Ornaments and condition: plumage patch sizes, nutritional reserve state, reserve accumulation, and reserve depletion

Abstract

Condition-dependence is considered as a dominant mechanism ensuring the fitness benefits of continued mate choice for heritable sexual signal traits, but crucial questions remain concerning the underlying physiological pathways. For example, it is unclear whether condition-dependence is mediated by the different amount of resource obtained, some uncheatable functional link with nutritional status, or the adverse effect of nutritional stress experienced by some individuals. Furthermore, the pattern of change in nutritional reserves in relation to ornamental traits has recently been proposed as a critical pillar of the condition-dependence concept, but this pattern is virtually unknown in natural populations. We quantified separate measures for actual body condition, lipid reserve accumulation rate, and lipid reserve depletion, and applied these measures to two white plumage ornaments of male collared flycatchers during courtship, during nestling rearing, and before the summer moult. Neither actual condition nor reserve accumulation rate before moult predicted the subsequent change of ornament sizes, but reserve depletion was accompanied by the reduction of forehead patch size to the following year. Wing patch size, a trait important in territoriality, was negatively related to both reserve accumulation and reserve depletion in the courtship period, but not related to current condition. Finally, irrespective of breeding phase, measures of current condition, and recent nutritional reserve depletion were negatively correlated, but both were unrelated to resource accumulation rate. These results indicate that measuring nutritional reserve trajectories in addition to actual condition may reveal functionally important processes underlying signal-condition correlations. Significance statement Ornamental signal characters are known to convey honest information to signal receivers through their dependence on nutritional condition. Here, we show that such signals can also indicate the temporal trends of condition. We examine plumage patch sizes and separate measures of actual condition, nutritional reserve accumulation, and nutritional reserve depletion in three contexts: Communicated by A. Pilastro

Sexual dichromatism, size dimorphism, and microscale anatomy of white wing stripe in blue tits

“…However, a similar relationship was not found for the crown and white dot UV chromas, and in none of the brightness metrics. Furthermore, we found no relationship between the dot size and the current condition, which is in line with the results of Hegyi et al. (2019) .…”

“…Condition index measured during breeding may also not reflect body condition experienced by individuals during molt, that is, when the ornamented feathers are produced. Nevertheless, we strongly encourage further studies to explore the condition dependence of the greater coverts coloration, perhaps with the application of other condition indices that could reflect more long-term trends, like lipid reserves accumulation or lipid reserves depletion (as suggested in Hegyi et al. 2019 ).…”

“…All covert’s parameters, as well as body mass, tarsus length, wing length, and crown color metrics were normally distributed. Residual body mass, that can be treated as a proxy of current condition ( Hegyi et al. 2019 ), was calculated as residuals from body mass regressed against the tarsus length.…”

“…According to the redundant signal hypothesis ( Møller and Pomiankowski 1993 ), a combination of several patches, each correlated with individual condition, can provide a female with a more complete evaluation of a male’s quality. Thus, we examine interrelations between the reflectance properties and size of covert dots and traits considered to signal individual quality in the blue tit: residual body mass as a proxy of current condition ( Hegyi et al. 2019 ) and the coloration of crown feathers.…”

Melanin‐based ornament darkness positively correlates with across‐season nutritional condition

“…First, signal deterioration has been highlighted as a possible condition indicator (Hegyi, et al., 2019; Surmacki et al., 2011). Second, signals have been demonstrated to indicate the trajectory of condition change (Hegyi, et al., 2019).…”