Uropygial gland volume and malaria infection are related to survival in migratory house martins

Pathogens such as bacteria, fungi and malaria and related haemosporidians provoke negative effects on the fitness of their hosts. Animals have developed a range of defensive mechanisms to resist or eliminate these parasitic infections and their negative fitness costs. The uropygial gland secretion has been proposed to act as defensive barrier of skin and plumage in the fight against bacteria and fungi, and may prevent birds from acquiring haemosporidian infections. Thus, the secretion of uropygial glands of birds may favour survival of individuals. However, whether uropygial gland secretion influence survival remains unknown. Here we explore if the size of the uropygial gland and malaria infection influence survival of house martins Delichon urbica. We showed, for the first time, that the volume of the uropygial gland positively predicted survival prospects of malaria infected house martins. Malaria infected birds had the lowest probability of survival, with the effect of gland size on survival prospects depending on infection: infected house martins with larger uropygial glands were better able to survive to the next breeding season, while infected birds with small uropygial glands were not. These results highlight the importance of uropygial gland secretion in the life history of wild birds.     

Examining the relationship between hemolymph phenoloxidase and resistance to a DNA virus, Plodia interpunctella granulosis virus (PiGV)

We have a detailed understanding of invertebrate immune responses to bacteria and fungal pathogens, but we know less about how insects respond to virus challenge. Phenoloxidase (PO) functions as an important immune response against many parasites and pathogens and is routinely used as a measure of immune competance. We examine the role of haemolymph PO activity in Plodia interpuncetella's response to its natural granulosis virus (PiGV). Larvae were challenged with virus by both oral inoculation of occluded virus (the natural infection route) and direct intrahaemocoelic injection of budded virus. Haemolymph was collected at time points post-viral challenge using a novel method that allows the volume of haemolymph to be quanitified. The haemolmyph was collected without killing the larvae so that haemolymph samples from individuals that developed viral disease could be distinguished from samples collected from those that fought off infection. The level of haemolymph PO activity in resistant larvae did not differ from control larvae. Therefore we have no evidence that PO is involved in resistance to virus in the haemocoel whether larvae are challenged naturally by oral innoculation or directly by intraheamocoelic injection. Phenoloxidase may therefore not be a relevant metric of immunocompetence for viral infection.     

Genetic Architecture Promotes the Evolution and Maintenance of Cooperation

When cooperation has a direct cost and an indirect benefit, a selfish behavior is more likely to be selected for than an altruistic one. Kin and group selection do provide evolutionary explanations for the stability of cooperation in nature, but we still lack the full understanding of the genomic mechanisms that can prevent cheater invasion. In our study we used Aevol, an agent-based, in silico genomic platform to evolve populations of digital organisms that compete, reproduce, and cooperate by secreting a public good for tens of thousands of generations. We found that cooperating individuals may share a phenotype, defined as the amount of public good produced, but have very different abilities to resist cheater invasion. To understand the underlying genetic differences between cooperator types, we performed bio-inspired genomics analyses of our digital organisms by recording and comparing the locations of metabolic and secretion genes, as well as the relevant promoters and terminators. Association between metabolic and secretion genes (promoter sharing, overlap via frame shift or sense-antisense encoding) was characteristic for populations with robust cooperation and was more likely to evolve when secretion was costly. In mutational analysis experiments, we demonstrated the potential evolutionary consequences of the genetic association by performing a large number of mutations and measuring their phenotypic and fitness effects. The non-cooperating mutants arising from the individuals with genetic association were more likely to have metabolic deleterious mutations that eventually lead to selection eliminating such mutants from the population due to the accompanying fitness decrease. Effectively, cooperation evolved to be protected and robust to mutations through entangled genetic architecture. Our results confirm the importance of second-order selection on evolutionary outcomes, uncover an important genetic mechanism for the evolution and maintenance of cooperation, and suggest promising methods for preventing gene loss in synthetically engineered organisms.     

What is an individual organism? A multilevel selection perspective

Most biologists implicitly define an individual organism as "one genome in one body." This definition is based on physiological and genetic criteria, but it is problematic for colonial organisms. We propose a definition based instead on the evolutionary criteria of alignment of fitness, export of fitness by germ-soma specialization, and adaptive functional organization. We consider how these concepts apply to various putative individual organisms. We conclude that complex multicellular organisms and colonies of eusocial insects satisfy these three criteria, but that, in most cases (with at least one notable exception), colonies of modular organisms and genetic chimeras do not. While species do not meet these criteria, they may meet the criteria for a broader concept--that of an evolutionary individual--and sexual reproduction may be a species-level exaptation for enhancing evolvability. We also review the costs and benefits of internal genetic heterogeneity within putative individuals, demonstrating that high relatedness is neither a necessary nor a sufficient condition for individuality, and that, in some cases, genetic variability may have adaptive benefits at the level of the whole.     

Wild immunology

In wild populations, individuals are regularly exposed to a wide range of pathogens. In this context, organisms must elicit and regulate effective immune responses to protect their health while avoiding immunopathology. However, most of our knowledge about the function and dynamics of immune responses comes from laboratory studies performed on inbred mice in highly controlled environments with limited exposure to infection. Natural populations, on the other hand, exhibit wide genetic and environmental diversity. We argue that now is the time for immunology to be taken into the wild. The goal of 'wild immunology' is to link immune phenotype with host fitness in natural environments. To achieve this requires relevant measures of immune responsiveness that are both applicable to the host-parasite interaction under study and robustly associated with measures of host and parasite fitness. Bringing immunology to nonmodel organisms and linking that knowledge host fitness, and ultimately population dynamics, will face difficult challenges, both technical (lack of reagents and annotated genomes) and statistical (variation among individuals and populations). However, the affordability of new genomic technologies will help immunologists, ecologists and evolutionary biologists work together to translate and test our current knowledge of immune mechanisms in natural systems. From this approach, ecologists will gain new insight into mechanisms relevant to host health and fitness, while immunologists will be given a measure of the real-world health impacts of the immune factors they study. Thus, wild immunology can be the missing link between laboratory-based immunology and human, wildlife and domesticated animal health.     

Infection of strawberry flowers by Botrytis cinerea and its relevance to grey mould development

Corn stunt spiroplasma (CSS) multiplied in all injected Dulbulus maidis, reaching titres of over 1 × 10⁶ colony forming units (cfu)/insect and 1 × 10⁴ cfu/salivary gland of each insect. Spiroplasmas could be isolated from the haemolymph and from the salivary glands 1 h after injection and at any time subsequently. Insect extract at a concentration greater than the equivalent of 0.1 insects/ml was inhibitory to the growth of CSS in cultures. Helices could be seen in the haemolymph at any time after injection. However, distorted or partially deformed cells and small aggregates were not present until 2–3 wk after injection. The salivary gland cells of injected insects contained membrane-bound ‘pockets’ or ‘colonies’ packed with pleomorphic organisms, which included some filamentous forms. Intracellular colonies were always on the periphery of cells and were easily detectable by fluorescent microscopy. Both pleomorphic and filamentous forms were also seen intercellularly in the salivary glands. Following injection, transmission of CSS to maize and to sterile feeding solution were compared using 1 day feeding periods. A proportion of injected leafhoppers began to transmit to maize by the third day following injection (5%) and reached a maximum of 72% by day 14. By day 9 , 82% of the population had transmitted at least once to plants and by day 12 , 100% had transmitted. Similar insects transmitted through membranes to sterile feeding solution on day 4 (3%) reaching a maximum of 62% by day 14.     

The clypeal gland: A new exocrine gland in termite imagoes (Isoptera: Serritermitidae,Rhinotermitidae, Termitidae)

Social insects possess a rich set of exocrine organs producing diverse pheromones and defensive compounds. This is especially true for termite imagoes, which are equipped with several glands producing, among others, sex pheromones and defensive compounds protecting imagoes during the dispersal flight and colony foundation. Here, we describe the clypeal gland, a new termite exocrine organ occurring in the labro-clypeal region of imagoes of most Rhinotermitidae, Serritermitidae and Termitidae species. The clypeal gland of Coptotermes testaceus consists of class 1 (modified epidermal cell) and class 3 (bicellular gland unit) secretory cells. Ultrastructural features suggest that the gland secretes volatile compounds and proteins, probably after starting the reproduction. One peculiar feature of the gland is the presence of multiple secretory canals in a single canal cell, a feature never observed before in other insect glands. Although the function of the gland remains unknown, we hypothesize that it could produce secretion signalling the presence of functional reproductives or their need to be fed.     

弯齿琵甲防御分泌物的化学成分测定及抗菌活性分析

弯齿琵甲Blaps femoralis Fischervon Waldheim是中国北方的优势土壤昆虫,其防御腺分泌物用于御敌和引起本种群体的集结,体外具有一定毒性,民间将该虫作为药用昆虫资源利用年代久远。由该虫防御腺体获得分泌物并经气相色谱-质谱联用技术(GC-MS)分析,共计获得14种小分子化合物,其中以2-甲基苯醌、1-十三碳烯和2,4-二甲基-3-呋喃乙酮含量较高,苯醌、苯二酚、3,5-二羟基甲苯和十二烷醛等小分子化合物次之。研究证实该分泌物具有较明显的抑菌能力。研究结果为今后进一步深入开展弯齿琵甲的防御腺化学分泌物天然产物的研究积累了工作。     

Fractionation of DNA from marine invertebrate (Maja crispata, Mytilus galloprovincialis) haemolymph by alkaline elution.

1. An alkaline elution procedure for the detection of DNA damage in marine invertebrate haemolymph has been developed. 2. Provided that three criteria are optimized, such as buffer composition, small filter pores (0.22 microns GVWP 025 00, Millipore), and optimal amounts of haemolymph applied, flow rates may be changed within the range of 0.2 ml/min to 0.05 ml/min without adverse back-pressure on the filter and without blocking filter pores. 3. Under optimal conditions, 70% of mussel haemolymph DNA, and 80% of crab haemolymph DNA will be retained on the filter after 6 hr of elution, indicating shorter DNA in mussel haemolymph. 4. The technique is applicable for testing the in vivo effects of different compounds on DNA in marine invertebrates, and to measurements of DNA damage in naturally exposed mussels. 5. This argues an important case for the use of alkaline elution technique for assessment of environmental genotoxicity, and especially for investigation of DNA damage in different marine organisms which cover a broad range in their DNA molecular weights.     

GENES WITH SOCIAL EFFECTS ARE EXPECTED TO HARBOR MORE SEQUENCE VARIATION WITHIN AND BETWEEN SPECIES

The equilibrium sequence diversity of genes within a population and the rate of sequence divergence between populations or species depends on a variety of factors, including expression pattern, mutation rate, nature of selection, random drift, and mating system. Here, we extend population genetic theory developed for maternal-effect genes to predict the equilibrium polymorphism within species and sequence divergence among species for genes with social effects on fitness. We show how the fitness effects of genes, mating system, and genetic system affect predicted gene polymorphism. We find that, because genes with indirect social effects on fitness effectively experience weaker selection, they are expected to harbor higher levels of polymorphism relative to genes with direct fitness effects. The relative increase in polymorphism is proportional to the inverse of the genetic relatedness between individuals expressing the gene and their social partners that experience the fitness effects of the gene. We find a similar pattern of more rapid divergence between populations or species for genes with indirect social effects relative to genes with direct effects. We focus our discussion on the social insects, organisms with diverse indirect genetic effects, mating and genetic systems, and we suggest specific examples for testing our predictions with emerging sociogenomic tools.     

Natural selection on extrafloral nectar production in Chamaecrista fasciculata: the costs and benefits of a mutualism trait

Cost-benefit models of the evolution of mutualism predict that the current state of mutualism results from trade-offs between fitness costs of mutualist traits and the fitness benefits of association. We test the assumptions of such models by measuring patterns of natural selection on a mutualist trait, extrafloral nectar production in Chamaecrista fasciculata. Selection was measured on plants from which ants had been excluded (removing the mutualist benefit of the trait), from which all insects had been excluded (removing costs of herbivory in addition to mutualist benefits), and unmanipulated plants (where both costs and benefits were present). Selection analysis based on half-sibling-mean regressions of fitness on the trait revealed no evidence of costs of extrafloral nectar production in the absence of all insects or in the absence of ants. However, examination of the selective surfaces for these treatments suggest that costs of nectar production may exist and are exacerbated by the presence of herbivory. In the presence of ants, natural selection favors high extrafloral nectar production, consistent with a fitness benefit to this mutualist trait in the presence of the mutualist partner. In this study, the interaction of costs and benefits did not produce an evolutionary optimum for the trait within the range of variation observed, suggesting that application of a cost-benefit framework to this trait will benefit from considering the influence of temporal and spatial variation on the quality of costs and benefits.     

Nondestructive DNA sampling from bumblebee faeces

Genetic studies provide valuable data to inform conservation strategies for species with small or declining populations. In these circumstances, obtaining DNA samples without harming the study organisms is highly desirable. Excrements are increasingly being used as a source of DNA in such studies, but such approaches have rarely been applied to arthropods. Bumblebees are ecologically and economically important as pollinators; however, some species have recently suffered severe declines and range contractions across much of Western Europe and North America. We investigated whether bumblebee faeces could be used for the extraction of DNA suitable for genotyping using microsatellite markers. We found that DNA could be extracted using a Chelex method from faecal samples collected either in microcapillary tubes or on filter paper, directly from captured individuals. Our results show that genotypes scored from faecal samples are identical to those from tissue samples. This study describes a reliable, consistent and efficient noninvasive method of obtaining DNA from bumblebees for use in population genetic studies. This approach should prove particularly useful in breeding and conservation programs for bumblebees and may be broadly applicable across insect taxa.     

Lack of patriline-specific differences in chemical composition of the metapleural gland secretion in <Emphasis Type="Italic">Acromyrmex octospinosus</Emphasis>

Summary. Multiple queen-mating (polyandry) in social insects increases the genetic variability among worker offspring, which may enhance colony survival, social productivity and defence against parasites. The unique and complex symbiosis of leaf-cutting ants with a clonal mutualistic fungus makes this social system particularly vulnerable to contamination by pathogenic and unwanted saprophytic fungi and bacteria. Proper defence against such threats requires effective and flexible chemical defence mechanisms. A prime candidate for providing such defences is the metapleural gland secretion, which is known to have broad antibiotic properties. Here we use the leaf-cutting ant Acromyrmex octospinosus to specifically test the hypothesis that genetically more diverse worker-offspring produce a more variable spectrum of metapleural gland compounds. We used DNA microsatellite markers to assign workers from two colonies to the six most common patrilines in each colony, and have analysed the degree to which the observed variance in the quantitative chemical composition of the metapleural gland secretion can be explained by genetic differences among patrilines. We found a marginally significant patriline-effect on the overall variability of metapleural gland compounds in one colony, but could not detect such effect in the other colony. We discuss a number of possible reasons why the genetic variance component for quantitative variation in metapleural gland secretion may be low.     

Fitness in invasive social wasps: the role of variation in viral load,immune response and paternity in predicting nest size and reproductive output

Within any one habitat, the relative fitness of organisms in a population can vary substantially. Social insects like the common wasp are among the most successful invasive animals, but show enormous variation in nest size and other fitness‐related traits. Some of this variation may be caused by pathogens such as viruses that can have serious consequences in social insects, which range from reduced productivity to colony death. Both individual immune responses and colony‐level traits such as genetic diversity are likely to influence effects of pathogen infections on colony fitness. Here we investigate how infections with Kashmir Bee Virus (KBV), immune response and intracolony genetic diversity (due to queen polyandry) affect nest size in the invasive common wasp Vespula vulgaris. We show that KBV is highly prevalent in wasps and expression of antiviral immune genes is significantly increased with higher viral loads across individuals. Patriline membership within a nest did not influence KBV susceptibility or immune response. A permutational MANCOVA revealed that polyandry, viral load and expression of the immune gene Dicer were significant predictors of variation in nest size. High intracolony genetic diversity due to polyandry has previously been hypothesized to improve colony‐level resistance to parasites and pathogens. Consistent with this hypothesis, we observed genetically diverse colonies to be significantly larger and to produce more queens, although this effect was not driven by the pathogen we investigated. Invasive wasps clearly suffer from pathogens and expend resources, as indicated here by elevated immune gene expression, toward reducing pathogen‐impact on colony fitness.     

Associations among cytoplasmic molecular markers,gender, and components of fitness in Silene vulgaris,a gynodioecious plant

It has been suggested that the dynamics of chloroplast DNA (cpDNA) or mitochondrial DNA (mtDNA) genetic markers used in studies of plant populations could be influenced by natural selection acting elsewhere in the genome. This could be particularly true in gynodioecious plants if cpDNA or mtDNA genetic markers are in gametic disequilibrium with genes responsible for sex expression. In order to investigate this possibility, a natural population of the gynodioecious plant Silene vulgaris was used to study associations among mtDNA haplotype, cpDNA haplotype, sex and some components of fitness through seed. Individuals were sampled for mtDNA and cpDNA haplotype as determined using restriction fragment length polymorphism (RFLP) methods, sex (female or hermaphrodite), fruit number, fruit set, seeds/fruit and seed germination. The sex of surviving germinating seeds was also noted. All individuals in the population fell into one of two cytoplasmic categories, designated haplotypes f and g by a unique electrophoretic signature in both the mtDNA and cpDNA. The subset of the population carrying haplotype g included a significantly higher proportion of females when compared with the sex ratio of the subset carrying the f haplotype. Haplotype g had a significantly higher fitness when measured by fruit number, fruit set and seeds/fruit, whereas haplotype f had significantly higher fitness when measured by seed germination. Offspring of individuals carrying haplotype g included a significantly greater proportion of females when compared with offspring of individuals carrying the f haplotype. Other studies of gynodioecious plants have shown that females generally have higher fitness through seed than hermaphrodites, but in this study not all fitness differences between haplotypes could be predicted from differences in haplotype-specific sex ratio alone. Rather, some differences in haplotype-specific fitness were due to differences in fitness between individuals of the same sex, but carrying different haplotypes. The results are discussed with regard to the potential for hitchhiking selection to influence the dynamics of the noncoding regions used to designate the cpDNA and mtDNA haplotypes.     

Isolation of Sperm Vesicles from Adult Male Mayflies and Other Insects to Prepare High Molecular Weight Genomic DNA Samples

We describe here a simple and efficient protocol for genomic DNA isolation from adult males of insects: e.g., Ephemeroptera, Odonata, Orthoptera and Dictyoptera. To minimize contamination of external DNA source, the sperm vesicles were isolated from male individuals from which high molecular weight genomic DNA was extracted. According to this protocol, the genomic DNA samples obtained were high quality (intact), and abundant enough for genotyping analyses and molecular cloning. The protocol reported here enables us to process a huge number of individuals at a time with escaping from cross-contamination, and thus it is quite useful for conducting genetic studies at least in some species of insects. The large yield of high molecular weight DNA from single individual may be advantageous for non PCR-based experiments. As a case study of the protocol, partial coding sequences of histone H3 and EF-1α genes are determined for some insects with PCR-amplified DNA fragments.     

昆虫的体外化学防卫物质简介

本文介绍了昆虫体外防御物质的释放部位、来源、化学成分及影响其释放的因素等的研究进展。     

Heritability of immune function in the caterpillar Spodoptera littoralis

Phenoloxidase (PO) is believed to be a key mediator of immune function in insects and has been implicated both in non-self recognition and in resistance to a variety of parasites and pathogens, including baculoviruses and parasitoids. Using larvae of the Egyptian cotton leafworm, Spodoptera littoralis, we found that despite its apparent importance, haemolymph PO activity varied markedly between individuals, even amongst insects reared under apparently identical conditions. Sib-analysis methods were used to determine whether individuals varied genetically in their PO activity, and hence in one aspect of immune function. The heritability estimate of haemolymph PO activity was high (h(2) = 0.690 +/- 0.069), and PO activity in the haemolymph was strongly correlated with PO activity in both the cuticle and midgut; the sites of entry for most parasites and pathogens. Haemolymph PO activity was also strongly correlated with the degree to which a synthetic parasite (a small piece of nylon monofilament) was encapsulated and melanized (r = 0.622 +/- 0.142), suggesting that the encapsulation response is also heritable. The mechanism maintaining this genetic variation has yet to be elucidated.     

Fluid secretion by single isolated Malpighian tubules of the house cricket, Acheta domesticus, and their response to diuretic hormone

ABSTRACT. A simple modification of the Ramsay method is described for the isolation in vitro of Malpighian tubules from Acheta domesticus. Isolated tubules continue to secrete for many hours in a simple Ringer solution. The rate of secretion is linearly related to the length of tubule within the bathing fluid.
Secretion rates during the immediate post-equilibration period relate to the physiological state of the donor insect. Highest rates are recorded in tubules removed from animals during the scotophase when the crickets are most actively feeding. Starvation reduces the rate of secretion and when previously starved insects are given access to food the rate increases. These results are consistent with variations in the haemolymph titre of DH that are induced by feeding.
Tubule fluid secretion is stimulated by either CC extract (1 gland pair/50 μ1) or dibutyryl cAMP (10^-3M). CC extracts increase the rate of fluid secretion by c. 200 pl/mm/min for up to 6 h after the tubules have been isolated. The response varies little with the age or physiological state of the donor insect. However, tubules from newly moulted insects secrete at very low rates and respond poorly to CC extract, although they are stimulated by cAMP. The significance of these results is discussed with particular reference to the use of Acheta tubules as a bioassay preparation for DH.     

Antagonistic pleiotropy and mutation accumulation contribute to age‐related decline in stress response

As organisms age, the effectiveness of natural selection weakens, leading to age‐related decline in fitness‐related traits. The evolution of age‐related changes associated with senescence is likely influenced by mutation accumulation (MA) and antagonistic pleiotropy (AP). MA predicts that age‐related decline in fitness components is driven by age‐specific sets of alleles, nonnegative genetic correlations within trait across age, and an increase in the coefficient of genetic variance. AP predicts that age‐related decline in a trait is driven by alleles with positive effects on fitness in young individuals and negative effects in old individuals, and is expected to lead to negative genetic correlations within traits across age. We build on these predictions using an association mapping approach to investigate the change in additive effects of SNPs across age and among traits for multiple stress‐response fitness‐related traits, including cold stress with and without acclimation and starvation resistance. We found support for both MA and AP theories of aging in the age‐related decline in stress tolerance. Our study demonstrates that the evolution of age‐related decline in stress tolerance is driven by a combination of alleles that have age‐specific additive effects, consistent with MA, as well as nonindependent and antagonistic genetic architectures characteristic of AP.