Negative association between parental care and sibling cooperation in earwigs: a new perspective on the early evolution of family life?

Abstract

The evolution of family life requires net fitness benefits for offspring, which are commonly assumed to mainly derive from parental care. However, an additional source of benefits for offspring is often overlooked: cooperative interactions among juvenile siblings. In this study, we examined how sibling cooperation and parental care could jointly contribute to the early evolution of family life. Specifically, we tested whether the level of food transferred among siblings (sibling cooperation) in the European earwig Forficula auricularia (1) depends on the level of maternal food provisioning (parental care) and (2) is translated into offspring survival, as well as female investment into future reproduction. We show that higher levels of sibling food transfer were associated with lower levels of maternal food provisioning, possibly reflecting a compensatory relationship between sibling cooperation and maternal care. Furthermore, the level of sibling food transfer did not influence offspring survival, but was associated with negative effects on the production of the second and terminal clutch by the tending mothers. These findings indicate that sibling cooperation could mitigate the detrimental effects on offspring survival that result from being tended by low-quality mothers. More generally, they are in line with the hypothesis that sibling cooperation is an ancestral behaviour that can be retained to compensate for insufficient levels of parental investment.

The population determines whether and how life-history traits vary between reproductive events in an insect with maternal care

“…Irrespective of the mechanism mediating the increased level of maternal care towards second clutch nymphs, the absence of a population-specific effect indicates that the environmental conditions experienced by females during first clutch family life (and egg care) are crucial in determining the subsequent expression of maternal care towards their second clutch offspring. This is supported by recent studies showing that maternal condition at egg hatching determines the nature of sibling and mother-offspring interactions in F. auricularia (Wong and Kölliker 2012;Kramer et al 2015;Kramer and Meunier 2016).…”

“…Isolated females and, upon hatching, their nymphs were set up in Petri dishes (diameters 8.5) containing humid sand as substrate and a plastic tube (cut in half) as shelter. All the tested individuals received an ad libitum amount of standard laboratory food (see composition in Kramer et al 2015). However, we did not provide food to the isolated females between egg laying and hatching, as they typically stop feeding during this period (Kölliker 2007).…”

“…(10) Food provisioning was measured in 102 clutches (a haphazard sample of 34 clutches was omitted from this measurements due to time constraints; see details in Table 1) using a standard method relying on the fact that ingested coloured food is visible through the partially transparent cuticle of first instar nymphs (Staerkle and Kölliker 2008;Köl-liker et al 2015;Kramer et al 2015). In brief, food was removed from each family on day 5 after hatching.…”

Stable eusociality via maternal manipulation when resistance is costless

“…There is a trade-off between offspring production and provisioning [defined by e mi in eqs. (1) and (2)], so reduction in provisioning releases resources for offspring production (see Savage et al, 2015 andKramer et al, 2015). The population grows once the mother starts to reduce care toward second-brood offspring which allows her to produce more offspring (Supporting Fig.…”

Adaptive evolution of synchronous egg-hatching in compensation for the loss of parental care

“…For example, in the European earwig Forficula auricularia , the incidence of food sharing among nymphs is greater when maternal food provisioning is lower [15]. Recent work on the burying beetle Nicrophorus vespilloides provides further evidence of a dynamic interplay between parental care and larval cooperation.…”