The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Ellen D. Ketterson - One of the best experts on this subject based on the ideXlab platform.
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local adaptation from afar migratory bird populations diverge in the initiation of reproductive timing while wintering in sympatry
Biology Letters, 2020Co-Authors: Sarah Wanamaker, Devraj Singh, A J Byrd, Tara M Smiley, Ellen D. KettersonAbstract:The initiation of reproduction in many seasonally breeding animals is controlled by photoperiod and tends to be clinal: populations at higher latitudes breed later than those at lower latitudes, often reflecting a higher photoperiodic threshold. Migratory animals presumably time reproduction to match conditions at their breeding grounds, at least in part, by cues perceived on their wintering grounds. We asked how closely related dark-eyed Junco (Junco hyemalis) populations that overwinter in sympatry but breed in allopatry respond to their shared winter environment by comparing early spring indices of readiness to migrate (fat and muscle condition) and breed (baseline and elevated testosterone). We measured stable hydrogen isotopes from feathers grown the preceding year and claws grown during winter to estimate breeding and wintering latitudes, respectively. We predicted that if reproductive initiation is adapted to the emergence of resources at their respective breeding destinations, then birds migrating to higher latitudes (slate-coloured Junco; J. h. hyemalis) should delay breeding as compared with those migrating to lower latitudes (pink-sided Junco; J. h. mearnsi) despite a common overwinter environment. We found higher testosterone in pink-sided Juncos, consistent with earlier reproductive initiation, suggesting local adaptation in reproductive phenology is achieved through differential responses to predictive environmental cues.
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experimental evidence that symbiotic bacteria produce chemical cues in a songbird
The Journal of Experimental Biology, 2019Co-Authors: Danielle J Whittaker, Samuel P Slowinski, Jonathan M Greenberg, Osama M Alian, Andrew D Winters, Madison M Ahmad, Mikayla J E Burrell, Helena A Soini, Milos V Novotny, Ellen D. KettersonAbstract:ABSTRACT Symbiotic microbes that inhabit animal scent glands can produce volatile compounds used as chemical signals by the host animal. Though several studies have demonstrated correlations between scent gland bacterial community structure and host animal odour profiles, none have systematically demonstrated a causal relationship. In birds, volatile compounds in preen oil secreted by the uropygial gland serve as chemical cues and signals. Here, we tested whether manipulating the uropygial gland microbial community affects chemical profiles in the dark-eyed Junco (Junco hyemalis). We found an effect of antibiotic treatment targeting the uropygial gland on both bacterial and volatile profiles. In a second experiment, we cultured bacteria from Junco preen oil, and found that all of the cultivars produced at least one volatile compound common in Junco preen oil, and that most cultivars produced multiple preen oil volatiles. In both experiments, we identified experimentally generated patterns in specific volatile compounds previously shown to predict Junco reproductive success. Together, our data provide experimental support for the hypothesis that symbiotic bacteria produce behaviourally relevant volatile compounds within avian chemical cues and signals.
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density dependent fitness not dispersal movements drives temporal variation in spatial genetic structure in dark eyed Juncos Junco hyemalis
Molecular Ecology, 2019Co-Authors: Eric B Liebgold, Nicole M. Gerlach, Ellen D. KettersonAbstract:Some studies have found that dispersal rates and distances increase with density, indicating that density-dependent dispersal likely affects spatial genetic structure. In an 11-year mark-recapture study on a passerine, the dark-eyed Junco, we tested whether density affected dispersal distance and/or fine-scale spatial genetic structure. Contrary to expectations, we found no effect of predispersal density on dispersal distance or the proportion of locally produced juveniles returning to the population from which they hatched. However, even though density did not affect dispersal distance or natal return rates, we found that density still did affect spatial genetic structure. We found significant positive spatial genetic structure at low densities of (postdispersal) adults but not at high densities. In years with high postdispersal (adult) densities that also had high predispersal (juvenile) densities in the previous year, we found negative spatial genetic structure, indicating high levels of dispersal. We found that density also affected fitness of recruits, and fitness of immigrants, potentially linking these population parameters with the spatial genetic structure detected. Immigrants and recruits rarely nested in low postdispersal density years. In contrast, in years with high postdispersal density, recruits were common and immigrants had equal success to local birds, so novel genotypes diluted the gene pool and effectively eliminated positive spatial genetic structure. In relation to fine-scale spatial genetic structure, fitness of immigrants and new recruits is poorly understood compared to dispersal movements, but we conclude that it can have implications for the spatial distribution of genotypes in populations.
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a role for differential gene regulation in the rapid diversification of melanic plumage coloration in the dark eyed Junco Junco hyemalis
bioRxiv, 2018Co-Authors: Mikus Abolinsabols, Ellen D. Ketterson, Etienne Kornobis, Paolo Ribeca, Kazumasa Wakamatsu, Mark P Peterson, Borja MilaAbstract:Color plays a prominent role in reproductive isolation, therefore understanding the proximal basis of pigmentation can provide insight into speciation. Subspecies of the dark-eyed Junco (Junco hyemalis) have evolved marked differences in plumage coloration since the Last Glacial Maximum, yet whether color differences are caused by mutations in coding regions of expressed genes or are instead the result of regulatory differences remains unknown. To address this question, we studied the pigment composition and the genetic basis of coloration in two divergent subspecies, the slate-colored and Oregon Juncos. We used HPLC and light microscopy to investigate pigment composition and deposition in feathers from four body areas. We then used RNAseq to compare the relative roles of differential gene expression in developing feathers and sequence divergence in transcribed loci under common garden conditions. Junco feathers differed in eumelanin and pheomelanin content and distribution. Within subspecies, in lighter feathers melanin synthesis genes were downregulated (including PMEL, TYR, TYRP1, OCA2, MLANA), ASIP was upregulated. Feathers from different body regions also showed differential expression of HOX and Wnt genes. Feathers from the same body regions that differed in color between the two subspecies showed differential expression of ASIP and three other genes (MFSD12, KCNJ13, HAND2) associated with pigmentation in other taxa. Sequence variation in the expressed genes was not related to color differences. Our findings support the hypothesis that differential regulation of a few genes can account for marked differences in coloration, a mechanism that may underlie the rapid diversification of Juncos.
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Female Dark-eyed Juncos (Junco hyemalis thurberi) produce male-like song in a territorial context during the early breeding season
Journal of Avian Biology, 2018Co-Authors: Dustin G. Reichard, Jonathan W. Atwell, Serena E. George, Ellen D. KettersonAbstract:Reports of female song, once considered a rarity, have recently increased across a variety of avian taxa. Females of many species can be induced to produce male-like song with exogenous testosterone, but observations of female song in free-living birds remain limited by incomplete sampling of females. Here, we report three independent observations of female dark-eyed Juncos (Junco hyemalis) producing male-like song early in the breeding season (i.e. post-territory establishment, pre-nesting) in a recently established non-migratory, urban population. To elicit song, we presented 17 free-living Junco pairs with a live, caged female conspecific. Three unique females responded to our trials by diving at the intruding female, chasing their (male) mate, fanning their tail feathers, and singing a trilled song similar in structure to male long-range (broadcast) song. We compared male and female songs quantitatively and found that the two sexes were statistically similar in many spectral and temporal characteristics, but female songs had significantly lower minimum and peak frequencies than males. This result is particularly surprising, as males in this urban population are known to sing at a significantly higher minimum frequency than males in a nearby montane population. Both the seasonal and social context in which these songs were observed suggest a potential function for female song in mate guarding and polygyny prevention, but more data are needed to test this hypothesis. Whether female song is common in all dark-eyed Juncos during the early breeding season or if it is restricted to this particular urban and non-migratory population remains an important question for future research. This article is protected by copyright. All rights reserved.
Pierre Deviche - One of the best experts on this subject based on the ideXlab platform.
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Central prolactin binding site densities change seasonally in an adult male passerine bird (Junco hyemalis).
Journal of chemical neuroanatomy, 2020Co-Authors: Kristina O. Smiley, Cynthia Corbitt, John D. Buntin, Pierre DevicheAbstract:Seasonal reproduction is common across temperate zone avian species. In these species, physiological and behavioral adaptations have evolved to change according to day length (i.e., seasonally) in order to maximize reproductive output. The hormone prolactin regulates many aspects of parental care, a critical component of reproductive success. It's secretion in birds has been shown to be under photoperiodic control, with the highest levels measured in the spring and summer months, when birds breed and show parental care. However, to date, no study has tested whether the densities of central prolactin binding sites vary seasonally, which may also account for prolactin's effect on parental care. To test this, we collected brains from free-ranging adult male dark-eyed Juncos, Junco hyemalis, a biparental songbird, in the spring, summer, and fall, and used quantitative in vitro autoradiography to compare the densities of specific prolactin binding sites across 20 different brain regions. Prolactin binding sites were found in regions that regulate parental behavior in other avian species. During the summer, several hypothalamic regions that regulate parental care, including the preoptic area and tuberal nucleus, contained lower densities of prolactin binding sites, suggesting exposure to higher endogenous prolactin levels, than at other times. This observation is consistent with the fact that circulating prolactin is highest during summer, when males would be providing care to young. Overall, these data suggest that prolactin binding sites are relatively conserved in the avian brain and that central prolactin activity supports parental care efforts in Juncos and other avian species.
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TESTOSTERONE TREATMENT TO FREE-RANGING MALE DARK-EYED JuncoS (Junco HYEMALIS) EXACERBATES HEMOPARASITIC INFECTION
The Auk, 2006Co-Authors: Pierre Deviche, Jennifer ParrisAbstract:Abstract The “immunocompetence handicap” hypothesis predicts that reproductive hormones, in particular testosterone (T), are immunosuppressive and consequently increase susceptibility to diseases and parasite infections, but this prediction has not been evaluated in free-living birds and the factors mediating the immunosuppressive influence of T remain poorly known. To address these issues, we administered supplemental T via implants to free-ranging adult male Dark-eyed Juncos (Junco hyemalis) and characterized the effects of this treatment on infection with the two most prevalent hematozoan parasites in this species, Leucocytozoon fringillinarum and Trypanosoma avium. Males caught at the beginning of their breeding season (May) received T-filled, empty (control), or no Silastic capsules, and were recaptured five weeks later. Capsule implantation had, by itself, no effect on parasite infections, body mass, or size of an androgen-dependent secondary sexual characteristic, the cloacal protuberance. Testoste...
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hypothalamic gnrh i and its precursor during photorefractoriness onset in free living male dark eyed Juncos Junco hyemalis of different year classes
General and Comparative Endocrinology, 2006Co-Authors: Simone Meddle, John C Wingfield, Robert P Millar, Pierre DevicheAbstract:The termination of seasonal breeding in most photoperiodic passerines is heralded by spontaneous gonadal regression as a result of long day exposure. This phenomenon is termed absolute photorefractoriness and this insensitivity to long days may only be dissipated by short photoperiod exposure. The timing of the transition to a photorefractory stage in adult free-living male Dark-eyed Juncos is age-dependent. Second-year males (SY, entering their first breeding season) molt earlier, suggesting that they become refractory earlier, than older males (ASY). We determined whether the earlier onset of photorefractoriness in SY males concurs with decreased expression of hypothalamic GnRH-I or its precursor, pro-GnRH-GAP. Male SY and ASY Juncos were caught at the end of the breeding season either during, or following, testicular regression. Immunoreactivity for GnRH-I and pro-GnRH-GAP was found in perikarya in the preoptic area, and fibers in the median eminence. The number and size of cells immunoreactive for GnRH-I and pro-GnRH-GAP did not significantly differ with age or time of year. In ASY Juncos, there was a significant decrease in both GnRH-I and pro-GnRH-GAP staining density at the median eminence following testicular regression at a time of photorefractoriness onset. Density of pro-GnRH-GAP at the median eminence was also reduced following testicular regression in SY males but GnRH-I staining density did not change. Thus, age-class differences in the transition to photorefractoriness do not appear to result from differences in GnRH-I synthesis. Instead, the regulation of GnRH-I secretion by non-photoperiodic factors may determine photorefractoriness onset.
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Region-specific testosterone modulation of the vasotocin-immunoreactive system in male dark-eyed Junco, Junco hyemalis.
Brain Research, 2004Co-Authors: L. Plumari, S. Plateroti, Pierre Deviche, Giancarlo PanzicaAbstract:The nonapeptide vasotocin (VT) is the avian equivalent of the mammalian antidiuretic hormone vasopressin and is believed to control aggressive and reproductive behaviors. Brain VT distribution has been described in several domesticated avian species. We previously demonstrated that VT distribution in the brain of a free-ranging male passerine, the dark-eyed Junco, Junco hyemalis, resembles that in domesticated birds. A preliminary study also suggested that the VT-immunoreactive (VT-ir) system of Juncos is regulated by testosterone (T), as is the case of galliforms. To test this hypothesis, we investigated the effects of castration and T replacement on brain VT-ir innervation in adult male Juncos. Castration reduced VT-ir innervation in the lateral septum (SL), the medial preoptic nucleus, the nucleus of the stria terminalis and the intercollicularis nucleus. These effects of castration were largely reversed by T treatment at high physiological doses, but significantly so only for the SL. Given the demonstrated behavioral role of the above VT-ir-containing brain regions, the results suggest that these regions may be sites of action of VT on reproductive behaviors.
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seasonal and age related changes in blood parasite prevalence in dark eyed Juncos Junco hyemalis aves passeriformes
Journal of Experimental Zoology, 2001Co-Authors: Pierre Deviche, Ellis C Greiner, X MantecaAbstract:We determined seasonal changes in blood parasite infections in a free-living population of Dark-eyed Juncos (Junco hyemalis) breeding in interior Alaska (65 degrees N; 148 degrees W). The common parasites found in blood smears were Leucocytozoon fringillinarum (56%), Trypanosoma avium (33%), and Haemoproteus fringillae (9%). In males, parasite prevalences were relatively high at arrival on breeding grounds and increased during the breeding season. Intensity of infection with Leucocytozoon also increased between spring and summer, and then decreased at the time of migration (September). This decrease did not occur in adult females. Elevated prevalences during the breeding season probably reflected the addition of new cases via vector activity to positive status resulting from spring relapse. We observed neither an association between parasite species nor a consistent relationship between parasite intensity and body condition. To further study relationships between reproductive system activity and parasite infections, we compared prevalences in adult males that were undergoing their first cycle of gonadal development and regression (males in their second calendar year, or SY) with those of older males (males in their third or more calendar year, i.e., after-second-year males or ASY). Circulating testosterone concentrations declined in both groups between arrival on breeding grounds (end of April-early May) and the end of the reproductive period (July), and they were higher in May in ASY than in SY males. At the peak of the breeding season (June), ASY males also had a higher parasite prevalence than SY males. This difference may have resulted from immunosuppressive effects of gonadal hormones and/or from behavioral differences between SY and ASY males such that older males were exposed to more insect vectors than younger males. .
Val Nolan - One of the best experts on this subject based on the ideXlab platform.
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acorn mast drives long term dynamics of rodent and songbird populations
Oecologia, 2007Co-Authors: Ethan D. Clotfelter, Eric Snajdr, Val Nolan, Amy B Pedersen, Jack A Cranford, Nilam Ram, Ellen D. KettersonAbstract:Resource pulses can have cascading effects on the dynamics of multiple trophic levels. Acorn mast is a pulsed resource in oak-dominated forests that has significant direct effects on acorn predators and indirect effects on their predators, prey, and pathogens. We evaluated changes in acorn mast, rodent abundance, raptor abundance, and reproductive success of a ground-nesting songbird over a 24-year period (1980–2004) in the southern Appalachian Mountains in an effort to determine the relationships among the four trophic levels. In particular, we examined the following: acorn mast from red oaks (Quercus rubra) and white oaks (Q. alba), abundance of white-footed mice (Peromyscus leucopus) and deer mice (P. maniculatus), population estimates of seven raptor species from three feeding guilds, and nest failure and number of juveniles of dark-eyed Juncos (Junco hyemalis). Finally, we recorded seasonal temperature and precipitation to determine the effects of weather on each trophic level. We found that weather patterns had delayed effects of up to 3 years on these trophic interactions. Variation in acorn mast, the keystone resource in this community, was explained by weather conditions as far back as 2 years before the mast event. Acorn mast, in turn, was a strongly positive predictor of rodent abundance the following year, whereas spring and summer temperature and raptor abundance negatively affected rodent abundance. Dark-eyed Junco nests were more likely to fail in years in which there were more rodents and raptors. Nest failure rate was a strong predictor of the number of juvenile Juncos caught at the end of the summer. Our results improve our understanding of the complex ecological interactions in oak-dominated forests by illustrating the importance of abiotic and biotic factors at different trophic levels.
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elevated testosterone reduces choosiness in female dark eyed Juncos Junco hyemalis evidence for a hormonal constraint on sexual selection
Proceedings of The Royal Society B: Biological Sciences, 2004Co-Authors: Joseph M. Casto, Joel W. Mcglothlin, Val Nolan, Diane L Neudorf, Ellen D. KettersonAbstract:Because testosterone (T) often mediates the expression of attractive displays and ornaments, in the absence of constraints sexual selection should lead to an evolutionary increase in male T levels. One candidate constraint would be a genetic correlation between the sexes that leads to a correlated response in females. If increased T in females were to have deleterious effects on mate choice, the effect of sexual selection on male T would be weakened. Using female dark-eyed Juncos (Junco hyemalis), we tested whether experimentally enhancing female T would lead to a decrease in discrimination between two classes of males, one treated with T (T-males) and one control (C-males). The two female treatments (T-implanted and C-females) spent equal amounts of time with both classes of males, but T-treated females failed to show a preference for either male treatment, whereas C-females showed a significant preference, albeit in an unexpected direction (for C-males). T-females were less discriminating than C-females, irrespective of the direction of their preference. To our knowledge, this is the first study to show that circulating hormones can alter female choosiness without reducing sexual motivation. Our results suggest that hormonal correlations between the sexes have the potential to constrain sexual selection on males.
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Mouth Color Signals Thermal State of Nestling Dark-Eyed Juncos (Junco hyemalis)
Ethology, 2003Co-Authors: Ethan D. Clotfelter, Val Nolan, Kristin A. Schubert, Ellen D. KettersonAbstract:In many species of birds, nestlings have brightly colored mouths. Some studies have found that mouth color is related to hunger, and may serve to solicit feedings from parents. We devised two experiments to test the hypothesis that mouth color is an indicator of hunger in nestling dark-eyed Juncos (Junco hyemalis), andneither experiment producedresults to support the hypothesis. We did find, however, that mouth redness saturation increased for the duration of our experiments (60 min). We deviseda thirdexperiment to investigate the effect of a different stressor, temperature. In the third experiment, mouth redness decreased in saturation when microenvironment temperature increasedfollowing a periodof cooling. These findings suggest that mouth color indicates thermal state of nestling dark-eyed Juncos and may function as a signal to the female to brood them.
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Offspring sex ratio is unrelated to male attractiveness in dark-eyed Juncos (Junco hyemalis)
Behavioral Ecology and Sociobiology, 2001Co-Authors: Jennifer L. Grindstaff, Joseph M. Casto, Val Nolan, Alex C. Buerkle, Ellen D. KettersonAbstract:Sex allocation theory predicts that parents should bias investment toward the offspring sex that confers higher relative fitness on the parents. When variance in reproductive success is higher in males than females, and some males are more attractive to females than others, thereby achieving higher reproductive success, female parents mated to attractive males are expected to bias reproductive allocation toward sons. Modification of the primary sex ratio is one mechanism by which avian parents may bias allocation. In mate choice trials, captive female dark-eyed Juncos (Junco hyemalis) prefer to associate with males whose circulating testosterone level has been elevated experimentally. We asked whether females socially mated to testosterone-treated males in nature might bias the sex ratio of progeny in favor of sons. We determined the primary sex ratio of broods using a sex-linked molecular marker, the CHD gene on the W chromosome. We found no relationship between the hormonal treatment of males and the primary or secondary sex ratios of offspring produced by their social mates. Sex ratio was also unrelated to breeding-season date, study year, male viability, or female age. While unlikely, it is possible that female Juncos are not able to manipulate the primary sex ratio of their broods. More likely, possible benefits to female Juncos of producing attractive sons may be small because (1) attractive males do not necessarily have higher fitness, depending on the trade-offs involved for males, and (2) when such benefits exist, they may be outweighed for females by the costs of compensating for the reduced paternal care of attractive males.
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the effects of experimentally elevated testosterone and food deprivation on food consumption and prey size preferences in male dark eyed Juncos Junco hyemalis emberizidae passeriformes
Ethology, 2001Co-Authors: Ethan D. Clotfelter, Val Nolan, Ellen D. KettersonAbstract:Numerous studies have shown that the experimental elevation of circulating levels of testosterone reduces parental behaviour in male birds, particularly the provisioning of young. The mechanisms responsible for this change in behaviour are not fully understood. In this study, we examine the effects of elevated testosterone on food consumption and prey selection, both of which have potential consequences for nestling provisioning behaviour. We manipulated testosterone and performed two experiments on a captive, non-breeding population of male dark-eyed Juncos (Junco hyemalis) on long day-lengths. In the first experiment, we subjected Juncos to 3 h of food deprivation and compared food consumption and prey size selection by males with elevated testosterone (testosterone males) to that of control males. Testosterone males consumed more food than control males and showed a preference for larger prey. In a second experiment in which small prey were more abundant than large prey, food consumption and prey size preferences did not differ between testosterone and control males. We also manipulated the duration of food deprivation in the second experiment. Males of both treatments consumed more small prey under conditions of mild (1 h) or moderate (5 h) food deprivation and consumed more large prey under conditions of intermediate (3 h) food deprivation. We discuss our results and the effects that testosterone has on self-maintenance behaviour and male parental effort.
Borja Mila - One of the best experts on this subject based on the ideXlab platform.
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change in sexual signalling traits outruns morphological divergence across an ecological gradient in the post glacial radiation of the songbird genus Junco
Journal of Evolutionary Biology, 2020Co-Authors: Guillermo Friis, Borja MilaAbstract:The relative roles of natural and sexual selection in promoting evolutionary lineage divergence remains controversial and difficult to assess in natural systems. Local adaptation through natural selection is known to play a central role in promoting evolutionary divergence, yet secondary sexual traits can vary widely among species in recent radiations, suggesting that sexual selection may also be important in the early stages of speciation. Here, we compare rates of divergence in ecologically relevant traits (morphology) and sexually selected signalling traits (coloration) relative to neutral structure in genome-wide molecular markers and examine patterns of variation in sexual dichromatism to explore the roles of natural and sexual selection in the diversification of the songbird genus Junco (Aves: Passerellidae). Juncos include divergent lineages in Central America and several dark-eyed Junco (J. hyemalis) lineages that diversified recently as the group recolonized North America following the last glacial maximum (ca. 18,000 years ago). We found an accelerated rate of divergence in sexually selected characters relative to ecologically relevant traits. Moreover, sexual dichromatism measurements suggested a positive relationship between the degree of colour divergence and the strength of sexual selection when controlling for neutral genetic distance. We also found a positive correlation between dichromatism and latitude, which coincides with the geographic axis of decreasing lineage age in Juncos but also with a steep ecological gradient. Finally, we found significant associations between genome-wide variants linked to functional genes and proxies of both sexual and natural selection. These results suggest that the joint effects of sexual and ecological selection have played a prominent role in the Junco radiation.
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Differential gene regulation underlies variation in melanic plumage coloration in the dark-eyed Junco ( Junco hyemalis )
Molecular Ecology, 2018Co-Authors: Mikus Abolins-abols, Mark Peterson, Etienne Kornobis, Paolo Ribeca, Kazumasa Wakamatsu, Ellen Ketterson, Borja MilaAbstract:Colour plays a prominent role in species recognition; therefore, understanding the proximate basis of pigmentation can provide insight into reproductive isolation and speciation. Colour differences between taxa may be the result of regulatory differences or be caused by mutations in coding regions of the expressed genes. To investigate these two alternatives, we studied the pigment composition and the genetic basis of coloration in two divergent dark-eyed Junco (Junco hyemalis) subspecies, the slate-coloured and Oregon Juncos, which have evolved marked differences in plumage coloration since the Last Glacial Maximum. We used HPLC and light microscopy to investigate pigment composition and deposition in feathers from four body areas. We then used RNA-seq to compare the relative roles of differential gene expression in developing feathers and sequence divergence in transcribed loci under common-garden conditions. Junco feathers differed in eumelanin and pheomelanin content and distribution. Within subspecies, in lighter feathers melanin synthesis genes were downregulated (including PMEL, TYR, TYRP1, OCA2 and MLANA), and ASIP was upregulated. Feathers from different body regions also showed differential expression of HOX and WNT genes. Feathers from the same body regions that differed in colour between the two subspecies showed differential expression of ASIP and three other genes (MFSD12, KCNJ13 and HAND2) associated with pigmentation in other taxa. Sequence variation in the expressed genes was not related to colour differences. Our findings support the hypothesis that differential regulation of a few genes can account for marked differences in coloration, a mechanism that may facilitate the rapid phenotypic diversification of Juncos.
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a role for differential gene regulation in the rapid diversification of melanic plumage coloration in the dark eyed Junco Junco hyemalis
bioRxiv, 2018Co-Authors: Mikus Abolinsabols, Ellen D. Ketterson, Etienne Kornobis, Paolo Ribeca, Kazumasa Wakamatsu, Mark P Peterson, Borja MilaAbstract:Color plays a prominent role in reproductive isolation, therefore understanding the proximal basis of pigmentation can provide insight into speciation. Subspecies of the dark-eyed Junco (Junco hyemalis) have evolved marked differences in plumage coloration since the Last Glacial Maximum, yet whether color differences are caused by mutations in coding regions of expressed genes or are instead the result of regulatory differences remains unknown. To address this question, we studied the pigment composition and the genetic basis of coloration in two divergent subspecies, the slate-colored and Oregon Juncos. We used HPLC and light microscopy to investigate pigment composition and deposition in feathers from four body areas. We then used RNAseq to compare the relative roles of differential gene expression in developing feathers and sequence divergence in transcribed loci under common garden conditions. Junco feathers differed in eumelanin and pheomelanin content and distribution. Within subspecies, in lighter feathers melanin synthesis genes were downregulated (including PMEL, TYR, TYRP1, OCA2, MLANA), ASIP was upregulated. Feathers from different body regions also showed differential expression of HOX and Wnt genes. Feathers from the same body regions that differed in color between the two subspecies showed differential expression of ASIP and three other genes (MFSD12, KCNJ13, HAND2) associated with pigmentation in other taxa. Sequence variation in the expressed genes was not related to color differences. Our findings support the hypothesis that differential regulation of a few genes can account for marked differences in coloration, a mechanism that may underlie the rapid diversification of Juncos.
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speciation on oceanic islands rapid adaptive divergence vs cryptic speciation in a guadalupe island songbird aves Junco
PLOS ONE, 2013Co-Authors: Pau Aleixandre, Borja Mila, Julio MontoyaAbstract:The evolutionary divergence of island populations, and in particular the tempo and relative importance of neutral and selective factors, is of central interest to the study of speciation. The rate of phenotypic evolution upon island colonization can vary greatly among taxa, and cases of convergent evolution can further confound the inference of correct evolutionary histories. Given the potential lability of phenotypic characters, molecular dating of insular lineages analyzed in a phylogenetic framework provides a critical tool to test hypotheses of phenotypic divergence since colonization. The Guadalupe Junco is the only insular form of the polymorphic dark-eyed Junco (Junco hyemalis), and shares eye and plumage color with continental morphs, yet presents an enlarged bill and reduced body size. Here we use variation in mtDNA sequence, morphological traits and song variables to test whether the Guadalupe Junco evolved rapidly following a recent colonization by a mainland form of the dark-eyed Junco, or instead represents a well-differentiated “cryptic” lineage adapted to the insular environment through long-term isolation, with plumage coloration a result of evolutionary convergence. We found high mtDNA divergence of the island lineage with respect to both continental J. hyemalis and J. phaeonotus, representing a history of isolation of about 600,000 years. The island lineage was also significantly differentiated in morphological and male song variables. Moreover, and contrary to predictions regarding diversity loss on small oceanic islands, we document relatively high levels of both haplotypic and song-unit diversity on Guadalupe Island despite long-term isolation in a very small geographic area. In contrast to prevailing taxonomy, the Guadalupe Junco is an old, well-differentiated evolutionary lineage, whose similarity to mainland Juncos in plumage and eye color is due to evolutionary convergence. Our findings confirm the role of remote islands in driving divergence and speciation, but also their potential role as repositories of ancestral diversity.
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recent postglacial range expansion drives the rapid diversification of a songbird lineage in the genus Junco
Proceedings of The Royal Society B: Biological Sciences, 2007Co-Authors: Borja Mila, John E Mccormack, Gabriela Castaneda, Robert K Wayne, Thomas B SmithAbstract:Pleistocene glacial cycles are thought to have played a major role in the diversification of temperate and boreal species of North American birds. Given that coalescence times between sister taxa typically range from 0.1 to 2.0 Myr, it has been assumed that diversification occurred as populations were isolated in refugia over long periods of time, probably spanning one to several full glacial cycles. In contrast, the rapid postglacial range expansions and recolonization of northern latitudes following glacial maxima have received less attention as potential promoters of speciation. Here we report a case of extremely rapid diversification in the songbird genus Junco as a result of a single continent-wide range expansion within the last 10 000 years. Molecular data from 264 Juncos sampled throughout their range reveal that as the yellow-eyed Junco ( Junco phaeonotus ) of Mesoamerica expanded northward following the last glacial maximum, it speciated into the dark-eyed Junco ( Junco hyemalis ), which subsequently diversified itself into at least five markedly distinct and geographically structured morphotypes in the USA and Canada. Patterns of low genetic structure and diversity in mitochondrial DNA and amplified fragment length polymorphism loci found in dark-eyed Juncos relative to Mesoamerican yellow-eyed Juncos provide support for the hypothesis of an expansion from the south, followed by rapid diversification in the north. These results underscore the role of postglacial expansions in promoting diversification and speciation through a mechanism that represents an alternative to traditional modes of Pleistocene speciation.
Joseph M. Casto - One of the best experts on this subject based on the ideXlab platform.
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relative abundance of males to females affects behaviour condition and immune function in a captive population of dark eyed Juncos Junco hyemalis
Journal of Avian Biology, 2007Co-Authors: Timothy J. Greives, Joseph M. Casto, Ellen D. KettersonAbstract:Relative numbers of males and females in breeding groups may vary from expected values owing to a variety of factors. To determine how sex ratio might influence individual phenotypes in a captive population of dark-eyed Juncos Junco hyemalis during the breeding season, we established three treatment groups: a male-biased (2:1), equal (1:1), and female-biased group (1:2). Within-group density (birds/m 2 ) was constant across groups. We assessed the frequency of flight chases (a proxy for social instability), measured changes in body mass and pectoral muscle condition, assayed plasma levels of testosterone (T) and compared cell-mediated immunity of individuals. We found significantly more chases in the male-biased group than in the female-biased group. Birds in the male-biased group lost more mass and displayed poorer pectoral-muscle condition than birds in the equal group. Cell-mediated immune responses were reduced in individuals in the male-biased group in comparison to the female-biased group. Plasma T levels in both sexes did not vary with sex ratio. Collectively, these results suggest that during the breeding season, social instability is greater in male-biased populations, and instability may lead to decreased general health and vigour.
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Seasonal and individual variation in response to GnRH challenge in male dark-eyed Juncos (Junco hyemalis)
General and Comparative Endocrinology, 2006Co-Authors: Jodie M Jawor, Timothy J. Greives, Eric Snajdr, Joseph M. Casto, Joel W. Mcglothlin, George E. Bentley, Ellen D. KettersonAbstract:Concentrations of gonadal steroids such as testosterone (T) often vary widely in natural populations, but the causes and particularly the consistency of this variation is relatively unexplored. In breeding males of a wild population of the dark-eyed Junco (Junco hyemalis), we investigated seasonal and individual variation in circulating T during two breeding seasons by measuring the responsiveness of the HPG axis to a standardized injection of gonadotropin-releasing hormone (GnRH). Individuals were bled prior to and 30 min after injection. Pre- and post-challenge levels of T were measured using EIA. Many subjects were sampled repeatedly across multiple breeding stages. Plasma T concentrations nearly doubled in response to GnRH during early spring, but showed signiWcantly smaller increases in later breeding stages. When controlling for seasonal variation in response to challenge, we also found repeatable diVerences among individuals, indicating individual consistency in the release of T in response to a standardized stimulus. These seasonal and individual diVerences may arise from comparable variation in responsiveness of the pituitary or a decline in gonadal sensitivity to downstream gonadotropins. In contrast, pre-challenge T showed almost no seasonal changes and did not diVer consistently among individuals. To our knowledge, this is the Wrst demonstration of individual repeatability of short-term hormonal changes in a wild population. Such repeatability suggests that hormonal plasticity might evolve in response to changing selection pressures.
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Behavioral and physiological responses to experimentally elevated testosterone in female dark-eyed Juncos (Junco hyemalis carolinensis).
Hormones and Behavior, 2006Co-Authors: Devin A. Zysling, Gregory E. Demas, Timothy J. Greives, Creagh W. Breuner, Joseph M. Casto, Ellen D. KettersonAbstract:Testosterone mediates the expression of many fitness-related traits in male vertebrates and is thought to account for numerous sex differences in trait expression. Testosterone is also secreted by females; however, far less is known regarding its effects on female physiology and behavior. Using a bird species in which the effects of testosterone on males are well characterized, the dark-eyed Junco (Junco hyemalis), we tested whether an increase in exogenous testosterone in females would alter the phenotypic expression of a suite of behavioral and physiological traits. We found that increased testosterone levels in female dark-eyed Juncos led to decreased cell-mediated immune function and increased intrasexual aggression, hypothalamo-pituitary–adrenal (HPA) axis responsiveness, baseline corticosterone and corticosterone-binding globulin (CBG) levels. Furthermore, immunosuppression following testosterone implantation was negatively correlated with total and free testosterone but did not appear to be related to either total or free corticosterone. These results demonstrate that the phenotypic impact of elevated testosterone is not confined to males in dark-eyed Juncos, and that the impact in adults can be similar in males and females. We discuss these results in the context of potential endocrine–immune interactions and the evolution of sexual dimorphism.
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elevated testosterone reduces choosiness in female dark eyed Juncos Junco hyemalis evidence for a hormonal constraint on sexual selection
Proceedings of The Royal Society B: Biological Sciences, 2004Co-Authors: Joseph M. Casto, Joel W. Mcglothlin, Val Nolan, Diane L Neudorf, Ellen D. KettersonAbstract:Because testosterone (T) often mediates the expression of attractive displays and ornaments, in the absence of constraints sexual selection should lead to an evolutionary increase in male T levels. One candidate constraint would be a genetic correlation between the sexes that leads to a correlated response in females. If increased T in females were to have deleterious effects on mate choice, the effect of sexual selection on male T would be weakened. Using female dark-eyed Juncos (Junco hyemalis), we tested whether experimentally enhancing female T would lead to a decrease in discrimination between two classes of males, one treated with T (T-males) and one control (C-males). The two female treatments (T-implanted and C-females) spent equal amounts of time with both classes of males, but T-treated females failed to show a preference for either male treatment, whereas C-females showed a significant preference, albeit in an unexpected direction (for C-males). T-females were less discriminating than C-females, irrespective of the direction of their preference. To our knowledge, this is the first study to show that circulating hormones can alter female choosiness without reducing sexual motivation. Our results suggest that hormonal correlations between the sexes have the potential to constrain sexual selection on males.
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Offspring sex ratio is unrelated to male attractiveness in dark-eyed Juncos (Junco hyemalis)
Behavioral Ecology and Sociobiology, 2001Co-Authors: Jennifer L. Grindstaff, Joseph M. Casto, Val Nolan, Alex C. Buerkle, Ellen D. KettersonAbstract:Sex allocation theory predicts that parents should bias investment toward the offspring sex that confers higher relative fitness on the parents. When variance in reproductive success is higher in males than females, and some males are more attractive to females than others, thereby achieving higher reproductive success, female parents mated to attractive males are expected to bias reproductive allocation toward sons. Modification of the primary sex ratio is one mechanism by which avian parents may bias allocation. In mate choice trials, captive female dark-eyed Juncos (Junco hyemalis) prefer to associate with males whose circulating testosterone level has been elevated experimentally. We asked whether females socially mated to testosterone-treated males in nature might bias the sex ratio of progeny in favor of sons. We determined the primary sex ratio of broods using a sex-linked molecular marker, the CHD gene on the W chromosome. We found no relationship between the hormonal treatment of males and the primary or secondary sex ratios of offspring produced by their social mates. Sex ratio was also unrelated to breeding-season date, study year, male viability, or female age. While unlikely, it is possible that female Juncos are not able to manipulate the primary sex ratio of their broods. More likely, possible benefits to female Juncos of producing attractive sons may be small because (1) attractive males do not necessarily have higher fitness, depending on the trade-offs involved for males, and (2) when such benefits exist, they may be outweighed for females by the costs of compensating for the reduced paternal care of attractive males.
