MHC haplotype involvement in avian resistance to an ectoparasite

Research on immune function in evolutionary ecology has frequently focused on avian ectoparasites (e.g., mites and lice). However, host immunogenetics involved with bird resistance to ectoparasites has not been determined. The critical role of the major histocompatibility complex (MHC) in adaptive immunity and high genetic variation found within the MHC make this gene complex useful for exploring the immunogenetic basis for bird resistance to ectoparasites. The objective of this study was to determine if the avian MHC influenced resistance to a blood-feeding ectoparasite. Four congenic lines of chickens, differing only at the MHC, were comparatively infested with a cosmopolitan ectoparasite of birds-northern fowl mite (NFM)-which is also a serious pest species of poultry. Mite infestations were monitored over time and mite densities (weekly and maximum) were compared among lines. Chickens with the MHC haplotype B21 were relatively resistant to NFM, compared with birds in the B15 congenic line (P < 0.02). To test for similar effects in an outbred genetic background, a separate experiment was performed with 107 commercial chickens (white leghorn, W-36 strain) infested with NFM. Hens were genotyped using a MHC microsatellite marker (LEI0258) and associations between MHC haplotype and NFM density were tested. The highest peak NFM populations occurred more often on hens with the B15 haplotype versus the B21 haplotype (P = 0.012), which supported the results of the congenic study. These data indicate the avian MHC influences ectoparasite resistance, which is relevant to disease ecology and avian-ectoparasite interaction.     

A comparison of lizard claw keratin proteins with those of avian beak and claw

Summary The outer shell of translucent keratin has been dissected from the claws of the lizard,Varanus gouldii. It is free of calcium and hydroxyproline, in contrast to the fibrous support, and contains proteins rich in glycine (28 residues %) and half-cystine (13%). These proteins have been obtained in soluble form by treatment with 2-mercaptoethanol in 8M urea at pH 11 followed by alkylation with iodoacetate to giveS-carboxymethyl kerateines. The three major components resolved by SDS polyacrylamide gel electrophoresis have been isolated by fractional precipitation with ammonium sulfate followed by chromatography on DEAE-cellulose or Sephadex. Two of the components, low in tryptophan content, appear to be homologous and are relatively homogeneous with respect to both size and charge whereas the third, a tryptophan-rich material, appears to contain about 20 different molecular species as judged by gel electrophoresis in urea at pH 8.9. The molecular weights of two of the isolated omponents (the tryptophan-rich and the major of the two tryptophanpoor components) are about 13000 as determined by equilibrium ultracentrifugation studies.The major lizard claw proteins are therefore similar in size and glycine content to the proteins of avian beak and claw but differ in containing more cystine and less tyrosine. On the other hand, the reptilian proteins resemble the mammalian high-tyrosine proteins (Type II) in cystine content and overall amino acid composition, but differ in size with the lizard proteins being larger. It is suggested however that they are unlikely to be homologous.     

Comprehensive investigation of ectoparasite community and abundance across life history stages of avian host

Fitness consequences of ectoparasitism are expressed over the lifetime of their hosts in relation to variation in composition and abundance of the entire ectoparasite community and across all host life history stages. However, most empirical studies have focused on parasite species-specific effects and only during some life history stages. We conducted a systematic, year-long survey of an ectoparasite community in a wild population of house finches Carpodacus mexicanus Müller in south-western Arizona, with a specific focus on ecological and behavioral correlates of ectoparasite prevalence and abundance. We investigated five ectoparasite species: two feather mite genera – both novel for house finches – Strelkoviacarus (Analgidae) and Dermoglyphus (Dermoglyphidae), the nest mite Pellonyssus reedi (Macronyssidae), and the lice Menacanthus alaudae (Menoponidae) and Ricinus microcephalus (Ricinidae). Mite P. reedi and louse Menacanthus alaudae abundance peaked during host breeding season, especially in older birds, whereas feather mite abundance peaked during molt. Overall, breeding birds had more P. reedi than non-breeders, molting males had greater abundance of feather mites than molting females and non-molting males, and young males had more feather mites than older males. We discuss these results in relation to natural history of ectoparasites under study and suggest that ectoparasites might synchronize their life cycles to those of their hosts. Pronounced differences in relative abundance of ectoparasite species among host's life history stages have important implications for evolution of parasite-specific host defenses.     

Functional morphology of the avian medullary cone

The organization of the renal medulla of the Gambel's quail, Callipepla gambelii, kidney was examined to determine the number of loops of Henle and collecting ducts and the surface area occupied by the different nephron segments as a function of distance down the medullary cones. Eleven medullary cones were dissected from the kidneys of four birds, and the tissue was processed and sectioned for light microscopy. In addition, individual nephrons were isolated on which total loop thin descending segment and thick prebend segment lengths were measured. The results show no correlation between the absolute number of loops of Henle and the length of the medullary cones. The number of thick and thin limbs of Henle and collecting ducts decrease exponentially with distance toward the apex of the cones and the rate of decrease is similar for cones of different lengths. Initially there is a rapid decrease in the number of thin limbs of Henle, indicating that most nephrons do not penetrate the cones a great distance. Thick descending limbs of Henle (prebend segment) ranged in length from 50 to 770 microm, and there was little correlation with the total length of the loop of Henle. However, the length of the thin limb of Henle correlated well with total loop length. The cell surface areas of the limbs of the loop of Henle and the collecting ducts decreased toward the apex of the cones.     

Adaptive significance of circadian clocks

Circadian clocks are ubiquitous and are found in organisms ranging from bacteria to mammals. This ubiquity of occurrence implies adaptive significance, but to date there has been no rigorous empirical evidence to support this. It is believed that an organism possessing circadian clocks gains fitness advantage in two ways: (i) by synchronizing its behavioral and physiological processes to cyclic environmental factors (extrinsic adaptive value); (ii) by coordinating its internal metabolic processes (intrinsic adaptive value). There is preliminary circumstantial evidence to support both. Several studies using organisms living in constant environments have shown that these organisms possess functional circadian clocks, suggesting that circadian clocks may have some intrinsic adaptive value. Studies to assess the adaptive value of circadian clocks in periodic environments suggest that organisms may have a fitness advantage in those periodic environments, which closely match their own intrinsic periodicity. Furthermore, evidence from organisms living in the wild, selection studies, and studies on latitudinal clines suggest that circadian clocks may have an extrinsic adaptive value as well. In this paper, I have presented several hypotheses for the emergence of circadian clocks and have reviewed some major empirical studies suggesting adaptive significance of circadian clocks.     

Genetic control of avian scleroderma

The inheritance of avian scleroderma, a fibrotic autoimmune disease of chickens resembling human scleroderma, was investigated. Comb inflammations and lesions were used to determine the state of disease of 4-week-old chickens. All line 200 males and 60% of female line 200 chicks showed abnormalities. Crosses (F₄) between line 200 and eight partially inbred lines of chickens maintained at the University of California at Davis were all normal. Backcrosses of F, cocks to line 200 hens showed a higher incidence of scleroderma in males than in females for all lines. The incidence of affected birds varied between backcrosses from a low of 42% for backcross line 217 males derived from a New Hampshire line, to 88% for males of backcross line 213 derived from a partially inbred Leghorn line, demonstrating the presence of genes modifying the penetrance of presumed major genes causing the disease. Backcross genotypes segregating for haplotypes of the major histocompatibility complex (MHC) derived from inbred lines showed consistently lower penetrance of scleroderma than homozygotes carrying the line 200 haplotype. Thus B³ B^S (lines 211 and 215), B¹⁴Bu^s (line 217), and B¹⁵B^S (lines 212, 213, 216, and 218) all had fewer affected individuals than B^SB^S homozygotes from the same families.     

Evidence of accelerated beak growth associated with avian keratin disorder in black-capped chickadees (Poecile atricapillus)

We recently documented an epizootic of beak deformities in more than 2,000 Blackcapped Chickadees (Poecile atricapillus) and other wild bird species in North America. This emerging avian disease, which has been termed avian keratin disorder, results in gross overgrowth of the rhamphotheca, the outer, keratinized layer of the beak. To test the hypothesis that the beak deformities characteristic of this disorder are associated with accelerated keratin production, we measured rates of beak growth and wear in affected Black-capped Chickadees (n=16) and a control sample of unaffected chickadees (n=14) collected from south-central (61°09'-61°38'N, 149°11' -149°48'W) and interior Alaska (64°51' -64°53'N, 147°49' -147°59'W). Rates of absolute growth were 50-100% higher in affected birds than they were in control birds and exceeded records from other passerine species. These results suggest that abnormally rapid epidermal growth is the primary physical mechanism by which beak deformities develop and are maintained in affected chickadees. Although beak overgrowth typically worsened over time, differential patterns of wear influenced the severity and morphology of deformities. In some cases, the effects of accelerated keratin growth were partially mitigated by frequent breakage of rhamphothecal tips. However, mortalities occurred in 9 of 16 birds (56%) with beak deformities during the study, suggesting that avian keratin disorder results in severe health consequences for affected birds. Additional study of factors that control beak keratin production is needed to understand the pathogenesis of this debilitating disease in wild birds.     

Effect of experimental ectoparasite control on bartonella infections in wild Richardson's ground squirrels

The purpose of this study was to investigate the role of ectoparasites in transmitting Bartonella infections in wild Richardson's ground squirrels (Spermophilus richardsonii). Richardson's ground squirrels were trapped, examined for fleas, and tested for Bartonella bacteremia once monthly, at six sites, from April to September 2004. After the initial trapping session in April, burrows at three sites were treated with deltamethrin insecticide. Richardson's ground squirrels trapped on treated sites were less likely to have fleas and had fewer fleas than squirrels on control sites in all months following treatment. We found no difference in the prevalence of Bartonella infections on control and treated sites in May, immediately following treatment; however, significantly fewer squirrels were infected with Bartonella on treated sites in June and July. We conclude that ectoparasites are a main route of transmission for Bartonella infections in Richardson's ground squirrels.     

Optimal control strategy for prevention of avian influenza pandemic

The spread of H5N1 virus to Europe and continued human infection in Southeast Asia have heightened pandemic concern. Although, fortunately, sustained human-to-human transmissions have not been reported yet, it is said that a pandemic virus which can be easily transmitted among humans certainly emerges in the future. In this study, we extended the previous studies for the prevention of the pandemic influenza to evaluate the time-dependent optimal prevention policies, which are associated with elimination policy and quarantine policy, considering its execution cost. Actually, the execution cost affects the optimal strategy of prevention policies and the prevention of the disease spread. We found that the quarantine policy is very important rather than the elimination policy during the disease spread, even if the unit execution cost of the quarantine policy is more expensive than that of the elimination policy. And also, the change of the unit execution cost does affect the total cumulative cost of the optimal prevention policies but does not affect the relative frequency of each cumulative execution cost. Furthermore, interestingly, we revealed that an optimal strategy to reduce the number of total infected humans might increase a chance of invadability of the mutant influenza.     

Host selection by the Louse Fly Crataerina pallida, an avian nest ectoparasite of the Common Swift Apus apus

Preferences by parasites for particular hosts may have important implications for the functioning of host–parasite systems, however, this parasitic life-history trait remains little studied. No detrimental effect of Louse Fly Crataerina pallida parasitism has been found on Common Swift Apus apus nestling hosts. Host selection choices may be mediating the effect this parasite has and account for this apparent avirulence. Two aspects of parasite host selection were studied at a breeding colony of Common Swifts during 2008; (1) intra-brood differences in C. pallida parasitism were studied to determine the influence of nestling rank, (2) differences in male and female C. pallida parasitism were investigated, as they may result in varying costs of parasitism to hosts. C. pallida populations were found to preferentially parasitize higher rather than lower ranking nestlings within broods of both two and three chicks. Greater proportions of females were seen upon nestlings than at the nest, and upon higher ranking than lower ranking nestlings within broods. These results indicate that host selection occurs and this may thus account for the lack of parasitic virulence reported within this host–parasite system.     

Adaptive significance of antipredator behaviour in artiodactyls

We used comparative data to test functional hypotheses for 17 antipredator behaviour patterns in artiodactyls. We examined the literature for hypotheses about auditory and visual signals, defensive behaviour and group-related antipredator behaviour in this taxon and derived a series of predictions for each hypothesis. Next, we documented occurrences of these behaviour patterns and morphological, ecological and behavioural variables for 200 species and coded them in binary format. We then pitted presence of an antipredator behaviour against presence of an independent variable for cervids, bovids and all artiodactyls together using nonparametric tests. Finally, we reanalysed the data using Maddison's (1990, Evolution, 44, 539-557) concentrated-changes tests and a consensus molecular and taxonomic phylogeny. We found evidence that snorting is both a warning signal to conspecifics and a pursuit-deterrent signal, lack of evidence that whistling alerts conspecifics and indications that foot stamping is a visual signal to warn group members. Evidence suggested that tail flagging was a signal to both conspecifics and predators, that bounding, leaping and stotting were used both as a signal and to clear obstacles and that prancing functioned similarly to foot stamping. Analyses of tail flicking, zigzagging and tacking were equivocal. We confirmed that inspection occurs in large groups, freezing enhances crypticity, and species seeking refuge in cliffs tend to be small. Entering water and attacks on predators had few correlates. Finally, group living, a putative antipredator adaptation, was associated with large body size and species living in open habitats, confirming Jarman's (1974, Behaviour, 48, 215-267) classic hypothesis. Bunching and group attack apparently deter predators. Despite limitations, comparative and systematic analyses can bolster adaptive hypotheses and raise new functional explanations for antipredator behaviour patterns in general.     

Adaptive significance of amylase polymorphism in Drosophila

Laboratory populations of D. busckii flies were kept for one generation on media containing different carbohydrate sources (maltose and rice, potato or maize starch). The flies maintained on standard potato medium served as a control. Progeny were analyzed for -amylase activity and Amy-electromorph frequencies.Spectrophotometrically assayed amylase activity was highest in the flies cultured on potato starch medium and lowest in specimens kept on maltose. Carbohydrate source in some substrates affected both frequencies of Amy-alleles and Amy-genotypes. Phenotypic differences at a biochemical level, i.e. in -amylase activity, might be connected to Amy-structural gene polymorphism in the examined Drosophila species.     

QTL and quantitative genetic analysis of beak morphology reveals patterns of standing genetic variation in an Estrildid finch

The intra- and interspecific diversity of avian beak morphologies is one of the most compelling examples for the power of natural selection acting on a morphological trait. The development and diversification of the beak have also become a textbook example for evolutionary developmental biology, and variation in expression levels of several genes is known to causally affect beak shape. However, until now, no genomic polymorphisms have been identified, which are related to beak morphology in birds. QTL mapping does reveal the location of causal polymorphisms, albeit with poor spatial resolution. Here, we estimate heritability and genetic correlations for beak length, depth and width and perform a QTL linkage analysis for these traits based on 1404 informative single-nucleotide polymorphisms genotyped in a four-generation pedigree of 992 captive zebra finches (Taeniopygia guttata). Beak size, relative to body size, was sexually dimorphic (larger in males). Heritability estimates ranged from 0.47 for beak length to 0.74 for beak width. QTL mapping revealed four to five regions of significant or suggestive genome-wide linkage for each of the three beak dimensions (nine different regions in total). Eight out of 11 genes known to influence beak morphology are located in these nine peak regions. Five QTL do not cover known candidates demonstrating that yet unknown genes or regulatory elements may influence beak morphology in the zebra finch.     

Molecular control of facial morphology

We present a developmental perspective on the concept of phylotypic and phenotypic stages of craniofacial development. Within orders of avians and mammals, a phylotypic period exists when the morphology of the facial prominences is minimally divergent. We postulate that species-specific facial variations arise as a result of subtle shifts in the timing and the duration of molecular pathway activity (e.g., heterochrony), and present evidence demonstrating a critical role for Wnt and FGF signaling in this process. The same molecular pathways that shape the vertebrate face are also implicated in craniofacial deformities, indicating that comparisons between and among animal species may represent a novel method for the identification of human craniofacial disease genes.     

Adaptive significance of maternal induction of density-dependent phenotypes

Density has been demonstrated to impact life history traits such as growth, fecundity and survival. Some authors have proposed that morphological and behavioral traits have evolved in response to density conditions. To escape the adverse effect of density, individuals can either adapt to crowding or avoid crowding by dispersing. The aim of this work is to study the interplay between local adaptation and dispersal in four populations of the common lizard, Lacerta vivipara, where densities of both the maternal and juvenile environment have been experimentally manipulated. Density was decreased in the spring by removing a quarter of the population at two sites and was un-manipulated in two other sites. One month later, we caught some pregnant females and kept them in the laboratory until parturition. To manipulate density of postnatal neonates and juveniles, we divided each clutch into two, and released half of the juveniles either in a reduced density site or in a control one. We then recaptured individuals a year after release and recorded their size and weight. When density was reduced, females increased their clutch size, but produced offspring of lower body condition than in the control sites. The conspicuous ventral color of females was likewise increased when density was reduced. However, offspring growth rate, local survival and dispersal were not influenced by maternal density. Juvenile females released in the reduced-density site had lower survival rate than those released in the control density site. Contrary to expectations, offspring dispersal was significantly higher at the reduced compared to control density sites. There was no interaction between maternal density habitat and the juvenile release habitat indicating that maternal effects did not influence juvenile life history traits in a different way according to the level of density. Moreover, clutch size and offspring size had no effect on juvenile growth or survival.