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The outcome of natural enemy attack in insects is commonly impacted by the presence of defensive microbial symbionts residing within the host. The thermal environment is a factor known to affect symbiont‐mediated traits in insects. Lower temperatures, for instance, have been shown to reduce Spiroplasma‐mediated protection in Drosophila. Our understanding of protective symbiosis requires a deeper understanding of environment–symbiont–protection links. Here, we dissect the effect of the thermal environment on Spiroplasma‐mediated protection against Leptopilina boulardi in Drosophila melanogaster by examining the effect of temperature before, during and after wasp attack on fly survival and wasp success. We observed that the developmental temperature of the mothers of attacked larvae, but not the temperature of the attacked larvae themselves during or after wasp attack, strongly determines the protective influence of Spiroplasma. Cooler maternal environments were associated with weaker Spiroplasma protection of their progeny. The effect of developmental temperature on Spiroplasma‐mediated protection is probably mediated by a reduction in Spiroplasma titre. These results indicate that historical thermal environment is a stronger determinant of protection than current environment. Furthermore, protection is a character with transgenerational nongenetic variation probably to produce complex short‐term responses to selection. In addition, the cool sensitivity of the Spiroplasma–Drosophila symbioses contrasts with the more common failure of symbioses at elevated temperatures, indicating a need to understand the mechanistic basis of low temperature sensitivity on this symbiosis. [ABSTRACT FROM AUTHOR]

While heritable symbionts are common in insects, strains that act as male-killers are considered rare. A new study in PLOS Biology identifies a novel male-killer hidden by coinfection and host resistance, highlighting the complexity of host-microbial interactions in natural systems. While heritable symbionts are common in insects, strains that act as male-killers are considered rare. This Primer explores a new study in PLOS Biology which reveals a novel male-killer hidden by co-infection and host resistance, highlighting the complexity of host-microbial interactions in natural systems. [ABSTRACT FROM AUTHOR]

When a parasite attacks an insect, the outcome is commonly modulated by the presence of defensive heritable symbionts residing within the insect host. Previous studies noted markedly different strengths of Spiroplasma‐mediated fly survival following attack by the same strain of wasp. One difference between the two studies was the strain of Spiroplasma used. We therefore performed a laboratory experiment to assess whether Spiroplasma‐mediated protection depends upon the strain of Spiroplasma. We perform this analysis using the two strains of male‐killing Spiroplasma used previously, and examined response to challenge by two strains of Leptopilina boulardi and two strains of Leptopilina heterotoma wasp. We found no evidence Spiroplasma strain affected fly survival following wasp attack. In contrast, analysis of the overall level of protection, including the fecundity of survivors of wasp attack, did indicate the two Spiroplasma strains tested varied in protective efficiency against three of the four wasp strains tested. These data highlight the sensitivity of symbiont‐mediated protection phenotypes to laboratory conditions, and the importance of common garden comparison. Our results also indicate that Spiroplasma strains can vary in protective capacity in Drosophila, but these differences may exist in the relative performance of survivors of wasp attack, rather than in survival of attack per se. The outcome of parasite attack is commonly modulated by the presence of defensive heritable symbionts residing within the insect host. We performed an experiment to determine whether the strength of symbiont‐mediated protection depends on the strain of defensive symbiont using the Spiroplasma–Drosophila–Leptopilina model system. We found no evidence that Spiroplasma strain affected the strength of Drosophila survival following attack by Leptopilina wasps. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the biology of heritable symbionts based on a diverse assemblage of maternally inherited bacteria present in a range of arthropods. Researchers have noted the effect of infection on a host as a complex aspect over the existence of heritable microbes in insect. It has been hypothesized that the parasites found in the reproductive system of arthropods were responsible for drive mechanisms through sex ratio distortion and cytoplasmic incompatibility.

Inherited microorganisms that manipulate the reproduction of their host are a common feature in arthropod biology. Although research initially concentrated on why these manipulations were observed, more recent study has emphasized the profound effects they may have on the ecology and evolution of their host. We review the natural history and evolutionary ecology of inherited reproductive parasites, before examining their impact on host ecology and evolution. We posit that sex-ratio distorting microorganisms sometimes dominate their host's microevolution and reproductive ecology, driving extremely rapid natural selection, altering the molecular evolution landscape, and potentially causing evolution in conserved systems such as sex determination. The evolutionary importance of symbionts inducing cytoplasmic incompatibility lies more in the barriers to gene flow they can produce, which may then contribute to reproductive isolation and speciation. Throughout, we link theory with empirical data, point to areas of ignorance, and identify promising avenues of future research. [ABSTRACT FROM AUTHOR]

Closely related pathogens and parasites often have distinctly different strategies for transmission. In some cases, presence of one potential mode of transmission reduces the rate of or forbids another. In these cases, one can ask what the conditions are that favor the use of one mode of transmission over the other. We constructed a mathematical model to examine this issue for the case of maternally inherited endosymbionts of insects. Here, killing males (to enhance transmission through the female line by reducing sibling competition) and retaining live males as a vehicle for sexual transmission are mutually exclusive strategies. Our model indicates that sexual transmission of a maternally inherited parasite can exclude a male-killing strain, provided that a sexually transmitted infection can take over an infection by a male-killing strain either following exposure or when male killing is incomplete and sexual transmission is efficient. The presence of sexual transmission may also explain why secondary symbionts do not degrade toward the evolution of male killing but remain as "beneficial partners" to both male and female hosts. This stabilization may be fundamental to the evolution toward obligate mutualism, and thus it is important in the ecology and evolution of many arthropod groups. [ABSTRACT FROM AUTHOR]

Inherited bacteria are now recognized as important players in arthropod evolution and ecology. Here, we test spiders, a group recently identified as possessing inherited bacteria commonly, for the presence of two reproductive parasites, Cardinium hertigii (Bacteroidetes group) and Wolbachia (α-proteobacteria), estimating incidence, prevalence, any sex bias in infection, and infection diversity, for a panel of field-collected specimens. We identify spiders as a hotspot for Cardinium. Present in 22% of the sampled species, incidence was significantly higher than that previously recorded in insects. Where present, Cardinium infection occurred at medium prevalence without evidence of sex bias in prevalence that would indicate sex-ratio distortion activity. Wolbachia was present in 37% of species, but revealed a gradation from being rare to very common. In one case, Wolbachia was found significantly more commonly in females than males, indicating it may act as a sex-ratio distorter in some species. Breeding work conducted on two species confirmed that Wolbachia and Cardinium were transmitted maternally, which represents the first proof of inheritance of these symbionts in spiders. Overall, this study demonstrates that the majority of spider species are infected with inherited bacteria, and their role in host biology clearly requires determination. [ABSTRACT FROM AUTHOR]

Male-killing bacteria are maternally inherited endosymbionts that selectively kill male offspring of their arthropod hosts. Using both analytical techniques and computer simulations, we studied the impact of these bacteria on the population genetics of their hosts. In particular, we derived and corroborated formulas for the fixation probability of mutant alleles, mean times to fixation and fixation or extinction, and heterozygosity for varying male-killer prevalence. Our results demonstrate that infections with male-killing bacteria impede the spread of beneficial alleles, facilitate the spread of deleterious alleles, and reduce genetic variation. The reason for this lies in the strongly reduced fitness of infected females combined with no or very limited gene flow from infected females to uninfected individuals. These two properties of male-killer-infected populations reduce the population size relevant for the initial emergence and spread of mutations. In contrast, use of Wright's equation relating sex ratio to effective population size produces misleading predictions. We discuss the relationship to the similar effect of background selection, the impact of other sex-ratio-distorting endosymbionts, and how our results affect the interpretation of empirical data on genetic variation in male-killer-infected populations. [ABSTRACT FROM AUTHOR]

The sex ratio is a key parameter in the evolution and ecology of a species. Selfish genetic elements that bias the sex ratio of affected individuals are well known and characterized, but their effect on populations has been considered limited, because either the element does not achieve high prevalence or the host rapidly evolves resistance to the distorting element reducing its prevalence. We tested whether the host necessarily prevails by using a butterfly system where records from the early part of the 20th century reported extreme sex-ratio bias in nature. We reexamined this population and found the bias was present today, 400 generations after the original record, with a population sex ratio of 100 females per male. The sex-ratio bias was associated with the presence of a heritable male-killing Wolbachia infection in 99% of adult females, against which the host butterfly has failed to evolve resistance. The resultant dearth of males causes an average 57% reduction in the reproductive output of adult females. Persistence of the population despite the very high frequency of the sex-ratio distorter appears to be associated with the ability of males to mate >50 times in their life combined with a high intrinsic rate of increase of the species. [ABSTRACT FROM AUTHOR]

Journal of Animal Ecology (2004) 73, 1–10 [ABSTRACT FROM AUTHOR]

Genes involved in the recognition of parasites by the acquired immune system are often subject to intense selection pressures. In some cases, selection to recognize a diverse range of parasites has resulted in high levels of polymorphism, while elsewhere the protein sequence has changed rapidly under directional selection. We tested whether parasite recognition genes in the innate immune system show similar patterns of evolution. We sequenced seven peptidoglycan recognition protein genes (PGRPs) from 12 lines of Drosophilamelanogaster and one line of D. simulans and used a variety of tests to determine whether the observed mutations were selectively neutral. We were unable to detect either balancing or directional selection. This suggests that the molecular cues used by insects to detect parasites are highly conserved and probably under strong functional constraints which prevent their evolving to evade the host immune response. Therefore, interactions between these genes are unlikely to be the focus of host–parasite coevolution, at least in Drosophila. We also found evidence of gene conversion occurring between two genes, PGRP-SC1A and PGRP-SC1B. [ABSTRACT FROM AUTHOR]

Insects and other arthropods have an effective innate immune system that can clear infections with bacteria and other microorganisms. Despite this ability, one group of bacteria, the spiroplasmas, survive unharmed within the haemolymph of a wide range of arthropod hosts. We investigated the interaction between one member of this clade, a relative of Spiroplasma poulsonii, and the immune system of its Drosophila host. Expression of antimicrobial genes in spiroplasmainfected flies did not differ from wild-type controls either in the naturally infected state, nor after septic shock. We therefore concluded that spiroplasma infection did not induce an immune response in its host, but that this absence of response was unlikely to be because the bacterium inhibited response. Further experiments revealed immune reactions induced ectopically did reduce parasite titre. We therefore conclude that this bacterium has a novel form of interaction with its host, being hidden from the host immune system, but potentially suppressible by it. [ABSTRACT FROM AUTHOR]

Selfish genetic elements that distort the sex ratio are common in arthropods. Theory predicts they will invade and spread to fixation if they are vertically transmitted with perfect fidelity, potentially leading to host extinction. For inherited microorganisms that distort the sex ratio, inefficient vertical transmission or incomplete sex ratio distorting ability is required for host persistence. However, the relative roles of genetic and environmental factors in permitting the survival of male hosts and preventing parasite transmission are poorly understood. We examined the causes of transmission infidelity and male survival for a male-killing Wolbachia strain in Drosophilabifasciata. Under standard laboratory conditions (18°C), in its standard genetic background, males are produced very rarely, and no case of reversion has been observed in 20 generations of laboratory rearing. To investigate the role of host genetic factors, Wolbachia was crossed into 27 different inbred lines of D.bifasciata, but in no case was reversion observed at preferred environmental temperatures. The role of elevated temperature in inducing inefficient transmission was examined. Whilst vertical transmission was perfect over three generations of maintenance at 23.5°, transmission infidelity was observed at 25°. We conclude that there is no evidence for the presence of either fixed or polymorphic host genes that repress transmission at standard environmental temperatures. However, severe temperature treatment does make vertical transmission imperfect. We suggest that the case of Wolbachia in D.bifasciata is one that is naturally balanced, the population being maintained polymorphic without the evolution of host resistance genes. [ABSTRACT FROM AUTHOR]

'Selfish genetic elements', such as transposons, homing endonucleases, meiotic drive chromosomes and heritable microorganisms, are common features of eukaryotes. However, their importance in the evolution of eukaryotic genomes is still controversial. In this review, we discuss these diverse elements and their potential importance in the evolution of genetic systems, adaptation, and the extinction and birth of species. [ABSTRACT FROM AUTHOR]

Inherited bacteria that kill male hosts early in their development are known from five insect orders. We ask to what extent the incidence of male-killers might be restricted by the rate at which new host–parasite interactions arise, by testing whether multiple male-killers have invaded a single host species. In Uganda, the butterflies Acraea encedon and A. encedana are both infected by the same strain of male-killing Wolbachia and there was no evidence of variation within the population. In Tanzanian A. encedon however, two phylogenetically distinct strains of male-killing Wolbachia were found within the same population. If this pattern of male-killer polymorphism is found to be general across infected species, it suggests that new male-killing infections arise frequently on an evolutionary time scale. Whether this polymorphism is stable, and what forces may be maintaining it, are unknown. [ABSTRACT FROM AUTHOR]

Arthropods host a range of sex-ratio-distorting selfish elements, including diverse maternally inherited endosymbionts that solely kill infected males. Male-killing heritable microbes are common, reach high frequency, but until recently have been poorly understood in terms of the host–microbe interaction. Additionally, while male killing should generate strong selection for host resistance, evidence of this has been scant. The interface of the microbe with host sex determination is integral to the understanding of how death is sex limited and how hosts can evolve evasion of male killing. We first review current knowledge of the mechanisms diverse endosymbionts use to induce male-specific death. We then examine recent evidence that these agents do produce intense selection for host nuclear suppressor elements. We argue, from our understanding of male-killing mechanisms, that suppression will commonly involve evolution of the host sex determination pathways and that the host's response to male-killing microbes thus represents an unrecognized driver of the diversity of arthropod sex determination. Further work is required to identify the genes and mechanisms responsible for male-killing suppression, which will both determine the components of sex determination (or other) systems associated with suppressor evolution, and allow insight into the mechanism of male killing itself. [ABSTRACT FROM AUTHOR]

Whilst parthenogenesis has evolved multiple times from sexual invertebrate and vertebrate lineages, the drivers and consequences of the sex-asex transition remain mostly uncertain. A model by Stouthamer et al. recently published in BMC Evolutionary Biology shows a pathway by which obligate asexuality could be selected for following endosymbiont infection. [ABSTRACT FROM AUTHOR]

Seven dinucleotide and one trinucleotide polymorphic microsatellite loci were isolated from the mite Coccipolipus hippodamiae. This mite is an ectoparasite of coccinellid beetles (ladybirds), principally the European two-spot ladybird Adalia bipunctata, where it causes sterility in the female host. Levels of genetic diversity were assessed using 32 mites from Warsaw, Poland. We observed moderate variability, with the number of alleles per locus varying between 2 and 4, and observed and expected heterozygosities ranging from 0.031 to 0.267 and between 0.062 and 0.526, respectively. This is the first description of microsatellite loci from the genus Coccipolipus and these loci are currently being employed to answer fundamental questions about the epidemiology of C. hippodamiae infections on A. bipunctata. [ABSTRACT FROM AUTHOR]

Diverse eukaryotic taxa carry facultative heritable symbionts, microbes that are passed from mother to offspring. These symbionts are coinherited with mitochondria, and selection favouring either new symbionts, or new symbiont variants, is known to drive loss of mitochondrial diversity as a correlated response. More recently, evidence has accumulated of episodic directional selection on mitochondria, but with currently unknown consequences for symbiont evolution. We therefore employed a population genetic mean field framework to model the impact of selection on mitochondrial DNA (mtDNA) upon symbiont frequency for three generic scenarios of host–symbiont interaction. Our models predict that direct selection on mtDNA can drive symbionts out of the population where a positively selected mtDNA mutation occurs initially in an individual that is uninfected with the symbiont, and the symbiont is initially at low frequency. When, by contrast, the positively selected mtDNA mutation occurs in a symbiont-infected individual, the mutation becomes fixed and in doing so removes symbiont variation from the population. We conclude that the molecular evolution of symbionts and mitochondria, which has previously been viewed from a perspective of selection on symbionts driving the evolution of a neutral mtDNA marker, should be reappraised in the light of positive selection on mtDNA. [ABSTRACT FROM AUTHOR]

Diverse eukaryotic taxa carry facultative heritable symbionts, microbes that are passed from mother to offspring. These symbionts are coinherited with mitochondria, and selection favouring either new symbionts, or new symbiont variants, is known to drive loss of mitochondrial diversity as a correlated response. More recently, evidence has accumulated of episodic directional selection on mitochondria, but with currently unknown consequences for symbiont evolution. We therefore employed a population genetic mean field framework to model the impact of selection on mitochondrial DNA (mtDNA) upon symbiont frequency for three generic scenarios of host–symbiont interaction. Our models predict that direct selection on mtDNA can drive symbionts out of the population where a positively selected mtDNA mutation occurs initially in an individual that is uninfected with the symbiont, and the symbiont is initially at low frequency. When, by contrast, the positively selected mtDNA mutation occurs in a symbiont-infected individual, the mutation becomes fixed and in doing so removes symbiont variation from the population. We conclude that the molecular evolution of symbionts and mitochondria, which has previously been viewed from a perspective of selection on symbionts driving the evolution of a neutral mtDNA marker, should be reappraised in the light of positive selection on mtDNA. [ABSTRACT FROM AUTHOR]

Symbiotic bacteria can alter host biology by providing protection from natural enemies, or alter reproduction or vectoral competence. Symbiont‐linked control of vector‐borne disease in Anopheles has been hampered by a lack of symbioses that can establish stable vertical transmission in the host. Previous screening found the symbiont 'Candidatus Tisiphia' in Anopheles plumbeus, an aggressive biter and potential secondary vector of malaria parasites and West Nile virus. We screened samples collected over 10‐years across Germany and used climate databases to assess environmental influence on incidence. We observed a 95% infection rate, and that the frequency of infection did not fluctuate with broad environmental factors. Maternal inheritance is indicated by presence in the ovaries through FISH microscopy. Finally, we assembled a high‐quality 1.6 Mbp draft genome of 'Ca. Tisiphia' to explore its phylogeny and potential metabolic competence. The infection is closely related to strains found in Culicoides biting midges and shows similar patterns of metabolism, providing no evidence of the capacity to synthesize B‐vitamins. This infection offers avenues for onward research in anopheline mosquito symbioses. Additionally, it provides future opportunity to study the impact of 'Ca. Tisiphia' on natural and transinfected hosts, especially in relation to reproductive fitness and vectorial competence and capacity. [ABSTRACT FROM AUTHOR]

The article focuses on a research done in order to determine microbial involvement in reproductive isolation it informs that the research demonstrated that environmentally induced changes in the composition of the gut microbiota could affect the genetic characters such as mate preference in Drosophila fruitflies. It informs that microbes that are symbiotic with the wasp can kill hybrid wasp larvae, to create barriers that keep species separate.

The article reports on a case study that examined the evolutionary effects of a bacterial symbiont that was introduced into a population of the whitefly Bemisia tabaci. Over a period of six years, the introduction of a symbiont of the bacteria Rickettsia dramatically increased the survival rate and fecundity of the host population in the southwestern U.S. While microbiologists have allegedly long known the importance of horizontal gene transfer between organisms, it has not been as commonly studied in multicellular organisms such as arthropods.

The resilience of populations to rapid environmental degradation is a major concern for biodiversity conservation. When environments deteriorate to lethal levels, species must evolve to adapt to the new conditions to avoid extinction. Here, we test the hypothesis that evolutionary rescue may be enabled by hybridization, because hybridization increases genetic variability. Using experimental evolution, we show that interspecific hybrid populations of Saccharomyces yeast adapt to grow in more highly degraded environments than intraspecific and parental crosses, resulting in survival rates far exceeding those of their ancestors. We conclude that hybridization can increase evolutionary responsiveness and that taxa able to exchange genes with distant relatives may better survive rapid environmental change. [ABSTRACT FROM AUTHOR]

Background: Insect symbionts employ multiple strategies to enhance their spread through populations, and some play a dual role as both a mutualist and a reproductive manipulator. It has recently been found that this is the case for some strains of Wolbachia, which both cause cytoplasmic incompatibility and protect their hosts against viruses. Here, we carry out the first test as to whether a male-killing strain of Wolbachia also provides a direct benefit to its host by providing antiviral protection to its host Drosophila bifasciata. We infected flies with two positive sense RNA viruses known to replicate in a range of Drosophila species (Drosophila C virus and Flock House virus) and measure the rate of death in Wolbachia positive and negative host lines with the same genetic background. Results: Both viruses caused considerable mortality to D. bifasciata flies, with Drosophila C virus killing 43% more flies than the uninfected controls and Flock House virus killing 78% more flies than the uninfected controls. However, viral induced mortality was unaffected by the presence of Wolbachia. Conclusion: In the first male-killing Wolbachia strain tested for antiviral effects, we found no evidence that it conferred protection against two RNA viruses. We show that although antiviral resistance is widespread across the Wolbachia phylogeny, the trait seems to have been lost or gained along some lineages. We discuss the potential mechanisms of this, and can seemingly discount protection against these viruses as a reason why this symbiont has spread through Drosophila populations. [ABSTRACT FROM AUTHOR]

Ecology Letters (2010) 13: 1139–1148 Inherited symbionts are important drivers of arthropod evolutionary ecology, with microbes acting both as partners that contribute to host adaptation, and as subtle parasites that drive host evolution. New symbioses are most commonly formed through lateral transfer, where a microbial symbiont passes infectiously from one host species to another, and then spreads through its new host population. However, the rate of horizontal transfer has been regarded as sufficiently low that population and coevolutionary processes can be approximated to one, where the symbiont interacts with a single host species. In this paper, we demonstrate experimentally that horizontal transfer of the son-killer infection of Nasonia wasps occurs readily following multi-parasitism events (two species of parasitoid wasp sharing a fly pupal host), and provide phylogenetic evidence of recent and likely ongoing transmission amongst members of the community of wasps utilizing filth flies. Combining per contact transmission rates estimated in the laboratory with rates of multiparasitism in the field produces an estimate that an infected Nasonia vitripennis individual in an Eastern US bird’s nest habitat has a 12% chance of passing the infection into N. giraulti. We conclude that the single host-single symbiont framework is therefore insufficient for understanding the population and evolutionary dynamics in this system and caution against blind acceptance of the single host/single symbiont framework. We conjecture that lateral transfer rates that require a multi-host framework will most likely be seen in symbionts that retain the ability to cross host epithelia, and that this will be correlated to the recency with which the symbionts have been free living. [ABSTRACT FROM AUTHOR]

Within the Diptera, two different selfish genetic elements are known to cause the production of female-biased sex ratios: maternally inherited bacteria that kill male zygotes (male-killers), and X chromosomes causing the degeneration of Y-bearing sperm in males (meiotic drive). We here develop a mathematical model for the dynamics of these two sex-ratio distorters where they co-occur. We show that X chromosome meiotic drive elements can be expected to substantially lower the equilibrium frequency of male-killers and can even lead to their extinction. Conversely, male-killers can also decrease the equilibrium frequency of X drivers and cause their extinction. Thus, we predict that there will be some complementarity in the incidence of X chromosome meiotic drive and male-killing in natural populations, with a lower than expected number of species bearing both elements. [ABSTRACT FROM AUTHOR]

Background: Selfish genetic elements that distort the sex ratio are found widely. Notwithstanding the number of records of sex ratio distorters, their incidence is poorly understood. Two factors can prevent a sex ratio distorter from invading: inability of the sex ratio distorter to function (failure of mechanism or transmission), and lack of drive if they do function (inappropriate ecology for invasion). There has been no test to date on factors causing variation in the incidence of sex ratio distorting cytoplasmic bacteria. We therefore examined whether absence of the male-killing Wolbachia infection in D. bifasciata in Hokkaido island of Japan, in contrast to the presence of infection on the proximal island of Honshu, was associated with failure of the infection to function properly on the Hokkaido genetic background. Results: The male-killer both transmitted and functioned well following introgression to each of 24 independent isofemale inbred lines carrying Hokkaido genetic backgrounds. This was maintained even under stringent conditions of temperature. We therefore reject the hypothesis that absence of infection is due to its inability to kill males and transmit on the Hokkaido genetic background. Further trap data indicates that D. bifasciata may occur at different densities in Hokkaido and Honshu populations, giving some credence to the idea that ecological differentiation could be important. Conclusions: The absence of the infection from the Hokkaido population is not caused by failure of the male-killer to function on the Hokkaido genetic background. [ABSTRACT FROM AUTHOR]

Background: Culicoides imicola (Diptera: Ceratopogonidae) is an important Afrotropical and Palearctic vector of disease, transmitting viruses of animal health and economic significance including African horse sickness and bluetongue viruses. Maternally inherited symbiotic bacteria (endosymbionts) of arthropods can alter the frequency of COI (cytochrome c oxidase subunit I) mitochondrial haplotypes (mitotypes) in a population, masking the true patterns of host movement and gene flow. Thus, this study aimed to assess the mtDNA structure of C. imicola in relation to infection with Candidatus Cardinum hertigii (Bacteroides), a common endosymbiont of Culicoides spp. Methods: Using haplotype network analysis, COI Sanger sequences from Cardinium-infected and -uninfected C. imicola individuals were first compared in a population from South Africa. The network was then extended to include mitotypes from a geographic range where Cardinium infection has previously been investigated. Results: The mitotype network of the South African population demonstrated the presence of two broad mitotype groups. All Cardinium-infected specimens fell into one group (Fisher's exact test, P = 0.00071) demonstrating a linkage disequilibrium between endosymbiont and mitochondria. Furthermore, by extending this haplotype network to include other C. imicola populations from the Mediterranean basin, we revealed mitotype variation between the Eastern and Western Mediterranean basins (EMB and WMB) mirrored Cardinium-infection heterogeneity. Conclusions: These observations suggest that the linkage disequilibrium of Cardinium and mitochondria reflects endosymbiont gene flow within the Mediterranean basin but may not assist in elucidating host gene flow. Subsequently, we urge caution on the single usage of the COI marker to determine population structure and movement in C. imicola and instead suggest the complementary utilisation of additional molecular markers. [ABSTRACT FROM AUTHOR]

Background: Culicoides imicola (Diptera: Ceratopogonidae) is an important Afrotropical and Palearctic vector of disease, transmitting viruses of animal health and economic significance including African horse sickness and bluetongue viruses. Maternally inherited symbiotic bacteria (endosymbionts) of arthropods can alter the frequency of COI (cytochrome c oxidase subunit I) mitochondrial haplotypes (mitotypes) in a population, masking the true patterns of host movement and gene flow. Thus, this study aimed to assess the mtDNA structure of C. imicola in relation to infection with Candidatus Cardinum hertigii (Bacteroides), a common endosymbiont of Culicoides spp. Methods: Using haplotype network analysis, COI Sanger sequences from Cardinium-infected and -uninfected C. imicola individuals were first compared in a population from South Africa. The network was then extended to include mitotypes from a geographic range where Cardinium infection has previously been investigated. Results: The mitotype network of the South African population demonstrated the presence of two broad mitotype groups. All Cardinium-infected specimens fell into one group (Fisher's exact test, P = 0.00071) demonstrating a linkage disequilibrium between endosymbiont and mitochondria. Furthermore, by extending this haplotype network to include other C. imicola populations from the Mediterranean basin, we revealed mitotype variation between the Eastern and Western Mediterranean basins (EMB and WMB) mirrored Cardinium-infection heterogeneity. Conclusions: These observations suggest that the linkage disequilibrium of Cardinium and mitochondria reflects endosymbiont gene flow within the Mediterranean basin but may not assist in elucidating host gene flow. Subsequently, we urge caution on the single usage of the COI marker to determine population structure and movement in C. imicola and instead suggest the complementary utilisation of additional molecular markers. [ABSTRACT FROM AUTHOR]

Investigates whether male Wolbachia bacterium choose to mate with uninfected rather than infected females in order to prevent fixation. Background on Acraea encedon; Factors affecting the prevalence of parasites; Information on bacterial symbionts; Details on the maternally transmitted bacteria among insects.

Background: Culicoides imicola (Diptera: Ceratopogonidae) is an important Afrotropical and Palearctic vector of disease, transmitting viruses of animal health and economic significance including African horse sickness and bluetongue viruses. Maternally inherited symbiotic bacteria (endosymbionts) of arthropods can alter the frequency of COI (cytochrome c oxidase subunit I) mitochondrial haplotypes (mitotypes) in a population, masking the true patterns of host movement and gene flow. Thus, this study aimed to assess the mtDNA structure of C. imicola in relation to infection with Candidatus Cardinum hertigii (Bacteroides), a common endosymbiont of Culicoides spp. Methods: Using haplotype network analysis, COI Sanger sequences from Cardinium-infected and -uninfected C. imicola individuals were first compared in a population from South Africa. The network was then extended to include mitotypes from a geographic range where Cardinium infection has previously been investigated. Results: The mitotype network of the South African population demonstrated the presence of two broad mitotype groups. All Cardinium-infected specimens fell into one group (Fisher's exact test, P = 0.00071) demonstrating a linkage disequilibrium between endosymbiont and mitochondria. Furthermore, by extending this haplotype network to include other C. imicola populations from the Mediterranean basin, we revealed mitotype variation between the Eastern and Western Mediterranean basins (EMB and WMB) mirrored Cardinium-infection heterogeneity. Conclusions: These observations suggest that the linkage disequilibrium of Cardinium and mitochondria reflects endosymbiont gene flow within the Mediterranean basin but may not assist in elucidating host gene flow. Subsequently, we urge caution on the single usage of the COI marker to determine population structure and movement in C. imicola and instead suggest the complementary utilisation of additional molecular markers. [ABSTRACT FROM AUTHOR]

Background: Culicoides imicola (Diptera: Ceratopogonidae) is an important Afrotropical and Palearctic vector of disease, transmitting viruses of animal health and economic significance including African horse sickness and bluetongue viruses. Maternally inherited symbiotic bacteria (endosymbionts) of arthropods can alter the frequency of COI (cytochrome c oxidase subunit I) mitochondrial haplotypes (mitotypes) in a population, masking the true patterns of host movement and gene flow. Thus, this study aimed to assess the mtDNA structure of C. imicola in relation to infection with Candidatus Cardinum hertigii (Bacteroides), a common endosymbiont of Culicoides spp. Methods: Using haplotype network analysis, COI Sanger sequences from Cardinium-infected and -uninfected C. imicola individuals were first compared in a population from South Africa. The network was then extended to include mitotypes from a geographic range where Cardinium infection has previously been investigated. Results: The mitotype network of the South African population demonstrated the presence of two broad mitotype groups. All Cardinium-infected specimens fell into one group (Fisher's exact test, P = 0.00071) demonstrating a linkage disequilibrium between endosymbiont and mitochondria. Furthermore, by extending this haplotype network to include other C. imicola populations from the Mediterranean basin, we revealed mitotype variation between the Eastern and Western Mediterranean basins (EMB and WMB) mirrored Cardinium-infection heterogeneity. Conclusions: These observations suggest that the linkage disequilibrium of Cardinium and mitochondria reflects endosymbiont gene flow within the Mediterranean basin but may not assist in elucidating host gene flow. Subsequently, we urge caution on the single usage of the COI marker to determine population structure and movement in C. imicola and instead suggest the complementary utilisation of additional molecular markers. [ABSTRACT FROM AUTHOR]

Resident microbes (microbiota) can shape host organismal function and adaptation in the face of environmental change. Invasion of new habitats exposes hosts to novel selection pressures, but little is known about the impact on microbiota and the host–microbiome relationship (e.g., how rapidly new microbial associations are formed, whether microbes influence invasion success). We used high‐throughput 16S rRNA sequencing of New Zealand (native) and European (invasive) populations of the freshwater snail Potamopyrgus antipodarum and found that while invaders do carry over some core microbial taxa from New Zealand, their microbial community is largely distinct. This finding highlights that invasions can result in the formation of novel host–microbiome relationships. We further show that the native microbiome is composed of fewer core microbes than the microbiome of invasive snails, suggesting that the microbiota is streamlined to a narrower set of core members. Furthermore, native snails exhibit relatively low alpha diversity but high inter‐individual variation, whereas invasive snails have higher alpha diversity but are relatively similar to each other. Together, our findings demonstrate that microbiota comparisons across native and invasive populations can reveal the impact of a long coevolutionary history and specialization of microbes in the native host range, as well as new associations occurring after invasion. We lay essential groundwork for understanding how microbial relationships affect invasion success and how microbes may be utilized in the control of invasive hosts. [ABSTRACT FROM AUTHOR]

Background Rickettsia are intracellular bacteria best known as the causative agents of human and animal diseases. Although these medically important Rickettsia are often transmitted via haematophagous arthropods, other Rickettsia , such as those in the Torix group, appear to reside exclusively in invertebrates and protists with no secondary vertebrate host. Importantly, little is known about the diversity or host range of Torix group Rickettsia. Results This study describes the serendipitous discovery of Rickettsia amplicons in the Barcode of Life Data System (BOLD), a sequence database specifically designed for the curation of mitochondrial DNA barcodes. Of 184,585 barcode sequences analysed, Rickettsia is observed in ∼0.41% of barcode submissions and is more likely to be found than Wolbachia (0.17%). The Torix group of Rickettsia are shown to account for 95% of all unintended amplifications from the genus. A further targeted PCR screen of 1,612 individuals from 169 terrestrial and aquatic invertebrate species identified mostly Torix strains and supports the "aquatic hot spot" hypothesis for Torix infection. Furthermore, the analysis of 1,341 SRA deposits indicates that Torix infections represent a significant proportion of all Rickettsia symbioses found in arthropod genome projects. Conclusions This study supports a previous hypothesis that suggests that Torix Rickettsia are overrepresented in aquatic insects. In addition, multiple methods reveal further putative hot spots of Torix Rickettsia infection, including in phloem-feeding bugs, parasitoid wasps, spiders, and vectors of disease. The unknown host effects and transmission strategies of these endosymbionts make these newly discovered associations important to inform future directions of investigation involving the understudied Torix Rickettsia. [ABSTRACT FROM AUTHOR]

The outcome of natural enemy attack in insects is commonly influenced by the presence of protective symbionts in the host. The degree to which protection functions in natural populations, however, will depend on the robustness of the phenotype and symbiosis to variation in the abiotic environment. We studied the impact of a key environmental parameter—temperature—on the efficacy of the protective effect of the symbiont Spiroplasma on its host Drosophila hydei, against attack by the parasitoid wasp Leptopilina heterotoma. In addition, we investigated the thermal sensitivity of the symbiont's vertical transmission, which may be a key determinant of the ability of the symbiont to persist. We found that vertical transmission was more robust than previously considered, with Spiroplasma being maintained at 25°C, at 18°C and with 18/15°C diurnal cycles, with rates of segregational loss only increasing at 15°C. Protection against wasp attack was ablated before symbiont transmission was lost, with the symbiont failing to rescue the fly host at 18°C. We conclude that the presence of a protective symbiosis in natural populations cannot be simply inferred from the presence of a symbiont whose protective capacity has been tested under narrow controlled conditions. More broadly, we argue that the thermal environment is likely to represent an important determinant of the evolutionary ecology of defensive symbioses in natural environments, potentially driving seasonal, latitudinal and altitudinal variation in symbiont frequency. [ABSTRACT FROM AUTHOR]

Background: Culicoides imicola (Diptera: Ceratopogonidae) is an important Afrotropical and Palearctic vector of disease, transmitting viruses of animal health and economic significance including African horse sickness and bluetongue viruses. Maternally inherited symbiotic bacteria (endosymbionts) of arthropods can alter the frequency of COI (cytochrome c oxidase subunit I) mitochondrial haplotypes (mitotypes) in a population, masking the true patterns of host movement and gene flow. Thus, this study aimed to assess the mtDNA structure of C. imicola in relation to infection with Candidatus Cardinum hertigii (Bacteroides), a common endosymbiont of Culicoides spp. Methods: Using haplotype network analysis, COI Sanger sequences from Cardinium-infected and -uninfected C. imicola individuals were first compared in a population from South Africa. The network was then extended to include mitotypes from a geographic range where Cardinium infection has previously been investigated. Results: The mitotype network of the South African population demonstrated the presence of two broad mitotype groups. All Cardinium-infected specimens fell into one group (Fisher's exact test, P = 0.00071) demonstrating a linkage disequilibrium between endosymbiont and mitochondria. Furthermore, by extending this haplotype network to include other C. imicola populations from the Mediterranean basin, we revealed mitotype variation between the Eastern and Western Mediterranean basins (EMB and WMB) mirrored Cardinium-infection heterogeneity. Conclusions: These observations suggest that the linkage disequilibrium of Cardinium and mitochondria reflects endosymbiont gene flow within the Mediterranean basin but may not assist in elucidating host gene flow. Subsequently, we urge caution on the single usage of the COI marker to determine population structure and movement in C. imicola and instead suggest the complementary utilisation of additional molecular markers. [ABSTRACT FROM AUTHOR]

Heritable microbes are an important component of invertebrate biology, acting both as beneficial symbionts and reproductive parasites. Whilst most previous research has focussed on the 'Wolbachia pandemic', recent work has emphasised the importance of other microbial symbionts. In this study, we present a survey of odonates (dragonflies and damselflies) for torix group Rickettsia, following previous research indicating that this clade can be common in other aquatic insect groups. PCR assays were used to screen a broad range of odonates from two continents and revealed 8 of 76 species tested were infected with Rickettsia. We then conducted further deeper screening of UK representatives of the Coenagrionidae damselfly family, revealing 6 of 8 UK coenagrionid species to be positive for torix Rickettsia. Analysis of Rickettsia gene sequences supported multiple establishments of symbiosis in the group. Some strains were shared between UK coenagrionid species that shared mtDNA barcodes, indicating a likely route for mitochondrial introgression between sister species. There was also evidence of coinfecting Rickettsia strains in two species. FISH analysis indicated Rickettsia were observed in the ovarioles, consistent with heritable symbiosis. We conclude that torix Rickettsia represent an important associate of odonates, being found in a broad range of species from both Europe and South America. There is evidence that coinfection can occur, vertical transmission is likely, and that symbiont movement following hybridisation may underpin the lack of 'barcoding gap' between well-established species pairs in the genus. Future work should establish the biological significance of the symbioses observed. [ABSTRACT FROM AUTHOR]

Termites are widely used as a food resource, particularly in Africa and Asia. Markets for insects as food are also expanding worldwide. To inform the development of insect-based foods, we analysed selected minerals (Fe-Mn-Zn-Cu-Mg) in wild-harvested and commercially available termites. Mineral values were compared to selected commercially available insects. Alate termites, of the genera Macrotermes and Odontotermes, showed remarkably high manganese (Mn) content (292–515 mg/100 gdw), roughly 50–100 times the concentrations detected in other insects. Other mineral elements occur at moderate concentrations in all insects examined. On further examination, the Mn is located primarily in the abdomens of the Macrotermes subhyalinus; with scanning electron microscopy revealing small spherical structures highly enriched for Mn. We identify the fungus comb, of Macrotermes subhyanus, as a potential biological source of the high Mn concentrations. Consuming even small quantities of termite alates could exceed current upper recommended intakes for Mn in both adults and children. Given the widespread use of termites as food, a better understanding the sources, distribution and bio-availability of these high Mn concentrations in termite alates is needed. [ABSTRACT FROM AUTHOR]

Summary: Maternally heritable symbionts are common in arthropods and represent important partners and antagonists. A major impediment to understanding the mechanistic basis of these symbioses has been lack of genetic manipulation tools, for instance, those enabling transgenic GFP expression systems for in vivo visualization. Here, we transform the 'son‐killer' reproductive parasite Arsenophonus nasoniae that infects the parasitic wasp Nasonia vitripennis with the plasmid pOM1‐gfp, re‐introduce this strain to N. vitripennis and then used this system to track symbiont life history in vivo. These data revealed transfer of the symbiont into the fly pupa by N. vitripennis during oviposition and N. vitripennis larvae developing infection over time through feeding. A strong tropism of A. nasoniae to the N. vitripennis ovipositor developed during wasp pupation, which aids onward transmission. The symbiont was also visualized in diapause larvae. Occasional necrotic diapause larvae were observed which displayed intense systemic infection alongside widespread melanotic nodules indicative of an active but failed immune response. Our results provide the foundation for the study of this symbiosis through in vivo tracking of the fate of symbionts through host development, which is rarely achieved in heritable microbe/insect interactions. [ABSTRACT FROM AUTHOR]

There is increasing interest in the heritable bacteria of invertebrate vectors of disease as they present novel targets for control initiatives. Previous studies on biting midges ( Culicoides spp .), known to transmit several RNA viruses of veterinary importance, have revealed infections with the endosymbiotic bacteria, Wolbachia and Cardinium. However, rickettsial symbionts in these vectors are underexplored. Here, we present the genome of a previously uncharacterized Rickettsia endosymbiont from Culicoides newsteadi (RiCNE). This genome presents unique features potentially associated with host invasion and adaptation, including genes for the complete non-oxidative phase of the pentose phosphate pathway, and others predicted to mediate lipopolysaccharides and cell wall modification. Screening of 414 Culicoides individuals from 29 Palearctic or Afrotropical species revealed that Rickettsia represent a widespread but previously overlooked association, reaching high frequencies in midge populations and present in 38% of the species tested. Sequence typing clusters the Rickettsia within the Torix group of the genus, a group known to infect several aquatic and hematophagous taxa. FISH analysis indicated the presence of Rickettsia bacteria in ovary tissue, indicating their maternal inheritance. Given the importance of biting midges as vectors, a key area of future research is to establish the impact of this endosymbiont on vector competence. [ABSTRACT FROM AUTHOR]

Heritable microbial symbionts have profound impacts upon the biology of their arthropod hosts. Whilst our current understanding of the dynamics of these symbionts is typically cast within a framework of vertical transmission only, horizontal transmission has been observed in a number of cases. For instance, several symbionts can transmit horizontally when their parasitoid hosts share oviposition patches with uninfected conspecifics, a phenomenon called superparasitism. Despite this, horizontal transmission, and the host contact structures that facilitates it, have not been considered in heritable symbiont epidemiology. Here, we tested for the importance of host contact, and resulting horizontal transmission, for the epidemiology of a male-killing heritable symbiont (Arsenophonus nasoniae) in parasitoid wasp hosts. We observed that host contact through superparasitism is necessary for this symbiont’s spread in populations of its primary host Nasonia vitripennis, such that when superparasitism rates are high, A. nasoniae almost reaches fixation, causes highly female biased population sex ratios and consequently causes local host extinction. We further tested if natural interspecific variation in superparasitism behaviours predicted symbiont dynamics among parasitoid species. We found that A. nasoniae was maintained in laboratory populations of a closely related set of Nasonia species, but declined in other, more distantly related pteromalid hosts. The natural proclivity of a species to superparasitise was the primary factor determining symbiont persistence. Our results thus indicate that host contact behaviour is a key factor for heritable microbe dynamics when horizontal transmission is possible, and that ‘reproductive parasite’ phenotypes, such as male-killing, may be of secondary importance in the dynamics of such symbiont infections. [ABSTRACT FROM AUTHOR]

Changes in the timing of life history events within the year alter the degree to which the activity patterns of different species coincide, making the dynamics of interspecific interactions sensitive to the phenology of the interacting parties. For parasites, the availability of suitable hosts to infect represents a crucial determinant of dynamics, and changes in the host (and parasite) phenology may thus alter disease epidemiology and the conditions for disease maintenance. We tested the hypothesis that the incidence of a sexually transmitted mite infection, Coccipolipus hippodamiae, in Adalia bipunctata ladybird beetles in Sweden was determined by host phenology, namely presence/absence of sexual contact between cohorts of the host. We observed that the pattern of mite presence/absence across Swedish A. bipunctata populations was highly reproducible between years, implying a persistent biological/ecological basis underlying the incidence. Further, ladybirds from populations where the mite was absent were able to acquire mites during copulation, develop a mite infection, and transmit infection onward, indicating an ecological (rather than biological) driver of mite incidence. Observations of ladybird phenology in natural populations provided evidence of sexual contact between overwintered and new cohort adults in populations where the mite was present. In contrast, new cohort ladybirds in the two northern Swedish populations where the mite was not present had not had sexual contact with the overwintered generation, creating a 'hard stop' to mite transmission. We conclude that variation in host phenology may be an important driver of the incidence of sexually transmitted infections (STIs) by determining the presence/absence of sexual contact between generations. More generally, we hypothesize that sensitivity to variation in host phenology will be highest for parasites like STIs that infect one host species, one host life stage and are directly transmitted on contact between host individuals. [ABSTRACT FROM AUTHOR]

The extent of female multiple mating (polyandry) can strongly impact on the intensity of sexual selection, sexual conflict, and the evolution of cooperation and sociality. More subtly, polyandry may protect populations against intragenomic conflicts that result from the invasion of deleterious selfish genetic elements (SGEs). SGEs commonly impair sperm production, and so are likely to be unsuccessful in sperm competition, potentially reducing their transmission in polyandrous populations. Here, we test this prediction in nature. We demonstrate a heritable latitudinal cline in the degree of polyandry in the fruitfly Drosophila pseudoobscura across the USA, with northern population females remating more frequently in both the field and the laboratory. High remating was associated with low frequency of a sex-ratio-distorting meiotic driver in natural populations. In the laboratory, polyandry directly controls the frequency of the driver by undermining its transmission. Hence we suggest that the cline in polyandry represents an important contributor to the cline in sex ratio in nature. Furthermore, as the meiotic driver causes sex ratio bias, variation in polyandry may ultimately determine population sex ratio across the USA, a dramatic impact of female mating decisions. As SGEs are ubiquitous it is likely that the reduction of intragenomic conflict by polyandry is widespread. [ABSTRACT FROM AUTHOR]

Inherited microbial symbionts can modulate host susceptibility to natural enemy attack. A wider range of symbionts influence host population demography without altering individual susceptibility, and it has been suggested that these may modify host disease risk through altering the rate of exposure to natural enemies. We present the first test of this thesis, specifically testing whether male-killing symbionts alter the epidemiology of a sexually transmitted infection (STI) carried by its host. STIs are typically expected to show female-biased epidemics, and we first present a simple model which indicates that male-biased STI epidemics may occur where symbionts create female-biased population sex ratios. We then examined the dynamics of a STI in the ladybird beetle Adalia bipunctata, which is also host to a male-killing bacterium. We present evidence that male-biased epidemics of the STI are observed in natural populations when the male-killer is common. Laboratory experiments did not support a role for differential susceptibility of male and female hosts to the STI, nor a protective role for the symbiont, in creating this bias. We conclude that the range of symbionts likely to alter parasite epidemiology will be much wider than previously envisaged, because it will additionally include those that impact host demography alone. [ABSTRACT FROM AUTHOR]

Background: The endosymbiont Wolbachia pipientis causes diverse and sometimes dramatic phenotypes in its invertebrate hosts. Four Wolbachia strains sequenced to date indicate that the constitution of the genome is dynamic, but these strains are quite divergent and do not allow resolution of genome diversification over shorter time periods. We have sequenced the genome of the strain wBol1-b, found in the butterfly Hypolimnas bolina, which kills the male offspring of infected hosts during embyronic development and is closely related to the non-male-killing strain wPip from Culex pipiens. Results: The genomes of wBol1-b and wPip are similar in genomic organisation, sequence and gene content, but show substantial differences at some rapidly evolving regions of the genome, primarily associated with prophage and repetitive elements. We identified 44 genes in wBol1-b that do not have homologs in any previously sequenced strains, indicating that Wolbachia's non-core genome diversifies rapidly. These wBol1-b specific genes include a number that have been recently horizontally transferred from phylogenetically distant bacterial taxa. We further report a second possible case of horizontal gene transfer from a eukaryote into Wolbachia. Conclusions: Our analyses support the developing view that many endosymbiotic genomes are highly dynamic, and are exposed and receptive to exogenous genetic material from a wide range of sources. These data also suggest either that this bacterial species is particularly permissive for eukaryote-to-prokaryote gene transfers, or that these transfers may be more common than previously believed. The wBol1-b-specific genes we have identified provide candidates for further investigations of the genomic bases of phenotypic differences between closely-related Wolbachia strains. [ABSTRACT FROM AUTHOR]

Males in many taxa exhibit behavioural plasticity in response to the perceived threat of sperm competition. Drosophila males prolong mating in response to the presence of competitor males before copulation. The benefits of this behaviour to males are evident in Drosophila melanogaster. However, the adaptive nature of the trait is challenged by the observation that it is present in four other Drosophila species, two of which are largely monandrous, raising the possibility that this plasticity is not evolutionarily labile. In the present study, behavioural plasticity and the mating system in Drosophila bifasciata Pominini (Diptera, Drosophilidae) are analyzed. By contrast to other Drosophila species, male D. bifasciata do not exhibit plasticity in copulation duration when competitor males are present before mating. Thus, plasticity in mating duration is not fixed in the genus Drosophila. The mating system of D. bifasciata is also examined. The species is polyandrous but, uncommonly for the genus Drosophila, males transfer a mating plug composed of sperm to females, which forms very shortly after copulation and fills the female uterus. The absence of plasticity observed in D. bifasciata may arise from the sperm plug. [ABSTRACT FROM AUTHOR]

Summary 1. Prey species often possess defences (e.g. toxins) coupled with warning signals (i.e. aposematism). There is growing evidence that the expression of aposematic signals often varies within species and correlates with the strength of chemical defences. This has led to the speculation that such signals may be 'honest', with signal reliability ensured by the costliness of producing or maintaining aposematic traits. 2. We reared larval seven-spot ladybirds ( Coccinella septempunctata) on a Low or High aphid diet and measured the effects on warning signal expression (elytral carotenoid pigmentation, conspicuousness, spot size), levels of defensive alkaloids (precoccinelline, coccinelline), and relationships between these traits. 3. High-diet individuals had greater total precoccinelline levels, and elytra carotenoid concentrations at adulthood which was detectable to a typical avian predator. However, larval diet did not significantly affect adult body mass or size, spot size or coccinelline levels. 4. Elytra carotenoid concentrations correlated positively with total precoccinelline levels in both diet groups and sexes. However, the relationship between elytra carotenoid concentrations and total levels of coccinelline depended on sex: in both diet groups, elytra carotenoids and coccinelline levels were positively correlated in females, but negatively correlated in males. Spot size and coccinelline levels correlated positively in Low-diet individuals, but negatively in High-diet individuals. 5. These results point to physiological linkages between components of aposematism, which are modulated by resource (i.e. food) availability and affect the honesty of signals. Developmental diet, but also sex, influenced the relationships between signals and toxin levels. Ladybirds are sexually size dimorphic, and thus in comparison with males, females may be more susceptible to resource limitation and more likely to be honest signallers. [ABSTRACT FROM AUTHOR]

Wolbachia is one of the most common symbionts of arthropods. Its establishment requires lateral transfer to and successful transmission within novel host species. However, Wolbachia performs poorly when introduced into new host species, and models predict that Wolbachia should seldom be able to establish from low initial frequencies. Recently, various symbionts, includingWolbachia, have been shown to protect their hosts from natural enemies. Hence, Wolbachia invasion may be facilitated by the dynamic interaction between it, its host, and a natural enemy. We model such an interaction whereby Wolbachia induces either complete resistance, partial resistance, or tolerance to a host-specific pathogen and also induces the common manipulation phenotype of cytoplasmic incompatibility (CI). We show that the presence of the pathogen greatly facilitates Wolbachia invasion from rare and widens the parameter space in which "imperfect" Wolbachia strains can invade. Furthermore, positive frequency-dependent selection through CI can drive Wolbachia to very high frequencies, potentially excluding the pathogen. These results may explain a poorly understood aspect of Wolbachia biology: it is widespread, despite performing poorly after transfer to new host species. They also support the intriguing possibility that Wolbachia strains that encode both CI and natural-enemy resistance could potentially rid insects, including human disease vectors, of important pathogens. [ABSTRACT FROM AUTHOR]