Fine‐tuned distribution of feather mites (Astigmata) on the wing of birds: the case of blackcaps Sylvia atricapilla

The distribution of feather mites (Astigmata) along the wing of passerine birds could change dramatically within minutes because of the rapid movement of mites between feathers. However, no rigorous study has answered how fine‐tuned is the pattern of distribution of feather mites at a given time. Here we present a multiscale study of the distribution of feather mites on the wing of non‐moulting blackcaps Sylvia atricapilla in a short time period and at a single locality. We found that the number and distribution of mites differed among birds, but it was extremely similar between the wings of each bird. Moreover, mites consistently avoided the first secondary feather, despite that it is placed at the centre of the feathers most used by them. Thus, our results suggest that feather mites do precise, feather‐level decisions on where to live, contradicting the current view that mites perform “mass”, or “blind” movements across wing feathers. Moreover, our findings indicate that “rare” distributions are not spurious data or sampling errors, but each distribution of mites on the wing of each bird is the outcome of the particular conditions operating on each ambient‐bird‐feather mite system at a given time. This study indicates that we need to focus on the distribution of feather mites at the level of the individual bird and at the feather level to improve our understanding of the spatial ecology of mites on the wings of birds.     

Social familiarity relaxes the constraints of limited attention and enhances reproduction of group‐living predatory mites

In many group‐living animals, within‐group associations are determined by familiarity, i.e. familiar individuals, independent of genetic relatedness, preferentially associate with each other. The ultimate causes of this behaviour are poorly understood and rigorous documentation of its adaptive significance is scarce. Limited attention theory states that focusing on a given task has interrelated cognitive, behavioural and physiological costs with respect to the attention paid to other tasks. In multiple signal environments attention has thus to be shared among signals. Assuming that familiar neighbours require less attention than unfamiliar ones, associating with familiar individuals should increase the efficiency in other tasks and ultimately increase fitness. We tested this prediction in adult females of the group‐living, plant‐inhabiting predatory mite Phytoseiulus persimilis. We evaluated the influence of social familiarity on within‐group association behaviour, activity, predation and reproduction. In mixed groups (familiar and unfamiliar), familiar predator females preferentially associated with each other. In pure groups (either familiar or unfamiliar), familiar predator females produced more eggs than unfamiliar females at similar predation rates. Higher egg production was correlated with lower activity levels, indicating decreased restlessness. In light of limited attention theory, we argue that the ability to discriminate between familiar and unfamiliar individuals and preferential association with familiar individuals confers a selective advantage because familiar social environments are cognitively and physiologically less taxing than unfamiliar social environments.     

Different scales of spatial segregation of two species of feather mites on the wings of a passerine bird

The "condition-specific competition hypothesis" proposes that coexistence of 2 species is possible when spatial or temporal variations in environmental conditions exist and each species responds differently to those conditions. The distribution of different species of feather mites on their hosts is known to be affected by intrinsic host factors such as structure of feathers and friction among feathers during flight, but there is also evidence that external factors such as humidity and temperature can affect mite distribution. Some feather mites have the capacity to move through the plumage rather rapidly, and within-host variation in intensity of sunlight could be one of the cues involved in these active displacements. We analyzed both the within- and between-feather spatial distribution of 2 mite species, Trouessartia bifurcata and Dolichodectes edwardsi , that coexist in flight feathers of the moustached warbler Acrocephalus melanopogon. A complex spatial segregation between the 2 species was observed at 3 spatial levels, i.e., "feather surfaces," "between feathers," and "within feathers." Despite certain overlapping distribution among feathers, T. bifurcata dominated proximal and medial regions on dorsal faces, while D. edwardsi preferred disto-ventral feather areas. An experiment to check the behavioral response of T. bifurcata to sunlight showed that mites responded to light exposure by approaching the feather bases and even leaving its dorsal face. Spatial heterogeneity across the 3 analyzed levels, together with response to light and other particular species adaptations, may have played a role in the coexistence and segregation of feather mites competing for space and food in passerine birds.     

Gene flow and range expansion in a mountain‐dwelling passerine with a fragmented distribution

We studied gene flow and bottleneck events in the population history of locally isolated citril finches endemic to European mountains. For the present study, we used two genetic markers with different rates of evolution: a fast evolving mitochondrial marker (ATPase6/8) and a more slowly evolving nuclear marker (02401). Populations north of the Pyrenees showed in general fewer haplotypes and a considerable lower nucleotide and gene diversity than the Iberian populations. Unexpectedly, we found very little genetic variability in the fast evolving mitochondrial marker, arguing for a strong and relatively recent bottleneck event in the species population history. This pattern potentially reflects a sudden decrease of crucial resources during Mid‐Holocene (mountain pine, Scots pine, and black pine) and a subsequent breakdown of the population. The bottleneck could also have been caused or coincide with a selective sweep in the mitochondrion. By contrast, the slowly evolving nuclear marker showed a much higher variability. This marker probably reflects major gene flow along a potential expansion pathway from the Eastern Pyrenees, northwards to the populations of Central Europe, and southwards to the more fragmented populations of central and southern Spain. The population of the Western Pyrenees (Navarra) appears to be cut‐off from this major gene flow and our data indicate a certain degree of partial isolation, probably reflecting more ancient events (e.g. the separation in distinct refuge sites during the last glacial maximum). © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 707–721.     

Caterpillars on the run – induced defences create spatial patterns in host plant damage

Herbivores usually consume a mere fraction of available plant biomass. Spatial patterns in feeding damage may be attributable to induced defences by the host plant; a damaged plant reacts by lowering its nutritional value, thereby forcing herbivores to move on before food gets worse. In this study, we test this general hypothesis on a specific model system: caterpillars of the alpine butterfly Parnassius smintheus feeding on lance-leaved stonecrop Sedum lanceolatum. We first describe spatial patterns in host distribution and feeding damage within alpine meadows. We then use laboratory experiments to test a key assumption behind the proposed mechanisms: that the host plant exhibits an induced response with a negative impact on larval performance, and that this response is activated with a delay. Finally, we relate the patterns observed to the actual behaviour of Parnassius larvae.
Overall, we found the level of feeding damage to be low (on damaged plants, only 5% of all leaves were fed upon). Within meadows, both host plants and feeding damage were clumped at a small spatial scale. This pattern seemed directly explicable by the timing of the host's induced defence. Laboratory experiments revealed a delay of 1–2 d before the defence reached a level affecting larval performance, and wild larvae switch plants more quickly than this. A simulation model demonstrated that the spatial distribution of host plant damage can be generated by a simple random walk, based on the empirically observed step frequency, length and turning angles. Hence, as the most parsimonious explanation for the observed level and pattern of host plant damage, we offer a scenario where induced changes in host-plant quality limits the time spent per plant, but the herbivore moves throughout the landscape without any particular directionality.     

Spatial distribution and abundance of bud galls caused by eriophyoid mites among host trees Carpinus tschonoskii

Abstract:  Differences in spatial distribution and abundance of bud galls caused by eriophyoid mites (Acari: Eriophyoidea) among Carpinus tschonoskii (Betulaceae) were studied. This mite preferentially induces galls on terminal buds. Four factors influencing gall abundance were examined: host tree size, host tree's reproductive status, altitude and study site. As tree size increased, the number of galls increased to an apparent asymptote. This result suggests that tree size-dependent characteristics such as number of terminal buds, temporal pattern of shoot elongation and reproductive status influence gall abundance.     

Phylogeny and co-speciation in feather mites of the subfamily Avenzoariinae (Analgoidea: Avenzoariidae)

A cladistic analysis of phylogenetic relationships is carried out for the feather mite subfamily Avenzoariinae. The analysis is made at two different taxonomic levels, for 19 genera of the all family Avenzoariidae and for taxa of species rank for the Avenzoaria and Bychovskiata generic groups. A subsequent comparative analysis of phylogenetic hypotheseis for the subfamily Avenzoariinae and recently accepted phylogenetic hypotheses of the shorebirds Charadriiformes indicates co-speciation of feather mites with their hosts. As a result of the comparative analysis it is suggested, that the subfamily Avenzoariinae originated from an ancestor of the order Charadriiformes and co-speciated with this host order. The expected pattern of parallel evolution is disturbed by different evolutionary events, such as host shifts, extinction of mites and differential evolutionary rates of mite lineages in different phyletic branches of feather parasites.     

Non-consumptive effects of predatory mites on thrips and its host plant

Recent reviews on trait-mediated interactions in food webs suggest that trait-mediated effects are as important in triggering top–down trophic cascades as are density-mediated effects. Trait-mediated interactions between predator and prey result from non-consumptive predator effects changing behavioural and/or life history traits of prey. However, in biological control the occurrence of trait-mediated interactions between predators, prey and plants has been largely ignored. Here, we show that non-consumptive predator effects on prey cascade down to the plant in an agro-ecological food chain. The study system consisted of the predatory mites P. persimilis and N. californicus , the herbivorous non-target prey western flower thrips F. occidentalis and the host plant bean. Irrespective of predator species and risk posed to prey, the presence of predator eggs led to increased ambulation, increased mortality and decreased oviposition of thrips. Furthermore, the presence of predator eggs reduced leaf damage caused by thrips. To our knowledge this is the first experimental evidence suggesting a positive trophic cascade triggered by non-consumptive predator effects on non-target prey in an augmentative biological control system.     

Independent and interactive effects of two facilitators on their habitat‐providing host plant,Spartina alterniflora

The role of habitat‐providing species in facilitating associated species abundance and diversity is recognized as a key structuring force in many ecosystems. Reciprocal facilitation by associates, often involving multiple species, can be important for the maintenance of the host species. As with other multi‐species interactions (e.g. multiple predator effects), non‐additive relationships may be common among these associates, yet relatively few studies have examined potential interactions among multiple facilitator species. We combined field surveys and a mesocosm experiment to examine the independent and interactive effects of two co‐occurring facilitator species, ribbed mussels Geukensia demissa and fiddler crabs Uca pugilator, on their host salt marsh plant species, cordgrass Spartina alterniflora. We also experimentally examined how these relationships varied across different host plant genotypes. Overall, facilitator effects increased with increasing facilitator density. There was a significant interaction between mussel and fiddler crab presence, indicating that the effects of each species on cordgrass were dependent on the presence of the other facilitator species. In addition, there were strong interactions among mussels, fiddler crabs, and plant genotype, with greater variation in the performance of individual genotypes when fiddler crabs were absent. Our work reinforces the importance of considering multiple responses when assessing the functional redundancy of co‐occurring facilitators, as species are seldom completely redundant across the range of services they provide. It also highlights that the strength and direction of species interactions can vary due to genetic variation within the interacting species.     

Divergent cellular phenotypes of human and mouse cells lacking the Werner syndrome RecQ helicase

Werner syndrome (WS) is a human autosomal recessive genetic instability and cancer predisposition syndrome with features of premature aging. Several genetically determined mouse models of WS have been generated, however, none develops features of premature aging or an elevated risk of neoplasia unless additional genetic perturbations are introduced. In order to determine whether differences in cellular phenotype could explain the discrepant phenotypes of Wrn^?/? mice and WRN-deficient humans, we compared the cellular phenotype of newly derived Wrn^?/? mouse primary fibroblasts with previous analyses of primary and transformed fibroblasts from WS patients and with newly derived, WRN-depleted human primary fibroblasts. These analyses confirmed previously reported cellular phenotypes of WRN-mutant and WRN-deficient human fibroblasts, and demonstrated that the human WRN-deficient cellular phenotype can be detected in cells grown in 5% or in 20% oxygen. In contrast, we did not identify prominent cellular phenotypes present in WRN-deficient human cells in Wrn^?/? mouse fibroblasts. Our results indicate that human and mouse fibroblasts have different functional requirements for WRN protein, and that the absence of a strong cellular phenotype may in part explain the failure of Wrn^?/? mice to develop an organismal phenotype resembling Werner syndrome.     

One,two and three‐dimensional geometric constraints and climatic correlates of North American tree species richness

The ‘mid‐domain effect’ (MDE) has received much attention recently as a candidate explanation for patterns in species richness over large geographic areas. Mid‐domain models generate a central peak in richness when species ranges are randomly placed within a bounded geographic area (i.e. the domain). The most common terrestrial mid‐domain models published to date have been 1‐D latitude or elevation models and 2‐D latitude‐longitude models. Here, we test 1‐D, 2‐D and 3‐D mid‐domain models incorporating latitude, longitude and elevation, and assess independent and concurrent effects of geometric constraints and climatic variables on species richness of North American trees. We use both the traditional ‘global’ regression models as well as geographically weighted regressions (‘local’ models) to examine local variation in the contribution of MDE and climatic variables to species richness across the domain. Our results show that in some dimensions the contribution of MDE to patterns of species richness can be quite substantial, and we show that in most cases a combination of MDE and climate predicted empirical species richness best in both local and global models. For the North American domain, MDE in the elevation dimension is clearly important in describing patterns of empirical species richness. We also show that the assumption of stationarity in global models is not met in the North American domain and that results of these models mask complex patterns in both the effect of MDE on richness and the response of species richness to climate. In particular we show the increased explanatory role of MDE in predicting species richness as domain edges are approached. Our results support the hypothesis that geometric constraints contribute to species richness patterns and we suggest the mid‐domain effect should be considered alongside more traditional environmental correlates in understanding patterns of species diversity.     

Investigation on the differentiation of two <Emphasis Type="Italic">Ustilago esculenta</Emphasis> strains - implications of a relationship with the host phenotypes appearing in the fields

Background

Ustilago esculenta, a pathogenic basidiomycete fungus, infects Zizania latifolia to form edible galls named Jiaobai in China. The distinct growth conditions of U. esculenta induced Z. latifolia to form three different phenotypes, named male Jiaobai, grey Jiaobai and white Jiaobai. The aim of this study is to characterize the genetic and morphological differences that distinguish the two U. esculenta strains.

Results

In this study, sexually compatible haploid sporidia UeT14/UeT55 from grey Jiaobai (T strains) and UeMT10/UeMT46 from white Jiaobai (MT strains) were isolated. Meanwhile, we successfully established mating and inoculation assays. Great differences were observed between the T and MT strains. First, the MT strains had a defect in development, including lower teliospore formation frequency and germination rate, a slower growth rate and a lower growth mass. Second, they differed in the assimilation of nitrogen sources in that the T strains preferred urea and the MT strains preferred arginine. In addition, the MT strains were more sensitive to external signals, including pH and oxidative stress. Third, the MT strains showed an infection defect, resulting in an endophytic life in the host. This was in accordance with multiple mutated pathogenic genes discovered in the MT strains by the non-synonymous mutation analysis of the genome re-sequencing data between the MT and T strains (GenBank accession numbers of the genome re-sequencing data: JTLW00000000 for MT strains and SRR5889164 for T strains).

Conclusion

The MT strains appeared to have defects in growth and infection and were more sensitive to external signals compared to the T strains. They displayed an absolutely stable endophytic life in the host without an infection cycle. Accordingly, they had multiple gene mutations occurring, especially in pathogenicity. In contrast, the T strains, as phytopathogens, had a complete survival life cycle, in which the formation of teliospores is important for adaption and infection, leading to the appearance of the grey phenotype. Further studies elucidating the molecular differences between the U. esculenta strains causing differential host phenotypes will help to improve the production and formation of edible white galls.

     

Phylogeny and evolution of parasitism in feather mites of the families Epidermoptidae and Dermationidae (Acari: Analgoidea)

A phylogenetic reconstruction of feather mites of the epidermoptid complex (Analgoidea: Epidermoptidae, Dermationidae, and Knemidocoptidae) was carried out by methods of parsimony-based cladistics. The epidermoptid complex splits into two major branches, Epidermoptidae and Dermationidae. The family Dermationidae is monophyletic, while the Epidermoptidae, as previously defined, is paraphyletic. The family Knemidocoptidae is reduced to the subfamilial rank because it arises from the core of the Epidermoptidae. The subfamily Myialginae Trouessart, 1906 stat. resur. is restored within the Epidermoptidae. The aberrant genera Lukoschuscoptes and Apocnemidocoptes are moved from Knemidocoptidae to Epidermoptidae and Dermationidae, respectively. A hypothesis explaining main trends in morphological and ecological adaptations to parasitism on birds within the epidermoptid complex is proposed. New taxonomic diagnoses for higher taxa (families and subfamilies) are provided, and three new genera—Archemyialges gen. n., Hemimyialges gen. n. (Epidermoptidae), and Trochiloptes gen. n. (Dermationidae)—and a new subfamily—Apocnemidocoptinae—are established.     

Relationships among nectar‐dwelling yeasts,flowers and ants: patterns and incidence on nectar traits

Nectar‐dwelling yeasts are emerging as widely distributed organisms playing a potentially significant and barely unexplored ecological role in plant pollinator mutualisms. Previous efforts at understanding nectar–pollinator–yeast interactions have focused on bee‐pollinated plants, while the importance of nectarivorous ants as vectors for yeast dispersal remains unexplored so far. Here we assess the abundance and composition of the nectar fungal microbiota of the ant‐pollinated plant Cytinus hypocistis, study whether yeast transmission is coupled with ant visitation, and discern whether ant‐ transported yeasts promote changes in nectar characteristics. Our results show that a high percentage of flowers (77%) and plants (94%) contained yeasts, with yeast cell density in nectar reaching up to 6.2 × 10⁴ cells mm^?3, being the highest densities associated with the presence of the nectar‐specialist yeast Metschnikowia reukaufii. The establishment of fungal microbiota in nectar required flower visitation by ants, with 70% of yeast species transported by them being also detected in nectar. Ant‐vectored yeasts diminished the nutritional quality of nectar, with flowers exposed to pollinators and yeasts containing significantly lower nectar sugar concentration than virgin flowers (13.4% and 22.8%, respectively). Nectar of flowers that harbored M. reukaufii showed the lowest quality, with nectar concentration declining significantly with increasing yeast density. Additionally, yeasts modified patterns of interpopulation variation in nectar traits, homo genizing differences between populations in some nectar attributes. We show for the first time that the outcome of the tripartite pollinator–flower–yeast interaction is highly dependent on the identity and inherent properties of the participants, even to the extent of influencing the species composition of this ternary system, and can be mediated by ecological characteristics of plant populations. Through their influence on plant functional traits, yeasts have the potential to alter nectar consumption, pollinator foraging behavior and ultimately plant reproduction.     

Population‐level influence of a recurring disease on a long‐lived wildlife host

Despite a heightened interest regarding the role of infectious diseases in wildlife conservation, few studies have explicitly addressed the impacts of chronic, persistent diseases on long‐term host population dynamics. Using mycoplasmal upper respiratory tract disease (URTD) within natural gopher tortoise Gopherus polyphemus populations as a model system, we investigated the influence of chronic recurring disease epizootics on host population dynamics and persistence using matrix population models and Markov chain models for temporally autocorrelated environments. By treating epizootics as a form of environmental stochasticity, we evaluated host population dynamics across varying levels of outbreak duration (ρ), outbreak recurrence (f), and disease‐induced mortality (μ). Baseline results indicated a declining growth rate (λ) for populations under unexposed or enzootic conditions (λ_Enzootic= 0.903, 95% CI: 0.765–1.04), and a median time to quasi‐extinction of 29 years (range: 28–30 years). Under recurring epizootics, stochastic growth rates overlapped with baseline growth rates, and ranged between 0.838–0.902. Median quasi‐extinction times under recurring epizootics also overlapped for most scenarios with those of baseline conditions, and ranged between 18–29 years, with both metrics decreasing as a function of f and μ. Overall, baseline (enzootic) conditions had a greater impact on λ than epizootic conditions, and demographic vital rates were proportionately more influential on λ than disease‐ or outbreak‐associated parameters. Lower‐level elasticities revealed that, among disease‐ and outbreak‐associated parameters, increases in μ, force of infection (φ), and f negatively influenced λ. The impact of disease on host population dynamics depended primarily on how often a population underwent an epizootic state, rather than how long the epizootic persisted within the exposed population. The modeling framework presented in this paper could be widely applied to a range of wildlife disease systems in which hosts suffer from persistent recurring diseases.     

Genetic and environmental effects on a condition‐dependent trait: feather growth in Siberian jays

Condition, defined as the amount of ‘internal resources’ an individual can freely allocate, is often assumed to be environmentally determined and to reflect an individual’s health and nutritional status. However, an additive genetic component of condition is possible if it ‘captures’ the genetic variance of many underlying traits as many fitness‐related traits appear to do. Yet, the heritability of condition can be low if selection has eroded much of its additive genetic variance, or if the environmental influences are strong. Here, we tested whether feather growth rate – presumably a condition‐dependent trait – has a heritable component, and whether variation in feather growth rate is related to variation in fitness. To this end, we utilized data from a long‐term population study of Siberian jays (Perisoreus infaustus), and found that feather growth rate, measured as the width of feather growth bars (GB), differed between age‐classes and sexes, but was only weakly related to variation in fitness as measured by annual and life‐time reproductive success. As revealed by animal model analyses, GB width was significantly heritable (h² = 0.10 ± 0.05), showing that this measure of condition is not solely environmentally determined, but reflects at least partly inherited genetic differences among individuals. Consequently, variation in feather growth rates as assessed with ptilochronological methods can provide information about heritable genetic differences in condition.     

Effects of antagonistic coevolution on parasite‐mediated host coexistence

Parasites can promote diversity by mediating coexistence between a poorer and superior competitor, if the superior competitor is more susceptible to parasitism. However, hosts and parasites frequently undergo antagonistic coevolution. This process may result in the accumulation of pleiotropic fitness costs associated with host resistance, and could breakdown coexistence. We experimentally investigated parasite‐mediated coexistence of two genotypes of the bacterium Pseudomonas fluorescens, where one genotype underwent coevolution with a parasite (a virulent bacteriophage), whereas the other genotype was resistant to the evolving phages at all time points, but a poorer competitor. In the absence of phages, the resistant genotype was rapidly driven extinct in all populations. In the presence of the phages, the resistant genotype persisted in four of six populations and eventually reached higher frequencies than the sensitive genotype. The coevolving genotype showed a reduction in the growth rate, consistent with a cost of resistance, which may be responsible for a decline in its relative fitness. These results demonstrate that the stability of parasite‐mediated coexistence of resistant and susceptible species or genotypes is likely to be affected if parasites and susceptible hosts coevolve.