Abstract
Females of many monandrous insect species announce their receptivity either by specialised sex-pheromones or by a signature mixture of cuticular hydrocarbons (CHCs). The trigger that shuts down the sex-pheromone release or initialises a change in CHC bouquet is thought to be either the mating per se or male pheromones transferred during copulation. Besides a conversion of female volatiles, the application of antiaphrodisiacs, male derived pheromones that render mated females unattractive to competitors, is another strategy to protect females from further sexual chasings. This simple pattern becomes more complicated in the monandrous mason bees Osmia bicornis (syn: O. rufa) and O. cornuta due to a post-copulation phase in their mating sequence. Males display a stereotypic behaviour right after the intromission that induces females’ unreceptivity. This post-copulatory display is predestined both to trigger a transition of the CHC profile and for the application of an antiaphrodisiac. However, the postulated antiaphrodisiac was not detectable even on freshly mated females. Moreover, the male’s post-copulatory display did not trigger a change in the CHC bouquet and neither did the insemination. Instead the CHC profile of freshly emerged females changes into the bouquet of nesting females simply by age as an ontogenetic process in both Osmia species. This autonomous change in the CHC profile coincides with an age-specific decrease of young female’s willingness to mate. How the resulting short period of female receptivity without back coupling by storage of sperm and the lack of an antiaphrodisiac fit into the behavioural ecology of the studied mason bee species is discussed.
Highlights
Females of most solitary bees are assumed to be monandrous and mate immediately after eclosion from the maternal nest to fill their spermatheca
In order to distinguish between the two possible stimuli due to mating, males were removed from an inseminated female immediately after ejaculation and transferred to a freshly emerged, virgin female to perform their post-copulatory display
Emerged and nesting females were clearly distinguishable both in O. bicornis and O. cornuta by a reduction of alkanes in favour of alkenes and a shift in the composition of the mono-alkene fraction regarding the position of the double bond
Summary
Females of most solitary bees are assumed to be monandrous and mate immediately after eclosion from the maternal nest to fill their spermatheca. In O. bicornis both the sperm transfer or the post-copulation could serve as trigger for the change in the CHC bouquet of mated females. This subtle distinction becomes relevant because virgin O. bicornis female’s willingness to mate decreases by age and independent from an effective copulation [11] It is not known whether this age-related loss of receptivity is accompanied by a change in the CHC bouquet, and if so, whether the CHC alterations are similar to regular mated O. bicornis females. In order to distinguish between the two possible stimuli due to mating, males were removed from an inseminated female immediately after ejaculation and transferred to a freshly emerged, virgin female to perform their post-copulatory display. First females have to mate to obtain the sperm for their whole reproductive live span They announce their receptivity to searching males by an attractive CHC profile. We wanted to prove how the postulated antiaphrodisiac fits into the CHC transitions to protect a freshly mated female for a time from further sexual harassment
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