Do Avian Mitochondria Recombine?

The dogma of strict maternal inheritance of mitochondria is now being tested with population genetics methods on sequence data from many species. In this study we investigated whether recombination occurs in the mitochondria of the blue tit (Parus caeruleus) by studying polymorphisms in the mitochondrial control region and in a recently identified (A)_n microsatellite on the W chromosome. The female heterogamety of avian sex chromosomes allows a test of whether mitochondrial recombination affects genealogical inference by comparison of mitochondrial and W-linked sequence variation. There is no discrepancy between mitochondrial and W-linked genealogies in blue tits, consistent with no recombination. We also analyzed mitochondrial sequence variation in both blue tits and peregrine falcons (Falco peregrinus) using a coalescent-based approach which accounts for recurrent mutation; in neither bird species did we find evidence of recombination. We conclude that it is unlikely that mitochondrial recombination has large effects on mitochondrial genetic variability in birds.     

Structure of Avian Thymic Hormone, a High-Affinity Avian β-Parvalbumin, in the Ca-Free and Ca-Bound States

Originally isolated on the basis of its capacity to stimulate T-cell maturation and proliferation, avian thymic hormone (ATH) is nevertheless a parvalbumin, one of two β-lineage isoforms expressed in birds. We recently learned that addition of Ca²⁺-free ATH to a solution of 8-anilinonaphthalene-1-sulfonate (ANS) markedly increases ANS emission. This behavior, not observed in the presence of Ca²⁺, suggests that apolar surface area buried in the Ca²⁺-bound state becomes solvent accessible upon Ca²⁺ removal. In order to elucidate the conformational alterations that accompany Ca²⁺ binding, we have obtained the solution structure of the Ca²⁺-free protein using NMR spectroscopy and compared it to the Ca²⁺-loaded protein, solved by X-ray crystallography. Although the metal-ion-binding (CD-EF) domains are largely coincident in the superimposed structures, a major difference is observed in the AB domains. The tight association of helix B with the E and F helices in the Ca²⁺-bound state is lost upon removal of Ca²⁺, producing a deep hydrophobic cavity. The B helix also undergoes substantial rotation, exposing the side chains of F24, Y26, F29, and F30 to solvent. Presumably, the increase in ANS emission observed in the presence of unliganded ATH reflects the interaction of these hydrophobic residues with the fluorescent probe. The increased solvent exposure of apolar surface area in the Ca²⁺-free protein is consistent with previously collected scanning calorimetry data, which indicated an unusually low change in heat capacity upon thermal denaturation. The Ca²⁺-free structure also provides added insight into the magnitude of ligation-linked conformational alteration compatible with a high-affinity metal-ion-binding signature. The exposure of substantial apolar surface area suggests the intriguing possibility that ATH could function as a reverse Ca²⁺ sensor.     

Avian flu pandemic: Can we prevent it?

Outbreaks of highly pathogenic H5N1 avian influenza in Southeast Asia, Europe and Africa have led to devastating consequences for poultry, and have resulted in numerous infections in humans. Although these infections from the animal reservoir continue to accumulate, the virus does not seem to spread extensively among humans. However, for example, a process of genetic reassortment could occur in a human who is co-infected with avian influenza A virus and a human strain of influenza A virus. The resulting new virus might then be able to easily infect humans and spread from human to human. Therefore, many experts expect the occurrence of a pandemic due to a mutant virus which can be easily transmitted among humans. Thus, currently, a major public health concern is the next influenza pandemic; yet it remains unclear how to control such a crisis. In this paper, we investigate relations between the evolution of virulence and an effectiveness of pandemic control measures after the emergence of mutant avian influenza; one is an elimination policy of infected birds with avian influenza and the other is a quarantine policy of infected humans with mutant avian influenza. We found that each of these prevention policies can be ineffective (i.e., increase human morbidity or mortality). Further, interestingly, the same intervention might, under the same conditions, increase human morbidity and decrease human mortality, or vice versa. Our practical findings are that the quarantine policy can effectively reduce both human morbidity and mortality but the elimination policy increases either human morbidity or mortality in a worst case situation.     

Avian sex determination: what, when and where?

Sex is determined genetically in all birds, but the underlying mechanism remains unknown. All species have a ZZ/ZW sex chromosome system characterised by female (ZW) heterogamety, but the chromosomes themselves can be heteromorphic (in most birds) or homomorphic (in the flightless ratites). Sex in birds might be determined by the dosage of a Z-linked gene (two in males, one in females) or by a dominant ovary-determining gene carried on the W sex chromosome, or both. Sex chromosome aneuploidy has not been conclusively documented in birds to differentiate between these possibilities. By definition, the sex chromosomes of birds must carry one or more sex-determining genes. In this review of avian sex determination, we ask what, when and where? What is the nature of the avian sex determinant? When should it be expressed in the developing embryo, and where is it expressed? The last two questions arise due to evidence suggesting that sex-determining genes in birds might be operating prior to overt sexual differentiation of the gonads into testes or ovaries, and in tissues other than the urogenital system.     

Evolutionary implications of Avian Infectious Bronchitis Virus （AIBV） analysis

For developing efficient vaccines, it is essential to identify which amino acid changes are most important to the survival of the virus. We investigate the amino acid substitution features in the Avian Infectious Bronchitis Virus （AIBV） antigenic domain of a vaccine serotype （DE072） and a virulent viral strain （GA98） to better understand adaptive evolution of AIBV. In addition, the SARS Coronavirus （SARS-CoV） was also analyzed in the same way. It is interesting to find that extreme comparability exists between AIBV and SARS in amino acid substitution pattern. It suggests that amino acid changes that result in overall shift of residue charge and polarity should be paid special attention to during the development of vaccines.     

Avian genetic ecotoxicology： DNA of the canary in a coalmine

Genotoxic chemicals, through damage and alteration of the genetic material of wild organisms, pose significant threats to the persistence of wild animal populations. Their damaging effects can ultimately impair the health of the ecosystem and its provision of services to human society. Bird species are good candidates for the role of sentinels of the effects of genotoxins, thanks to （i） the diversity of their ecological niches, （ii） their ubiquity across environments, （iii） their conspicuousness, abundance and approachability, together with （iv） their well-known life histories and the availability of historical data series. Avian diversity increases the likelihood that adequate model species be available for monitoring genotoxicants and assessing their impact. This paper reviews the methods utilized by genetic ecotoxicological studies of wild birds, highlighting their benefits and shortcomings. It also summarizes the genetic ecotoxicological studies so far conducted. In spite of a paucity of studies, several classes of genotoxicants have already been investigated across a variety of species and environments, thus supporting the versatility of birds as monitors of genotoxic contamination. Future technical advancements and applications are suggested, with par- ticular reference to the analysis of mutational events, gene expression and methylation patterns. Finally, I argue that the development of avian genetic ecotoxicology will contribute to the understanding of natural variation in the underlying machinery for coping with DNA damage and oxidative stress, both of which are increasingly recognized as proximate factors in the evolution of life history adaptations [Current Zoology 60 （2）： 285-298, 2014].     

Quantifying Variability of Avian Colours: Are Signalling Traits More Variable?

Background

Increased variability in sexually selected ornaments, a key assumption of evolutionary theory, is thought to be maintained through condition-dependence. Condition-dependent handicap models of sexual selection predict that (a) sexually selected traits show amplified variability compared to equivalent non-sexually selected traits, and since males are usually the sexually selected sex, that (b) males are more variable than females, and (c) sexually dimorphic traits more variable than monomorphic ones. So far these predictions have only been tested for metric traits. Surprisingly, they have not been examined for bright coloration, one of the most prominent sexual traits. This omission stems from computational difficulties: different types of colours are quantified on different scales precluding the use of coefficients of variation.

Methodology/Principal Findings

Based on physiological models of avian colour vision we develop an index to quantify the degree of discriminable colour variation as it can be perceived by conspecifics. A comparison of variability in ornamental and non-ornamental colours in six bird species confirmed (a) that those coloured patches that are sexually selected or act as indicators of quality show increased chromatic variability. However, we found no support for (b) that males generally show higher levels of variability than females, or (c) that sexual dichromatism per se is associated with increased variability.

Conclusions/Significance

We show that it is currently possible to realistically estimate variability of animal colours as perceived by them, something difficult to achieve with other traits. Increased variability of known sexually-selected/quality-indicating colours in the studied species, provides support to the predictions borne from sexual selection theory but the lack of increased overall variability in males or dimorphic colours in general indicates that sexual differences might not always be shaped by similar selective forces.     

Avian higher level biogeography: Southern Hemispheric origins or Southern Hemispheric relicts?

A recent analysis of a comprehensive phylogenetic data set suggested Southern Hemispheric origins for various higher level taxa of neornithine (crown group) birds. These results contrast with hypotheses derived from the fossil record, with the occurrence of successively branching stem group representatives of many “Southern Hemispheric” bird groups in the early Cenozoic of Europe and North America suggesting relict extant distributions. However, a selective consideration of the fossil record and the merging of extant ranges may have resulted in a skewed picture of the past biogeographical history of birds. For future studies, it is proposed that multiple taxa of successively branching Northern Hemispheric stem group representatives are considered to narrow down the ancestral areas of the crown group representatives.     

Social Dimensions of the Human–Avian Bond: Parrots and Their Persons

Though birds are among the most popular companion animals in the United States, little scholarly research has focused on the human– companion parrot relationship. This study uses an ethnographic approach and qualitative analysis to examine the parrot–pet owner relationship. Two and onehalf weeks of ethnographic fieldwork were carried out in a veterinary clinic specializing in avian and exotic medicine. These observations complement the results of quantitative data and qualitative analysis of texts from questionnaires completed by 100 parrot owners outside the clinic. Both textual analysis and observations in the veterinary clinic revealed some interesting insights into the social dimensions of the human–companion parrot relationship, which was rated superior to that of cats and dogs by some bird owners. Various patterns of human–avian interactions emerged from the data, including childhood experience with birds, affection and physical contact with birds, birds as family members and the nature of the human–parrot bond, infantilization (delayed weaning and parrot as child surrogate), anthropomorphism (celebration of holidays, diet, death and spirituality, and misinterpretation of bird behavior), intersubjectivity and cognition, and anthropocentrism (bird as object). Misinterpretation of bird behavior and failure to recognize the unique physiological and social needs of their species may lead to impaired welfare. On the other hand, according the bird a social status as cherished family member, may enhance their welfare. In addition, other factors are considered that may enhance or detract from the welfare of companion parrots. In a discussion of hypotheses regarding the human–pet bond, it is concluded that the data presented by this study best support the social support hypothesis.     

Avian body size changes and climate change: warming or increasing variability?

There has been a growing interest in whether established ecogeographical patterns, such as Bergmann's rule, explain changes in animal morphology related to climate change. Bergmann's rule has often been used to predict that body size will decrease as the climate warms, but the predictions about how body size will change are critically dependent on the mechanistic explanation behind the rule. To investigate change in avian body size in western North America, we used two long‐term banding data sets from central California, USA; the data spanned 40 years (1971–2010) at one site and 27 years (1983–2009) at the other. We found that wing length of birds captured at both sites has been steadily increasing at a rate of 0.024–0.084% per year. Although changes in body mass were not always significant, when they were, the trend was positive and the magnitudes of significant trends were similar to those for wing length (0.040–0.112% per year). There was no clear difference between the rates of change of long‐distance vs. short‐distance migrants or between birds that bred locally compared to those that bred to the north of the sites. Previous studies from other regions of the world have documented decreases in avian body size and have used Bergmann's rule and increases in mean temperature to explain these shifts. Because our results do not support this pattern, we propose that rather than responding to increasing mean temperatures, avian body size in central California may be influenced by changing climatic variability or changes in primary productivity. More information on regional variation in the rates of avian body size change will be needed to test these hypotheses.     

Are Poultry or Wild Birds the Main Reservoirs for Avian Influenza in Bangladesh?

Avian influenza viruses (AIV) are of great socioeconomic and health concern, notably in Southeast Asia where highly pathogenic strains, such as highly pathogenic avian influenza (HPAI) H5N1 and other H5 and H7 AIVs, continue to occur. Wild bird migrants are often implicated in the maintenance and spread of AIV. However, little systematic surveillance of wild birds has been conducted in Southeast Asia to evaluate whether the prevalence of AIV in wild birds is higher than in other parts of the world where HPAI outbreaks occur less frequently. Across Bangladesh, we randomly sampled a total of 3585 wild and domestic birds to assess the prevalence of AIV and antibodies against AIV and compared these with prevalence levels found in other endemic and non-endemic countries. Our study showed that both resident and migratory wild birds in Bangladesh do not have a particularly elevated AIV prevalence and AIV sero-prevalence compared to wild birds from regions in the world where H5N1 is not endemic and fewer AIV outbreaks in poultry occur. Like elsewhere, notably wild birds of the orders Anseriformes were identified as the main wild bird reservoir, although we found exceptionally high sero-prevalence in one representative of the order Passeriformes, the house crow (Corvus splendens), importantly living on offal from live bird markets. This finding, together with high sero- and viral prevalence levels of AIV in domestic birds, suggests that wild birds are not at the base of the perpetuation of AIV problems in the local poultry sector, but may easily become victim to AIV spill back from poultry into some species of wild birds, potentially assisting in further spread of the virus.     

Avian Influenza Virus Surveillance in Wild Birds in Georgia: 2009–2011

The Caucasus, at the border of Europe and Asia, is important for migration and over-wintering of wild waterbirds. Three flyways, the Central Asian, East Africa-West Asia, and Mediterranean/Black Sea flyways, converge in the Caucasus region. Thus, the Caucasus region might act as a migratory bridge for influenza virus transmission when birds aggregate in high concentrations in the post-breeding, migrating and overwintering periods. Since August 2009, we have established a surveillance network for influenza viruses in wild birds, using five sample areas geographically spread throughout suitable habitats in both eastern and western Georgia. We took paired tracheal and cloacal swabs and fresh feces samples. We collected 8343 swabs from 76 species belonging to 17 families in 11 orders of birds, of which 84 were real-time RT-PCR positive for avian influenza virus (AIV). No highly pathogenic AIV (HPAIV) H5 or H7 viruses were detected. The overall AIV prevalence was 1.6%. We observed peak prevalence in large gulls during the autumn migration (5.3–9.8%), but peak prevalence in Black-headed Gulls in spring (4.2–13%). In ducks, we observed increased AIV prevalence during the autumn post-moult aggregations and migration stop-over period (6.3%) but at lower levels to those observed in other more northerly post-moult areas in Eurasia. We observed another prevalence peak in the overwintering period (0.14–5.9%). Serological and virological monitoring of a breeding colony of Armenian Gulls showed that adult birds were seropositive on arrival at the breeding colony, but juveniles remained serologically and virologically negative for AIV throughout their time on the breeding grounds, in contrast to gull AIV data from other geographic regions. We show that close phylogenetic relatives of viruses isolated in Georgia are sourced from a wide geographic area throughout Western and Central Eurasia, and from areas that are represented by multiple different flyways, likely linking different host sub-populations.     

Avian β-defensin variation in bottlenecked populations: the Seychelles warbler and other congeners

β-defensins are important components of the vertebrate innate immune system responsible for encoding a variety of anti-microbial peptides. Pathogen-mediated selection is thought to act on immune genes and potentially maintain allelic variation in the face of genetic drift. The Seychelles warbler, Acrocephalus sechellensis, is an endemic passerine that underwent a recent bottleneck in its last remaining population, resulting in a considerable reduction in genome-wide variation. We genotyped avian β-defensin (AvBD) genes in contemporary (2000–2008) and museum samples (1876–1940) of the Seychelles warbler to investigate whether immunogenetic variation was lost through this bottleneck, and examined AvBD variation across four other Acrocephalus species with varying demographic histories. No variation was detected at four of the six AvBD loci screened in the post-bottleneck population of Seychelles warbler, but two silent nucleotide polymorphisms were identified at AvBD8 and one potentially functional amino-acid variation was observed at AvBD11. Variation in the Seychelles warbler was significantly lower than in the mainland migratory congeneric species investigated, but it similar to that found in other bottlenecked species. In addition, screening AvBD7 in 15 museum specimens of Seychelles warblers sampled prior to the bottleneck (1877–1905) revealed that this locus possessed two alleles previously, compared to the single allele in the contemporary population. Overall, the results show that little AvBD variation remains in the Seychelles warbler, probably as a result of having low AvBD diversity historically rather than the loss of variation due to drift associated with past demographic history. Given the limited pathogen fauna, this lack of variation at the AvBD loci may currently not pose a problem for this isolate population of Seychelles warblers, but it may be detrimental to the species’ long-term survival if new pathogens reach the population in the future.     

αB-Crystallin is Expressed in Myelinating Oligodendrocytes of the Developing and Adult Avian Retina

It is well known that the expression of αB-crystallin (aBC) is increased in neurons and glia under pathologic conditions. However, the expression of aBC during the normal development of the central nervous system has not been reported. This study aimed to clarify the cell type in the chick retina in which aBC is expressed and timing of aBC expression in this cell type during development. Double immunofluorescence with cell-specific markers demonstrated that aBC was selectively expressed in oligodendrocytes (OLs) in the embryonic day 20 (E20) chick retina. A small number of aBC-expressing OLs first appeared in the nerve fiber layer of the central and peripheral retina at E16. Faint aBC expression was also observed in myelin sheaths near cell bodies in the central retina. The number of aBC-expressing OLs and intensity of aBC expression in myelin sheaths were increased in the periphery as well as in the center of the E19 retina. aBC signals in the post-hatching day 120 retina were observed in the entire nerve fiber layer. The spatiotemporal expression pattern of aBC was identical to that of myelin basic protein. These data indicate that aBC-expressing OLs are myelinating OLs among OL-lineage cells. Besides, intrayolk injection of tocopherol, an antioxidant, provoked a decrease in the levels of aBC expression in myelinating OLs. These data suggest that aBC expression in myelinating OLs responds to the change of physiological oxidative stress.     

Avian responses to tourism in the biogeographically isolated high Córdoba Mountains,Argentina

Species do not respond identically to the presence of humans, and this may have consequences at higher-levels of ecological organization. We established bird transects on and off recreational trails in the high Córdoba Mountains of Argentina, a biogeographic island characterized by high levels of endemism, to examine the effect of human visitation at three different levels: (a) community (avian species richness and diversity), (b) guild (relative density of carnivores, granivores, insectivores, and omnivores), and (c) population (relative density of individual bird species). Human presence in the high Córdoba Mountains decreased avian species richness and diversity, and reduced insectivorous relative density, but we did not detect significant effects on granivores, omnivores, and carnivores. At the population level, 6 of 28 species were negatively affected by human visitation; four of these species are of conservation concern. Our results show negative responses to recreationists at multiple levels (e.g., reductions in density, displacement of species from highly visited areas), which may be related to spatial and temporal access to suitable resources, physical disturbance or species-specific tolerance thresholds. Our study area had lower levels of human visitation relative to other protected areas in the Northern Hemisphere, which raises the issue of whether this kind of biogeographically isolated habitat may be too fragile to sustain increasing levels of tourism.