The proximate cause of asynchronous hatching in the burying beetle Nicrophorus quadripunctatus

Abstract

In some species, a brood hatches or is born asynchronously over an extended period of time. This asynchronous hatching establishes competitive asymmetries between offspring, and younger offspring usually exhibit a higher mortality risk and/or lower growth rate. A large body of research suggests that selection favours asynchronous hatching, though a consensus is yet to be reached on the nature of its adaptive benefits. One of the possible causes of this is that previous studies have focused mostly on avian species, who must incubate their eggs. Thus, studying non-avian species may provide an opportunity to improve our understanding of the wider importance of asynchronous hatching, for example in invertebrates, which do not incubate their eggs. In the burying beetle, Nicrophorus quadripunctatus, asynchronous hatching has been shown to maximize parental fitness. However, there is currently no information on the proximate cause of asynchronous hatching in this species. Here we investigated the influence of timing of egg-laying and the duration of embryonic development on the timing of hatching. We found that the timing of egg-laying by the parent was a major determinant of the timing of hatching, although the duration of embryonic development was also important. Our results suggest that the principal proximate cause of asynchronous hatching is parental asynchronous egg-laying.

Asynchronous hatching in a nonavian species: a test of the hurry-up hypothesis

“…Burying beetles of 75 the genus Nicrophorus are an ideal non-avian study system in which to test the hurryup hypothesis because they exhibit hatching asynchrony similar to that of many altricial birds (Muller and Eggert 1990;Smiseth et al 2006;Takata et al 2015). These beetles breed on carcasses of small vertebrates, which are buried underground (Scott 1998).…”

“…Females lay eggs in the surrounding soil (Pukowski 1933) and the hatching pattern is 80 determined by the period of time over which the eggs are laid, termed 'laying spread' (Smiseth et al 2006;Takata et al 2015). The degree of hatching asynchrony is highly variable in N. vespilloides, ranging from 16 to 56 h with a mean of 30 h, which is considerable relative to the duration embryonic development (59 h) and the duration of parental food provisioning (72 h) (Smiseth et al 2006).…”

“…The decrease in egg size across the laying order would further disadvantage the last larvae to hatch because smaller eggs have lower survival as shown in N. 430 quadripunctatus (Takata et al 2015). The last offspring to hatch are out-competed by their siblings that hatched earlier and have already grown to a larger size (Smiseth et al 2007).…”

Asynchronous hatching provides females with a means for increasing male care but incurs a cost by reducing offspring fitness

“…In contrast to birds, burying beetles do not incubate the eggs. Instead, the asynchronous hatching pattern is determined by the period of time over which the eggs are laid, which is termed ‘laying spread’ (Smiseth et al ., ; Takata et al ., ) and the extent to which laying is skewed towards the earlier part of the laying period, which is termed ‘laying skew’ (Smiseth et al ., ) Thus, females can control the hatching pattern simply by adjusting laying spread and laying skew. In Nicrophorus vespilloides (Herbst), the mean interval between the hatching of the first and last larvae of a brood (i.e.…”

“…Burying beetles of the genus Nicrophorus exhibit hatching asynchrony similar to that of many altricial birds Smiseth et al, 2006;Takata et al, 2015). These beetles breed on small vertebrate carcasses, which are buried underground (Scott, 1998).…”