Experimental evolution of a more restrained clutch size when filial cannibalism is prevented in burying beetles Nicrophorus vespilloides

Abstract

The overproduction of offspring is commonly associated with high hatching failure and a mechanism for dispensing with surplus young. We used experimental evolution of burying beetle populations Nicrophorus vespilloides to determine causality in these correlations. We asked does eliminating the mechanism for killing "spare" offspring cause the evolution of a more restrained clutch size and consequently select for reduced hatching failure? N. vespilloides typically overproduces eggs but kills 1^st instar larvae through partial filial cannibalism during brood care. We established replicate evolving populations that either could practice filial cannibalism (Full Care) or could not, by removing parents before their young hatched (No Care). After 20+ generations of experimental evolution, we measured clutch size and hatching success. We found that No Care females produced fewer eggs than Full Care females when allowed to breed on a small corpse, a finding not explained by differences in female quality. On larger corpses, females from both populations laid similar numbers of eggs. Furthermore, hatching success was greater in the No Care populations on small corpses. Our results suggest that the adaptive overproduction of offspring depends on a mechanism for eliminating surplus young and that killing offspring, in turn, relaxes selection against hatching failure.

Keywords: lack clutch size; optimistic clutch size; parental care; plasticity; reaction norm.

FIGURE 1

The relative fitness of (a) brood size at dispersal and (b) mean larval mass at dispersal in relation to standardized clutch size of offspring from generation 13 of the Full Care experimental populations but reared without any post‐hatching parental care. Offspring developed on a carcass prepared by a donor pair of Full Care beetles until dispersal. The slopes of the lines denote the strength of direct selection (estimated through the selection gradient; β). Data were collected in some of the experiments described in Duarte et al. (2021)

FIGURE 2

The relationship between clutch size and carcass mass for females that evolved in the Full care (blue) and No care (red) experimental populations. Lines show linear regression lines fitted through data collected from both replicates of each type of experimental population

FIGURE 3

The (a) proportion of eggs that hatched and (b) size of clutches laid by Full Care (blue) and No Care (red) females across three carcass classes. Hatching success was measured by transferring clutches to agar plates and so was independent of the Full Care/No Care manipulations. The raw data and the means ±SE are displayed