Darker eumelanic barn owls better withstand food depletion through resistance to food deprivation and lower appetite

Abstract

The intensity of selection exerted on ornaments typically varies between environments. Reaction norms may help to identify the conditions under which ornamented individuals have a selective advantage over drab conspecifics. It has been recently hypothesized that in vertebrates eumelanin-based coloration reflects the ability to regulate the balance between energy intake and expenditure. We tested two predictions of this hypothesis in barn owl nestlings, namely that darker eumelanic individuals have a lower appetite and lose less weight when food-deprived. We found that individuals fed ad libitum during 24 h consumed less food when their plumage was marked with larger black spots. When food-deprived for 24 h nestlings displaying larger black spots lost less weight. Thus, in the barn owl the degree of eumelanin-based coloration reflects the ability to withstand periods of food depletion through lower appetite and resistance to food restriction. Eumelanic coloration may therefore be associated with adaptations to environments where the risk of food depletion is high.

Association between melanism, physiology and behaviour: A role for the melanocortin system

“…3A), and when food-deprived during 24 h they lost less weight (Fig. 3B) (Dreiss et al, 2010). Thus, darker eumelanic individuals may better regulate the balance between food intake and energy expenditure, and hence be better Fig.…”

“…Experimental test of the prediction that compared to pale individuals, darker eumelanic barn owls better regulate the balance between food intake and energy expenditure. (A) Nestlings displaying large black spots consumed fewer mice over a period of 24 h than conspecifics with smaller black spots (adapted from Dreiss et al, 2010). (B) When food-deprived during 24 h, nestlings displaying large black spots lost less weight than individuals showing smaller spots (adapted from Dreiss et al, 2010).…”

“…(A) Nestlings displaying large black spots consumed fewer mice over a period of 24 h than conspecifics with smaller black spots (adapted from Dreiss et al, 2010). (B) When food-deprived during 24 h, nestlings displaying large black spots lost less weight than individuals showing smaller spots (adapted from Dreiss et al, 2010). (C) Females displaying large black spots are significantly heavier than females with small spots in the afternoon but not in the morning (adapted from Roulin, 2009 (Ducrest et al, 2008), it is possible that these alternative genetic solutions to produce similar pigmentation have evolved under natural selection.…”

Corticosterone shifts reproductive behaviour towards self-maintenance in the barn owl and is linked to melanin-based coloration in females

“…Further, darker eumelanic individuals are better able to cope with a stressful situation (i.e. better withstand food depletion (Dreiss et al, 2010), breeding barn owl males with larger eumelanic spots reduce their provisioning rate less when corticosterone is elevated compared to males with less eumelanic spots , salmons with more eumelanic skin pigments are less infected by parasites and show a lower corticosterone secretion to an acute stress situation (Kittilsen et al, 2012)). A possible explanation for the association between melanin and stress sensitivity is the pleiotropic effects of genes encoding for enzymes that both regulate melanin synthesis and the stress-response axis (reviewed in Ducrest et al, 2008).…”

Vocal communication regulates sibling competition over food stock

“…For each individual, we broadcast 14 times in a row the same 45-min playback sequence, each sequence followed by 15 min of silence. Owlets react in a similar way in front of unfamiliar playback calls and live nestlings' calls (they avoid overlapping playback calls, Dreiss et al 2013b; they refrain from calling in front of a highly vocal playback, Ruppli et al 2013a; they insert their calls between playback calls in the same way they do with live nestlings, Dreiss et al 2015) and are not physiologically stressed in nest boxes placed in the laboratory (Dreiss et al 2010a). …”