Sense and sensitivity: responsiveness to offspring signals varies with the parents' potential to breed again

Abstract

How sensitive should parents be to the demands of their young? Offspring are under selection to seek more investment than is optimal for parents to supply, which makes parents vulnerable to losing future fitness by responding to manipulative displays. Yet, parents cannot afford to ignore begging and risk allocating resources inefficiently. Here, we show that parents may solve this problem by adjusting their sensitivity to begging behaviour in relation to their own likelihood of breeding again, a factor largely neglected in previous analyses of parent-offspring interactions. In two carotenoid-supplementation experiments on a New Zealand passerine, the hihi Notiomystis cincta, we supplemented adults to enhance their propensity to breed again, and supplemented entire broods to increase their mouth colour, thus enhancing their solicitation display. We found that adults that attempted two breeding attempts a season were largely insensitive to the experimentally carotenoid-rich gapes of their brood, whereas those that bred just once responded by increasing their rate of provisioning at the nest. Our results show that parents can strategically vary their sensitivity to begging in relation to their future reproductive potential. By restricting opportunities for offspring to influence provisioning decisions, parents greatly limit the potential for offspring to win parent-offspring conflict.

Sibling conflict and dishonest signaling in birds

“…For example, European starlings can lay two broods per year, and offspring only signal need honestly if they are in the second brood, when parents cannot lay another brood (49). Hihi bird parents' response to offspring signals in their first brood decreases if their likelihood of breeding again is experimentally increased (50).…”

“…These results suggest that siblings that are not even born yet, and, indeed, may never be born, cast a competitive shadow back in time, which selects for exaggerating need to parents. The logical next step would be to explore how parents' response to begging is affected by the same life history factors (6,49,50,58). Longevity and lifetime fecundity have already been shown to influence other aspects of parental care, such as how parents respond to nest predators, with species that have less potential for future reproduction engaging in riskier defense behavior (59).…”

Growing in Cities: An Urban Penalty for Wild Birds? A Study of Phenotypic Differences between Urban and Rural Great Tit Chicks (Parus major)

“…In addition to these physiological functions, carotenoids are also allocated into carotenoid-based signals (e.g., plumage) in developing animals Isaksson et al, 2006). Such signaling is crucial because it is used by parents to assess the viability/quality of the chicks and therefore to determine their parental investment (Saino et al, 2003a;Pike et al, 2007;Thorogood et al, 2011). Therefore, carotenoids mediate a tradeoff between protective physiological functions (e.g., immunity, growth, and antioxidants) and signaling in developing animals.…”

Context-dependent effects of an experimental increase of hunger level in house sparrow nestlings

“…The use of number of breeding events as indicative of intrinsic costs of reproduction and of probability of reproducing several times during the same season as a proxy of individual phenotypic quality of adults is not new (Thorogood et al 2011). Probability of laying subsequent clutches is related to experimental food supply (Nagy and Holmes 2005a;Thorogood et al 2011;Seward et al 2014) and/or to intrinsic phenotypic quality of adults (Hoffmann et al 2015) and, on average, nestlings of multi-brooded females are of better phenotypic quality than those from single-brooded (Nagy and Holmes 2005b).…”