Right after her eggs hatch, a female burying beetle undergoes a temporary period of infertility, and she releases an anti-aphrodisiac hormone that signals this status to her male partner. That way, the pair work on taking care of their needy new offspring, rather than try to create more, according to findings published in Nature Communications this week.
Being a parent can require a lot of time and energy, and new moms and dads are sometimes faced with a reproductive dilemma: take care of their current offspring or produce additional ones.
Burying beetles (Nicrophorus vespilloides) reproduce on small dead vertebrates, and they feed their developing young pre-digested carcasses (pictured). These larvae beg for food: They rear up and wave their legs to touch their parents’ mouthparts. They do this until they’re about three days old, after which they can feed on the carrion by themselves. But until then, both females and males feed the brood. With biparental care, the larvae have higher survival rates, and they’re bigger by the time they disperse. That's helpful later on because adults with bigger body sizes are better at securing carcasses.
It’s unclear how burying beetles balance the demands of their current offspring with sexual activity (or future offspring). To investigate, University of Ulm’s Sandra Steiger and colleagues analyzed the mating behavior, egg production, and hormone profiles and expression of related genes of hundreds of burying beetles – the descendants of wild beetles collected from carrion-baited pitfall traps in a deciduous forest in Germany. They conducted a series of experiments using male and female pairs housed in a plastic container half-filled with moist peat and provisioned with a mouse carcass.
The researchers found that egg-laying is suppressed when the survival of the offspring depends on parental feeding. When her current offspring need the most care, a female displays temporary infertility that's mediated by a hormone called juvenile hormone III. Females resume egg laying if they don't have access to their larvae or if their larvae have become nutritionally independent (typically just a few days after they hatch).
Furthermore, the female communicates this reproductive state to her male partner. She signals her offspring-induced temporary infertility using a chemical called methyl geranate, which reduces the number of copulation attempts from her male partner. Otherwise, the male would copulate more often – a lot more often. "In the beginning of a reproductive event during the time the female lays eggs, he copulates about 100 times," Steiger explains to IFLScience. "If the larvae never reach the carcass, he will continue to mate up to 300 times."
Female infertility combined with male sexual abstinence – together with effective communication – allow the parents to invest their time and energy into the developing larvae.
Father and mother burying beetles on a mouse carcass. The pair has removed the fur. Heiko Bellmann
Image in the text: burying beetles copulating. Heiko Bellmann