Do honest signalling models of offspring solicitation apply to insects?

Abstract

Honest signalling models predict that the intensity of solicitation by o¡spring in£uences the level of provisioning provided by parents and re£ects o¡spring need. The empirical evidence supporting these predictions primarily comes from studies of birds or mammals. Thus, although parental care of altricial o¡spring is taxonomically widespread, the generality of these models is not well known. To investigate whether honest signalling models apply to insects, we manipulated parent and o¡spring behaviour in the burying beetle Nicrophorus orbicollis, a species with advanced parental care. First, within biparental care, we manipulated the brood size to alter the parents' perception of o¡spring need. We measured the care giving behaviour of male and female parents to examine whether either adjusts its level of care according to o¡spring need. In the second experiment, because two parents together provision the brood more often than single parents, we manipulated the number of care givers (uniparental and biparental care) and measured o¡spring solicitation to assess whether o¡spring change their behaviour in response to need. Our results show that parent behaviour is broadly consistent with the ¢rst prediction of the models; both sexes provisioned larger broods more often than smaller broods. Larval solicitation was also consistent with the second prediction; larvae that were provisioned less often begged more. Our results provide evidence that honest signalling models can be applied to insects as well as vertebrates, although there are also subtle di¡erences in care giving behaviour that may be important.

Intrafamilial conflict and parental investment: a synthesis

“…This assumption is made by both scramble and signal approaches and conforms with the biological data (Teather 1992;Kacelnik et al 1995;Leonard & Horn 1998;Rauter & Moore 1999). So gradient Ј(x * ) or YЈ(x * ) is positive.…”

Partial begging: an empirical model for the early evolution of offspring signalling

“…Because begging occurs only when parents are near the larvae (Rauter & Moore 1999;Smiseth & Moore 2002), we tested whether females exercised control by moving away from or not approaching the larvae. We did this by noting the number of scans where a female was in near proximity to the larvae, defined as within a distance of less than the width of its pronotum from the larvae.…”

“…We used instantaneous scan sampling (Martin & Bateson 1986) every 1 min for 30 min, and counted, at each scan, the number of larvae that were begging. A larva was considered to be begging when raising its head towards the parent while waving its legs or touching the parent with their feet (Rauter & Moore 1999;Smiseth & Moore 2002). For use in the analyses, we calculated the average percentage of time spent begging by each larva in the brood, b i , as b i = Σb/L × 100/30, where Σb is the total number of begging events occurring during the 30 scans in an observation session and L is the brood size at the time of observation (Smiseth & Moore 2002).…”

“…The parent could control the transition to nutritional independence by changing its behaviour towards the larvae. Burying beetle larvae beg only when the parent is nearby (Rauter & Moore 1999;Smiseth & Moore 2002). Thus, the parent could exercise control by reducing (i) the time they spend near the larvae or (ii) the frequency with which it responded to begging attempts with regurgitation.…”

“…Existing studies suggest that larval begging reflects need, that parents respond to begging and that the larvae adjust their begging according to the number of competing siblings (Rauter & Moore 1999;Smiseth & Moore 2002). In some species, such as Nicrophorus vespilloides and N. pustulatus, the larvae can survive in the absence of posthatching parental care Rauter & Moore 2002;but see Trumbo 1992), suggesting that begging and self-feeding coexist as alternative foraging strategies from hatching until the larvae cease begging.…”