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At least 775 records · Page 43Linked to original sources
PubMed2005

Corticosterone inhibits feather growth: potential mechanism explaining seasonal down regulation of corticosterone during molt.

Corticosterone (CORT) is seasonally modulated in many passerines, with plasma CORT concentrations lowest during the prebasic molt when all feathers are replaced. To explain why, we proposed that the birds downregulate natural CORT release during molt in order to avoid CORT's degradative effects on proteins and its inhibition of protein synthesis. If CORT exerted these effects during molt, it could slow protein deposition during feather production and potentially result in a longer period of degraded flight performance. To test this hypothesis, either empty or CORT-filled silastic implants were inserted into captive European starlings (Sturnus vulgaris) and white-crowned sparrows (Zonotrichia leucophrys) undergoing induced (feather replacement after plucking) and natural molts. We then measured the rate of feather re-growth by regularly measuring the length of primary, secondary, and tail feathers. CORT implanted birds showed a significantly decreased rate of feather growth compared to control animals. Basal CORT concentrations of induced molt and non-molting birds were also compared but no difference was noted. The results suggest a tradeoff; a complete set of new feathers may be more important to the survival of a bird than the ability of CORT to respond maximally to a stressor.

Animals↗
PubMed2005

Sexual selection: the importance of long-term fitness measures.

New results from a 20-year study of free-living song sparrows confirm that attractive males contribute more offspring than less attractive males. They also reveal that the offspring of preferred males produce more descendents themselves. Females prefer males with a large song repertoire, which further work shows is a condition-dependent indicator of male quality.

Animals↗
PubMed2005

Animal navigation: northern exposure.

A recent study has found that sparrows moved gradually east above the Arctic Circle completely altered their migration strategy after encountering the massive natural change in declination near the magnetic pole. This should not happen--or should it?

Animal Migration↗
PubMed2006

Inbreeding: when parents transmit more than genes.

Inbreeding in wild populations can have devastating effects on fitness, but the genetic causes should not be transmitted across generations. A new study of song sparrows has revealed a parent-offspring resemblance for inbreeding, resulting from population structuring, with important implications for understanding the genetic causes of phenotypic variation in wild populations.

Animals↗
PubMed2005

Exposure of garden birds to aflatoxins in Britain.

Aflatoxins are potent biological toxins that have been shown to exert a range of acute and chronic pathological effects. Multiple mortality events of waterfowl caused by acute aflatoxicosis have been documented in the USA. However, international concern has recently been expressed regarding the potential effects of chronic exposure of wildlife species to low levels of dietary aflatoxin. This study documents for the first time the presence of hepatic aflatoxin residues in British wild birds: two passerine species, the house sparrow (Passer domesticus) and greenfinch (Carduelis chloris). Further research is required to investigate the source of the dietary aflatoxins and their pathological significance, if any, for wild birds in Britain.

Aflatoxins↗
PubMed2006

Rapid inhibition of female sexual behavior by gonadotropin-inhibitory hormone (GnIH).

Gonadotropin-releasing hormone (GnRH) is largely responsible for the initiation of sexual behaviors; one form of GnRH activates a physiological cascade causing gonadal growth and gonadal steroid feedback to the brain, and another form is thought to act as a neurotransmitter to enhance sexual receptivity. In contrast to GnRH, gonadotropin-inhibitory hormone (GnIH) inhibits gonadotropin release. The distribution of GnIH in the avian brain suggests that it has not only hypophysiotropic actions but also unknown behavioral actions. GnIH fibers are present in the median eminence (ME) and are in apparent contact with chicken GnRH (cGnRH)-I and -II neurons and fibers. In birds, cGnRH-I regulates pituitary gonadotropin release, whereas cGnRH-II enhances copulation solicitation in estradiol-primed females exposed to male song. In the present study, we determined the effects of GnIH administered centrally to female white-crowned sparrows. A physiological dose of GnIH reduced circulating LH and inhibited copulation solicitation, without affecting locomotor activity. Using rhodaminated GnIH, putative GnIH binding sites were seen in the ME close to GnRH-I fiber terminals and in the midbrain on or close to GnRH-II neurons. These data demonstrate direct effects of GnIH upon reproductive physiology and behavior, possibly via separate actions on two forms of GnRH.

Animals↗
PubMed1989

The distribution of heavy-chain isoforms of myosin in airways smooth muscle from adult and neonate humans.

Changes in the expression of heavy chains of myosin during development determine the functional characteristics of striated muscles. The distribution of heavy-chain isoforms of smooth-muscle myosin was determined in the airways of adult and infant humans to see whether it might underlie the hyperreactivity of human airways. The protein bands corresponding to myosin were separated using SDS/polyacrylamide-gel electrophoresis (4% gels) and identified by immunoblotting using both monoclonal and polyclonal antibodies against smooth-muscle myosin and non-muscle myosin. The relative proportion of each heavy chain stained by Coomassie Blue was measured by densitometric scanning. Three major bands corresponding to myosin heavy-chain isoforms were found; the two slower migrating bands (MHC1 and MHC2) were smooth-muscle myosin, and the third band was non-muscle myosin. The MHC1/MHC2 ratio was 0.69:1 in adult bronchus, and in infant bronchus and trachea. This contrasted with the airway smooth muscle in pigs, which was run concurrently, where the smooth-muscle heavy-chain ratio changed with development [Mohammad & Sparrow (1988) FEBS Lett. 228, 109-112]. The non-muscle myosin heavy chain comprised 63% of the smooth-muscle myosin. In both adult and infant lungs an additional putative myosin heavy chain which migrated slightly more rapidly than non-muscle myosin heavy chain was identified using the monoclonal smooth-muscle myosin antibody BF 48. This was unique to the human species.

Aged↗
PubMed1992

Type II intermediate-filament proteins from wool. The amino acid sequence of component 5 and comparison with component 7c.

Component 5 is one of the four type II intermediate-filament proteins found in the hard keratin wool. It was isolated as the S-carboxymethyl derivative from Merino wool and its amino acid sequence was determined by manual and automatic sequencing of peptides produced by chemical and enzymic cleavage. Component 5 is an N-terminally blocked molecule of 503 residues and Mr (not including the blocking group) of 56,600. The blocking group has not been identified. The amino acid sequence of component 5 shows 77% sequence identity with that of component 7c, another type II wool intermediate-filament protein [Sparrow, Robinson, McMahon & Rubira (1989) Biochem. J. 261, 1015-1022]. The sequence similarity extends from the N-termini of the two molecules to residue 459 (component 5 sequence); however, there is no recognizable sequence similarity in the remaining C-terminal 43 amino acid residues. Details of procedures used in determining the sequence of component 5 have been deposited as a Supplementary Publication SUP 50168 (80 pages) at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire, LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1992) 281, 5. The information comprises: (1) details of chemical and enzymic methods used for cleavage of component 5, peptide CN1, the peptide mixture CN2/3 and various other peptides, (2) details of the procedures used for the fractionation and purification of peptides from (1), including Figures showing the elution profiles from the chromatographic steps used, and (3) details of the method used to determine the C-terminal sequence of component 5.

Amino Acid Sequence↗
PubMed2005

Variable rate of singing and variable song duration are associated with high immediate early gene expression in two anterior forebrain song nuclei.

The duration of songs and the intervals between these songs are more variable when wild, adult, free-ranging chipping sparrows sing at dawn than when they sing during the day. The more variable delivery is used to interact with males, and the stereotyped delivery is used to attract females. In captive birds, however, the variability observed at dawn persists during the day. We quantified the expression of an immediate early gene, ZENK, in wild and captive birds and found that the level of song-associated ZENK expression in two song nuclei, Area X and lMAN, was positively related to variability in song duration and intersong interval and could be dissociated from the social context in which the song occurred. Thus, a combination of field and laboratory approaches helped us identify nuclei, context, and behavioral features associated with a change in gene expression thought to be a marker of behavioral variability.

Analysis of Variance↗
PubMed2004

New proposals for training in neurosurgery.

The rapidly evolving changes in working patterns, career structure and the regulation of training of doctors have provided an ideal opportunity for proposals to improve the programme for the training of neurosurgeons. The Education and Training Committee of the Society of British Neurological Surgeons (D.G. Hardy, A. J. W. Steers, N. T. Gurusinghe, P. M. Foy, P. van Hille, R. A. Cowie, H. A. Crockard, O. Sparrow and S. Burn) has, in recent months, worked closely with the Specialist Advisory Committee (SAC) in neurosurgery, Department of Health (Modernizing Medical Careers Group, H. A. Crockard, A. Havers, T. Hobbs) and colleagues from the major neuroscience specialties to develop a new programme based on a 'Common Stem' approach. This article describes the principles of the programme. The proposals have received approval by the Council of the SBNS, the Presidents of the four Surgical Royal Colleges and the Senate of Surgery.

Curriculum↗
PubMed2004

Linking optimal foraging behavior to bird community structure in an urban-desert landscape: field experiments with artificial food patches.

Urban bird communities exhibit high population densities and low species diversity, yet mechanisms behind these patterns remain largely untested. We present results from experimental studies of behavioral mechanisms underlying these patterns and provide a test of foraging theory applied to urban bird communities. We measured foraging decisions at artificial food patches to assess how urban habitats differ from wildlands in predation risk, missed-opportunity cost, competition, and metabolic cost. By manipulating seed trays, we compared leftover seed (giving-up density) in urban and desert habitats in Arizona. Deserts exhibited higher predation risk than urban habitats. Only desert birds quit patches earlier when increasing the missed-opportunity cost. House finches and house sparrows coexist by trading off travel cost against foraging efficiency. In exclusion experiments, urban doves were more efficient foragers than passerines. Providing water decreased digestive costs only in the desert. At the population level, reduced predation and higher resource abundance drive the increased densities in cities. At the community level, the decline in diversity may involve exclusion of native species by highly efficient urban specialists. Competitive interactions play significant roles in structuring urban bird communities. Our results indicate the importance and potential of mechanistic approaches for future urban bird community studies.

Animals↗
PubMed2006

Plasma metabolite profiles: effects of dietary phospholipids in a migratory passerine (Zonotrichia leucophrys gambelii).

Plasma metabolites, including triglycerides, beta -hydroxybutyrate, and glycerol, can be used to estimate mass change in birds. Although dietary fatty acids can be ingested and absorbed as phospholipids, they have been largely overlooked as a potential indicator of mass change. The plasma ratio of triglyceride to phospholipid could also provide insight into diet quality because a high ratio in food items indicates high relative energy content. Variability in dietary phospholipid content and triglyceride : phospholipid may also affect the relationships between metabolites and mass change. We fed Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) diets differing in phospholipid content and triglyceride : phospholipid and measured metabolites during mass loss and mass gain. Plasma phospholipids were higher and triglyceride : phospholipid was lower in birds fed a diet higher in phospholipid content and lower in triglyceride : phospholipid. Contrary to our expectations, plasma phospholipids were negatively related to mass change. Plasma triglyceride levels were positively related to mass change and unaffected by diet. The relationships between mass change and both plasma beta -hydroxybutyrate and glycerol were affected by diet. Plasma triglyceride appears to be the most reliable metabolite predicting body mass changes, but inclusion of plasma phospholipids and triglyceride : phospholipid into metabolite profiles may provide additional information on diet quality.

Animal Migration↗
PubMed2005

Parasite-mediated heterozygote advantage in an outbred songbird population.

Coevolution with parasites is thought to maintain genetic diversity in host populations. However, while there are sound theoretical reasons to expect heterozygosity and parasite resistance to be related, this pattern has generally been shown only in inbred laboratory and island populations. This leaves doubt as to whether parasite-mediated selection for genetic diversity is in fact a general process. Here we show that haematozoan parasite load is linked to two complementary measures of microsatellite variability in an outbred population of mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) for which we know that parasites reduce fitness. Moreover, each of the genetic measures predicts a subtly different aspect of parasitism. Microsatellite heterozygosity is related to an individual's risk of parasitism, and mean d2 (a broader, more long-term measure of parental relatedness) to the severity of infection among parasitized individuals.

Animals↗
PubMed2004

Balancing food and predator pressure induces chronic stress in songbirds.

The never-ending tension between finding food and avoiding predators may be the most universal natural stressor wild animals experience. The 'chronic stress' hypothesis predicts: (i) an animal's stress profile will be a simultaneous function of food and predator pressures given the aforesaid tension; and (ii) these inseparable effects on physiology will produce inseparable effects on demography because of the resulting adverse health effects. This hypothesis was originally proposed to explain synergistic (inseparable) food and predator effects on demography in snowshoe hares (Lepus americanus). We conducted a 2 x 2, manipulative food addition plus natural predator reduction experiment on song sparrows (Melospiza melodia) that was, to our knowledge, the first to demonstrate comparable synergistic effects in a bird: added food and lower predator pressure in combination produced an increase in annual reproductive success almost double that expected from an additive model. Here we report the predicted simultaneous food and predator effects on measures of chronic stress in the context of the same experiment: birds at unfed, high predator pressure (HPP) sites had the highest stress levels; those at either unfed or HPP sites showed intermediate levels; and fed birds at low predator pressure sites had the lowest stress levels.

Analysis of Variance↗
PubMed2006

Complex Mhc-based mate choice in a wild passerine.

The extreme polymorphism of the vertebrate major histocompatibility complex (Mhc) is famous for protecting hosts against constantly evolving pathogens. Mate choice is often evoked as a means of maintaining Mhc variability through avoidance of partners with similar Mhc alleles or preference for heterozygotes. Evidence for these two hypotheses mostly comes from studies on humans and laboratory mice. Here, we tested these hypotheses in a wild outbred population of house sparrows (Passer domesticus). Females were not more or less closely related to the males they paired with when considering neutral genetic variation. However, males failed to form breeding pairs when they had too few Mhc alleles and when they were too dissimilar from females at Mhc loci (i.e. had no common alleles). Furthermore, pairs did not form at random as Mhc diversity positively correlated in mating pairs. These results suggest that mate choice evolves in response to (i) benefits in terms of parasite resistance acquired from allelic diversity, and (ii) costs associated with the disruption of co-adapted genes.

Animals↗
PubMed2004

Habitat selection, acoustic adaptation, and the evolution of reproductive isolation.

We examined barriers to gene flow in a hybrid zone of two subspecies of the song sparrow (Melospiza melodia). We focused on how mating signals and mate choice changed along an environmental gradient and gathered data on the morphology, genetics, ecology, and behavior across the zone. Melospiza m. heermanni of the Pacific slope of California and M. m. fallax of the Sonoran Desert, each distinct in plumage, meet across a steep environmental gradient in southeastern California. Although both subspecies occur in riparian habitat, their occupied habitat differs structurally, the former subspecies occurring in areas with denser understory and greater vertical heterogeneity. Song elements varied concomitantly, as predicted by the acoustic adaptation hypothesis, with heermanni having lower-pitched, more widely spaced elements. Females of both subspecies responded more strongly to homotypic than heterotypic song, and addition of subspecific plumage cues increased response if song was homotypic but not if heterotypic. Females thus assess multiple male traits, weighing song more heavily. Males of both subspecies showed significantly greater agonistic response to homotypic song. Microsatellite variation is correlated significantly with plumage variation across the zone and suggests limited gene flow between the taxa. The association of song and plumage with the environment and in turn with assortative mating suggests a means by which reproductive isolation may evolve or be maintained in hybrid zones.

Adaptation, Physiological↗
PubMed2006

Interactive effects of environmental stress and inbreeding on reproductive traits in a wild bird population.

1. Conservation biologists are concerned about the interactive effects of environmental stress and inbreeding because such interactions could affect the dynamics and extinction risk of small and isolated populations, but few studies have tested for these interactions in nature. 2. We used data from the long-term population study of song sparrows Melospiza melodia on Mandarte Island to examine the joint effects of inbreeding and environmental stress on four fitness traits that are known to be affected by the inbreeding level of adult birds: hatching success, laying date, male mating success and fledgling survival. 3. We found that inbreeding depression interacted with environmental stress to reduce hatching success in the nests of inbred females during periods of rain. 4. For laying date, we found equivocal support for an interaction between parental inbreeding and environmental stress. In this case, however, inbred females experienced less inbreeding depression in more stressful, cooler years. 5. For two other traits, we found no evidence that the strength of inbreeding depression varied with environmental stress. First, mated males fathered fewer nests per season if inbred or if the ratio of males to females in the population was high, but inbreeding depression did not depend on sex ratio. Second, fledglings survived poorly during rainy periods and if their father was inbred, but the effects of paternal inbreeding and rain did not interact. 6. Thus, even for a single species, interactions between the inbreeding level and environmental stress may not occur in all traits affected by inbreeding depression, and interactions that do occur will not always act synergistically to further decrease fitness.

Animals↗
PubMed2006

Estrogen-dependent selectivity of genomic responses to birdsong.

Behavioral responses to sociosexual signals often depend on gonadal steroid hormones, which are thought to modulate behavior by acting on motivational systems in the brain. There is mounting evidence that sex steroids may also modulate perception of sociosexual signals by affecting sensory processing. In seasonally breeding songbirds such as the white-throated sparrow (Zonotrichia albicollis), the female's behavioral response to hearing male song depends on her plasma levels of estradiol (E2). Here, we examined whether plasma E2 also affects the selectivity of the song-induced zenk (egr-1) response in the auditory forebrain, which is known to vary according to the behavioral relevance of song stimuli. Non-breeding females were held on a winter-like photoperiod and implanted with silastic capsules containing either no hormone or E2. E2-treated birds hearing 42 min of conspecific song had more cells immunoreactive for the protein product of zenk in the auditory forebrain than did those hearing frequency-matched synthetic tones. In birds not treated with E2, however, the zenk response to song did not differ from that to tones. We found similar effects in the avian homolog of the inferior colliculus, indicating that E2 may affect the processing of auditory information upstream of the forebrain. Our data suggest that in females, zenk induction in the auditory system is selective for song only when plasma E2 exceeds non-breeding levels. E2-dependent plasticity of auditory pathways and processing centres may promote recognition of and attention to conspecific song during the breeding season.

Acoustic Stimulation↗