Differences in the reliance on cuticular hydrocarbons as sexual signaling and species discrimination cues in parasitoid wasps

Abstract

BackgroundCuticular hydrocarbons (CHC) have been documented to play crucial roles as species- and sex-specific cues in the chemical communication systems of a wide variety of insects. However, whether they are sufficient by themselves as the sole cue triggering sexual behavior as well as preference of con- over heterospecific mating partners is rarely assessed. We conducted behavioral assays in three representative species of parasitoid wasps (Hymenoptera: Pteromalidae) to determine their reliance on CHC as species-specific sexual signaling cues.ResultsWe found a surprising degree of either unspecific or insufficient sexual signaling when CHC are singled out as recognition cues. Most strikingly, the cosmopolitan species Nasonia vitripennis, expected to experience enhanced selection pressure to discriminate against other co-occurring parasitoids, did not discriminate against CHC of a partially sympatric species from another genus, Trichomalopsis sarcophagae. Focusing on the latter species, in turn, it became apparent that CHC are even insufficient as the sole cue triggering conspecific sexual behavior, hinting at the requirement of additional, synergistic sexual cues particularly important in this species. Finally, in the phylogenetically and chemically most divergent species Muscidifurax uniraptor, we intriguingly found both CHC-based sexual signaling as well as species discrimination behavior intact although this species is naturally parthenogenetic with sexual reproduction only occurring under laboratory conditions.ConclusionsOur findings implicate a discrepancy in the reliance on and specificity of CHC as sexual cues in our tested parasitioid wasps. CHC profiles were not sufficient for unambiguous discrimination and preference behavior, as demonstrated by clear cross-attraction between some of our tested wasp genera. Moreover, we could show that only in T. sarcophagae, additional behavioral cues need to be present for triggering natural mating behavior, hinting at an interesting shift in signaling hierarchy in this particular species. This demonstrates the importance of integrating multiple, potentially complementary signaling modalities in future studies for a better understanding of their individual contributions to natural sexual communication behavior.Electronic supplementary materialThe online version of this article (10.1186/s12983-018-0263-z) contains supplementary material, which is available to authorized users.

Chemical Ecology of the Parasitoid Wasp Genus Nasonia (Hymenoptera, Pteromalidae)

“…However, in bioassays with fractionated female extracts (containing only CHCs), Nv males showed courtship and copulation attempts equally often toward both dummies applied with CHCs of Nv females and those applied with CHCs of Ng females (Mair et al, 2017). Furthermore, in bioassays with living couples, Nv males seem to even court females of T. sarcophagae, a species closely related to the genus Nasonia which possesses a relatively similar CHC composition compared to Nv (Niehuis et al, 2013;Buellesbach et al, 2018). Overall, Nv males are hardly selective in the choice of their mating partners (Giesbers et al, 2013;Buellesbach et al, 2014Buellesbach et al, , 2018 indicating that mating with the wrong partner does not impose considerable fitness costs on them.…”

“…In addition, when two or more females emerge in a quick succession, it may happen that the territorial male is still occupied with courting the first female when the second female emerges, giving nearby subordinate males the opportunity to court and mate with the female themselves . Ruther et al, 2007Ruther et al, , 2009Abdel-Latief et al, 2008;Niehuis et al, 2013;Diao et al, 2016 RR Ruther et al, 2008Ruther et al, , 2011Niehuis et al, 2013 ( Carlson et al, 1999;Steiner et al, 2006;Niehuis et al, 2010;Raychoudhury et al, 2010a;Buellesbach et al, 2013Buellesbach et al, , 2018Mair et al, 2017;Bien et al, 2019 ( Visser, 1976;van den Assem et al, 1980bvan den Assem et al, , 1981Steiner and Ruther, 2009a;Ruther et al, 2010;Ruther and Hammerl, 2014;Boulton and Shuker, 2015 Host finding ...…”

“…In Nv, males recognize females based on the females' CHCs alone and do not rely on additional, more polar compounds (Steiner et al, 2006). The CHC profile in Nasonia detectable by classical GC/MS techniques consists of hydrocarbons ranging from C25 to C37 including n-alkanes, mono-, di-, tri-, and tetramethylalkanes as well as few alkenes (Carlson et al, 1999;Steiner et al, 2006;Niehuis et al, 2010;Buellesbach et al, 2013Buellesbach et al, , 2018Mair et al, 2017). Both quantitative and qualitative differences in the composition of CHCs exist between females and males of Nv (Carlson et al, 1999;Steiner et al, 2006;Buellesbach et al, 2013Buellesbach et al, , 2018.…”

“…The CHC profile in Nasonia detectable by classical GC/MS techniques consists of hydrocarbons ranging from C25 to C37 including n-alkanes, mono-, di-, tri-, and tetramethylalkanes as well as few alkenes (Carlson et al, 1999;Steiner et al, 2006;Niehuis et al, 2010;Buellesbach et al, 2013Buellesbach et al, , 2018Mair et al, 2017). Both quantitative and qualitative differences in the composition of CHCs exist between females and males of Nv (Carlson et al, 1999;Steiner et al, 2006;Buellesbach et al, 2013Buellesbach et al, , 2018. Compared to males, Nv females possess higher relative amounts of hydrocarbons with chain lengths shorter than C30 as well as higher relative amounts of methyl-branched alkanes with central branching positions (e.g., 9-, 11-, 13-, 15-methylalkanes or 9,x-, 11,x-, 13,x-, 15,xdimethylalkanes) whereas males possess higher relative amounts of methyl-branched alkanes with marginal branching positions (e.g., 3-, 5-, 7-methylalkanes or 3,x-, 5,x-, 7,x-dimethylalkanes) as well as higher relative amounts of alkenes (Steiner et al, 2006;Buellesbach et al, 2013Buellesbach et al, , 2018.…”

“…Both quantitative and qualitative differences in the composition of CHCs exist between females and males of Nv (Carlson et al, 1999;Steiner et al, 2006;Buellesbach et al, 2013Buellesbach et al, , 2018. Compared to males, Nv females possess higher relative amounts of hydrocarbons with chain lengths shorter than C30 as well as higher relative amounts of methyl-branched alkanes with central branching positions (e.g., 9-, 11-, 13-, 15-methylalkanes or 9,x-, 11,x-, 13,x-, 15,xdimethylalkanes) whereas males possess higher relative amounts of methyl-branched alkanes with marginal branching positions (e.g., 3-, 5-, 7-methylalkanes or 3,x-, 5,x-, 7,x-dimethylalkanes) as well as higher relative amounts of alkenes (Steiner et al, 2006;Buellesbach et al, 2013Buellesbach et al, , 2018. Males of Nv use the sexspecific differences in the CHCs to distinguish females from males by means of antennal contact during encounters (Steiner et al, 2006).…”