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Chemical communication via pheromones is considered the oldest and most widespread form of communication in nature. However, the way that the enormous diversity of species-specific pheromones evolved is still of debate. One possible process driving pheromone evolution is the mate-finding and dispersal behavior, as long-distance mate-finding requires highly volatile compounds. In contrast, less volatile compounds might be sufficient attractants in species that search for mates within proximity. In the parasitoid wasp genus Leptopilina, the composition of species-specific sex pheromones ranges from highly volatile iridoid compounds through combinations of iridoids with low volatile cuticular hydrocarbons (CHCs) to only CHCs. To study the selective forces shaping the composition of sex pheromones in Leptopilina, we examined the dispersal behavior, i.e., the proportion of male and female wasps dispersing after emergence, in four species with known sex pheromone compositions. If males and females disperse immediately, long-range mate attraction might become necessary, favoring volatile iridoids over CHCs. If mating occurs directly on the host patch, short-range mate attraction by low volatile CHCs might suffice. Our analyses have revealed that the dispersal behavior of Leptopilina males and females after emergence does indeed differ between species with differently volatile sex pheromones. Specifically, males of species with iridoid sex pheromones start to disperse immediately before their females’ emergence, whereas males of species with CHC sex pheromones delay dispersal until their conspecific females emerge. While the differences in female dispersal behavior turned out to be species-specific, differences in male dispersal correlated with the volatility of female-produced sex pheromones of each species. This study significantly contributes to our understanding of the evolution of sex pheromones by differences in dispersal behavior.

According to current evolutionary theory, insect pheromones can originate from extant precursor compounds being selected for information transfer. This is exemplified by females of the parasitoid wasp Leptopilina heterotoma whose defensive secretion consisting mainly of (−)-iridomyrmecin has evolved secondary functions as cue to avoid other females during host search and as female sex pheromone. To promote our understanding of pheromone evolution from defensive secretions we studied the chemical ecology of Leptopilina clavipes. We show here that L. clavipes also produces a defensive secretion that contains (−)-iridomyrmecin as major component and that females use it to detect and avoid host patches occupied by other females. However, the female sex pheromone of L. clavipes consists solely of cuticular hydrocarbons (CHCs) and males did not respond to female CHCs if presented in combination with the defensive secretion containing (−)-iridomyrmecin. This is in contrast to other species of Leptopilina, in which the iridoid compounds have no inhibiting effect or even function as sex pheromone triggering courtship behaviour. This indicates that Leptopilina species differ in the cost-benefit ratio for males searching for females, which might explain the strong divergence in the composition of the sex pheromone in the genus.

Male antennal aphrodisiac pheromones have been suggested to elicit female receptiveness in several parasitic Hymenoptera, including Leptopilina boulardi. None of the proposed pheromones, however, has been fully identified to date. It is also unknown whether these antennal pheromones are species specific, because the species specificity of mate recognition and courtship elicitation in Leptopilina prevented such experiments. In this study we present an experimental design that allows the investigation of the species specificity of the putative male aphrodisiac pheromone of L. heterotoma, L. boulardi, and L. victoriae. This is achieved by chemical manipulation of the odour profile of heterospecific females, so that males perceive them as conspecifics and show antennal courtship behaviour. Males courted the manipulated heterospecific females and antennal contact between the male and the female was observed. However, males elicited receptiveness only in conspecific females, never in the manipulated heterospecific females. Chemical analysis showed the presence of species specific unsaturated hydrocarbons on the antennae of males. Only trace amounts of these hydrocarbons are found on the antennae of females. Our results are an important step towards the understanding and identification of antennal pheromones of parasitic wasps.

Finding a suitable mate for reproduction is one of the most important tasks for almost all animals. In insects this task is often facilitated by pheromone-mediated communication. While insect pheromones in general show enormous chemical diversity, closely related species often use structurally similar compounds in their pheromones. Despite this similarity, pheromones of congeneric species living in sympatry need to be species specific. We investigated the pheromone-mediated mate recognition by males of three closely related species of Leptopilina, a genus of parasitoid wasps that utilize the larvae of Drosophila as hosts. The study species, L. heterotoma, L. boulardi, and L. victoriae, occur sympatrically and have a similar ecology and life history. We have found that mate recognition is species specific in all three species. This species specificity is achieved by a differing importance of cuticular hydrocarbons (CHCs) and iridoids in the female mate recognition pheromones. In L. heterotoma the iridoids are of major importance while CHCs play a negligible role. In L. boulardi, however, the CHCs are as important as the iridoids, while in L. victoriae, the CHCs alone elicit a full behavioral response of males. Our results provide novel insights into pheromone evolution in insects by showing that selection on two completely different classes of chemical compounds may generate conditions where compounds from both classes contribute to a varying degree to the chemical communication of closely related species and that this variation also generates the species specificity of the signals.

Adaptation requires genetic variation, but founder populations are generally genetically depleted. Here we sequence two populations of an inbred ant that diverge in phenotype to determine how variability is generated. Cardiocondyla obscurior has the smallest of the sequenced ant genomes and its structure suggests a fundamental role of transposable elements (TEs) in adaptive evolution. Accumulations of TEs (TE islands) comprising 7.18% of the genome evolve faster than other regions with regard to single-nucleotide variants, gene/exon duplications and deletions and gene homology. A non-random distribution of gene families, larvae/adult specific gene expression and signs of differential methylation in TE islands indicate intragenomic differences in regulation, evolutionary rates and coalescent effective population size. Our study reveals a tripartite interplay between TEs, life history and adaptation in an invasive species., Genetic variation is key to species evolution. Here the authors sequence two phenotypically distinct populations of the ant Cardiocondyla obscurior, and find accumulations of transposable elements correlating with genetic variation that may have a role in differentiation, adaptation and speciation.

Reproductive isolation of sexually deceptive orchid species of the genus Ophrys is based on the specific attraction of a single pollinator species by mimicking the female sex-pheromone of its pollinator. The attraction of a new pollinator caused by changes in the flower odour by drift or hybridization could lead to sympatric speciation. I investigated putative hybrid swarms of Ophrys on Sardinia and Majorca using behavioural experiments, electrophysiology, chemical analysis, and molecular markers (AFLP). On Sardinia I investigated hybrid swarms between O. lupercalis and O. iricolor. In behavioural experiments I found cross attraction of pollinators between species, as well as flowers that were attractive to both pollinators. The analysis of the EAD-active odour compounds showed a significant difference in the flower odour between both parental species, but with a huge overlap between species. AFLP data of the same plant specimen clearly showed the hybridization between O. lupercalis and O. iricolor. A different situation was found on Majorca, where O. lupercalis, O. bilunulata, and O. fabrella bloom consecutively. In the genetic analyses O. bilunulata did not form a distinct group, due to hybridization with both other species. In contrast to this, the analysis of flower odour shows a distinct odour for each species. My results show that reproductive isolation in Ophrys is not as complete as thought so far and that pollinator shifts may have played an important role in the evolution of this group.