patch will lay just enough sons to fertilize her daughters. As the number of ‘foundresses’ laying eggs on a patch increases (and LMC declines), females produce increasingly male-biased sex ratios. Phenotypic studies have revealed the cues females use to estimate the level of LMC their sons will experience, but our understanding of the genetics underlying sex allocation is limited. Here, we exposed females to three foundress number conditions, i.e. three LMC conditions, and allowed them to oviposit. mRNA was extracted from only the heads of these females to target the brain tissue. The subsequent RNA-seq experiment confirmed that differential gene expression is not associated with the response to sex allocation cues and that we must instead turn to the underlying neuroscience to reveal the underpinnings of this impressive behavioural plasticity.

Highlights

The genomics revolution has brought several new technologies to behaviour genetics
Work by Orzack and co-workers confirmed the presence of genetic variation in sex allocation in N. vitripennis [26], and more recent work has measured the mutational heritability of single-foundress sex ratios [27] and identified quantitative trait loci associated with sex ratio variation [28]
To move beyond these quantitative genetic approaches, Pannebakker et al [11] used a 3 whole-transcriptome approach to explore changes in gene expression associated with oviposition

Summary

Introduction

The genomics revolution has brought several new technologies to behaviour genetics. For instance, the top-down assessment of genetic variation underlying quantitative traits can be extended through genome-wide association studies using large-scale single nucleotide polymorphism datasets [1,2]. Work by Orzack and co-workers confirmed the presence of genetic variation in sex allocation in N. vitripennis [26], and more recent work has measured the mutational heritability of single-foundress sex ratios [27] and identified quantitative trait loci associated with sex ratio variation [28] To move beyond these quantitative genetic approaches, Pannebakker et al [11] used a 3 whole-transcriptome approach to explore changes in gene expression associated with oviposition (a necessary part of sex allocation, as eggs are fertilized or not immediately prior to oviposition: as a haplodiploid insect, fertilized diploid eggs develop into females, and unfertilized haploid eggs develop into males [29]). We allowed females to lay eggs in one of three foundress conditions (alone, with four co-foundresses or with nine co-foundresses) and tested whether the facultative sex allocation in response to foundress number is associated with DGE across the N. vitripennis transcriptome

Study species

Experimental design

RNA extraction

Library preparation and sequencing

Statistical analyses

Results