Decay of Sexual Trait Genes in an Asexual Parasitoid Wasp

• Published in: Genome biology and evolution 2016-12, Vol.8 (12), p.3685-3695
• Main Authors: Kraaijeveld, Ken, Anvar, Seyed Yahya, Frank, Jeroen, Schmitz, Arnoud, Bast, Jens, Wilbrandt, Jeanne, Petersen, Malte, Ziesmann, Tanja, Niehuis, Oliver, de Knijff, Peter, den Dunnen, Johan T, Ellers, Jacintha
• Format: Article
• Language: English
• Subjects: Animals; Female; Genes, Insect; Male; Mutation; Phenotype; Phylogeny; Polymorphism, Single Nucleotide; Reproduction, Asexual; Wasps - genetics; Wasps - physiology
• ISSN: 1759-6653; 1759-6653
• DOI: 10.1093/gbe/evw273

Trait loss is a widespread phenomenon with pervasive consequences for a species’ evolutionary potential. The genetic changes underlying trait loss have only been clarified in a small number of cases. None of these studies can identify whether the loss of the trait under study was a result of neutral mutation accumulation or negative selection. This distinction is relatively clear-cut in the loss of sexual traits in asexual organisms. Male-specific sexual traits are not expressed and can only decay through neutral mutations, whereas female-specific traits are expressed and subject to negative selection. We present the genome of an asexual parasitoid wasp and compare it to that of a sexual lineage of the same species. We identify a short-list of 16 genes for which the asexual lineage carries deleterious SNP or indel variants, whereas the sexual lineage does not. Using tissue-specific expression data from other insects, we show that fifteen of these are expressed in male-specific reproductive tissues. Only one deleterious variant was found that is expressed in the female-specific spermathecae, a trait that is heavily degraded and thought to be under negative selection in L. clavipes. Although the phenotypic decay of male-specific sexual traits in asexuals is generally slow compared with the decay of female-specific sexual traits, we show that male-specific traits do indeed accumulate deleterious mutations as expected by theory. Our results provide an excellent starting point for detailed study of the genomics of neutral and selected trait decay.