Specific interactions between parasite genotypes and host genotypes (Gₚ × Gₕ) are commonly found in invertebrate systems, but are largely lacking a mechanistic explanation. The genotype of ...invertebrate hosts can be complemented by the genomes of microorganisms living on or within the host (‘microbiota’). We investigated whether the bacterial gut microbiota of bumble bees (Bombus terrestris) can account for the specificity of interactions between individuals from different colonies (previously taken as host genotype proxy) and genotypes of the parasite Crithidia bombi. For this, we transplanted the microbiota between individuals of six colonies. Both the general infection load and the specific success of different C. bombi genotypes were mostly driven by the microbiota, rather than by worker genotype. Variation in gut microbiota can therefore be responsible for specific immune phenotypes and the evolution of gut parasites may be driven by interactions with ‘microbiota types’ as well as with host genotypes.
Climate change is predicted to affect host–parasite interactions, and for some hosts, parasite infection is expected to increase with rising temperatures. Global population declines of important ...pollinators already have been attributed to climate change and parasitism. However, the role of climate in driving parasite infection and the genetic basis for pollinator hosts to respond often remain obscure. Based on decade‐long field data, we investigated the association between climate and Nosema bombi (Microsporidia) infection of buffed‐tailed bumblebees (Bombus terrestris), and whether host genotypes play a role. For this, we genotyped 876 wild bumblebee queens and screened for N. bombi infection of those queens between 2000 and 2010. We recorded seven climate parameters during those 11 years and tested for correlations between climate and infection prevalence. Here we show that climatic factors drive N. bombi infection and that the impact of climate depends on mitochondrial DNA cytochrome oxidase I (COI) haplotypes of the host. Infection prevalence was correlated with climatic variables during the time when queens emerge from hibernation. Remarkably, COI haplotypes best predict this association between climatic factors and infection. In particular, two host haplotypes (“A” and “B”) displayed phenotypic plasticity in response to climatic variation: Temperature was positively correlated with infection of host haplotype B, but not haplotype A. The likelihood of infection of haplotype A was associated with moisture, conferring greater resistance to parasite infection during wetter years. In contrast, infection of haplotype B was unrelated to moisture. To the best of our knowledge, this is the first study that identifies specific host genotypes that confer differential parasite resistance under variable climatic conditions. Our results underscore the importance of mitochondrial haplotypes to ward off parasites in a changing climate. More broadly, this also suggests that COI may play a pertinent role in climate change adaptations of insect pollinators.
Our decade‐long study shows that climate change impacts parasite infection of wild bumblebees (Bombus terrestris), depending on the genotypes of the bumblebees. With increasing temperatures and drier conditions, more bumblebees were infected. Surprisingly, this impact of climate change depends on mitochondrial DNA variants of the host. Bumblebees who possessed one variant were more resilient to infection under warmer, wetter conditions. In contrast, those with the other variant showed greater resilience to parasite infection in a cooler, drier climate. Therefore, these mitochondrial variants may play a crucial role for bumblebees to adapt to parasite infection in a changing climate.
The animal gut is a habitat for diverse communities of microorganisms (microbiota). Honeybees and bumblebees have recently been shown to harbour a distinct and species poor microbiota, which may ...confer protection against parasites. Here, we investigate diversity, host specificity and transmission mode of two of the most common, yet poorly known, gut bacteria of honeybees and bumblebees: Snodgrassella alvi (Betaproteobacteria) and Gilliamella apicola (Gammaproteobacteria). We analysed 16S rRNA gene sequences of these bacteria from diverse bee host species across most of the honeybee and bumblebee phylogenetic diversity from North America, Europe and Asia. These focal bacteria were present in 92% of bumblebee species and all honeybee species but were found to be absent in the two related corbiculate bee tribes, the stingless bees (Meliponini) and orchid bees (Euglossini). Both Snodgrassella alvi and Gilliamella apicola phylogenies show significant topological congruence with the phylogeny of their bee hosts, albeit with a considerable degree of putative host switches. Furthermore, we found that phylogenetic distances between Gilliamella apicola samples correlated with the geographical distance between sampling locations. This tentatively suggests that the environmental transmission rate, as set by geographical distance, affects the distribution of G. apicola infections. We show experimentally that both bacterial taxa can be vertically transmitted from the mother colony to daughter queens, and social contact with nest mates after emergence from the pupa greatly facilitates this transmission. Therefore, sociality may play an important role in vertical transmission and opens up the potential for co‐evolution or at least a close association of gut bacteria with their hosts.
Populations of important pollinators, such as bumble bees and honey bees, are declining at alarming rates worldwide. Parasites are likely contributing to this phenomenon. A distinct resident ...community of bacteria has recently been identified in bumble bees and honey bees that is not shared with related solitary bee species. We now show that the presence of these microbiota protects bee hosts against a widespread and highly virulent natural parasite (Crithidia bombi) in an experimental setting. We add further support to this antagonistic relationship from patterns found in field data. For the successful establishment of these microbiota and a protective effect, exposure to feces from nest mates was needed after pupal eclosion. Transmission of beneficial gut bacteria could therefore represent an important benefit of sociality. Our results stress the importance of considering the host microbiota as an "extended immune phenotype" in addition to the host immune system itself and provide a unique perspective to understanding bees in health and disease.
The discussion of host-parasite interactions, and of parasite virulence more specifically, has so far, with a few exceptions, not focused much attention on the accumulating evidence that immune ...evasion by parasites is not only almost universal but also often linked to pathogenesis, i.e. the appearance of virulence. Now, the immune evasion hypothesis offers a deeper insight into the evolution of virulence than previous hypotheses. Sensitivity analysis for parasite fitness and life-history theory shows promise to generate a more general evolutionary theory of virulence by including a major element, immune evasion to prevent parasite clearance from the host. Also, the study of dose-response relationships and multiple infections should be particularly illuminating to understand the evolution of virulence. Taking into account immune evasion brings immunological processes to the core of understanding the evolution of parasite virulence and for a range of related issues such as dose, host specificity or immunopathology. The aim of this review is to highlight the mechanism underlying immune evasion and to discuss possible consequences for the evolutionary ecology analysis of host-parasite interactions.
The antagonistic co-evolution of hosts and their parasites is considered to be a potential driving force in maintaining host genetic variation including sexual reproduction and recombination. The ...examination of this hypothesis calls for information about the genetic basis of host-parasite interactions - such as how many genes are involved, how big an effect these genes have and whether there is epistasis between loci. We here examine the genetic architecture of quantitative resistance in animal and plant hosts by concatenating published studies that have identified quantitative trait loci (QTL) for host resistance in animals and plants.
Collectively, these studies show that host resistance is affected by few loci. We particularly show that additional epistatic interactions, especially between loci on different chromosomes, explain a majority of the effects. Furthermore, we find that when experiments are repeated using different host or parasite genotypes under otherwise identical conditions, the underlying genetic architecture of host resistance can vary dramatically - that is, involves different QTLs and epistatic interactions. QTLs and epistatic loci vary much less when host and parasite types remain the same but experiments are repeated in different environments.
This pattern of variability of the genetic architecture is predicted by strong interactions between genotypes and corroborates the prevalence of varying host-parasite combinations over varying environmental conditions. Moreover, epistasis is a major determinant of phenotypic variance for host resistance. Because epistasis seems to occur predominantly between, rather than within, chromosomes, segregation and chromosome number rather than recombination via cross-over should be the major elements affecting adaptive change in host resistance.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Evolutionary ecology seeks to understand the selective reasons for the design features of the immune defense, especially with respect to parasitism. The molecular processes thereby set limitations, ...such as the failure to recognize an antigen, response specificity, the cost of defense, and the risk of autoimmunity. Sex, resource availability, and interference by parasites also affect a response. In turn, the defense repertoire consists of different kinds of immune responses--constitutive or induced, general or specific--and involves memory and lasting protection. Because the situation often defies intuition, mathematical analysis is typically required to identify the costs and benefits of variation in design, but such studies are few. In all, insect immune defense is much more similar to that of vertebrates than previously thought. In addition, the field is now rapidly becoming revolutionized by molecular data and methods that allow unprecedented access to study evolution in action.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Recent studies on the microbial flora of the honeybee gut have revealed an apparently highly specific community of resident bacteria that might play a role in immune defence and food preservation for ...their hosts. However, at present, very little is known about the diversity and ecology of bacteria occurring in non-domesticated bees like bumblebees, which are of similar importance as honeybees for the pollination of agricultural and wild flowers. To fill this gap in knowledge, we examined six of the most common bumblebee species in Central Europe from three locations in Germany and Switzerland for their bacterial communities. We used a culture-independent molecular approach based on sequencing the 16S rRNA gene from a selection of individuals and examining a larger number of samples by terminal restriction fragment length polymorphism profiles. The gut flora was dominated by very few and mostly undescribed groups of bacteria belonging to the Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria. This core set of bacteria was present in all of the examined bumblebee species. These bacteria are similar to, but distinct from, bacteria previously described from the honeybee gut. Significant differences were observed between the communities of bacteria in the different bumblebee species; the effect of sampling location was less strong. A novel group of Betaproteobacteria additionally shows evidence for host species-specific genotypes. The gut flora of bumblebees therefore is apparently composed of relatively few highly specialized bacteria, indicating a strong interaction and possibly important functions with their hosts.
The evolutionary-ecology approach to studying immune defences has generated a number of hypotheses that help to explain the observed variance in responses. Here, selected topics are reviewed in an ...attempt to identify the common problems, connections and generalities of the approach. In particular, the cost of immune defence, response specificity, sexual selection, neighbourhood effects and questions of optimal defence portfolios are discussed. While these questions still warrant further investigation, future challenges are the development of synthetic concepts for vertebrate and invertebrate systems and also of the theory that predicts immune responses based on a priori principles of evolutionary ecology.
1. The Palaearctic Bombus ruderatus (in 1982/1983) and Bombus terrestris (1998) have both been introduced into South America (Chile) for pollination purposes. We here report on the results of ...sampling campaigns in 2004, and 2010–2012 showing that both species have established and massively expanded their range. 2. Bombus terrestris, in particular, has spread by some 200 km year -1 and had reached the Atlantic coast in Argentina by the end of 2011. Both species, and especially B. terrestris, are infected by protozoan parasites that seem to spread along with the imported hosts and spillover to native species. 3. Genetic analyses by polymorphic microsatellite loci suggest that the host population of B. terrestris is genetically diverse, as expected from a large invading founder population, and structured through isolation by distance. Genetically, the populations of the trypanosomatid parasite, Crithidia bombi, sampled in 2004 are less diverse, and distinct from the ones sampled later. Current C. bombi populations are highly heterozygous and also structured through isolation by distance correlating with the genetic distances of B. terrestris, suggesting the latter's expansion to be a main structuring factor for the parasite. 4. Remarkably, wherever B. terrestris spreads, the native Bombus dahlbomii disappears although the reasons remain unclear. Our ecological and genetic data suggest a major invasion event that is currently unfolding in southern South America with disastrous consequences for the native bumblebee species.
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