Conor C. Taff

Experimental Chronic Noise Is Related to Elevated Fecal Corticosteroid Metabolites in Lekking Male Greater Sage- Grouse (Centrocercus urophasianus)

There is increasing evidence that individuals in many species avoid areas exposed to chronic anthropogenic noise, but the impact of noise on those who remain in these habitats is unclear. One potential impact is chronic physiological stress, which can affect disease resistance, survival and reproductive success. Previous studies have found evidence of elevated stress-related hormones (glucocorticoids) in wildlife exposed to human activities, but the impacts of noise alone are difficult to separate from confounding factors. Here we used an experimental playback study to isolate the impacts of noise from industrial activity (natural gas drilling and road noise) on glucocorticoid levels in greater sage-grouse (Centrocercus urophasianus), a species of conservation concern. We non-invasively measured immunoreactive corticosterone metabolites from fecal samples (FCMs) of males on both noise-treated and control leks (display grounds) in two breeding seasons. We found strong support for an impact of noise playback on stress levels, with 16.7% higher mean FCM levels in samples from noise leks compared with samples from paired control leks. Taken together with results from a previous study finding declines in male lek attendance in response to noise playbacks, these results suggest that chronic noise pollution can cause greater sage-grouse to avoid otherwise suitable habitat, and can cause elevated stress levels in the birds who remain in noisy areas.

SEXUAL SELECTION, MULTIPLE MALE ORNAMENTS, AND AGE- AND CONDITION-DEPENDENT SIGNALING IN THE COMMON YELLOWTHROAT

In many animals, sexual selection has resulted in complex signaling systems in which males advertise aspects of their phenotypic or genetic quality through elaborate ornamentation and display behaviors. Different ornaments might convey different information or be directed at different receivers, but they might also be redundant signals of quality that function reliably at different times (ages) or in different contexts. We explored sexual selection and age‐ and condition‐dependent signaling in the common yellowthroat (Geothlypis trichas), a sexually dichromatic warbler with two prominent plumage ornaments—a melanin‐based, black facial “mask” and carotenoid‐based, UV‐yellow “bib.” In a three‐year study, variance among males in the number of social (Mw) and extra‐pair (Me) mates generated strong sexual selection on mask and bib attributes. Some traits (mask size, bib yellow brightness) were correlated with male age and did not experience selection beyond age‐related increases in Mw and Me. Other traits showed age‐specific (bib size) or age‐reversed (ultraviolet brightness) patterns of selection that paralleled changes in the information‐content of each ornament. The components of male fitness generating selection in young versus old males were distinct, reflecting different sources of variation in male fertilization success. Age‐ and context‐dependent changes in the strength, direction, and target of selection may help explain the maintenance of multiple ornaments in this and other species.

Endocrine Flexibility: Optimizing Phenotypes in a Dynamic World?

Responding appropriately to changing conditions is crucial in dynamic environments. Individual variation in the flexibility of physiological mediators of phenotype may influence the capacity to mount an integrated response to unpredictable changes in social or ecological context. We propose here a conceptual framework of rapid endocrine flexibility that integrates ecological endocrinology with theoretical and empirical studies of phenotypic plasticity and behavioral syndromes. We highlight the need for research addressing variation in the scope and speed of flexibility, and provide suggestions for future studies of these potentially evolving traits. Elucidating the causes and consequences of variation in endocrine flexibility may have important implications for the evolution of behavior, and for predicting the response of individuals and populations to rapidly changing environments.

Spatial distribution of nests constrains the strength of sexual selection in a warbler

In socially monogamous species, extra‐pair paternity may increase the strength of intersexual selection by allowing males with preferred phenotypes to monopolize matings. Several studies have found relationships between male signals and extra‐pair mating, but many others fail to explain variation in extra‐pair mating success. A greater appreciation for the role that ecological contingencies play in structuring behavioural processes may help to reconcile contradictory results. We studied extra‐pair mating in a spatial context in the common yellowthroat (Geothlypis trichas), a territorial wood warbler. Over the course of 6 years, we observed 158 breeding attempts by 99 males, resulting in a total of 369 nests and 520 sampled nestlings. The spatial distribution of territories varied greatly, with males having between 0 and 10 close neighbours and between three and 39 neighbouring nestlings close enough to represent extra‐pair siring opportunities. Both within‐pair and extra‐pair reproductive success increased with breeding density, but the opportunity for sexual selection and strength of selection varied with density. Total variance in reproductive success was highest at low density and was mostly explained by variation in within‐pair success. In contrast, at high density, both within‐pair and extra‐pair successes contributed substantially to variance in reproductive success. The relationships between plumage and extra‐pair mating also varied by density; plumage was under strong sexual selection via extra‐pair mating success at high density, but no selection was detected at low density. Thus, ecological factors that structure social interactions can drive patterns of sexual selection by facilitating or constraining the expression of mating preferences.

Multimodal sexual selection in a warbler: plumage and song are related to different fitness components

Many species possess multiple sexual signals that are produced in different modalities. Signals from different modalities may convey different or similar (redundant) information, or be intended for different receivers. We studied sexual selection on two such signals (plumage and song) in the common yellowthroat, Geothlypis trichas. We measured the coloration and size of both a carotenoid-based and a melanin-based plumage ornament and defined singing consistency as the lack of variability between repeated renditions of the same song. Overall, we found that plumage ornaments predicted within-pair mating success, while song consistency predicted extrapair success. Only plumage was related to male condition but, among experienced males, consistent singers had higher survival rates. Singing consistency was more variable than plumage, as performance varied across observations of the same male in relation to social context and date. Our results suggest that visual and acoustic signals in this species are most important in different sexual selection contexts.

Relationship Between Brood Sex Ratio and Male Ornaments Depends on Male Age in a Warbler

Sex allocation theory predicts that females should bias the sex ratio of their offspring in response to differences in the reproductive value of sons and daughters. For example, paternal traits (ornaments) that are associated with male quality and reproductive success may result in male-biased sex ratios when inheritance of these traits is more beneficial to sons than to daughters. However, the information content of male ornaments, as well as the ornaments themselves, may change with male experience. If females are responsive to changes in the information content of signals, the result may be context-specific patterns of sex allocation. In a 3-year study of 50 common yellowthroat, Geothlypis trichas, females and their 287 young, we found that biased sex ratios were associated with male ornamentation, but that these deviations were not consistent across male experience classes. Females produced clutches with male-biased sex ratios when they were mated to young males with elaborate ornaments, but not when they were mated to older males. Male-biased broods were also associated with differences in offspring quality, as measured by average nestling mass. At our field site in New York, U.S.A., ornaments are generally more indicative of viability and condition among young, inexperienced males than among older males. We suggest that the relationship between male traits and the relative value of sons and daughters may change across male experience classes. Such changes may obscure patterns of adaptive sex-ratio bias and contribute to mixed results in the sex allocation literature.

Different Ornaments Signal Male Health and MHC Variation in Two Populations of a Warbler

Male traits that signal health and vigour are used by females to choose better quality mates, but in some cases the male trait selected by females differs among populations. Multiple male traits can be maintained through female mate choice if both traits are equally honest indicators of male quality, but tests of this prediction are rare. By choosing males based on such traits, females could gain direct benefits from males (assistance with parental care), but when females choose extra‐pair mates based on these traits, females gain only male sperm, and potentially indirect genetic benefits for their offspring. In common yellowthroats (Geothylpis trichas), female choice of extra‐pair mates targets two different plumage ornaments: the black mask in a Wisconsin population and the yellow bib in a New York population. Previously, we found that the black mask in Wisconsin is related to greater major histocompatibility complex (MHC) class II variation, which in turn signals better survival and disease resistance. In this study, we examined the signalling function of the yellow bib in New York to test whether it signals the same aspects of male quality as the black mask in Wisconsin. As predicted, we found that the yellow bib in New York is most closely associated with MHC variation, which also signals survival and resistance to blood parasites. Thus, the ornament preferred by females differs between the two populations, but the different ornaments signal similar aspects of male health and genetic quality, specifically information regarding MHC variation and potential indirect genetic benefits to females.

Genomic Comparison of Campylobacter spp. and Their Potential for Zoonotic Transmission between Birds, Primates, and Livestock

ABSTRACT Campylobacter is the leading cause of human gastroenteritis worldwide. Wild birds, including American crows, are abundant in urban, suburban, and agricultural settings and are likely zoonotic vectors of Campylobacter. Their proximity to humans and livestock increases the potential spreading of Campylobacter via crows between the environment, livestock, and humans. However, no studies have definitively demonstrated that crows are a vector for pathogenic Campylobacter. We used genomics to evaluate the zoonotic and pathogenic potential of Campylobacter from crows to other animals with 184 isolates obtained from crows, chickens, cows, sheep, goats, humans, and nonhuman primates. Whole-genome analysis uncovered two distinct clades of Campylobacter jejuni genotypes; the first contained genotypes found only in crows, while a second genotype contained “generalist” genomes that were isolated from multiple host species, including isolates implicated in human disease, primate gastroenteritis, and livestock abortion. Two major β-lactamase genes were observed frequently in these genomes (oxa-184, 55%, and oxa-61, 29%), where oxa-184 was associated only with crows and oxa-61 was associated with generalists. Mutations in gyrA, indicative of fluoroquinolone resistance, were observed in 14% of the isolates. Tetracycline resistance (tetO) was present in 22% of the isolates, yet it occurred in 91% of the abortion isolates. Virulence genes were distributed throughout the genomes; however, cdtC alleles recapitulated the crow-only and generalist clades. A specific cdtC allele was associated with abortion in livestock and was concomitant with tetO. These findings indicate that crows harboring a generalist C. jejuni genotype may act as a vector for the zoonotic transmission of Campylobacter. IMPORTANCE This study examined the link between public health and the genomic variation of Campylobacter in relation to disease in humans, primates, and livestock. Use of large-scale whole-genome sequencing enabled population-level assessment to find new genes that are linked to livestock disease. With 184 Campylobacter genomes, we assessed virulence traits, antibiotic resistance susceptibility, and the potential for zoonotic transfer to observe that there is a “generalist” genotype that may move between host species.

Large-Scale Release of Campylobacter Draft Genomes: Resources for Food Safety and Public Health from the 100K Pathogen Genome Project.

ABSTRACT Campylobacter is a food-associated bacterium and a leading cause of foodborne illness worldwide, being associated with poultry in the food supply. This is the initial public release of 202 Campylobacter genome sequences as part of the 100K Pathogen Genome Project. These isolates represent global genomic diversity in the Campylobacter genus.

The repeatability of glucocorticoids: A review and meta-analysis

Glucocorticoids are highly conserved hormones that mediate a suite of responses to changing conditions in vertebrates. Recent work has focused on understanding how selection operates on glucocorticoid secretion in natural populations. Because heritability is rarely estimated and difficult to measure in the wild, many studies report within-individual repeatability as an estimate of stable between individual differences in glucocorticoid secretion. We conducted a systematic review and meta-analysis on estimates of within-individual glucocorticoid repeatability to elucidate general patterns of repeatability, and to test for relationships between covariates and estimates of repeatability. To this end, we collected 203 estimates of within-individual glucocorticoid repeatability drawn from 71 separate studies and 55 species. Overall, we found moderate levels of repeatability (0.29). We also found that repeatability varied by sample type. Long-term measures (e.g., fecal and feather samples) and acute stress-induced plasma glucocorticoids had higher repeatability (long-term: 0.44, stress-induced: 0.38), than baseline glucocorticoid levels (0.18). Repeatability also decreased with increasing time between repeated sampling events. Despite significant overall repeatability, there was substantial heterogeneity in estimates from different studies, suggesting that repeatability of glucocorticoid secretion varies substantially across systems and conditions. We discuss the implications of our results for understanding selection on glucocorticoid traits and suggest that continuing work should focus on evaluating the repeatability of within-individual glucocorticoid reaction norms.