Love at first sniff: a spermatophore-associated pheromone mediates partner attraction in a collembolan species

Small animals with unique chemistry - the natural product chemistry of Collembola

Covering up to September 2024Collembola, commonly known as springtails, are abundant and important members of soil ecosystems. Due to their small size and hidden life, not much is known about their secondary metabolites. This chemistry is remarkably different from that of insects, with which they share a common ancestor, although they diverged already around 450 mya. Here we describe what is known so far, mainly compounds for chemical defence and cuticular lipids, as well as chemical signals. The uniqueness of the structures found is striking, many of which are not known from other natural sources. These include polychlorinated benzopyranones, small alkaloids, hetero-substituted aromatic compounds, and a diverse terpene chemistry, including highly branched compounds.

The unique epicuticular chemistry of Collembola - A cross-species analysis

Springtails (Collembola), tiny hexapod arthropods, are abundant in the soil of most ecosystems, but our knowledge of their secondary metabolites is limited, in contrast to that of insects. In insects, the outer cuticle is usually covered by mixtures of long-chain hydrocarbons serving different functions, such as water regulation or chemical communication. In contrast, the knowledge of the epicuticular chemistry of springtails is scarce. We analyzed the cuticular lipids of 23 species covering different lineages. The often complicated structures were elucidated using gas chromatography/mass spectrometry, microderivatization, and synthesis. In contrast to insects, the terpene biosynthetic pathway is used for many of these lipids, producing unprecedented higher terpenes. In addition, evidence for de novo cholesterol biosynthesis in springtails was found, which is absent in insects. Finally, diverse non-insect linear compounds originating from the fatty acid biosynthetic pathway were identified. Our comparative analysis showed clear differences compared to insects and shed light on phylogenetic relationships.

Chemical communication and its role in sexual selection across Animalia

Sexual selection has been studied as a major evolutionary driver of animal diversity for roughly 50 years. Much evidence indicates that competition for mates favors elaborate signaling traits. However, this evidence comes primarily from a few taxa, leaving sexual selection as a salient evolutionary force across Animalia largely untested. Here, we reviewed the evidence for sexual selection on communication across all animal phyla, classes, and orders with emphasis on chemoreception, the only sense shared across lifeforms. An exhaustive literature review documented evidence for sexual selection on chemosensory traits in 10 of 34 animal phyla and indications of sexual selection on chemosensory traits in an additional 13 phyla. Potential targets of sexual selection include structures and processes involved in production, delivery, and detection of chemical signals. Our review suggests sexual selection plays a widespread role in the evolution of communication and highlights the need for research that better reflects animal diversity.

High-throughput behavioral phenotyping of tiny arthropods: Chemosensory traits in a mesostigmatic hematophagous mite

Pest management using attractive and/or repellent semiochemicals is a key alternative to synthetic insecticides. Its implementation requires a good understanding of the intra- and interspecific chemical interactions of arthropod pests, their interactions with their abiotic environment, as well as their evolutionary dynamics. Although mites include many pest species and biocontrol agents of economic importance in agriculture, their chemical ecology is largely understudied compared to insects. We developed a high-throughput ethomics system to analyze these small arthropods and conducted a study on Dermanyssus gallinae, a problematic poultry parasite in the egg industry. Our purpose was to elucidate the role played by host-derived odorants (synthetic kairomone) and conspecific odorants (mite body odors) in D. gallinae. After validating our nanocomputer controlled olfactometric system with volatile semiochemicals of known biological activity, we characterized response traits to kairomonal and/or pheromonal volatile blends in mites from different populations. We were able to accurately characterize the repulsion or attraction behaviors in >1000 individual specimens in a standardized way. Our results confirm the presence of a volatile aggregation pheromone emitted by D. gallinae and bring new elements to the effect of odor source presentation. Our results also confirm the attractive effect on Dermanyssus gallinae of a blend of volatile compounds contained in hen odor, while highlighting a repellent effect at high concentration. Significant interindividual and interpopulation variation was noted particularly in responses to synthetic kairomone. This information lays a valuable foundation for further exploring the emergence risk of resistance to semiochemicals.

Male Sexual Trait Decay in Two Asexual Springtail Populations Follows Neutral Mutation Accumulation Theory

The transition to asexual reproduction is frequent and widespread across the tree of life and constitutes a major life history change. Without sexual reproduction, selection on sexually selected traits is expected to be weaker or absent, allowing the decay and ultimately loss of sexual traits. In this study, we applied an experimental approach to investigate the decay of reproductive traits under asexuality in two asexual populations of the springtail Folsomia candida. Specifically, we compared several key male sexual traits of a sexual population and two distinct parthenogenetic lines. To allow direct comparisons between sexual and asexual individuals we first determined a suite of life history characteristics in the sexual F. candida population, which performs an indirect transfer of sperm packages (spermatophores).To investigate the decay of male sexual traits under asexuality we measured the size of spermatophores, quantified the amount of sperm DNA material, and tested spermatophore attractiveness to females in all three populations. The amount of sperm DNA material in the sperm droplets and the attractiveness of spermatophores were lower in the asexual lines compared to the sexual population. However, the two asexual lines differed in the extent of decay of these traits. Our results are consistent with predictions from neutral mutation accumulation theory, and thus suggest this to be the main evolutionary process underlying the decay of male traits in F. candida.