Abstract
Background: Immature stages of many animals can forage and feed on their own, whereas others depend on their
parents’ assistance to obtain or process food. But how does such dependency evolve, and which offspring and
parental traits are involved? Burying beetles (Nicrophorus) provide extensive biparental care, including food provisioning
to their offspring. Interestingly, there is substantial variation in the reliance of offspring on post-hatching care among
species. Here, we examine the proximate mechanisms underlying offspring dependence, focusing on the larvae of
N. orbicollis, which are not able to survive in the absence of parents. We specifically asked whether the high offspring
dependence is caused by (1) a low starvation tolerance, (2) a low ability to self-feed or (3) the need to obtain parental
oral fluids. Finally, we determined how much care (i.e. duration of care) they require to be able to survive.
Results: We demonstrate that N. orbicollis larvae are not characterized by a lower starvation tolerance than larvae of the
more independent species. Hatchlings of N. orbicollis are generally able to self-feed, but the efficiency depends on the
kind of food presented and differs from the more independent species. Further, we show that even when providing
highly dependent N. orbicollis larvae with easy ingestible liquefied mice carrion, only few of them survived to pupation.
However, adding parental oral fluids significantly increased their survival rate. Finally, we demonstrate that survival and
growth of dependent N. orbicollis larvae is increased greatly by only a few hours of parental care.
Conclusions: Considering the fact that larvae of other burying beetle species are able to survive in the absence of care,
the high dependence of N. orbicollis larvae is puzzling. Even though they have not lost the ability to self-feed, an easily
digestible, liquefied carrion meal is not sufficient to ensure their survival. However, our results indicate that the transfer of
parental oral fluids is an essential component of care. In the majority of mammals, offspring rely on the exchange of fluids
(i.e. milk) to survive, and our findings suggest that even in subsocial insects, such as burying beetles, parental fluids can
significantly affect offspring survival.
