Exploiting an extraordinary case of intrasexual cuticular hydrocarbon profile dimorphism in a mason wasp, Odynerus spinipes, to shed new light on cuticular hydrocarbon genetics and evolution

• Applicants: Professor Dr. Oliver Niehuis; Professor Dr. Thomas Schmitt
• Subject Area: Evolution, Anthropology ; Evolutionary Cell and Developmental Biology (Zoology)
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 282602688

• Final Report Year: 2020

Final Report Abstract

Cuticular hydrocarbons (CHC) are essential for insects. They function as anti-desiccation agents and are used as chemical cues and signals. Knowing the genetic basis of their biosynthesis is fundamental for better understand how the diversity of CHC profiles observed in insects evolved. Even though the main steps of CHC biosynthesis are known, only few genes coding for the involved enzymes have been identified. In this study, we exploited an extraordinary case of CHC profile dimorphism in females of the mason wasp, Odynerus spinipes (Hymenoptera: Vespidae) to find genes involved in the CHC biosynthesis. O. spinipes females are able to express one of two different CHC profiles (chemotypes) that differ quantitatively and qualitatively from each other. Females with different chemotypes seem to differ exclusively in this specific trait. While a previous study reported both chemotypes to occur in about equal population frequency at three study sites in Southern Germany, we were able to show by analyzing the CHCs over 1,000 museum specimens that the two chemotypes differ geographically in their population frequencies. By sampling the CHC profile of 45 females (in the laboratory and in the field) at multiple times of their life, we discovered that females keep their chemotype during their entire lifespan. However, the abundance of specific CHCs on females of a given chemotype and on males shows age-dependent shifts. Notably, young females express a high abundance of methyl-branched alkanes, a compound group expressed in high abundance by conspecific males. Mating experiments conducted with dummies covered with CHCs of very young and of older females suggest that these methyl-branched alkanes could act as a repulsive cue to males. Intriguingly, the abundance shift in methylbranched alkanes correlates with the expression of a fatty acid synthase. Comparative analysis of twelve whole-gaster transcriptomes of age-controlled females differing in their CHC chemotype from each other revealed 28 candidate genes likely involved in CHC biosynthesis. Identification and knock-down of their orthologs in the honeybee, Apis mellifera, provided further evidence for nine genes being involved in CHC biosynthesis. The identified genes encode for four desaturases, four elongases, and for one hydrolase. Knock-down of fatty acid syntheses caused the treated bees to die. While the involvement of desaturases and of elongases in the biosynthesis of CHC is well established, hydrolases have not been implicated with the biosynthesis of CHC. In situ hybridization experiments indicate that six (possibly seven) of the identified candidate genes are expressed in oenocytes (known site of CHC biosynthesis). Intriguingly, however, two of the candidate genes whose knock-down results in a CHC profile alteration are seemingly only expressed in trophocytes closely associated with coenocytes. Phylogenetic analysis of the genes in those gene families implicated with the biosynthesis of CHC suggest that the diversification in CHCs in insects is possibly driven by high turnover of genes coding for desaturases and elongases. It further suggests that the last common ancestor of all euarthropods already possessed the enzymatic machinery to synthesize CHCs.

Publications

• (2017): Pseudochrysis Semenov, 1891 is the valid genus name for a group of cuckoo wasps frequently referred to as Pseudospinolia Linsenmaier, 1951 (Hymenoptera, Chrysididae). Deutsche Entomologische Zeitschrift 64: 69–75
  Rosa P, Pavesi M, Soon V, Niehuis O
  
• (2017): Transcriptome and target DNA enrichment sequence data provide new insights into the phylogeny of vespid wasps (Hymenoptera: Aculeata: Vespidae). Molecular Phylogenetics and Evolution 116: 213–226
  Bank S, Sann M, Mayer C, Meusemann K, Donath A, Podsiadlowski L, Kozlov A, Petersen M, Krogmann L, Meier R, Rosa P, Schmitt T, Wurdack M, Liu S, Zhou X, Misof B, Peters RS, Niehuis O
  
• (2018): How to find genes involved in cuticular hydrocarbon biosynthesis of Hymenoptera? 1st Münster Evolution meeting, Münster, Germany, October 4–6, 2018
  Moris VC, Schmitt T, Niehuis O
  
• (2019): Looking back in time: study of old pinned museum samples of Odynerus spinipes females (Insecta: Hymenoptera: Vespidae) reveals the geographic structure of the two chemotypes across the species’ distributional range. 35th annual meeting of the International Society of Chemical Ecology, Atlanta, United-States of America, June 2–7, 2019
  Moris VC, Christmann K, Schmitt T, Niehuis O
  
• (2019): Phylogenetic analysis of cuckoo wasps (Hymenoptera: Chrysididae) reveals a partially artificial classification at the genus level and a species-rich clade of bee parasitoids. Systematic Entomology 44: 322–335
  Pauli T, Castillo-Cajas RF, Rosa P, Kukowka S, Berg A, van den Berghe E, Fornoff F, Hopfenmüller S, Niehuis M, Peters RS, Staab M, Strumia F, Tischendorf S, Schmitt T, Niehuis O
  
• (2020): Nachweise von Polistes gallicus (Linnaeus 1767) in Rheinland-Pfalz und Baden-Württemberg (Hymenoptera: Vespidae). Ampulex 11: 9–13
  Schweitzer F, Reder G, Moris VC, Pauli T, Niehuis O
  
• (2020): Sawfly genomes reveal evolutionary acquisitions that fostered the megaradiation of parasitoid and eusocial Hymenoptera. Genome Biology and Evolution, evaa106
  Oeyen JP, ..., Niehuis O