Allopatric Host Research Articles

Consequences of the arms race between Maculinea teleius social parasite and Myrmica host ants for myrmecophilous butterfly conservation

The arms race between Maculinea butterflies and Myrmica host ants leads to local host-parasite adaptations. In our study, we assessed whether sympatric and allopatric Myrmica scabrinodis populations exhibit behavioural differences towards Maculinea teleius larvae during the adoption-period when butterfly larvae need to be taken inside the Myrmica nest. The second aim was to assess the butterfly survival rate inside ant colonies from different populations. We used one sympatric host population and three allopatric populations: one infested by M. teleius and two uninfested populations. We found that ants from the sympatric population showed a higher number of positive behaviours toward M. teleius larvae during adoption than ants from the allopatric populations. There were no differences in the number of inspection or negative behaviour events. The survival of butterfly larvae was highest inside sympatric host colonies and differed from the survival of M. teleius reared by ants from the allopatric, uninfested populations. No difference was found for the survival rate of M. teleius raised by infested, allopatric host colonies compared to sympatric host populations. Our results suggest the lack of behavioural counter-adaptations of local hosts of M. teleius that more easily adopt and rear butterfly caterpillars compared to naive M. scabrinodis colonies. Our results may also have implications for Maculinea butterfly conservation, especially for reintroduction programmes. We suggest that the existence of behavioural host defences should be checked for the source host population, as well as for the Myrmica population from the reintroduction site. It may also be reasonable to introduce several Myrmica host colonies from the source butterfly host population.

Molecular systematics and Holarctic phylogeography of cestodes of the genus Anoplocephaloides Baer, 1923 s. s. (Cyclophyllidea, Anoplocephalidae) in lemmings (Lemmus,Synaptomys)

The present molecular systematic and phylogeographic analysis is based on sequences of cytochrome c oxidase subunit 1 (cox1) (mtDNA) and 28S ribosomal DNA and includes 59 isolates of cestodes of the genus Anoplocephaloides Baer, 1923 s. s. (Cyclophyllidea, Anoplocephalidae) from arvicoline rodents (lemmings and voles) in the Holarctic region. The emphasis is on Anoplocephaloides lemmi (Rausch 1952) parasitizing Lemmus trimucronatus and Lemmus sibiricus in the northern parts of North America and Arctic coast of Siberia, and Anoplocephaloides kontrimavichusi (Rausch 1976) parasitizing Synaptomys borealis in Alaska and British Columbia. The cox1 data, 28S data and their concatenated data all suggest that A. lemmi and A. kontrimavichusi are both non‐monophyletic, each consisting of two separate, well‐defined clades, that is independent species. As an example, the sister group of the clade 1 of A. lemmi, evidently representing the ‘type clade’ of this species, is the clade 1 of A. kontrimavichusi. For A. kontrimavichusi, it is not known which one is the type clade. There is also fairly strong evidence for the non‐monophyly of Anoplocephaloides dentata (Galli‐Valerio, 1905)‐like species, although an earlier phylogeny suggested that this multispecies assemblage may be monophyletic. The results suggest a deep phylogenetic codivergence of Lemmus spp. and A. lemmi, primarily separating the two largely allopatric host and parasite species at the Kolyma River in east Siberia. There are also two allopatric sublineages within each main clade/species of A. lemmi and Lemmus, but the present distributions of the sublineages within the eastern L. trimucronatus and clade 1 of A. lemmi are not concordant. This discrepancy may be most parsimoniously explained by an extensive westward distributional shift of the easternmost parasite subclade. The results further suggest that the clade 1 of A. kontrimavichusi has diverged through a host shift from the precursor of L. trimucronatus to S. borealis.

落叶松八齿小蠹与长喙壳真菌间的种特异性伴生关系

PDF HTML阅读 XML下载 导出引用 引用提醒 落叶松八齿小蠹与长喙壳真菌间的种特异性伴生关系 DOI: 10.5846/stxb201304010576 作者: 作者单位: 中国林业科学研究院,中国林业科学研究院,中国林业科学研究院,内蒙古赤峰市克什克腾旗广兴林场,中国林业科学研究院,中国林业科学研究院 作者简介: 通讯作者: 中图分类号: 基金项目: 中央级公益性科研院所基本科研业务费专项资金(CAFRIFEEP201102); 国家自然科学基金(31070571) The species specific associations between Ips subelongatus and ophiostomatoid fungi Author: Affiliation: Chinese Academy of Forestry,Chinese Academy of Forestry,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:小蠹虫与长喙壳类真菌(Ophiostomatoid fungi)在自然界中形成稳定的伴生关系,是森林生态系统内一种普遍的生态学现象。已有研究表明欧亚大陆的齿小蠹属(Ips)昆虫与多种长喙壳类真菌形成广泛的伴生关系,其中部分真菌是重要的针叶树病原菌。随着借助于DNA信息特征的系统发育分析,揭示出形态特征和亲缘关系十分接近的3种齿小蠹属昆虫,云杉八齿小蠹(I. typographus),欧洲落叶松八齿小蠹(I. cembrae)和亚洲落叶松八齿小蠹(I. subelongatus)确定为不同种之后,相应地与之稳定伴生的长喙壳类真菌Ceratocystis polonica也由过去一个种揭示为3个种的复合体,各自与3种小蠹虫稳定伴生,形成密切的种特异性伴生关系。小蠹虫与真菌的种特异性伴生被认为是处于同一森林生态系统内的生物协同进化的结果。通过对我国东北地区落叶松八齿小蠹虫体、坑道标本上伴生真菌菌株的采集、分离和生理学、形态学特征观察,以及基于ITS、β-tubulin、MAT-2 HMG box多位点DNA序列的系统发育分析,首次确定了长喙壳真菌Ceratocystis fujiensis在我国东北地区异域分布的3种落叶松林内普遍存在,与落叶松八齿小蠹形成稳定的伴生关系。作为亚洲落叶松八齿小蠹伴生的主要真菌,也是伴生菌区系中的先锋种和致病力最强的病原菌,C. fujiensis在我国落叶松人工林的广泛分布值得高度重视,将为制定防治病虫复合危害的有效策略和措施提供科学基础。研究结果进一步支持了齿小蠹属昆虫与长喙壳真菌间的种特异性伴生假说。同时,多基因序列特征表明落叶松八齿小蠹与C. fujiensis在亚洲范围内的不同地理种群存在着显著的遗传多样性,预示特异性伴生在不同种群间发生的可能,可以为种特异性伴生假说和小蠹虫-真菌间共生关系的研究提供良好的模式材料。 Abstract:The bark-beetles and ophiostomatoid fungi formed a stable association relationship in nature. It is a universal ecology phenomenon occurring frequently in forest ecological systems. The association between the beetles and fungi are regarded to some extent as a symbiosis in a broad sense. They have been extensively and intensively documented and illustrated from all over the world since it was first realized. Some research showed that Ips beetles spread over Eurasia were extensively associated with a number of ophiostomatoid fungi species. Among which, some species are important pathogens of conifers. Although the morphology and ecology characteristics of three Ips beetles, I. typographus, I. cembrae, and I. subelongatus were almost identical, these beetles were evidenced in a series studies as distinct species based on the phylogenetic analysis of DNA information and critical morphological comparison. In parallel, an ophiostomatoid fungus, Ceratocystis polonica previously recognized as a closely associated fungus with these beetles was also separated into three distinct entities resided in the Ceratocystis coerulescens species complex, and stably associated with three kinds of bark beetles, respectively, where a species specific association between bark beetles and ophiostomatoid fungi was established. The species specific association was understood as a result of co-evolution in forests where both partners lived together in a common habitat. The samples collected in this study from three allopatric Larix hosts which Ips subelongatus attacked seriously. The ophiostomatoid strains were isolated from the body surface of Ips subelongatus, blue-stain tissue or the galleries bark-beetles attacked. Observations of the colony, physiology and morphology characteristic, and comparisons of anamorph and teleomorph structures of all Ceratocystis strains, confirmed that the strains are indistinguishable from Ceratocystis fujiensis M.J.Wingf. The phylogenetic analysis based on sequences derived from the ITS regions of the rDNA operon, the partial β-tubulin gene and the MAT-2 HMG box gene, further determined a total of nineteen fungal strains as species Ceratocystis fujiensis. The study first determined Ceratocystis fujiensis extensively existed in three allopatric larch forests in northeast and north China, which formed a stable association relationship with Ips subelongatus under such ecological conditions. Ceratocystis fujiensis was proved as a dominant fungus associated with Ips subelongatus in Japan, and a pioneer species and the strongest pathogenic fungus in all the bark-beetles associated fungi. Because C. fujiensis widely infesting Larix spp. plants in China, inevitably, this phenomenon should be paid high attention. The study provides scientific basis to make the policies and measures for the government to prevent and control the composite damages of diseases and pests effectively. The result in this paper provides support to the hypothesis of species specific association between Ips beetles and ophiostomatoid fungi. Meanwhile, the multi-gene sequences characteristic indicates that I. subelongatus and C. fujiensis exist significant genetic diversity in different geographic populations, which probably predict the possibility of the species specific association occurred under species levels. The associations between Ips beetles and ophiostomatoid fungi exhibit an ideal insight into completely understanding the symbiotic relationship between the bark beetles and ophiostomatoid fungi, and species specific association as well. 参考文献 相似文献 引证文献

Female biased sex-ratio in Schistosoma mansoni after exposure to an allopatric intermediate host strain of Biomphalaria glabrata

For parasites that require multiple hosts to complete their development, the interaction with the intermediate host may have an impact on parasite transmission and development in the definitive host. The human parasite Schistosoma mansoni needs two different hosts to complete its life cycle: the freshwater snail Biomphalaria glabrata (in South America) as intermediate host and a human or rodents as final host. To investigate the influence of the host environment on life history traits in the absence of selection, we performed experimental infections of two B. glabrata strains of different geographic origin with the same clonal population of S. mansoni. One B. glabrata strain is the sympatric host and the other one the allopatric host. We measured prevalence in the snail, the cercarial infectivity, sex-ratio, immunopathology in the final host and microsatellite frequencies of individual larvae in three successive generations.We show that, even if the parasite population is clonal based on neutral markers, S. mansoni keeps the capacity of generating phenotypic plasticity and/or variability for different life history traits when confront to an unusual environment, in this study the intermediate host. The most dramatic change was observed in sex-ratio: in average 1.7 times more female cercariae were produced when the parasite developed in an allopatric intermediate host.

PATHOGEN LIFE‐HISTORY TRADE‐OFFS REVEALED IN ALLOPATRY

Trade-offs in life-history traits is a central tenet in evolutionary biology, yet their ubiquity and relevance to realized fitness in natural populations remains questioned. Trade-offs in pathogens are of particular interest because they may constrain the evolution and epidemiology of diseases. Here, we studied life-history traits determining transmission in the obligate fungal pathogen, Podosphaera plantaginis, infecting Plantago lanceolata. We find that although traits are positively associated on sympatric host genotypes, on allopatric host genotypes relationships between infectivity and subsequent transmission traits change shape, becoming even negative. The epidemiological prediction of this change in life-history relationships in allopatry is lower disease prevalence in newly established pathogen populations. An analysis of the natural pathogen metapopulation confirms that disease prevalence is lower in newly established pathogen populations and they are more prone to go extinct during winter than older pathogen populations. Hence, life-history trade-offs mediated by pathogen local adaptation may influence epidemiological dynamics at both population and metapopulation levels.

Sympatric chimpanzees and gorillas harbor convergent gut microbial communities.

The gut microbial communities within great apes have been shown to reflect the phylogenetic history of their hosts, indicating codiversification between great apes and their gut microbiota over evolutionary timescales. But because the great apes examined to date represent geographically isolated populations whose diets derive from different sources, it is unclear whether this pattern of codiversification has resulted from a long history of coadaptation between microbes and hosts (heritable factors) or from the ecological and geographic separation among host species (environmental factors). To evaluate the relative influences of heritable and environmental factors on the evolution of the great ape gut microbiota, we assayed the gut communities of sympatric and allopatric populations of chimpanzees, bonobos, and gorillas residing throughout equatorial Africa. Comparisons of these populations revealed that the gut communities of different host species can always be distinguished from one another but that the gut communities of sympatric chimpanzees and gorillas have converged in terms of community composition, sharing on average 53% more bacterial phylotypes than the gut communities of allopatric hosts. Host environment, independent of host genetics and evolutionary history, shaped the distribution of bacterial phylotypes across the Bacteroidetes, Firmicutes, Proteobacteria, and Actinobacteria, the four most common phyla of gut bacteria. Moreover, the specific patterns of phylotype sharing among hosts suggest that chimpanzees living in sympatry with gorillas have acquired bacteria from gorillas. These results indicate that geographic isolation between host species has promoted the evolutionary differentiation of great ape gut bacterial communities.

Allopatric tuberculosis host–pathogen relationships are associated with greater pulmonary impairment

BackgroundHost pathogen relationships can be classified as allopatric, when the pathogens originated from separate, non-overlapping geographic areas from the host; or sympatric, when host and pathogen shared a common ancestral geographic location. It remains unclear if host–pathogen relationships, as defined by phylogenetic lineage, influence clinical outcome. We sought to examine the association between allopatric and sympatric phylogenetic Mycobacterium tuberculosis lineages and pulmonary impairment after tuberculosis (PIAT). MethodsPulmonary function tests were performed on patients 16years of age and older who had received ⩾20weeks of treatment for culture-confirmed M. tuberculosis complex. Forced Expiratory Volume in 1min (FEV1) ⩾80%, Forced Vital Capacity (FVC) ⩾80% and FEV1/FVC >70% of predicted were considered normal. Other results defined pulmonary impairment. Spoligotype and 12-locus mycobacterial interspersed repetitive units-variable number of tandem repeats (MIRU-VNTR) were used to assign phylogenetic lineage. PIAT severity was compared between host–pathogen relationships which were defined by geography and ethnic population. We used multivariate logistic regression modeling to calculate adjusted odds ratios (aOR) between phylogenetic lineage and PIAT. ResultsSelf-reported continental ancestry was correlated with Mycobacterium. tuberculosis lineage (p<0.001). In multivariate analyses adjusting for phylogenetic lineage, age and smoking, the overall aOR for subjects with allopatric host–pathogen relationships and PIAT was 1.8 (95% confidence interval [CI]: 1.1, 2.9) compared to sympatric relationships. Smoking >30pack-years was also associated with PIAT (aOR: 3.2; 95% CI: 1.5, 7.2) relative to smoking <1pack-years. ConclusionsPIAT frequency and severity varies by host–pathogen relationship and heavy cigarette consumption, but not phylogenetic lineage alone. Patients who had disease resulting from allopatric–host–pathogen relationship were more likely to have PIAT than patients with disease from sympatric–host–pathogen relationship infection. Further study of this association may identify ways that treatment and preventive efforts can be tailored to specific lineages and racial/ethnic populations.

HIV Infection Disrupts the Sympatric Host–Pathogen Relationship in Human Tuberculosis

The phylogeographic population structure of Mycobacterium tuberculosis suggests local adaptation to sympatric human populations. We hypothesized that HIV infection, which induces immunodeficiency, will alter the sympatric relationship between M. tuberculosis and its human host. To test this hypothesis, we performed a nine-year nation-wide molecular-epidemiological study of HIV–infected and HIV–negative patients with tuberculosis (TB) between 2000 and 2008 in Switzerland. We analyzed 518 TB patients of whom 112 (21.6%) were HIV–infected and 233 (45.0%) were born in Europe. We found that among European-born TB patients, recent transmission was more likely to occur in sympatric compared to allopatric host–pathogen combinations (adjusted odds ratio [OR] 7.5, 95% confidence interval [95% CI] 1.21–infinity, p = 0.03). HIV infection was significantly associated with TB caused by an allopatric (as opposed to sympatric) M. tuberculosis lineage (OR 7.0, 95% CI 2.5–19.1, p<0.0001). This association remained when adjusting for frequent travelling, contact with foreigners, age, sex, and country of birth (adjusted OR 5.6, 95% CI 1.5–20.8, p = 0.01). Moreover, it became stronger with greater immunosuppression as defined by CD4 T-cell depletion and was not the result of increased social mixing in HIV–infected patients. Our observation was replicated in a second independent panel of 440 M. tuberculosis strains collected during a population-based study in the Canton of Bern between 1991 and 2011. In summary, these findings support a model for TB in which the stable relationship between the human host and its locally adapted M. tuberculosis is disrupted by HIV infection.

No effect of host–parasite co‐evolution on host range expansion

Antagonistic co-evolution between hosts and parasites (reciprocal selection for resistance and infectivity) is hypothesized to play an important role in host range expansion by selecting for novel infectivity alleles, but tests are lacking. Here, we determine whether experimental co-evolution between a bacterium (Pseudomonas fluorescens SBW25) and a phage (SBW25Φ2) affects interstrain host range: the ability to infect different strains of P.fluorescens other than SBW25. We identified and tested a genetically and phenotypically diverse suite of co-evolved phage variants of SBW25Φ2 against both sympatric and allopatric co-evolving hosts (P.fluorescens SBW25) and a large set of other P.fluorescens strains. Although all co-evolved phage had a greater host range than the ancestral phage and could differentially infect co-evolved variants of P.fluorescens SBW25, none could infect any of the alternative P.fluorescens strains. Thus, parasite generalism at one genetic scale does not appear to affect generalism at other scales, suggesting fundamental genetic constraints on parasite adaptation for this virus.

Ecological drift and local exposures drive enteric bacterial community differences within species of Galápagos iguanas

Diet strongly influences the intestinal microbial communities through species sorting. Alternatively, these communicates may differ because of chance variation in local microbial exposures or species losses among allopatric host populations (i.e. ecological drift). We investigated how these forces shape enteric communities of Galápagos marine and land iguanas. Geographically proximate populations shared more similar communities within a host ecotype, suggesting a role for ecological drift during host colonization of the islands. Additionally, evidence of taxa sharing between proximate heterospecific host populations suggests that contemporary local exposures also influence the gut community assembly. While selective forces such as host-bacterial interactions or dietary differences are dominant drivers of intestinal community differences among hosts, historical and contemporary processes of ecological drift may lead to differences in bacterial composition within a host species. Whether such differences in community structure translate into geographic variation in benefits derived from these intimate microbial communities remains to be explored.

Abiotic heterogeneity drives parasite local adaptation in coevolving bacteria and phages

Spatial abiotic heterogeneity can result in divergent selection, hence might increase the magnitude of host-parasite local adaptation (the mean difference in fitness of sympatric vs. allopatric host-parasite combinations). We explicitly tested this hypothesis by measuring local adaptation in experimentally coevolved populations of bacteria and viruses evolved in the same or different nutrient media. Consistent with previous work, we found that mean levels of evolved phage infectivity and bacteria resistance varied with nutrient concentration, with maximal levels at nutrient concentrations that supported the greatest densities of bacteria. Despite this variation in evolved mean infectivity and resistance between treatments, we found that parasite local adaptation was greatly increased when measured between populations evolved in different, compared with the same, media. This pattern is likely to have resulted from different media imposing divergent selection on bacterial hosts, and phages in turn adapting to their local hosts. These results demonstrate that the abiotic environment can play a strong and predictable role in driving patterns of local adaptation.

Host–parasite interactions in sympatric and allopatric populations of European bitterling

Susceptibility to parasite infection was examined in a field experiment for four populations of 0+ juvenile European bitterling (Rhodeus amarus): one sympatric to local parasite fauna, one allopatric, and two hybrid populations. Significantly higher parasite abundance was recorded in the allopatric bitterling population, suggesting a maladaptation of parasites to their sympatric host. Type of parasite life cycle played an important role in host-parasite interactions. While the abundance of allogenic species between populations was comparable, a significant difference was found in abundance of autogenic parasite species between fish populations, with the allopatric population more infected. These results correspond with a prediction of higher dispersion probability and higher gene flow among geographically distant populations of allogenic species as compared to autogenic species. Increased susceptibility to parasites that do not occur within the natural host's geographical distribution was found in the allopatric host, but only for autogenic species. A difference in infection susceptibility was detected among populations of early-hatched bitterling exposed to infection during a period of high parasite abundance and richness in the environment. Differences in parasite abundance and species diversity among populations diminished, however, with increasing time of exposure. No difference was found within late-hatched populations, probably due to a lower probability of infection in late-hatched cohorts.

Infection dynamics of the monogenean parasite Gyrodactylus gasterostei on sympatric and allopatric populations of the three-spined stickleback Gasterosteus aculeatus

Parasites with high host specificity maximally depend on their hosts, which should increase the likelihood of coevolution. However, coevolution requires reciprocal selection exerted by the host and the parasite, and thus a considerable level of parasite virulence. In species of the monogenean ectoparasite genus Gyrodactylus consecutive generations are confronted with a single host, which may constrain the evolution of virulence. Transmission, which is often important in the ecology of Gyrodactylus species, may have the opposite effect, but may also lead to the avoidance of coevolutionary arms races. We investigated the potential outcome of coevolution between Gyrodactylus gasterostei Gläser, 1974 and its host, the three-spined stickleback (Gasterosteus aculeatus L.) by determining the strength of genotype by genotype (GxG) interactions on two levels: within and between sympatric and allopatric host populations. To do so, we compared the parasite's infection dynamics on laboratory-reared sympatric (Belgian) and allopatric (German) hosts. We found that a parasite line successfully infected a range of sympatric host genotypes (represented by families), while it failed to establish on allopatric hosts. Phylogeographic studies suggest that neutral genetic divergence between the host populations cannot explain this dramatic difference. Provided that this result can be generalised towards other parasite lines, we conclude that coevolution in this host-parasite system is more likely to lead to local adaptation on the population level than to GxG interactions within populations.

A geographical mosaic of coevolution in a slave‐making host–parasite system

Three different isolated populations of the slave-making ant Rossomyrmex minuchae, sympatric with its obligate host Proformica longiseta, are known from the high mountains of southern Spain. To test the prediction that the slave-maker and its host represent a coevolutionary geographical mosaic, we studied the variation in the cuticular hydrocarbons (CHCs) as the trait most likely to show the selection mosaic, plus trait remixing by the gene flow in the populations of each species by means of microsatellites. We found within populations, host and parasite had more similar CHC profiles than between the populations or between parasites and allopatric hosts. The differences between the CHC profiles of the host and parasite, which may be responsible for the level of tolerance towards the parasite, varied between the populations suggesting the existence of a selection mosaic of coevolution. Furthermore, P.longiseta showed higher gene flow than R.minuchae, which would allow local variation in the coevolution of the host and parasite while allowing some trait remixing.

Isolation by time and habitat and coexistence of distinct host races of the common cuckoo

Isolation by time occurs when different populations of a single species reproduce at different times and thereby reduce the probability of interbreeding, potentially causing divergent adaptation to timing of reproduction, eventually resulting in ecological species separated by timing of reproduction. We analysed extensive data on timing of reproduction by different host races of the common cuckoo Cuculus canorus that is an obligate brood parasite laying eggs in the nests of many different species of passerine birds. Because different hosts breed at different times, specific host races of cuckoos have adapted to specific hosts by laying eggs when nests of these hosts are available, and such divergence may be further exaggerated by differences in timing of breeding among host races with similar habitat requirements. Host species accounted for a quarter of the variance in timing of breeding by the cuckoo. Common cuckoos reproduced at a similar, but narrower subset of dates as did possible hosts, showing that only a fraction of hosts with specific breeding dates were parasitized. Common cuckoo eggs laid in the 'right' kind of nests, phenotypically matching the eggs of the host, were laid later during the season than cuckoo eggs laid in the 'wrong' kind of nests where the eggs did not mimic those of the host. Pairs of sympatric cuckoo host races differed more in timing of breeding than pairs of allopatric host races, and pairs of cuckoo host races with similar breeding habitat differed more in breeding date than pairs of cuckoo host races with dissimilar habitat, as expected from reproductive character displacement. These findings are consistent with cuckoo host races being isolated by timing of breeding and habitat.

Local exposure shapes spatial patterns in infectivity and community structure of Daphnia parasites

1. Spatial patterns in parasite community structure are probably driven by the availability of infectious stages. This is because hosts become infected through picking up infectious stages from their environment. Several studies have, however, reported strong genotype by genotype interactions and parasite-mediated selection in hosts. This leads to the prediction of a parasite by host population interaction with respect to infection rates and intensities, which may also shape spatial patterns in parasite community structure. 2. Using the water flea Daphnia magna and its microparasites as a model, we carried out a laboratory experiment to test explicitly to what extent parasite community structure in host populations is determined by the availability of infectious stages in the sediment they are exposed to, and to what extent host population identity and location play a role. 3. We exposed 10 D. magna host populations each to sediment of their own habitat and sediment of the other nine habitats, and monitored the parasite community of the resulting experimental populations. 4. Sediment seems to be a strong determinant of parasite infection rates, while there was no overall effect of host population. Sympatric parasite and host population combinations did in most cases not result in significantly different infection rates than allopatric parasite and host combinations. Our results indicate that spore availability could be the key variable determining parasite community structure in natural Daphnia populations.

Local adaptation in a plant herbivore interaction depends on the spatial scale

Local adaptation has central importance in the understanding of co-evolution, maintenance of sexual reproduction, and speciation. We investigated local adaptation in the alkaloid-bearing legume Crotalaria pallida and its seed predator, the arctiid moth Utetheisa ornatrix, at different spatial scales. When we studied three populations from south-east Brazil (150 km apart), we did not find evidence of local adaptation, although we did find interpopulational differences in herbivore performance, and a significant interaction between herbivore sex and plant population. These results indicate that both moth and plant populations are differentiated at the regional scale. In a comparison of populations from Brazil and Florida, the herbivore showed local adaptation to its host plant; for both moth populations, the pupae were heavier when the larvae ate the sympatric than the allopatric host population. We discuss the scale dependence of our results and the possible causes for the lack of local adaptation at the regional scale, even in the presence of plant and moth differentiation. The results obtained demonstrate the importance of studying co-evolution and local adaptation at different geographical scales. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 494–502.

Hybrid Fitness in a Locally Adapted Parasite

The parasite (Red Queen) hypothesis for the maintenance of sexual reproduction and genetic diversity assumes that host-parasite interactions result from tight genetic specificity. Hence, hybridization between divergent parasite populations would be expected to disrupt adaptive gene combinations, leading to reduced infectivity on exposure to parental sympatric hosts, as long as gene effects are nonadditive. In contrast, hybridization would not cause reduced infectivity on allopatric hosts unless the divergent parasite populations possess alleles that are intrinsically incompatible when they are combined. In three different experiments, we compared the infectivity of locally adapted parasite (trematode) populations with that of F(1) hybrid parasites when exposed to host (snail) populations that were sympatric to one of the two parasite populations. We tested for intrinsic genetic incompatibilities in two experiments by including one host population that was allopatric to both parasite populations. As predicted, when the target host populations were sympatric to the parasite populations, the hybrids were significantly less infective than the parental average, while hybrid parasites on allopatric hosts were not, thereby ruling out intrinsic genetic incompatibilities. The results are consistent with nonadditive gene effects and tightly specific host-driven selection underlying parasite divergence, as envisioned by coevolutionary theory and the Red Queen hypothesis.

Adaptation to the most abundant host genotype in an agricultural plant–pathogen system – potato late blight

This study investigated local adaptation of Phytophthora infestans populations, the causal agent of potato late blight, to two susceptible potato cultivars, each grown for a number of years and over large areas in separate French regions. We measured aggressiveness (quantitative pathogenicity) of each pathogen population to sympatric and allopatric hosts in a reciprocal cross-inoculation experiment. There was no evidence for specific host adaptation in this pathosystem. At both local and regional scales, the distribution of aggressiveness fits a pattern of adaptation to the most common host genotype. Our observations support the theoretical predictions that large pathogen dispersal rates and genetic drift, revealed by the comparisons of the genotypic structures of the populations tested, can lead to a local adaptation pattern detectable only at a large spatial scale. The unravelling of adaptive patterns at different spatial scales can be used for a more efficient management of the disease.

Redundant species, cryptic host-associated divergence, and secondary shift in Sennertia mites (Acari: Chaetodactylidae) associated with four large carpenter bees (Hymenoptera: Apidae: Xylocopa) in the Japanese island arc

Sennertia mites live as inquilines in the nests of carpenter bees and disperse as deutonymphs on newly emerged adult bees. Because their life cycle is tightly linked to that of the host bees, Sennertia may diverge in response to speciation in the hosts. However, the majority of Sennertia species are associated with several closely related carpenter bees, suggesting that host speciation may not be reflected in mite genetic structure. Here we investigate the extent of host-associated genetic differentiation in two Sennertia mites ( S. alfkeni and S. japonica) that share four closely related, strictly allopatric large carpenter bees ( Xylocopa). Analysis of the mitochondrial cytochrome oxidase subunit I (COI) gene in Sennertia unexpectedly indicates that the two species represent morphological variants of a single species, and they collectively group into four distinct, allopatric clades that are uniquely associated with a single Xylocopa host. An exception is the mites associated with X. amamensis of the northernmost populations, which have genotypes typical of those associated with neighboring X. appendiculata circumvolans. Additional analysis using amplified fragment length polymorphism (AFLP) further corroborates the presence of four mite clades but contrary to the COI data, suggests that the mites of the southernmost population of X. appendiculata circumvolans have genetic profiles typical of those associated with X. amamensis. These results indicate that some mites have undergone secondary host switch after the formation of the four mite lineages and further experienced mitochondrial introgression during period of lineage coexistence. Overall, our results strongly urge reappraisal of deutonymph-based mite taxonomy and illuminate the importance of host-associated divergence during incipient stage of speciation in chaetodactylid mites. Furthermore, the occurrence of host switch and introgression between genetically differentiated mites entails that two host species have co-occurred in the past, thus providing a unique source of evidence for migration and competitive exclusion between the presently allopatric Xylocopa hosts.