Parental care masks a density‐dependent shift from cooperation to competition among burying beetle larvae

Abstract

Studies of siblings have focused mainly on their competitive interactions and to a lesser extent on their cooperation. However, competition and cooperation are at opposite ends on a continuum of possible interactions and the nature of these interactions may be flexible with ecological factors tipping the balance toward competition in some environments and cooperation in others. Here we show that the presence of parental care and the density of larvae on the breeding carcass change the outcome of sibling interactions in burying beetle broods. With full parental care there was a strong negative relationship between larval density and larval mass, consistent with sibling competition for resources. In the absence of care, initial increases in larval density had beneficial effects on larval mass but further increases in larval density reduced larval mass. This likely reflects a density-dependent shift between cooperation and competition. In a second experiment, we manipulated larval density and removed parental care. We found that the ability of larvae to penetrate the breeding carcass increased with larval density and that feeding within the carcass resulted in heavier larvae than feeding outside the carcass. However, larval density did not influence carcass decay.

Joint effects of brood size and resource availability on sibling competition

“…Our results have important implications for the potential utility of offspring density (brood size/resource availability) as a proxy for the mismatch between supply and demand (e.g. Schrader, Jarrett & Kilner, 2015).…”

“…First, we focused on sibling competition, thus ignoring the 370 potential for sibling cooperation (Forbes, 2007;Falk, Wong, Kölliker & Meunier, 2014). A recent study on our study species suggests that sibling cooperation occurs in the absence of caring parents (Schrader, Jarrett, & Kilner, 2015). Thus, one potential avenue for further work is to examine the joint effects of brood size and resource availability on sibling cooperation.…”

“…Although previous work on this species has manipulated either brood size or resource availability, no prior studies have manipulated both. Previous work on this species shows that siblings compete through sublethal scramble competition, either by begging for food from parents or by self-feeding directly off the carcass (Smiseth, 90 Lennox & Moore, 2007;Schrader, Jarrett, & Kilner, 2015).…”

“…We then repeated the analyses using larval density (i.e. brood size/carcass size) as a proxy for the shortage of resources to the brood (Schrader, Jarrett & Kilner, 2015). We did 105 this to examine whether the conclusions from these analyses were similar to those where we treated brood size and resource availability as two separate treatments.…”

A limit on the extent to which increased egg size can compensate for a poor postnatal environment revealed experimentally in the burying beetle, Nicrophorus vespilloides

“…These pairs were mated as described above; however, we used smaller carcasses (10–16 g) to be consistent with our previous work (Schrader et al. 2015a,b). Fifty‐three hours after pairing these individuals, we removed the parents and counted the number of eggs that had been laid in the soil (clutch size).…”