Synchronous Hatching of 2-Day Delayed Intruders in Reproductive Competition in the Burying Beetle

Appropriate hatching time is important for successful brood parasitism in some bird and insect groups. Parental burying beetles typically rear their larvae on carcasses buried in nests; however, they occasionally raise brood-parasitic larvae from eggs dumped by other females. Parasitic larvae must hatch synchronously with host larvae because the host parents indiscriminately accept any larvae during that period. However, parasites in burying beetles are assumed to have more severe restrictions on synchronous hatching than those in birds because of less predictability of reproductive sites, the necessity for ovarian development at the site, and difficulty in adjusting by oviposition. Is the hatching of parasitic larvae synchronized with that of host larvae, even if the reproductive behavior of the parasites lags behind that of the host owing to restrictions? In the burying beetle Nicrophorus quadripunctatus Kraatz, we observed the hatching of host and parasite offspring under experimental conditions in which female parasites (intruders) encountered carcasses that had been secured by female hosts (residents) two days earlier. In 14 of the 40 replicates, defeated intruders dumped eggs, residents laid 36 eggs, and intruders laid six eggs on average. The hatching of intruder offspring was synchronized with that of the resident offspring despite the two-day lag. Egg dumping is regarded as brood parasitism. Notably, the period from contact with carcasses to hatching was significantly shorter for intruders than for residents. Advances in hatching time may contribute to the success of brood parasitism.