Population genetics of beneficial heritable symbionts

Most species of insects are infected with heritable, facultative symbionts. Such symbionts first appear within a host lineage as a result of lateral transfer from other host species. Although some facultative symbionts are reproductive parasites and thus adversely affect the transmission of host nuclear genes, there is growing evidence that many are beneficial to their hosts by, for example, conferring protection from natural enemies. The origin, spread, and maintenance of such symbionts bears many similarities to, as well as important differences from, the process of adaptive evolution by beneficial nuclear mutations. The time is ripe for the development of a coherent theory of the 'population genetics' of beneficial heritable symbionts.     

Extensive proliferation of transposable elements in heritable bacterial symbionts

We found that insertion sequence (IS) elements are unusually abundant in the relatively recently evolved bacterial endosymbionts of maize weevils. Because multicopy elements can facilitate genomic recombination and deletion, this IS expansion may represent an early stage in the genomic reduction that is common in most ancient endosymbionts.     

Metacommunity theory for transmission of heritable symbionts within insect communities

Microbial organisms are ubiquitous in nature and often form communities closely associated with their host, referred to as the microbiome. The microbiome has strong influence on species interactions, but microbiome studies rarely take interactions between hosts into account, and network interaction studies rarely consider microbiomes. Here, we propose to use metacommunity theory as a framework to unify research on microbiomes and host communities by considering host insects and their microbes as discretely defined “communities of communities” linked by dispersal (transmission) through biotic interactions. We provide an overview of the effects of heritable symbiotic bacteria on their insect hosts and how those effects subsequently influence host interactions, thereby altering the host community. We suggest multiple scenarios for integrating the microbiome into metacommunity ecology and demonstrate ways in which to employ and parameterize models of symbiont transmission to quantitatively assess metacommunity processes in host‐associated microbial systems. Successfully incorporating microbiota into community‐level studies is a crucial step for understanding the importance of the microbiome to host species and their interactions.     

Transitions in symbiosis: evidence for environmental acquisition and social transmission within a clade of heritable symbionts

A dynamic continuum exists from free-living environmental microbes to strict host-associated symbionts that are vertically inherited. However, knowledge of the forces that drive transitions in symbiotic lifestyle and transmission mode is lacking. Arsenophonus is a diverse clade of bacterial symbionts, comprising reproductive parasites to coevolving obligate mutualists, in which the predominant mode of transmission is vertical. We describe a symbiosis between a member of the genus Arsenophonus and the Western honey bee. The symbiont shares common genomic and predicted metabolic properties with the male-killing symbiont Arsenophonus nasoniae, however we present multiple lines of evidence that the bee Arsenophonus deviates from a heritable model of transmission. Field sampling uncovered spatial and seasonal dynamics in symbiont prevalence, and rapid infection loss events were observed in field colonies and laboratory individuals. Fluorescent in situ hybridisation showed Arsenophonus localised in the gut, and detection was rare in screens of early honey bee life stages. We directly show horizontal transmission of Arsenophonus between bees under varying social conditions. We conclude that honey bees acquire Arsenophonus through a combination of environmental exposure and social contacts. These findings uncover a key link in the Arsenophonus clades trajectory from free-living ancestral life to obligate mutualism, and provide a foundation for studying transitions in symbiotic lifestyle.Subject terms: Microbial ecology, Molecular evolution, Bacterial evolution, Bacterial genetics, Phylogenetics     

Adaptation in perennial coastal plants-with particular reference to heritable variation in Puccinellia maritima and Ammophila arenaria

Perennial species invading the early stages of primary successions face constant, and often rapid, change in their biotic and abiotic environment. The relative abilities of different species to adapt to this change is reflected in the zonation patterns which characterize coastal vegetation. Variation in those species with wide ecological amplitudes, particularly in populations near the boundary of the realized niche, is likely to be particularly revealing.The pattern of heritable variation in Puccinellia maritima on salt marshes indicates directional selection for traits increasing plant vigour and competitive ability; presumably the effect of increasing plant density. Adaptation is by both genetic differentiation and phenotypic flexibility, the former being evident in adjacent grazed and ungrazed marshes and the latter in a mosaic of tall and short vegetation types. By contrast variation in Ammophila arenaria on dunes exhibits high levels of phenotypic flexibility, growth in a range of environments indicating that plants from fore-dune populations are higher responders than those from mature dunes.Among the implications of these results, and by comparison with other species, is the fact that, ironically, niche expansion for some salt marsh perennials may require the evolution of an annual strategy, and that a Darwinian selection model may help to explain variation in Ammophila's apparent vigour in dunes of different age.Nomenclature follows Tutin et al.: Flora Europaea (1964–1980).I am grateful to several colleagues and students, past and present, who have helped with the studies of Puccinellia and Ammophila and I am particularly indebted in this respect to Richard Scott.     

Molecular phylogeny of heritable symbionts and microbiota diversity analysis in phlebotominae sand flies and Culex nigripalpus from Colombia

BackgroundSecondary symbionts of insects include a range of bacteria and fungi that perform various functional roles on their hosts, such as fitness, tolerance to heat stress, susceptibility to insecticides and effects on reproduction. These endosymbionts could have the potential to shape microbial communites and high potential to develop strategies for mosquito-borne disease control.Methodology/Principal findingsThe relative frequency and molecular phylogeny of Wolbachia, Microsporidia and Cardinium were determined of phlebotomine sand flies and mosquitoes in two regions from Colombia. Illumina Miseq using the 16S rRNA gene as a biomarker was conducted to examine the microbiota. Different percentages of natural infection by Wolbachia, Cardinium, and Microsporidia in phlebotomines and mosquitoes were detected. Phylogenetic analysis of Wolbachia shows putative new strains of Lutzomyia gomezi (wLgom), Brumptomyia hamata (wBrham), and a putative new group associated with Culex nigripalpus (Cnig) from the Andean region, located in Supergroup A and Supergroup B, respectively. The sequences of Microsporidia were obtained of Pi. pia and Cx. nigripalpus, which are located on phylogeny in the IV clade (terrestrial origin). The Cardinium of Tr. triramula and Ps. shannoni were located in group C next to Culicoides sequences while Cardinium of Mi. cayennensis formed two putative new subgroups of Cardinium in group A. In total were obtained 550 bacterial amplicon sequence variants (ASVs) and 189 taxa to the genus level. The microbiota profiles of Sand flies and mosquitoes showed mainly at the phylum level to Proteobacteria (67.6%), Firmicutes (17.9%) and Actinobacteria (7.4%). High percentages of relative abundance for Wolbachia (30%-83%) in Lu. gomezi, Ev. dubitans, Mi. micropyga, Br. hamata, and Cx. nigripalpus were found. ASVs assigned as Microsporidia were found in greater abundance in Pi. pia (23%) and Cx. nigripalpus (11%). An important finding is the detection of Rickettsia in Pi. pia (58,8%) and Bartonella sp. in Cx. nigripalpus.Conclusions/SignificanceWe found that Wolbachia infection significantly decreased the alpha diversity and negatively impacts the number of taxa on sand flies and Culex nigripalpus. The Principal Coordinate Analysis (PCoA) is consistent, which showed statistically significant differences (PERMANOVA, F = 2.4744; R2 = 0.18363; p-value = 0.007) between the microbiota of sand flies and mosquitoes depending on its origin, host and possibly for the abundance of some endosymbionts (Wolbachia, Rickettsia).     

Molecular interactions between bacterial symbionts and their hosts

Symbiotic bacteria are important in animal hosts, but have been largely overlooked as they have proved difficult to culture in the laboratory. Approaches such as comparative genomics and real-time PCR have provided insights into the molecular mechanisms that underpin symbiont-host interactions. Studies on the heritable symbionts of insects have yielded valuable information about how bacteria infect host cells, avoid immune responses, and manipulate host physiology. Furthermore, some symbionts use many of the same mechanisms as pathogens to infect hosts and evade immune responses. Here we discuss what is currently known about the interactions between bacterial symbionts and their hosts.     

Designing databases to store biological information

The increasing amount of data produced by large-scale biological experiments has highlighted the inadequacies of traditional scientific data management methods such as laboratory notebooks. Databases designed to store biological information are becoming increasingly common, but there is little guidance in the literature about the best practices of biological database design. This paper suggests best practices, and provides examples for the implementation of these practices.     

Metabolic interactions between algal symbionts and invertebrate hosts

Some invertebrates have enlisted autotrophic unicellular algae to provide a competitive metabolic advantage in nutritionally demanding habitats. These symbioses exist primarily but not exclusively in shallow tropical oceanic waters where clear water and low nutrient levels provide maximal advantage to the association. Mostly, the endosymbiotic algae are localized in host cells surrounded by a host-derived membrane (symbiosome). This anatomy has required adaptation of the host biochemistry to allow transport of the normally excreted inorganic nutrients (CO₂, NH₃ and PO₄³⁻) to the alga. In return, the symbiont supplies photosynthetic products to the host to meet its energy demands. Most attention has focused on the metabolism of CO₂ and nitrogen sources. Carbon-concentrating mechanisms are a feature of all algae, but the products exported to the host following photosynthetic CO₂ fixation vary. Identification of the stimulus for release of algal photosynthate in hospite remains elusive. Nitrogen assimilation within the symbiosis is an essential element in the host's control over the alga. Recent studies have concentrated on cnidarians because of the impact of global climate change resulting in coral bleaching. The loss of the algal symbiont and its metabolic contribution to the host has the potential to result in the transition from a coral-dominated to an algal-dominated ecosystem.     

Complex co-evolutionary relationships between cicadas and their symbionts

Previous evidence suggests that cicadas lacking Hodgkinia may harbour the yeast-like fungal symbionts (YLS). Here, we reinforce an earlier conclusion that the pathogenic ancestor of YLS independently infected different cicada lineages instead of the common ancestor of Cicadidae. Five independent replacement events in the loss of Hodgkinia/acquisition of YLS and seven other replacement events of YLS (from an Ophiocordyceps fungus to another Ophiocordyceps fungus) are hypothesised to have occurred within the sampled cicada taxa. The divergence time of YLS lineages was later than that of corresponding cicada lineages. The rapid shift of diversification rates of YLS and related cicada-parasitizing Ophiocordyceps began at approximately 32.94 Ma, and the diversification rate reached the highest value at approximately 24.82 Ma, which corresponds to the cooling climate changes at the Eocene–Oligocene boundary and the Oligocene–Miocene transition respectively. Combined with related acquisition/replacement events of YLS occurred during the cooling-climate periods, we hypothesise that the cooling-climate changes impacted the interactions between cicadas and related Ophiocordyceps, which coupled with the unusual life cycle and the differentiation of cicadas may finally led to the diversification of YLS in Cicadidae. Our results contribute to a better understanding of the evolutionary transition of YLS from entomopathogenic fungi in insects.     

Conditioning honeybees to discriminate between heritable odors from full and half sisters

Summary Differential conditioning of the proboscis extension reflex in honeybees is used to assess whether worker honeybees can be trained to discriminate between volatile odors emanating from different kin groups consisting of 2 or 20 workers. These odor source group workers are all reared and maintained under identical environmental conditions. They are the progeny of a queen that has been instrumentally inseminated so that eclosing adult workers can be sorted into colormorph full sister patrilines (workers are half sisters across patrilines). We demonstrate that workers are able to discriminate between the odors from groups of 20 individuals only if the groups represent individuals from different patrilines. However, discrimination occurs between groups of 2 individuals even if groups do not represent different patrilines. A number of environmental control experiments are also conducted. From our results we infer that there is heritable variation in the production of volatile odors by worker honeybees at a level that can be detected by the workers.     

Avoiding conflicts between insect and weed biological control: selection of non-target species to assess host specificity of cabbage seedpod weevil parasitoids

Abstract:  Classical biological control of insect pests and weeds may lead to potential conflicts, where insect pests are closely related to weed biological control agents. Such a conflict may occur in the classical biological control of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) in North America, which belongs to the same subfamily, Ceutorhynchinae, as a number of agents introduced or proposed for introduction against non-indigenous invasive weed species. We propose a step-by-step procedure to select non-target species and thereby to develop a non-target species test list for screening candidate entomophagous biological control agents of a herbivore pest insect in a way that would simultaneously evaluate non-target potential on weed biological control agents and other non-target species. Using these recommendations, we developed a non-target test list for host specificity evaluations in the area of origin (Europe) and the area of introduction (North America) for cabbage seedpod weevil parasitoids. Scientifically based predictions on expected host–parasitoid interactions and ecological information about the ecological host range in the area of origin can help avoid conflicts, while still allowing the introduction of safe and effective agents against both insect pests and weeds.     

Regressive biological evolution due to environmental change

Simulation results are presented which suggest that regressive evolution (i.e., evolution to a less adapted state) often occurs in response to environmental change, by a process analogous to the stress-induced reversal of aging in glassy materials. The key to this process is the stress-induced disappearance of fitness optima that lead to irreversible changes in the location of a population in genotype space. Even though the population may always evolve to higher fitness states, this irreversible process will often act to bring an initially well-adapted system to a less adapted state upon a return to initial conditions.     

蚜虫与其胞内共生细菌的相互作用

蚜虫—巴克纳氏菌之间是一种典型的互利共生关系,两者相互依存,缺少一方,另一方便不能生存。研究表明,共生细菌能为寄主蚜虫提供必需氨基酸和维生索,并对寄主具有一些非营养功能,如促进蚜虫传播循环性病毒等。寄主蚜虫则是为共生菌提供一个合适的生存场所,并对共生菌的生长和繁殖进行调控。现代分子生物学技术从基因水平证明了蚜虫与共生菌的相互依赖性。     

Yeasts as biological agents to control Botrytis cinerea

Yeasts, isolated from different sources, were identified and tested for inhibition using YMA-MB plates seeded with Botrytis cinerea strains. A total of 42 yeast strains of 20 different species were tested in vitro for antagonism against 18 pathogenic B. cinerea strains. Pichia membranifaciens, P. anomala and Debaryomyces hansenii displayed the most important inhibitory effect against Botrytis strains. In small-scale trials, post-harvest application of P. membranifaciens CYC 1106 to apple wounds inhibited B. cinerea CYC 20010. Purified killer toxin from P. membranifaciens CYC 1106 inhibited B. cinerea CYC 20010. Results indicated that certain yeasts, or their toxins such us P. membranifaciens CYC 1106 killer toxin, might have potential as novel agents to control B. cinerea.     

Co-niche construction between hosts and symbionts: ideas and evidence

Symbiosis is a process that can generate evolutionary novelties and can extend the phenotypic niche space of organisms. Symbionts can act together with their hosts to co-construct host organs, within which symbionts are housed. Once established within hosts, symbionts can also influence various aspects of host phenotype, such as resource acquisition, protection from predation by acquisition of toxicity, as well as behaviour. Once symbiosis is established, its fidelity between generations must be ensured. Hosts evolve various mechanisms to screen unwanted symbionts and to facilitate faithful transmission of mutualistic partners between generations. Microbes are the most important symbionts that have influenced plant and animal phenotypes; multicellular organisms engage in developmental symbioses with microbes at many stages in ontogeny. The co-construction of niches may result in composite organisms that are physically nested within each other. While it has been advocated that these composite organisms need new evolutionary theories and perspectives to describe their properties and evolutionary trajectories, it appears that standard evolutionary theories are adequate to explore selection pressures on their composite or individual traits. Recent advances in our understanding of composite organisms open up many important questions regarding the stability and transmission of these units.     

An application of information theory to biological evolution

An evolving population of two alleles which generates another new allele is investigated within the framework of information theory. A communication system model of self-reproducing organisms which reproduce the genetic information by the self-reproduction is proposed and the concept of distortion when the genetic information is reproduced is introduced. What genetic information should be transmitted to the next generation? This question may be answered by so called rate distortion theory. The theory is applied to our model and the exact solution is obtained. Numerical results show that in low distortion region, new allele cannot survive, hence no evolution occurs; in intermediate distortion region, all alleles coexist; and in high distortion region, minor allele cannot survive. Moreover, diversity of the progeny takes its maximum value in the intermediate distortion region. This suggests that there may exist an optimal distortion for a population to evolve.     

Antagonism between entomopathogenic fungi and bacterial symbionts of entomopathogenic nematodes

Mutual effects between the symbiotic bacteria of entomopathogenic nematodes, Photorhabdus luminescens and Xenorhabdus poinarii, and entomopathogenic fungi were investigated in vitro. A dual culture assay on nutrient agar supplemented with bromothymol blue and triphenyltetrazolium chloride (NBTA) medium revealed that P. luminescens is antagonistic to Metarhizium anisopliae, Beauveria bassiana, B. brongniartii and Paecilomyces fumosoroseus by inhibiting their growth and conidial production; the fungal growth was not inhibited by X. poinarii. In a second laboratory experiment, crude extract produced by M. anisopliae was tested for its activity against P. luminescens and X. poinarii. Crude extract from M. anisopliae was antibacterial to P. luminescens and X. poinarii at 1000 g/ml and inhibited their growth on NBTA, but had no effect at 100 or 10 g/ml. The influence of the crude extract of M. anisopliae on the dispersal of infective juveniles (IJs) of Heterorhabditis megidis and Steinernema glaseri was assayed on Sabouraud Dextrose Agar (SDA) plates. Results showed that the crude extract of M. anisopliae had no toxic effects even at highest concentration (1000 g/ml).