Phaeomelanin- and carotenoid-based pigmentation reflect oxidative status in two populations of the yellow warbler (Setophaga petechia)

Multi-character approach reveals a new mangrove population of the Yellow Warbler complex, Setophaga petechia, on Cozumel Island, Mexico

The Setophaga petechia complex includes 43 subspecies distributed within the new world, of which some are migratory and others are resident, with only two resident subspecies in the Mexican Caribbean: Setophaga petechia bryanti a mangrove subspecies belonging to the erithachorides group resident on the mainland of the Yucatan Peninsula and Setophaga petechia rufivertex endemic to Cozumel Island and belonging to the petechia group. Recently, a new population of individuals presenting intermediate phenotypic traits and living in mangrove ecosystems was discovered and reported for Cozumel Island. In this study, we used a multi-character approach including genetic (five ISSR genetic markers), morphometric (eight traits), phenotypic (four characteristics of males), and acoustic dataset (11 parameters) to understand the process of differentiation and the status of these new island individuals in relation to the two well-established subspecies using a total of 60 individuals (20 for each group). Through multivariate analyses based on different dataset used in our study, we show how the new population is related to the endemic island subspecies, S. p. rufivertex and to the mainland subspecies, S. p. bryanti while demonstrating finite differences. We conclude that the new population of S. petechia on Cozumel Island is a well-established population with high level of differentiation.

Anthropogenic noise is associated with telomere length and carotenoid-based coloration in free-living nestling songbirds

Growing evidence suggests that anthropogenic noise has deleterious effects on the behavior and physiology of free-living animals. These effects may be particularly pronounced early in life, when developmental trajectories are sensitive to stressors, yet studies investigating developmental effects of noise exposure in free-living populations remain scarce. To elucidate the effects of noise exposure during development, we examined whether noise exposure is associated with shorter telomeres, duller carotenoid-based coloration and reduced body mass in nestlings of a common urban bird, the great tit (Parus major). We also assessed how the noise environment is related to reproductive success. We obtained long-term measurements of the noise environment, over a ∼24-h period, and characterized both the amplitude (measured by LA_eq, LA_90, LA₁₀, LA_max) and variance in noise levels, since more stochastic, as well as louder, noise regimes might be more likely to induce stress. In our urban population, noise levels varied substantially, with louder, but less variable, noise characteristic of areas adjacent to a highway. Noise levels were also highly repeatable, suggesting that individuals experience consistent differences in noise exposure. The amplitude of noise near nest boxes was associated with shorter telomeres among smaller, but not larger, brood members. In addition, carotenoid chroma and hue were positively associated with variance in average and maximum noise levels, and average reflectance was negatively associated with variance in background noise. Independent of noise, hue was positively related to telomere length. Nestling mass and reproductive success were unaffected by noise exposure. Results indicate that multiple dimensions of the noise environment, or factors associated with the noise environment, could affect the phenotype of developing organisms, that noise exposure, or correlated variables, might have the strongest effects on sensitive groups of individuals, and that carotenoid hue could serve as a signal of early-life telomere length.

Carotenoid- but not melanin-based plumage coloration is negatively related to metal exposure and proximity to the road in an urban songbird

Rapid urbanization is a global phenomenon that is increasingly exposing organisms to novel stressors. These novel stressors can affect diverse aspects of organismal function, including development of condition-dependent ornaments, which play critical roles in social and sexual selection. We investigated the relationship between metal pollution, proximity to roads, and carotenoid- and melanin-based plumage coloration in a common songbird, the great tit (Parus major). We studied populations located across a well-characterized metal pollution gradient and surrounded by roadway networks. Metal exposure and road-associated pollution could reduce carotenoid-based pigmentation by inducing oxidative stress or affecting habitat quality, but metals could also enhance melanin-based pigmentation, through effects on melanogenesis and testosterone concentrations. Using a large sample size (N > 500), we found that birds residing close to a point source for metals had reduced ultraviolet chroma, a component of carotenoid-based pigmentation. Moreover, birds with high feather metal concentrations had lower carotenoid chroma, hue, and ultraviolet chroma, with effects modified by age class. Birds residing closer to roads also had lower carotenoid chroma and hue. Melanin-based pigmentation showed high between-year repeatability, and no association with anthropogenic pollution. Results suggest that carotenoid-, but not melanin-, based pigmentation is negatively affected by multiple anthropogenic stressors. We are the first to demonstrate a negative association between roads and a plumage-based signaling trait, which could have important implications for sexual signaling dynamics in urban landscapes.

Eumelanin levels in rufous feathers explain plasma testosterone levels and survival in swallows

Pigment-based plumage coloration and its physiological properties have attracted many researchers to explain the evolution of such ornamental traits. These studies, however, assume the functional importance of the predominant pigment while ignoring that of other minor pigments, and few studies have focused on the composition of these pigments. Using the pheomelanin-based plumage in two swallow species, we studied the allocation of two pigments (the predominant pigment, pheomelanin, and the minor pigment, eumelanin) in relation to physiological properties and viability in populations under a natural and sexual selection. This is indispensable for studying the evolution of pheomelanin-based plumage coloration. Pheomelanin and eumelanin share the same pathway only during their initial stages of development, which can be a key to unravel the functional importance of pigment allocation and thus of plumage coloration. Using the barn swallow, Hirundo rustica, a migratory species, we found that plasma testosterone levels increased with increasing the proportion of eumelanin pigments compared with pheomelanin pigments, but not with the amount of pheomelanin pigments, during the mating period. In the Pacific swallow Hirundo tahitica, a nonmigratory congener, we found that, during severe winter weathers, survivors had a proportionally smaller amount of eumelanin pigments compared with pheomelanin pigments than that in nonsurvivors, but no detectable difference was found in the pheomelanin pigmentation itself. These results indicated that a minor pigment, eumelanin, matters at least in some physiological measures and viability. Because the major pigment, pheomelanin, has its own physiological properties, a combination of major and minor pigments provides multiple information to the signal receivers, potentially enhancing the signaling function of pheomelanic coloration and its diversification across habitats.

Phylogeography indicates incomplete genetic divergence among phenotypically differentiated montane forest populations of Atlapetesalbinucha (Aves, Passerellidae)

The White-naped Brushfinch (Atlapetesalbinucha) comprises up to eight allopatric subspecies mainly identified by the color of the underparts (gray vs. yellow belly). Yellow and gray bellied forms were long considered two different species (A.albinucha and A.gutturalis), but they are presently considered as one polytypic species. Previous studies in the genus Atlapetes have shown that the phylogeny, based on molecular data, is not congruent with characters such as coloration, ecology, or distributional patterns. The phylogeography of A.albinucha was analyzed using two mitochondrial DNA regions from samples including 24 different localities throughout montane areas from eastern Mexico to Colombia. Phylogeographic analyses using Bayesian inference, maximum likelihood and haplotype network revealed incomplete geographic structure. The genetic diversity pattern is congruent with a recent process of expansion, which is also supported by Ecological Niche Models (ENM) constructed for the species and projected into three past scenarios. Overall, the results revealed an incomplete genetic divergence among populations of A.albinucha in spite of the species’ ample range, which contrasts with previous results of phylogeographic patterns in other Neotropical montane forest bird species, suggesting idiosyncratic evolutionary histories for different taxa throughout the region.

Meta-analysis reveals that reproductive strategies are associated with sexual differences in oxidative balance across vertebrates

Oxidative stress is a key physiological mechanism underlying life-history tradeoffs. Here, I use meta-analytic techniques to test whether sexual differences in oxidative balance are common in vertebrates and to identify which factors are associated with such differences. The dataset included 732 effect size estimates from 100 articles (82 species). Larger unsigned effect size (meaning larger sexual differences in a given marker) occurred in: reptiles and fish; those species that do not provide parental care; and oviparous species. Estimates of signed effect size (positive values meaning higher oxidative stress in males) indicated that females were less resistant to oxidative stress than males in: reptiles while males and females were similar in fish, birds, and mammals; those species that do not provide parental care; and oviparous species. There was no evidence for a significant sexual differentiation in oxidative balance in fish, birds, and mammals. Effect size was not associated with: the number of offspring; whether the experimental animals were reproducing or not; biomarker (oxidative damage, non-enzymatic, or enzymatic antioxidant), the species body mass; the strain (wild vs. domestic); or the study environment (wild vs. captivity). Oxidative stress tended to be higher in females than males across most of the tissues analyzed. Levels of residual heterogeneity were high in all models tested. The findings of this meta-analysis indicate that diversification of reproductive strategies might be associated with sexual differences in oxidative balance. This explorative meta-analysis offers a starting platform for future research to investigate the relationship between sex and oxidative balance further.

Effects of energy and thermoregulation time on physiological state and sexual signal in a lizard

Theory of sexual selection states that males often develop showy signals, which reduce their survival but increase their reproductive success. During mate choice, these conspicuous signals can be honest indicators of individual quality conveying information about the signaler's physiological state. Sexually selected signals are influenced by many environmental factors; however, whether signals and physiological state are affected together is rarely studied. The ultraviolet-blue throat color of male Lacerta viridis is an intra- and intersexually selected signal connected to blood parasite infection and influenced by environmental factors. The aim of this study was to experimentally investigate how ecologically relevant environmental factors affect color signal intensity and key physiological traits parallel. During the mating season, we exposed 40 adult male lizards infected with blood parasites to food and basking time treatments in a full factorial design. We measured color, amount of reactive oxygen metabolites (ROMs), hematocrit, immunocompetence, and blood parasite intensity before and after treatments. High basking time resulted in elevated immunocompetence coupled with increased ROMs. The high food treatment increased nuptial color brightness, but also increased ROMs and decreased immunocompetence. In summary, our study provides experimental evidence about environmentally induced parallel changes in an honest sexual signal and several quality-indicator physiological traits. We showed that available energy and time for high metabolism have independent and sometimes opposite effects on individual state.