Abstract
Interactions among siblings are finely balanced between rivalry and cooperation, but the factors that tip the balance towards cooperation are incompletely understood. Previous observations of insect species suggest that (i) sibling cooperation is more likely when siblings hatch at the same time, and (ii) this is more common when parents provide little to no care. In this paper, we tested these ideas experimentally with the burying beetle, Nicrophorus vespilloides. Burying beetles convert the body of a small dead vertebrate into an edible nest for their larvae, and provision and guard their young after hatching. In our first experiment, we simulated synchronous or asynchronous hatching by adding larvae at different intervals to the carrion-breeding resource. We found that ‘synchronously’ hatched broods survived better than ‘asynchronously’ hatched broods, probably because ‘synchronous hatching’ generated larger teams of larvae, that together worked more effectively to penetrate the carrion nest and feed upon it. In our second experiment, we measured the synchronicity of hatching in experimental populations that had evolved for 22 generations without any post-hatching care, and control populations that had evolved in parallel with post-hatching care. We found that larvae were more likely to hatch earlier, and at the same time as their broodmates, in the experimental populations that evolved without post-hatching care. We suggest that synchronous hatching enables offspring to help each other when parents are not present to provide care. However, we also suggest that greater levels of cooperation among siblings cannot compensate fully for the loss of parental care.
Highlights
Offspring that develop alongside each other in the same nursery commonly compete for limited resources such as food [1]
We determined 2 whether larvae within broods from these No Care populations were more likely to hatch at the same time as each other than larvae from experimental populations, kept in parallel, which had been continuously exposed to parental care
Consistent with our previous work [16], and with the hypothesis that the presence of siblings is beneficial to larvae that do not have post-hatching parental care, we found that larval mass at dispersal increased with brood size (t 1⁄4 2.74, p 1⁄4 0.008)
Summary
Offspring that develop alongside each other in the same nursery commonly compete for limited resources such as food [1]. Experiments on the subsocial burrower bug Adomerus triguttulus explicitly link the extent of hatching synchrony to the nature of larval interactions and the supply of maternal care In this species, maternal care is facultative and, when mothers are absent, earlier hatched offspring eat their unhatched siblings. In species with facultative parental care we predict that: (i) an increase in the extent of hatching synchrony within the brood should promote offspring fitness in the absence of parental care, and (ii) after sustained exposure to no post-hatching parental care, we should see an evolved increase in the degree to which hatching is synchronized within each brood We tested these predictions with experiments on the burying beetle N. vespilloides. We determined 2 whether larvae within broods from these No Care populations were more likely to hatch at the same time as each other than larvae from experimental populations, kept in parallel, which had been continuously exposed to parental care
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