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In large groups of vertebrates and invertebrates, aggregation can affect biological characters such as gene expression, physiological, immunological and behavioral responses. The insect cuticle is covered with hydrocarbons (cuticular hydrocarbons; CHCs) which reduce dehydration and increase protection against xenobiotics. Drosophila melanogaster and D. simulans flies also use some of their CHCs as contact pheromones. In these two sibling species, males also produce the volatile pheromone 11-cis-Vaccenyl acetate (cVa). To investigate the effect of insect density on the production of CHCs and cVa we compared the level of these male pheromones in groups of different sizes. These compounds were measured in six lines acclimated for many generations in our laboratory - four wild-type and one CHC mutant D. melanogaster lines plus one D. simulans line. Increasing the group size substantially changed pheromone amounts only in the four D. melanogaster wild-type lines. To evaluate the role of laboratory acclimation in this effect, we measured density-dependent pheromonal production in 21 lines caught in nature after 1, 12 and 25 generations in the laboratory. These lines showed varied effects which rarely persisted across generations. Although increasing group size often affected pheromone production in laboratory-established and freshly-caught D. melanogaster lines, this effect was not linear, suggesting complex determinants., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Experimental studies of insects are often based on strains raised for many generations in constant laboratory conditions. However, laboratory acclimation could reduce species diversity reflecting adaptation to varied natural niches. Hydrocarbons covering the insect cuticle (cuticular hydrocarbons; CHCs) are reliable adaptation markers. They are involved in dehydration reduction and protection against harmful factors. CHCs can also be involved in chemical communication principally related to reproduction. However, the diversity of CHC profiles in nature and their evolution in the laboratory have rarely been investigated. Here, we sampled CHC natural diversity in Drosophila melanogaster flies from a particular location in a temperate region. We also measured cis -Vaccenyl acetate, a male-specific volatile pheromone. After trapping flies using varied fruit baits, we set up 21 D. melanogaster lines and analysed their pheromones at capture and after 1 to 40 generations in the laboratory. Under laboratory conditions, the broad initial pheromonal diversity found in male and female flies rapidly changed and became more limited. In some females, we detected CHCs only reported in tropical populations: the presence of flies with a novel CHC profile may reflect the rapid adaptation of this cosmopolitan species to global warming in a temperate area.

Insect exocrine gland products can be involved in sexual communication, defense, territory labelling, aggregation and alarm. In the vinegar fly Drosophila melanogaster the ejaculatory bulb synthesizes and releases 11-cis-Vaccenyl acetate (cVa). This pheromone, transferred to the female during copulation, affects aggregation, courtship and male-male aggressive behaviors. To determine the ability of male flies to replenish their cVa levels, males of a control laboratory strain and from the desat1 pheromone-defective mutant strain were allowed to mate successively with several females. We measured mating frequency, duration and latency, the amount of cVa transferred to mated females and the residual cVa in tested males. Mating duration remained constant with multiple matings, but we found that the amount of cVa transferred to females declined with multiple matings, indicating that, over short, biologically-relevant periods, replenishment of the pheromone does not keep up with mating frequency, resulting in the transfer of varying quantities of cVa. Adult responses to cVa are affected by early developmental exposure to this pheromone; our revelation of quantitative variation in the amount of cVa transferred to females in the event of multiple matings by a male suggests variable responses to cVa shown by adults produced by such matings. This implies that the natural role of this compound may be richer than suggested by laboratory experiments that study only one mating event and its immediate behavioral or neurobiological consequences., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)