| peptides for calling? an immunohistochemical study of the avian n. intercollicularis. | we used two phylogenetically distant avian species (dark-eyed junco, hyemalis, passeriformes; domestic pigeon, columba livia, columbiformes) to determine the immunocytochemical distribution of opioid (leucine-enkephalin, dynorphin b) and non-opioid (adrenocorticotropic hormone) peptides in the n. intercollicularis (ico), a midbrain region which plays a central role in the control of vocalizations. we found that, in both species, the peptides under study are present as fibers and terminal-like st ... | 1992 | 1351774 |
| experimental induction of equine protozoal myeloencephalitis in horses using sarcocystis sp. sporocysts from the opossum (didelphis virginiana). | sarcocystis sp. sporocysts isolated from eight feral opossums (didelphis virginiana) were pooled and fed to 18 commercially reared budgerigars (melopsittacus undulatus), 14 wild-caught sparrows (passer domesticus), one wild-caught slate-colored junco (junco hyemalis) and five weanling horses (equus caballus). all budgerigars died within 5 weeks post inoculation (wpi). histologic examination revealed meronts within the pulmonary epithelia and typical sarcocystis falcatula sarcocysts developing in ... | 1997 | 9066066 |
| effects of vasoactive intestinal peptide on plasma prolactin in passerines. | vasoactive intestinal peptide (vip) is a potent releaser of prolactin (prl) in domestic fowl, turkey, and ring doves. however, few comparative studies have investigated this in wild species. we tested the effects of intravenously administered chicken vip on plasma prl concentrations in four passerine species: the white-crowned sparrow (zonotrichia leucophrys gambelii), the dark-eyed junco (junco hyemalis), the florida scrub-jay (aphelocoma coerulescens), and the western scrub-jay (a. californica ... | 1999 | 10068494 |
| egg yolk layers vary in the concentration of steroid hormones in two avian species. | maternally derived steroid hormones are known to be present in the yolks of avian eggs; however, the physiological mechanisms involved in their deposition remain largely unexplored. investigations of steroid production by avian follicles have demonstrated temporal differences in the concentrations of progesterone, 17beta-estradiol, and testosterone during yolk formation. because yolk is deposited peripherally in concentric spheres as the oocyte develops, differences in the production of follicul ... | 1999 | 10417235 |
| changes in brain gonadotropin-releasing hormone- and vasoactive intestinal polypeptide-like immunoreactivity accompanying reestablishment of photosensitivity in male dark-eyed juncos (junco hyemalis). | in seasonally breeding, photoperiodic birds, the development of photorefractoriness is associated with decreased brain expression of gonadotropin-releasing hormone-like immunoreactivity (gnrh-li ir) and increased expression of vasoactive intestinal polypeptide-like immunoreactivity (vip-li ir). dissipation of photorefractoriness and reestablishment of photosensitivity are associated with increased gnrh-li ir brain production, but concurrent changes in vip-li ir expression have not been investiga ... | 2000 | 10620420 |
| effects of testosterone and photoperiodic condition on song production and vocal control region volumes in adult male dark-eyed juncos (junco hyemalis). | in seasonally breeding male oscines, song learning and expression are controlled by brain regions (vocal control regions, vcrs) that exhibit seasonal neural plasticity in adulthood. several vcrs contain androgen receptors, and gonadal androgens play important roles in the control of seasonal structural and functional changes of vcrs. recent studies also found that adult vcrs are influenced by factors other than gonadal hormones, including photoperiod, but the relative importance of these factors ... | 2001 | 11243737 |
| interspecific variability of prevalence in blood parasites of adult passerine birds during the breeding season in alaska. | blood parasite prevalence based on microscopic examination of stained blood smears was determined in adults of 11 passerine bird species sampled during their breeding season (may and june 1997-98) in interior alaska (usa). these species included primarily nearctic migratory species such as the dark-eyed junco (junco hyemalis) and neotropical migratory species such as the blackpoll warbler (dendroica striata), alder flycatcher (empidonax alnorum), swainson's thrush (catharus ustulatus), northern ... | 2001 | 11272501 |
| seasonal and age-related changes in blood parasite prevalence in dark-eyed juncos (junco hyemalis, aves, passeriformes). | 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 i ... | 2001 | 11351333 |
| the roles of birds, lizards, and rodents as hosts for the western black-legged tick ixodes pacificus. | we compared the infestation by ixodid ticks of lizards, rodents, and birds collected simultaneously within areas representing common habitat types in mendocino county, ca. lizards were infested only by ixodes pacificus cooley and kohls, birds by i. pacificus and haemaphysalis leporispalustris (packard), and rodents by i. pacificus, i. spinipalpis hadwen and nuttall, i. woodi bishopp, dermacentor occidentalis marx, and d. variabilis (say). infestation by i. pacificus larvae and nymphs of lizards ... | 2004 | 15709249 |
| arsenic speciation in terrestrial birds from yellowknife, northwest territories, canada: the unexpected finding of arsenobetaine. | the surrounding area of yellowknife, northwest territories, canada, is known for naturally and anthropogenically elevated concentrations of arsenic. five bird species (gray jay [perisoreus canadensis], american tree sparrow [spizella arborea], dark-eyed junco [junco hyemalis], yellow-rumped warbler [dendroica coronata], and spruce grouse [dendragapus canadensis]) were collected from this area. their tissues were analyzed for total arsenic and for arsenic species, allowing us to report, to our kn ... | 2005 | 16117124 |
| dietary phytoestrogens and photoperiodic response in a male songbird, the dark-eyed junco (junco hyemalis). | many commercial bird diets are made with soy products that contain phytoestrogens (i.e., plant compounds that have weak agonist activity at estrogen receptors), but the effects of these compounds on bird physiology and behavior are largely unknown. the primary phytoestrogens present in soy are the isoflavones genistin and diadzin, which have been shown to affect reproductive measures in many taxa. two groups of wild-caught male dark-eyed juncos (junco hyemalis) were fed a diet either made with w ... | 2007 | 17678927 |
| acorn mast drives long-term dynamics of rodent and songbird populations. | 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 relationshi ... | 2007 | 17924149 |
| an investigation of arsenic compounds in fur and feathers using x-ray absorption spectroscopy speciation and imaging. | the accumulation of arsenic in fur and feathers has been used as an indicator of environmental quality and animal health. however, difficulties remain in distinguishing between arsenic present from external sources versus ingestion. in addition, low extraction efficiencies limit the complete characterization of arsenic compounds in such tissues by conventional analytical techniques (e.g. high performance liquid chromatography inductively coupled plasma mass spectrometry, hplc-icp-ms). x-ray abso ... | 2008 | 17988717 |
| west nile virus antibodies in permanent resident and overwintering migrant birds in south-central kansas. | we conducted serological studies, using epitope-blocking elisas directed at west nile virus (wnv) and flavivirus antibodies, of wild birds in south-central kansas, the first for this state, in the winters of 2003-04 through 2005-06. overwintering migratory species (primarily the american tree sparrow and dark-eyed junco) consistently showed significantly lower seropositivity than permanent residents (primarily the northern cardinal). the cardinal showed annual variation in seropositivity between ... | 2008 | 18471059 |
| effects of vinclozolin, an anti-androgen, on affiliative behavior in the dark-eyed junco, junco hyemalis. | endocrine disrupting chemicals (edcs) produce changes in physiology and behavior via diverse mechanisms including acting as hormone mimics or antagonists, affecting intracellular signaling pathways, and altering hormone production pathways. the fungicide vinclozolin acts as an anti-androgen and is known to affect affiliative behaviors in rodents, fish and amphibians. to investigate the possible effects of exposure to edcs on reproductive behavior in a wild population of songbirds, we examined th ... | 2009 | 19261272 |
| a test of comparative equilibration for determining non-exchangeable stable hydrogen isotope values in complex organic materials. | comparative equilibration has been proposed as a methodological approach for determining the hydrogen isotopic composition (deltad) of non-exchangeable hydrogen in complex organic materials, from feathers to blood and soils. this method depends on using homogenized standards that have been previously calibrated for their deltad values of non-exchangeable h, that are compositionally similar to unknown samples, and that span an appropriate isotopic range. currently no certified organic reference m ... | 2009 | 19575406 |
| androgen receptor location in the dark-eyed junco using a probe for in situ hybridization histochemistry generated from zebra finch cdna. | due to the role of sex steroids, namely testosterone (t), in the development and production of song in songbirds, androgen receptor (ar) densities in the brain regions controlling this behavior (i.e., the song control system) have long been studied. many methods have been used to determine ar density and location to investigate the functional role of t in song development and production; however, a riboprobe developed from zebra finch (taeniopygia guttata) cdna was shown to be much more sensitiv ... | 2011 | 21835199 |
| Widespread dispersal of Borrelia burgdorferi-infected ticks collected from songbirds across Canada. | Abstract Millions of Lyme disease vector ticks are dispersed annually by songbirds across Canada, but often overlooked as the source of infection. For clarity on vector distribution, we sampled 481 ticks (12 species and 3 undetermined ticks) from 211 songbirds (42 species/subspecies) nationwide. Using PCR, 52 (29.5%) of 176 Ixodes ticks tested were positive for the Lyme disease spirochete, Borrelia burgdorferi s.l. Immature blacklegged ticks, Ixodes scapularis, collected from infested songbird ... | 2011 | 21864130 |
| avian hosts of ixodes pacificus (acari: ixodidae) and the detection of borrelia burgdorferi in larvae feeding on the oregon junco. | larval and nymphal western blacklegged tick, ixodes pacificus cooley & kohls (acari: ixodidae), were collected from birds, rodents, and lizards at quail ridge reserve located in napa county in northwestern california. species from three vertebrate classes were sampled simultaneously from two transects during two consecutive spring seasons. feeding larval and nymphal ticks were removed and preserved for counting, examination and testing for the presence of borrelia burgdorferi johnson, schmid, hy ... | 2011 | 21845945 |
| use of observed wild bird activity on poultry farms and a literature review to target species as high priority for avian influenza testing in 2 regions of canada. | the risk of avian influenza outbreaks in poultry is partially dependent on the probability of contact between domestic poultry and wild birds shedding avian influenza (ai) virus. the major objective of this study was to document wild bird activity on poultry farms to determine which wild bird species should be targeted for ai surveillance in canada. we collected data in 2 major poultry producing regions of canada, southwestern ontario and the fraser valley of british columbia, on the relative ab ... | 0 | 22851777 |
| de novo transcriptome sequencing in a songbird, the dark-eyed junco (junco hyemalis): genomic tools for an ecological model system. | though genomic-level data are becoming widely available, many of the metazoan species sequenced are laboratory systems whose natural history is not well documented. in contrast, the wide array of species with very well-characterized natural history have, until recently, lacked genomics tools. it is now possible to address significant evolutionary genomics questions by applying high-throughput sequencing to discover the majority of genes for ecologically tractable species, and by subsequently dev ... | 2012 | 22776250 |
| competitive females are successful females; phenotype, mechanism and selection in a common songbird. | in a variety of taxa, male reproductive success is positively related to expression of costly traits such as large body size, ornaments, armaments, and aggression. these traits are thought to improve male competitive ability, and thus access to limited reproductive resources. females of many species also express competitive traits. however, we know very little about the consequences of individual variation in competitive traits and the mechanisms that regulate their expression in females. conseq ... | 0 | 22345899 |
| surveillance for ixodes pacificus and the tick-borne pathogens anaplasma phagocytophilum and borrelia burgdorferi in birds from california's inner coast range. | we investigated the involvement of birds in the ecology of the western black-legged tick, ixodes pacificus, and its associated zoonotic bacteria, borrelia burgdorferi and anaplasma phagocytophilum, at two interior coast-range study sites in northern california. anaplasma phagocytophilum, the agent of granulocytic anaplasmosis (ga), and b. burgdorferi s.s., the agent of lyme disease (ld), are tick-borne pathogens that are well established in california. we screened blood and ticks from 349 indivi ... | 2014 | 24690191 |
| absorption, distribution, and excretion of [14c]-3-chloro-4-methylaniline hydrochloride in two species of birds following a single oral dose. | ring-labeled [14c]-3-chloro-4-methylaniline hydrochloride (250 microg per bird) was delivered to 21 red-winged blackbirds (agelaius phoeniceus) and 21 dark-eyed juncos (junco hyemalis) via oral gavage, and the distribution and excretion of radioactivity were determined at 15 and 30 min and 1, 4, 8, 12, and 24 h (n = 3 per time point). direct measurement of radioactivity as well as measurement following combustion was accomplished using a liquid scintillation counter. elimination from most tissue ... | 2004 | 15612798 |
| new records and new species of mites of the subfamily harpirhynchinae (acariformes: harpirhynchidae) infesting birds in manitoba, canada. | five new species and one new genus of the subfamily harpirhynchinae (acariformes: harpirhynchidae) are described from birds in canada: harpyrhynchoides heatherae sp. nov. from junco hyemalis (passeriformes: emberizidae), h. botaurus sp. nov. from botaurus lentiginosus (pelecaniformes: ardeidae), h. phalaropus sp. nov. from phalaropus lobatus (charadriiformes: scolopacidae), neharpyrhynchus loxia sp. nov. from loxia curvirostra (passeriformes: fringillidae), and fainharpirhynchus contopus gen. no ... | 2013 | 24338301 |
| the distribution of substance p and neuropeptide y in four songbird species: a comparison of food-storing and non-storing birds. | the distributions of the neuropeptides substance p (sp) and neuropeptide y (npy) were investigated in four songbird species that differ in their food-storing behavior. the food-storing black-capped chickadee (parus atricapillus) was compared to the non-storing blue tit (parus caeruleus) and great tit (parus major) within the avian family paridae, as well as to the non-storing dark-eyed junco (junco hyemalis). all four species showed a similar distribution of sp throughout the brain with the exce ... | 2001 | 11684045 |
| avian seed preference and weight loss experiments: the effect of fungal endophyte-infected tall fescue seeds. | the impact of endophytic fungus-infected seeds on seed predators is poorly understood. in this multiple trophic level investigation, seed preference experiments were conducted to determine whether five species of passerines (dark-eyed juncos, junco hyemalis; american tree sparrows, spizella arborea; song sparrows, melospiza melodia; chipping sparrows, spizella pusilla; and house sparrows, passer domesticus) recognize and preferentially consume noninfected (ni) over infected (i) seeds of tall fes ... | 1991 | 28312146 |
| breeding dispersal by birds in a dynamic urban ecosystem. | changes in land cover during urbanization profoundly affect the diversity of bird communities, but the demographic mechanisms affecting diversity are poorly known. we advance such understanding by documenting how urbanization influences breeding dispersal-the annual movement of territorial adults-of six songbird species in the seattle, wa, usa metropolitan area. we color-banded adults and mapped the centers of their annual breeding activities from 2000-2010 to obtain 504 consecutive movements by ... | 2016 | 28030559 |
| chemosignaling diversity in songbirds: chromatographic profiling of preen oil volatiles in different species. | large foraging seabirds are known to navigate to food sources using their excellent sense of smell, but much less is known about the use of olfaction by the songbirds (passerine birds). some evidence of individual recognition based on the bird preen oil volatile organic compound (voc) compositions, which is the main odor source in birds, have been reported for dark-eyed junco and house finch. in this study we have investigated preen oil vocs in 16 different songbird species and two other small b ... | 2013 | 23998336 |
| within-winter flexibility in muscle masses, myostatin, and cellular aerobic metabolic intensity in passerine birds. | metabolic rates of passerine birds are flexible traits that vary both seasonally and among and within winters. seasonal variation in summit metabolic rates (msum = maximum thermoregulatory metabolism) in birds is consistently correlated with changes in pectoralis muscle and heart masses and sometimes with variation in cellular aerobic metabolic intensity, so these traits might also be associated with shorter-term, within-winter variation in metabolic rates. to determine whether these mechanisms ... | 2017 | 28277951 |
| lipid signaling and fat storage in the dark-eyed junco. | seasonal hyperphagia and fattening promote survivorship in migratory and wintering birds, but reduced adiposity may be more advantageous during the breeding season. factors such as photoperiod, temperature, and food predictability are known environmental determinants of fat storage, but the underlying neuroendocrine mechanisms are less clear. endocannabinoids and other lipid signaling molecules regulate multiple aspects of energy balance including appetite and lipid metabolism. however, these fu ... | 2017 | 28161439 |
| seasonal variation in group size is related to seasonal variation in neuropeptide receptor density. | in many species, seasonal variation in grouping behavior is widespread, with shifts towards territoriality in the breeding season and grouping in the winter. compared to the hormonal and neural mechanisms of seasonal territorial aggression, the mechanisms that promote seasonal grouping have received little attention. we collected brains in spring and winter from wild-caught males of two species of emberizid sparrows that seasonally flock (the field sparrow, spizella pusilla, and the dark-eyed ju ... | 2016 | 27788503 |
| effect of acute stressor on reproductive behavior differs between urban and rural birds. | the life-history trade-off between self-maintenance and reproduction posits that investment in one function decreases investment in the other. manipulating the costs and benefits of functions involved in a trade-off may alter this interaction. here we ask whether investment in self-maintenance during a stress response alters territorial behavior in wild dark-eyed juncos and whether rural and urban birds, which are known to differ in the magnitude of the stress response (greater in rural), also d ... | 2016 | 27777728 |
| communication value of mistakes in dark-eyed junco song. | sexual signals contain information on individual quality or motivation, and most explanations for their reliability are based on signal costs. a recent suggestion is that signaling mistakes, defined as deviations from typical signal design, provide cues on individual quality, contributing to reliable communication even when signal design is not costly. we describe several atypical song traits in dark-eyed juncos (junco hyemalis) that may be mistakes during song production or development and occu ... | 2016 | 27501087 |
| shared songs are of lower performance in the dark-eyed junco. | social learning enables the adjustment of behaviour to complex social and ecological tasks, and underlies cultural traditions. understanding when animals use social learning versus other forms of behavioural development can help explain the dynamics of animal culture. the dark-eyed junco (junco hyemalis) is a songbird with weak cultural song traditions because, in addition to learning songs socially, male juncos also invent or improvise novel songs. we compared songs shared by multiple males (i. ... | 2016 | 27493786 |
| early spring sex differences in luteinizing hormone response to gonadotropin releasing hormone in co-occurring resident and migrant dark-eyed juncos (junco hyemalis). | to optimally time reproduction, animals must coordinate changes in the hypothalamo-pituitary-gonadal (hpg) axis. the extent of intra-species variation in seasonal timing of reproductive function is considerable, both within and among populations. dark-eyed junco (junco hyemalis) populations are known to differ in their reproductive timing response to cues experienced in the same habitat in late winter/early spring. specifically in juncos cohabitating on shared wintering grounds, residents initia ... | 2016 | 27374492 |
| gonads and the evolution of hormonal phenotypes. | hormones are dynamic signaling molecules that influence gene activity and phenotype, and they are thus thought to play a central role in phenotypic evolution. in vertebrates, many fitness-related traits are mediated by the hormone testosterone (t), but the mechanisms by which t levels evolve are unclear. here, we summarize a series of studies that advance our understanding of these mechanisms by comparing males from two subspecies of dark-eyed junco (junco hyemalis) that differ in aggression, bo ... | 2016 | 27252189 |
| divergence along the gonadal steroidogenic pathway: implications for hormone-mediated phenotypic evolution. | across a range of taxa, hormones regulate suites of traits that influence survival and reproductive success; however, the mechanisms by which hormone-mediated traits evolve are still unclear. we hypothesized that phenotypic divergence might follow from differential regulation of genes encoding key steps in hormone biosynthesis and thus the rate of hormone production. we tested this hypothesis in relation to the steroid hormone testosterone by comparing two subspecies of junco (junco hyemalis) in ... | 2016 | 27206546 |
| reproductive allochrony in seasonally sympatric populations maintained by differential response to photoperiod: implications for population divergence and response to climate change. | reproductive allochrony presents a potential barrier to gene flow and is common in seasonally sympatric migratory and sedentary birds. mechanisms mediating reproductive allochrony can influence population divergence and the capacity of populations to respond to environmental change. we asked whether reproductive allochrony in seasonally sympatric birds results from a difference in response to supplementary or photoperiodic cues and whether the response varies in relation to the distance separati ... | 2016 | 27028072 |
| differential gene expression in seasonal sympatry: mechanisms involved in diverging life histories. | in an era of climate change, understanding the genetic and physiological mechanisms underlying flexibility in phenology and life history has gained greater importance. these mechanisms can be elucidated by comparing closely related populations that differ in key behavioural and physiological traits such as migration and timing of reproduction. we compared gene expression in two recently diverged dark-eyed junco ( junco hyemalis) subspecies that live in seasonal sympatry during winter and early s ... | 2016 | 26979563 |
| hypothalamic-pituitary-adrenal axis activity is not elevated in a songbird (junco hyemalis) preparing for migration. | during spring, increasing daylengths stimulate gonadal development in migratory birds. however, late-stage reproductive development is typically postponed until migration has been completed. the hypothalamic-pituitary-adrenal (hpa) axis regulates the secretion of glucocorticoids, which have been associated with pre-migratory hyperphagia and fattening. the hpa-axis is also known to suppress the hypothalamic-pituitary-gonadal (hpg) axis, suggesting the possibility that final transition into the br ... | 2016 | 26718082 |
| regulatory mechanisms of metabolic flexibility in the dark-eyed junco (junco hyemalis). | small temperate birds reversibly modify their aerobic performance to maintain thermoregulatory homeostasis under seasonally changing environmental conditions and these physiological adjustments may be attributable to changes in the expression of genes in the underlying regulatory networks. here, we report the results of an experimental procedure designed to gain insight into the fundamental mechanisms of metabolic flexibility in the dark-eyed junco (junco hyemalis). we combined genomic transcrip ... | 2015 | 25617458 |
| hormonal, behavioral, and life-history traits exhibit correlated shifts in relation to population establishment in a novel environment. | climate change, habitat alteration, range expansions, and biological invasions are all predicted to require rapid shifts in multiple traits including behavior and life history, both for initial population establishment and subsequent adaptation. hormonal mechanisms likely play a key role in facilitating or constraining plastic and genetic responses for suites of traits, but few studies have evaluated their role in shaping contemporary adaptation or diversification. we examined multiple phenotypi ... | 2014 | 25438184 |
| behavioral effects of social challenges and genomic mechanisms of social priming: what's testosterone got to do with it? | social challenges from rival conspecifics are common in the lives of animals, and changes in an animal's social environment can influence physiology and behavior in ways that appear to be adaptive in the face of continued social instability (i.e. social priming). recently, it has become clear that testosterone, long thought to be the primary mediator of these effects, may not always change in response to social challenges, an observation that highlights gaps in our understanding of the proximate ... | 2014 | 27721823 |
| mechanistic drivers of flexibility in summit metabolic rates of small birds. | flexible metabolic phenotypes allow animals to adjust physiology to better fit ecological or environmental demands, thereby influencing fitness. summit metabolic rate (msum = maximal thermogenic capacity) is one such flexible trait. skeletal muscle and heart masses and myocyte metabolic intensity are potential drivers of msum flexibility in birds. we examined correlations of skeletal muscle and heart masses and pectoralis muscle citrate synthase (cs) activity (an indicator of cellular metabolic ... | 2014 | 24992186 |
| similarity in temporal variation in sex-biased dispersal over short and long distances in the dark-eyed junco, junco hyemalis. | patterns of sex-biased dispersal (sbd) are typically consistent within taxa, for example female-biased in birds and male-biased in mammals, leading to theories about the evolutionary pressures that lead to sbd. however, generalizations about the evolution of sex biases tend to overlook that dispersal is mediated by ecological factors that vary over time. we examined potential temporal variation in between- and within-population dispersal over an 11-year period in a bird, the dark-eyed junco (jun ... | 2013 | 24730036 |
| highly context-specific activation of the hpg axis in the dark-eyed junco and implications for the challenge hypothesis. | one of the best studied hormone-behavior interactions is the transient rise in testosterone (t) associated with male-male aggression. however, recent research on songbirds has demonstrated numerous exceptions to this pattern.one species previously thought to elevate t in response to a simulated territorial intrusion is the dark-eyed junco (junco hyemalis). here, we show that under most circumstances male juncos do not elevate circulating t or cort levels in response to social stimuli, despite be ... | 2014 | 24698788 |
| relative roles of temperature and photoperiod as drivers of metabolic flexibility in dark-eyed juncos. | seasonal phenotypic flexibility in small birds produces a winter phenotype with elevated maximum cold-induced metabolic rates (=summit metabolism, msum). temperature and photoperiod are candidates for drivers of seasonal phenotypes, but their relative impacts on metabolic variation are unknown. we examined photoperiod and temperature effects on msum, muscle masses and activities of key catabolic enzymes in winter dark-eyed juncos (junco hyemalis). we randomly assigned birds to four treatment gro ... | 2014 | 24622893 |
| is testis variation the key to understanding why males seem so different from one another? commentary on "examining sources of variation in hpg axis function among individuals and populations of the dark-eyed juncos". by christine m. bergeon burns, kimberly a. rosvall thomas p. hahn, gregory e. demas and ellen d. ketterson. | | 2014 | 24239584 |
| costs and benefits of competitive traits in females: aggression, maternal care and reproductive success. | recent research has shown that female expression of competitive traits can be advantageous, providing greater access to limited reproductive resources. in males increased competitive trait expression often comes at a cost, e.g. trading off with parental effort. however, it is currently unclear whether, and to what extent, females also face such tradeoffs, whether the costs associated with that tradeoff overwhelm the potential benefits of resource acquisition, and how environmental factors might ... | 2013 | 24204980 |
| potential for sexual conflict assessed via testosterone-mediated transcriptional changes in liver and muscle of a songbird. | males and females can be highly dimorphic in metabolism and physiology despite sharing nearly identical genomes, and both sexes respond phenotypically to elevated testosterone, a steroid hormone that alters gene expression. only recently has it become possible to learn how a hormone such as testosterone affects global gene expression in non-model systems, and whether it affects the same genes in males and females. to investigate the transcriptional mechanisms by which testosterone exerts its met ... | 2014 | 24198265 |
| proximate perspectives on the evolution of female aggression: good for the gander, good for the goose? | female-female aggression often functions in competition over reproductive or social benefits, but the proximate mechanisms of this apparently adaptive behaviour are not well understood. the sex steroid hormone testosterone (t) and its metabolites are well-established mediators of male-male aggression, and several lines of evidence suggest that t-mediated mechanisms may apply to females as well. however, a key question is whether mechanisms of female aggression primarily reflect correlated evolut ... | 2013 | 24167313 |
| examining sources of variation in hpg axis function among individuals and populations of the dark-eyed junco. | gonadal steroids are important mediators of traits relevant to fitness, and thus may be targets of selection. however, more knowledge is needed about sources of variation along the endocrine axes that may contribute to functional variation in steroid levels. in a controlled captive environment, we studied males of two closely related subspecies of the dark-eyed junco (junco hyemalis) that differ in testosterone-related phenotype, asking whether they also differ in testosterone (t), and assessing ... | 2014 | 24140626 |
| sources of variation in hpg axis reactivity and individually consistent elevation of sex steroids in a female songbird. | understanding sources of individual differences in steroid hormone production has important implications for the evolution of reproductive and social behaviors. in females in particular, little is known about the mechanistic sources of these individual differences, despite established linkages between sex steroids and a variety of fitness-related traits. using captive female dark-eyed juncos (junco hyemalis) from two subspecies, we asked how variation in different components of the hypothalamo-p ... | 2013 | 24090613 |
| individual variation in testosterone and parental care in a female songbird; the dark-eyed junco (junco hyemalis). | when competition for sex-specific resources overlaps in time with offspring production and care, trade-offs can occur. steroid hormones, particularly testosterone (t), play a crucial role in mediating such trade-offs in males, often increasing competitive behaviors while decreasing paternal behavior. recent research has shown that females also face such trade-offs; however, we know little about the role of t in mediating female phenotypes in general, and the role of t in mediating trade-offs in ... | 2013 | 24060498 |
| speciation on oceanic islands: rapid adaptive divergence vs. cryptic speciation in a guadalupe island songbird (aves: junco). | 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 fr ... | 2013 | 23675466 |
| testosterone affects neural gene expression differently in male and female juncos: a role for hormones in mediating sexual dimorphism and conflict. | despite sharing much of their genomes, males and females are often highly dimorphic, reflecting at least in part the resolution of sexual conflict in response to sexually antagonistic selection. sexual dimorphism arises owing to sex differences in gene expression, and steroid hormones are often invoked as a proximate cause of sexual dimorphism. experimental elevation of androgens can modify behavior, physiology, and gene expression, but knowledge of the role of hormones remains incomplete, inclu ... | 2013 | 23613935 |
| experimental elevation of testosterone lowers fitness in female dark-eyed juncos. | testosterone (t) is often referred to as the "male hormone," but it can influence aggression, parental behavior, and immune function in both males and females. by experimentally relating hormone-induced changes in phenotype to fitness, it is possible to ask whether existing phenotypes perform better or worse than alternative phenotypes, and hence to predict how selection might act on a novel or rare phenotype. in a songbird, the dark-eyed junco (junco hyemalis), we have examined the effects of e ... | 2013 | 23523740 |
| neural steroid sensitivity and aggression: comparing individuals of two songbird subspecies. | hormones coordinate the expression of complex phenotypes and thus may play important roles in evolutionary processes. when populations diverge in hormone-mediated phenotypes, differences may arise via changes in circulating hormones, sensitivity to hormones or both. determining the relative importance of signal and sensitivity requires consideration of both inter- and intrapopulation variation in hormone levels, hormone sensitivity and phenotype, but such studies are rare, particularly among clo ... | 2013 | 23517519 |
| boldness behavior and stress physiology in a novel urban environment suggest rapid correlated evolutionary adaptation. | novel or changing environments expose animals to diverse stressors that likely require coordinated hormonal and behavioral adaptations. predicted adaptations to urban environments include attenuated physiological responses to stressors and bolder exploratory behaviors, but few studies to date have evaluated the impact of urban life on codivergence of these hormonal and behavioral traits in natural systems. here, we demonstrate rapid adaptive shifts in both stress physiology and correlated boldne ... | 2012 | 22936840 |
| robust behavioral effects of song playback in the absence of testosterone or corticosterone release. | some species of songbirds elevate testosterone in response to territorial intrusions while others do not. the search for a general explanation for this interspecific variation in hormonal response to social challenges has been impeded by methodological differences among studies. we asked whether song playback alone is sufficient to bring about elevation in testosterone or corticosterone in the dark-eyed junco (junco hyemalis), a species that has previously demonstrated significant testosterone e ... | 2012 | 22850247 |
| to flock or fight: neurochemical signatures of divergent life histories in sparrows. | many bird species exhibit dramatic seasonal switches between territoriality and flocking, but whereas neuroendocrine mechanisms of territorial aggression have been extensively studied, those of seasonal flocking are unknown. we collected brains in spring and winter from male field sparrows (spizella pusilla), which seasonally flock, and male song sparrows (melospiza melodia), which are territorial year-round in much of their range. spring collections were preceded by field-based assessments of a ... | 2012 | 22723363 |
| maintenance of mhc class iib diversity in a recently established songbird population. | we examined variation at mhc class iib genes in a recently established population of dark-eyed juncos (junco hyemalis) in a coastal urban environment in southern california, usa relative to an ancestral-range population from a nearby species-typical montane environment. the founding population is estimated to have been quite small, but we predicted that variation at the major histocompatibility complex (mhc) among the founders would nevertheless be preserved owing to the high functional signific ... | 2012 | 22685370 |
| neural sensitivity to sex steroids predicts individual differences in aggression: implications for behavioural evolution. | testosterone (t) regulates many traits related to fitness, including aggression. however, individual variation in aggressiveness does not always relate to circulating t, suggesting that behavioural variation may be more closely related to neural sensitivity to steroids, though this issue remains unresolved. to assess the relative importance of circulating t and neural steroid sensitivity in predicting behaviour, we measured aggressiveness during staged intrusions in free-living male and female d ... | 2012 | 22673360 |
| intraspecific correlations of basal and maximal metabolic rates in birds and the aerobic capacity model for the evolution of endothermy. | the underlying assumption of the aerobic capacity model for the evolution of endothermy is that basal (bmr) and maximal aerobic metabolic rates are phenotypically linked. however, because bmr is largely a function of central organs whereas maximal metabolic output is largely a function of skeletal muscles, the mechanistic underpinnings for their linkage are not obvious. interspecific studies in birds generally support a phenotypic correlation between bmr and maximal metabolic output. if the aero ... | 2012 | 22479584 |
| role of testosterone in stimulating seasonal changes in a potential avian chemosignal. | songbird preen oil contains volatile and semivolatile compounds that may contain information about species, sex, individual identity, and season. we examined the relationship between testosterone (t) and the amounts of preen oil volatile and semivolatile compounds in wild and captive dark-eyed juncos (junco hyemalis). in wild males and females, we observed an increase in volatile compound relative concentration early in the breeding season. this increase mirrored previously described seasonal el ... | 2011 | 22173888 |
| two sides of the same coin? consistency in aggression to conspecifics and predators in a female songbird. | different forms of aggression have traditionally been treated separately according to function or context (e.g. aggression towards a conspecific versus a predator). however, recent work on individual consistency in behavior predicts that different forms of aggression may be correlated across contexts, suggesting a lack of independence. for nesting birds, aggression towards both conspecifics and nest predators can affect reproductive success, yet the relationship between these behaviors, especial ... | 2011 | 21927524 |
| promiscuous mating produces offspring with higher lifetime fitness. | in many species, each female pairs with a single male for the purpose of rearing offspring, but may also engage in extra-pair copulations. despite the prevalence of such promiscuity, whether and how multiple mating benefits females remains an open question. multiple mating is typically thought to be favoured primarily through indirect benefits (i.e. heritable effects on the fitness of offspring). this prediction has been repeatedly tested in a variety of species, but the evidence has been equivo ... | 2012 | 21881136 |
| early elevation of testosterone advances migratory preparation in a songbird. | the timing of events associated with spring migration can be an important determinant of fitness for migratory birds. the need to prepare and maintain physical condition for migration is one demand that must be met for early arrival on breeding areas, and this demand is compounded by the energetic demands of the physiological transition to breeding. here, we examined whether migratory birds, specifically males, can adequately meet both of these demands by elevating the sex steroid testosterone e ... | 2011 | 21795574 |
| the effect of winter sex ratio on immune function and condition in a differential migrant. | the dark-eyed junco (junco h. hyemalis) is a differential migrant in which females migrate farther south in winter than males. hypotheses to explain this difference in migratory behavior have given limited consideration to physiological differences between the sexes, particularly with respect to immune function. we hypothesized that female migratory behavior could either be directly dependent on climate if migratory distance traveled is a product of interactions between climate and inherent sex ... | 2011 | 21134388 |
| effects of nutritional condition on spring migration: do migrants use resource availability to keep pace with a changing world? | because of their reliance on temporally predictable resources across large spatial scales, migratory birds may be especially vulnerable to anthropogenic climate and land-use changes. although some long-distance migrants appear unable to adjust to phenological shifts on their wintering grounds, several short- and medium-distance migrants appear to have altered the timing and/or distance of their yearly movements to compensate for the environmental effects of global warming. which environmental cu ... | 2010 | 20581272 |
| opioid receptor densities analyzed across seasons in the pom and vta of the dark-eyed junco, junco hyemalis. | the motivation of songbirds to sing is influenced by two brain regions, the medial preoptic area (pom) and ventral tegmental area (vta), which are located outside the song control system itself. these areas receive opioidergic innervation. furthermore, the opioid enkephalin has been proposed to play a role in the reward for singing. in order to determine whether seasonal changes in song output relate to seasonal changes in opioid receptor (or) densities in the pom and vta, we measured the densit ... | 2010 | 20471470 |
| songbird chemosignals: volatile compounds in preen gland secretions vary among individuals, sexes, and populations. | chemical signaling has been documented in many animals, but its potential importance in avian species, particularly songbirds, has received far less attention. we tested whether volatile compounds in the preen oil of a songbird (junco hyemalis) contain reliable information about individual identity, sex, or population of origin by repeated sampling from captive male and female juncos originating from 2 recently diverged junco populations in southern california. one of the populations recently co ... | 2010 | 22475692 |
| natural selection on testosterone production in a wild songbird population. | because of their role in mediating life-history trade-offs, hormones are expected to be strongly associated with components of fitness; however, few studies have examined how natural selection acts on hormonal variation in the wild. in a songbird, the dark-eyed junco (junco hyemalis), field experiments have shown that exogenous testosterone alters individuals' resolution of the survival-reproduction trade-off, enhancing reproduction at the expense of survival. here we used standardized injection ... | 2010 | 20394524 |
| combining selective episodes to estimate lifetime nonlinear selection. | studies measuring natural selection acting via different components of fitness may provide insight into such central questions in evolutionary biology as the evolution of life histories and sexual dimorphism. it is often desirable to combine estimates of selection at different episodes to understand how they interact to produce total lifetime selection. when selective episodes are sequential, total directional selection may be calculated by summing directional selection across episodes. however, ... | 2010 | 19958384 |
| species-specific injury-induced cell proliferation in the hippocampus and subventricular zone of food-storing and nonstoring wild birds. | cells are continuously born and incorporated into the adult hippocampus (hp). adult neurogenesis might act to increase the total number of cells or replace dead cells. thus, neurogenesis might be a primary factor in augmenting, maintaining, or even recovering functions. in zebra finches, hp injury increases cell proliferation in the hp and stem cell rich subventricular zone (svz). it is unknown what effect injury has on a species dependent upon the hp for survival in the wild. in food-storing bi ... | 2010 | 19885828 |
| phenotypic integration and independence: hormones, performance, and response to environmental change. | hormones coordinate the co-expression of behavioral, physiological, and morphological traits, giving rise to correlations among traits and organisms whose parts work well together. this article considers the implications of these hormonal correlations with respect to the evolution of hormone-mediated traits. such traits can evolve owing to changes in hormone secretion, hormonal affinity for carrier proteins, rates of degradation and conversion, and interaction with target tissues to name a few. ... | 2009 | 21665827 |
| high and low, fast or slow: the complementary contributions of altitude and latitude to understand life-history variation. | dark-eyed juncos (junco hyemalis) from two elevations in the rocky mountains of canada display different life histories. birds breeding at high elevation face a later and compressed reproductive season during which they raise on average half the number of broods (young) than their low-elevation conspecifics. fledglings at high elevation are heavier, fatter, and have an increased chance of surviving to 25 days of age. likewise, survival of adults (males) increases at higher elevation. put into a ... | 2009 | 19302124 |
| breeding in high-elevation habitat results in shift to slower life-history strategy within a single species. | 1. elevational gradients create environmental variation that is hypothesized to promote variation in life-history strategies. we tested whether differences in life-history strategies were associated with elevation in a songbird, the dark-eyed junco (junco hyemalis; aves; a.o.u. 1998). 2. we monitored birds in four replicated sites per elevation, at 2000 m a.s.l. (high elevation) and 1000 m a.s.l. (low elevation), in the rocky mountains of canada. 3. over 5 years, we measured the following traits ... | 2009 | 19007385 |
| steroid hormones and immune function: experimental studies in wild and captive dark-eyed juncos (junco hyemalis). | monogamous and polygynous male songbirds generally differ in their breeding season profiles of circulating testosterone. testosterone level spikes early in the breeding season of monogamists and then declines, but it remains high in polygynists. male dark-eyed juncos (junco hyemalis) are socially monogamous and exhibit the usual pattern, but experimental maintenance of high testosterone throughout the breeding season alters normal behavior and physiology and affects various components of annual ... | 2001 | 18707250 |
| experimentally-elevated testosterone, female parental care, and reproductive success in a songbird, the dark-eyed junco (junco hyemalis). | in male dark-eyed juncos (junco hyemalis), experimentally elevated testosterone (t) decreases male parental care and offspring survival, but results in higher overall fitness through greater mating success. to help address the ensuing question of what prevents selection from favoring higher levels of t in male juncos, we manipulated t in female juncos. a previous study demonstrated no effect of experimentally elevated t on female incubation behavior, suggesting that female parental behavior migh ... | 2008 | 18585386 |
| phenotypic plasticity and the evolution of a socially selected trait following colonization of a novel environment. | novel selection pressures in new environments arise through two distinct processes. first, environmental conditions directly affect the fitness of different phenotypes. second, phenotypic plasticity alters the distribution of phenotypes, thereby placing populations in new selective regimes. a small isolated population of dark-eyed juncos junco hyemalis became established in san diego, probably in the early 1980s and probably from the nearby mountains. the relatively mild coastal climate has resu ... | 2008 | 18554144 |
| phylogeny and classification of the old world emberizini (aves, passeriformes). | the phylogeny of the avian genus emberiza and the monotypic genera latoucheornis, melophus and miliaria (collectively the old world emberizini), as well as representatives for the new world emberizini, the circumpolar genera calcarius and plectrophenax and the four other generally recognized tribes in the subfamily emberizinae was estimated based on the mitochondrial cytochrome b gene and introns 6-7 of the nuclear ornithine decarboxylase (odc) gene. our results support monophyly of the old worl ... | 2008 | 18411062 |
| natural variation in a testosterone-mediated trade-off between mating effort and parental effort. | male birds frequently face a trade-off between acquiring mates and caring for offspring. hormone manipulation studies indicate that testosterone often mediates this trade-off, increasing mating effort while decreasing parental effort. little is known, however, about individual covariation between testosterone and relevant behavior on which selection might act. using wild, male dark-eyed juncos (junco hyemalis), we measured individual variation in testosterone levels before and after standardized ... | 2007 | 18171169 |
| circulating prolactin and corticosterone concentrations during the development of migratory condition in the dark-eyed junco, junco hyemalis. | endogenous plasma prolactin and baseline corticosterone concentrations were measured in dark-eyed juncos (junco hyemalis, n=27) photostimulated into migratory condition to look at how these hormones may be linked to the development of migratory condition. in addition to the commonly used assay for corticosterone, a recombinant-derived european starling prolactin assay validated for dark-eyed juncos was used to measure endogenous prolactin in order to detect small but significant changes in plasm ... | 2008 | 18164708 |
| hormone-mediated suites as adaptations and evolutionary constraints. | hormones mediate the expression of suites of correlated traits and hence may act both to facilitate and constrain adaptive evolution. selection on one trait within a hormone-mediated suite may, for example, lead to a change in the strength of the hormone signal, causing either beneficial or detrimental changes in correlated traits. theory and empirical methods for studying correlated trait evolution have been developed by the field of evolutionary quantitative genetics, and here we suggest that ... | 2008 | 18048296 |
| hormones and honest signals: males with larger ornaments elevate testosterone more when challenged. | when male investment in mating varies with quality, reliable sexual signals may evolve. in many songbirds, testosterone mediates mating investment, suggesting that signals should be linked to testosterone production. however, because testosterone may change rapidly during behaviour such as territorial aggression and courtship, efforts to establish such a relationship have proved challenging. in a population of dark-eyed juncos, we measured individual variation in the production of short-term tes ... | 2008 | 18034801 |
| mountain chickadees discriminate between potential cache pilferers and non-pilferers. | evolution of complex cognition in animals has been linked to complex social behaviour. one of the costs of sociality is increased competition for food which may be reduced by food caching, but cache theft may undermine the benefits of caching. in birds, sophisticated food-caching-related cognition has been demonstrated only for corvids and attributed to their highly social behaviour. many non-corvid food-caching species exhibit similar complex social behaviour and here i provide experimental evi ... | 2008 | 17939981 |
| recent postglacial range expansion drives the rapid diversification of a songbird lineage in the genus junco. | 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 fol ... | 2007 | 17725978 |
| the role of corticosterone in supporting migratory lipogenesis in the dark-eyed junco, junco hyemalis: a model for central and peripheral regulation. | the functional role of corticosterone (cort) in regulating migratory hyperphagia and lipogenesis was investigated in an annual migrant, the dark-eyed junco (junco hyemalis). intraperitoneal injections of either dexamethasone (9 microg dxm/500 microl of 5% etoh in saline, n=10) to inhibit an increase in baseline cort or saline (5% etoh, n=9) were given every 48 h for 15 d after transfer from short (10.5l:13.5d) to long (15.5l:8.5d) days. food intake, body mass, furcular fat deposition scores, and ... | 2013 | 17160885 |
| seasonal variation in volatile compound profiles of preen gland secretions of the dark-eyed junco (junco hyemalis). | quantitative stir bar sorptive extraction methodology, followed by gas chromatography-mass spectrometry (gc-ms) and element-specific atomic emission detection (aed) were utilized to analyze seasonal changes in volatile components of preen oil secretions in junco hyemalis. juncos were held in long days to simulate breeding conditions, or short days to simulate nonbreeding conditions. linear alcohols (c(10)-c(18)) were the major volatile compounds found in preen oil, and in both sexes their levels ... | 2007 | 17146717 |
| the relationship of plasma indicators of lipid metabolism and muscle damage to overnight temperature in winter-acclimatized small birds. | plasma glycerol and triglyceride levels and creatine kinase (ck) activity may increase during long-distance flights in migratory birds, but plasma profiles of these metabolites have not previously been reported for small birds during thermoregulation in cold climates. we measured early morning levels of plasma glycerol, triglycerides and ck activity in four species of small birds overwintering in south dakota, junco hyemalis, spizella arborea, passer domesticus, and carduelis tristis. we hypothe ... | 2007 | 17049895 |
| seasonal and individual variation in response to gnrh challenge in male dark-eyed juncos (junco hyemalis). | 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 w ... | 2006 | 16814785 |
| behavioral and physiological responses to experimentally elevated testosterone in female dark-eyed juncos (junco hyemalis carolinensis). | 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 th ... | 2006 | 16678179 |
| physiological effects on demography: a long-term experimental study of testosterone's effects on fitness. | understanding physiological and behavioral mechanisms underlying the diversity of observed life-history strategies is challenging because of difficulties in obtaining long-term measures of fitness and in relating fitness to these mechanisms. we evaluated effects of experimentally elevated testosterone on male fitness in a population of dark-eyed juncos studied over nine breeding seasons using a demographic modeling approach. elevated levels of testosterone decreased survival rates but increased ... | 2006 | 16671011 |
| hypothalamic gnrh-i and its precursor during photorefractoriness onset in free-living male dark-eyed juncos (junco hyemalis) of different year classes. | 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 th ... | 2006 | 16277984 |
| females competing to reproduce: dominance matters but testosterone may not. | the associations among aggression, testosterone (t), and reproductive success have been well studied, particularly in male birds. in many species, males challenged with simulated or real territorial intrusions increase t and levels of aggression, outcomes linked to higher dominance status and greater reproductive success. for females, the patterns are less clear. females behave aggressively towards one another, and in some species, females respond to a social challenge with increases in t, but i ... | 2006 | 16226754 |
| testosterone in females: mediator of adaptive traits, constraint on sexual dimorphism, or both? | when selection on males and females differs, the sexes may diverge in phenotype. hormones serve as a proximate regulator of sex differences by mediating sex-biased trait expression. to integrate these perspectives, we consider how suites of traits mediated by the same hormone in both sexes might respond to selection. in male birds, plasma testosterone (t) varies seasonally and among species according to mating system. when elevated experimentally, it is known to enhance some components of fitnes ... | 2005 | 16224714 |
| correlational selection leads to genetic integration of body size and an attractive plumage trait in dark-eyed juncos. | when a trait's effect on fitness depends on its interaction with other traits, the resultant selection is correlational and may lead to the integration of functionally related traits. in relation to sexual selection, when an ornamental trait interacts with phenotypic quality to determine mating success, correlational sexual selection should generate genetic correlations between the ornament and quality, leading to the evolution of honest signals. despite its potential importance in the evolution ... | 2005 | 15856707 |
| age-related difference in size of brain regions for song learning in adult male dark-eyed juncos (junco hyemalis). | in seasonally breeding adult male songbirds, the volumes of several song control regions (scrs) change seasonally in parallel with plasma testosterone (t) levels and decrease following gonadectomy. testosterone treatment to castrates prevents this decrease, indicating t dependency. during the breeding season, second-year (sy: birds entering their first breeding season) free-ranging male dark-eyed juncos (junco hyemalis) have smaller testes than older (after second-year, asy: birds entering at le ... | 2005 | 15761218 |