Age-dependent relationships between multiple sexual pigments and condition in males and females

The reliability of sexual signaling may change across age classes due to shifts in resource allocation patterns. Two contrasting hypotheses exist regarding how the condition dependence of ornaments may shift with age, and both have received empirical support. On one hand, ornaments may more reliably reflect condition and quality in older individuals, because younger individuals of high quality invest in survival over signaling effort. On the other hand, the condition dependence of ornaments may decline with age, if older individuals in poor condition terminally invest in ornaments, or if resource constraints decline with age. Further, the expression and condition dependence of different ornaments may shift with age in unique ways, such that multifaceted sexual displays maintain reliable signaling across age classes. In yellow warblers (Setophaga petechia) of both sexes, we assessed how relationships between carotenoid-and phaeomelanin-based sexual pigmentation, prenesting body reserves, and condition at molt (reflected by growth bars and feather quality) vary across age classes. Melanin coverage correlated with condition at molt across age classes in males and showed high repeatability in both sexes. In contrast, carotenoid saturation increased longitudinally with age in males and correlated with condition at molt in different age classes in the 2 sexes. Specifically, carotenoid saturation correlated positively with condition at molt in younger, but not older males, whereas in females, the situation was reversed, with a positive correlation present only in older females. Results suggest that age-dependent signaling may promote maintenance of multifaceted sexual displays and that agedependent signaling dynamics depend on sex. © The Author 2013. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved

Condition-Dependence, Reproductive Strategies, and the Information Content of Multiple Sexual Pigments in the Yellow Warbler (Setophaga petechia)

Sexual ornaments and reproductive behaviors represent life history investments, whose expression trades off against other allocation options. Thus, levels of sexual ornamentation may not always positively correlate with metrics of condition, performance, and fitness. Further, diversity in allocation strategy may select for multifaceted sexual displays in which some ornaments signal allocation strategy, whereas others signal individual quality. In this dissertation, I use the yellow warbler (Setophaga petechia) as a model species to explore whether carotenoid- and phaeomelanin-based sexual pigmentation play distinct or complementary roles in signaling individual condition, oxidative stress, and condition-dependent parental capacity, versus reproductive allocation strategy. Past research has suggested that carotenoid-based pigmentation is highly condition-dependent and linked to antioxidant defenses, whereas melanin-based pigmentation signals differences in reproductive strategy. However, others have suggested that this dichotomous view of the two pigment types is overly simplistic. I performed an intensive field study to achieve my research objectives. I quantified pigmentation using reflectance spectrometry and digital photography, used feather quality to indirectly quantify condition at molt, assayed oxidative stress across two populations, and video-recorded nests to measure reproductive behavior. Finally, I employed microsatellite-based paternity analysis to quantify reproductive success. This research yielded the following important conclusions. First, the condition-dependence and overall expression of carotenoid pigmentation was age-dependent, whereas melanin pigmentation displayed age-independent expression and correlated with condition metrics across age classes. These results suggest that multifaceted sexual displays may maintain reliable signaling of individual quality across age classes, suggesting an underexplored age-dependent mechanism for maintenance of multifaceted displays. Second, contrary to predictions, carotenoid-based pigmentation was not more strongly associated with condition metrics than melanin-based pigmentation in yellow warblers. Rather, in males, melanin-based pigmentation was more consistently linked to condition at molt, good oxidative status, and paternal performance, although both types of pigmentation affected patterns of extrapair paternity. Thus, results are contrary to dichotomous signaling functions of carotenoid- versus melanin-based pigmentation. Finally, highly melanic male warblers adjusted patterns of mating and paternal effort across the nesting cycle, suggesting that behavioral flexibility may be an underappreciated mechanism by which highly ornamented males ameliorate reproductive tradeoffs between mating and paternal performance

Personality and plasticity in neophobia levels vary with anthropogenic disturbance but not toxic metal exposure in urban great tits Urban disturbance, metal pollution and neophobia

Animal personalities, as defined by repeatable among individual differences in behavior, can vary across urbanization gradients. However, how urbanization affects personalities remains incompletely understood, especially because different urban stressors could affect personality traits in opposing ways, whereas most previous studies have considered only one urban disturbance factor. For instance, novel habitat features could favor reduced neophobia, whereas exposure to pollutants could increase risk sensitivity through neurotoxic or hormonal effects. To address this contingency, we studied object neophobia in four urban populations of great tits (Parus major) that vary in exposure to metal pollution and anthropogenic disturbance, as quantified by proximity to roads and pathways. We measured the return latency of incubating females when flushed from the nest and presented with up to two different novel objects, allowing quantification of behavioral repeatability and plasticity. To separate neophobia from sensitivity to disturbance, we also conducted baseline trials, in which females were flushed but no object was presented. We additionally measured exploration behavior and aggression (hissing) during nest defense, to explore whether suites of behaviors covary with urbanization, and examined whether neophobia affects reproductive success. Sensitivity to disturbance and neophobia were repeatable, and thus represent personality traits. Moreover, females occupying territories near roads and pathways had shorter return latencies during novel object but not baseline trials, suggesting a specific reduction in neophobia in disturbed areas. Plasticity in neophobia also increased with disturbance level. In contrast, metal exposure did not affect neophobia or sensitivity to disturbance, despite negatively correlating with exploration behavior. Neophobia correlated with exploration behavior, but not aggression or reproductive success. Results suggest that shifts in personality types in urbanized areas might involve specific reductions in neophobia, rather than general reductions in sensitivity to disturbance, and unexpectedly indicate no effect of toxic metals on risk sensitivity

Data from: Elevating perceived predation risk modifies the relationship between parental effort and song complexity in the song sparrow (Melospiza melodia)

Adult-directed predation risk elevates costs of parental care, and may modify relationships between sexually selected ornaments and parental effort by accentuating the tradeoff between survival and parental investment. We assessed multiple hypotheses regarding the relationship between maternal effort, paternal effort, and the sexually selected trait of male song complexity in the song sparrow Melospiza melodia. Further, we explored whether experimentally elevating perceived adult-directed predation risk near nests affected these relationships. We quantified two dimensions of song complexity: song repertoire size and residual syllable number (the relative number of syllables for a given song repertoire size). Under elevated perceived predation risk, but not in the absence of the predator stimuli, females mated to males with higher residual syllable number displayed higher nestling provisioning rates and performed a greater proportion of nestling provisioning trips. In other words, elevating perceived predation risk induced a pattern of maternal investment consistent with differential allocation. In contrast, under elevated perceived predation risk, only, females performed a lesser proportion of provisioning trips when mated to males with large song repertoire sizes. Further, consistent with the good parent hypothesis, males with large song repertoire sizes displayed lower latencies to return to the nest, independent of the predator stimuli. Results suggest that residual syllable number may reflect some aspect of male genetic quality, such that females are more willing to maintain maternal effort while facing heightened predation risk. On the other hand, females may gain paternal benefits when mated to males with large song repertoires. Our study supports the hypothesis that increased costs of parental care associated with predation risk may induce relationships between sexually selected traits and parental behavior, which may increase the strength of sexual selection. Additionally, results suggest that different aspects of song complexity may fulfill non-equivalent signaling roles