In cadaver caves, baby beetles grow better with parental goo

Growing up inside a dead mouse could really stink, but not for some burying beetles. Their parents’ gut microbes keep the cadaver fresh, creating a nursery where the larvae can thrive.

What burying beetle parents can do with a small dead animal is remarkable, says coauthor Shantanu Shukla of the Max Planck Institute for Chemical Ecology in Jena, Germany.  “It looks different. It smells different. It’s completely transformed by the beetles.”

The carrion beetles Nicrophorus vespilloides start family life by burying a small dead vertebrate, which they keep fresh enough for baby food. Parents open a little flesh-cave in the cadaver, and hatchlings creep in to gorge. As the beetle youngsters grow inside this, the parents regularly refresh a dark microbial film inside the cavity. That helpful goo is not the usual slime that blooms in carcasses but resembles the parent beetles’ gut microbiomes, Shukla and colleagues report October 15 in the Proceedings of the National Academy of Sciences.

The carcass that parents smear with oral and anal secretions develops a “peculiar smell,” but “it definitely isn’t as bad as a dead animal that is buried in soil for several days,” Shukla says. “You can hold it under your nose, and there’s no offensive smell.”

Both the beetle parents and larvae produce antimicrobial substances, and biologists at first wondered if these prevented rot just by suppressing microbial growth. In recent years, however, Shukla’s lab and others have switched the focus to beetle secretions that spread desirable microbes: The beetles aren’t eliminating a microbial community. They’re just restructuring it.

In lab experiments on these carcass nurseries, Shukla and colleagues checked for benefits of the restructured microbial community. Some beetle broods got full exposure to the living film of microbes that parents tend inside the cavity. With others, Shukla daily swabbed out the parent-made biofilm as the parents renewed it. As larvae reached the end of their gorging phase, those raised in scrubbed cavities had used their food less efficiently. The deprived larvae gained roughly a third less weight per gram of carcass consumed than those that got their parents’ gut goo, the team reports.

Shukla and colleagues kept beetles under conditions as natural as possible in the lab. Parents tended the cavity and guarded the young. But this approach makes it hard to separate how the larvae and parents contribute to the biofilms, says Daniel Rozen of Leiden University in the Netherlands, who has also studied the burying beetle microbiome. The youngsters also manipulate the cavity, adding their own secretions and eating away bacteria — and sometimes, almost everything else. 

“What will remain is the tail of the mouse,” Shukla says, “and the skull and a few pieces of skin.”