Abstract
BackgroundTheoretical models predict that a cost is necessary to guarantee honesty in begging displays given by offspring to solicit food from their parents. There is evidence for begging costs in the form of a reduced growth rate and immunocompetence. Moreover, begging implies vigorous physical activity and attentiveness, which should increase metabolism and thus the releasing of pro-oxidant substances. Consequently, we predict that soliciting offspring incur a cost in terms of oxidative stress, and growth rate and immune response (processes that generate pro-oxidants substances) are reduced in order to maintain oxidative balance.Methodology/Principal FindingsWe test whether magpie (Pica pica) nestlings incur a cost in terms of oxidative stress when experimentally forced to beg intensively, and whether oxidative balance is maintained by reducing growth rate and immune response. Our results show that begging provokes oxidative stress, and that nestlings begging for longer bouts reduce growth and immune response, thereby maintaining their oxidative status.Conclusions/SignificanceThese findings help explaining the physiological link between begging and its associated growth and immunocompetence costs, which seems to be mediated by oxidative stress. Our study is a unique example of the complex relationships between the intensity of a communicative display (begging), oxidative stress, and life-history traits directly linked to viability.
Highlights
Evolutionary theory hypothesizes that many animal signals have to be costly in order to reliably indicate signaler quality [1,2,3]
There were no significant differences in initial body mass, food ingested and feces mass excreted, between high begging (HB, n = 16) and low begging (LB, n = 16) nestlings (Table 1)
When we controlled for differences in immune response, mass gained was significantly lower in HB (6.061.1 g) than in Low begging (LB) nestlings (10.061.1 g; F1, 17 = 6.68, P = 0.019)
Summary
Evolutionary theory hypothesizes that many animal signals have to be costly in order to reliably indicate signaler quality [1,2,3]. Showy begging displays may have evolved either as selfish attempts to influence parental decisions in scramble sibling competition for limited resources [7,8] and/or as honest signals of need allowing parents to allocate food in relation to begging intensity [9]. In both cases, costly begging may limit offspring behavior, preventing runaway escalation of begging intensity over evolutionary time, and allowing a stable equilibrium for conflict resolution [9,10]. We predict that soliciting offspring incur a cost in terms of oxidative stress, and growth rate and immune response (processes that generate pro-oxidants substances) are reduced in order to maintain oxidative balance
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