Testing parasite 'intimacy': the whipworm Trichuris muris in the European house mouse hybrid zone.

Host-parasite interaction studies across hybrid zones often focus on host genetic variation, treating parasites as homogeneous. 'Intimately' associated hosts and parasites might be expected to show similar patterns of genetic structure. In the literature, factors such as no intermediate host and no free-living stage have been proposed as 'intimacy' factors likely constraining parasites to closely follow the evolutionary history of their hosts. To test whether the whipworm, Trichuris muris, is intimately associated with its house mouse host, we studied its population genetics across the European house mouse hybrid zone (HMHZ) which has a strong central barrier to gene flow between mouse taxa. T. muris has a direct life cycle and nonmobile free stage: if these traits constrain the parasite to an intimate association with its host we expect a geographic break in the parasite genetic structure across the HMHZ. We genotyped 205 worms from 56 localities across the HMHZ and additionally T. muris collected from sympatric woodmice (Apodemus spp.) and allopatric murine species, using mt-COX1, ITS1-5.8S-ITS2 rDNA and 10 microsatellites. We show four haplogroups of mt-COX1 and three clear ITS1-5.8S-ITS2 clades in the HMHZ suggesting a complex demographic/phylogeographic history. Microsatellites show strong structure between groups of localities. However, no marker type shows a break across the HMHZ. Whipworms from Apodemus in the HMHZ cluster, and share mitochondrial haplotypes, with those from house mice. We conclude Trichuris should not be regarded as an 'intimate' parasite of the house mouse: while its life history might suggest intimacy, passage through alternate hosts is sufficiently common to erase signal of genetic structure associated with any particular host taxon

Sympatric Occurrence of 3 Arenaviruses, Tanzania

To determine the specificity of Morogoro virus for its reservoir host, we studied its host range and genetic diversity in Tanzania. We found that 2 rodent species other than Mastomys natalensis mice carry arenaviruses. Analysis of 340 nt of the viral RNA polymerase gene showed sympatric occurrence of 3 distinct arenaviruses

Evolutionary genetics of MHC class II beta genes in the brown hare, Lepus europaeus

The genes of the major histocompatibility complex (MHC) are attractive candidates for investigating the link between adaptive variation and individual fitness. High levels of diversity at the MHC are thought to be the result of parasite-mediated selection and there is growing evidence to support this theory. Most studies, however, target just a single gene within the MHC and infer any evidence of selection to be representative of the entire gene region. Here we present data from three MHC class II beta genes (DPB, DQB, and DRB) for brown hares in two geographic regions and compare them against previous results from a class II alpha-chain gene (DQA). We report moderate levels of diversity and high levels of population differentiation in the DQB and DRB genes (Na = 11, Dest = 0.071 and Na = 15, Dest = 0.409, respectively), but not for the DPB gene (Na = 4, Dest = 0.00). We also detected evidence of positive selection within the peptide binding region of the DQB and DRB genes (95% CI, ω > 1.0) but found no signature of selection for DPB. Mutation and recombination were both found to be important processes shaping the evolution of the class II genes. Our findings suggest that while diversifying selection is a significant contributor to the generally high levels of MHC diversity, it does not act in a uniform manner across the entire MHC class II region. The beta-chain genes that we have characterized provide a valuable set of MHC class II markers for future studies of the evolution of adaptive variation in Leporids

Variation in Phenotype, Parasite Load and Male Competitive Ability across a Cryptic Hybrid Zone

BackgroundMolecular genetic studies are revealing an increasing number of cryptic lineages or species, which are highly genetically divergent but apparently cannot be distinguished morphologically. This observation gives rise to three important questions: 1) have these cryptic lineages diverged in phenotypic traits that may not be obvious to humans; 2) when cryptic lineages come into secondary contact, what are the evolutionary consequences: stable co-existence, replacement, admixture or differentiation and 3) what processes influence the evolutionary dynamics of these secondary contact zones?Methodology/principal findingsTo address these questions, we first tested whether males of the Iberian lizard Lacerta schreiberi from two highly genetically divergent, yet morphologically cryptic lineages on either side of an east-west secondary contact could be differentiated based on detailed analysis of morphology, coloration and parasite load. Next, we tested whether these differences could be driven by pre-copulatory intra-sexual selection (male-male competition). Compared to eastern males, western males had fewer parasites, were in better body condition and were more intensely coloured. Although subtle environmental variation across the hybrid zone could explain the differences in parasite load and body condition, these were uncorrelated with colour expression, suggesting that the differences in coloration reflect heritable divergence. The lineages did not differ in their aggressive behaviour or competitive ability. However, body size, which predicted male aggressiveness, was positively correlated with the colour traits that differed between genetic backgrounds.Conclusions/significanceOur study confirms that these cryptic lineages differ in several aspects that are likely to influence fitness. Although there were no clear differences in male competitive ability, our results suggest a potential indirect role for intra-sexual selection. Specifically, if lizards use the colour traits that differ between genetic backgrounds to assess the size of potential rivals or mates, the resulting fitness differential favouring western males could result in net male-mediated gene flow from west to east across the current hybrid zone.Devi Stuart-Fox, Raquel Godinho, Joëlle Goüy de Bellocq, Nancy R. Irwin, José Carlos Brito, Adnan Moussalli, Pavel Široký, Andrew F. Hugall and Stuart J. E. Bair

The biogeography of host-parasite interactions : from nested assemblages to comparative phylogeography

In this review we combine various sources of information from community assemblages to studies in comparative phylogeography, in order to understand the processes that are responsible for the current distribution of hosts and parasites. By using Apodemus sylvaticus and its parasites in the western Palaearctic as an illustrating model, we highlight that (i) parasite species richness increases with host biogeographical range; (ii) the geographic range of parasite and host species is positively correlated with the local population abundance; (iii) there is covariance between local species richness of assemblages of hosts and corresponding assemblages of parasites; (iv) host and parasite species in depauperate assemblages constitute subset samples occurring in richer assemblages, related to the life cycle of the parasites and the phylogeography of the host; (v) the presence/absence of certain parasite species can inform about host ecology and geographic origin; (vi) congruence between parasite and host phylogenetic trees can be seen as the co-evolutionary complement of the macroecological patterns. Eventually, we suggest that all these patterns are related and provide an overview and a framework for further geographic studies of host-parasite interactions

Insularité et parasitisme (impacts sur l'investissement dans la réponse immune et la diversité génétique du CMH chez le mulot sylvestre, Apodemus sylvaticus, dans le bassin méditerranéen)

La caractéristique majeure des faunes insulaires est de présenter une diminution de leurs diversités spécifiques. De plus, les populations insulaires montrent de nombreuses modifications de traits de vie en comparaison avec leurs homologues continentaux (syndrome d'insularité). Les hypothèses proposées pour expliquer ces manifestations insulaires n'ont jamais tenu compte de la pression de sélection exercée par le parasitisme. D'autres part, la pression de sélection exercée par les parasites sur l'évolution des traits de vie hôtes et sur le maintien de la diversité génétique est rarement envisagée sous la forme de diversité parasitaire. Le but de cette thèse est de montrer que la diversité parasitaire peut affecter la diversité génétique d'un marqueur sélectionné et modifier les traits de vie par une variation de l'investissement dans la défense immune dans des populations insulaires et continentales. L'étude de la diversité parasitaire en condition insulaire a été réalisée sur les micromammifères et en particulier sur Rattus rattus, Mus musculus et Apodemus sylvaticus. Ce dernier a été retenu comme modèle pour étudier la variation de la diversité génétique de l'exon 2 du gène DQA du CMH de classe II et la variation de l'investissement dans la réponse immune, et plus précisément dans l'immunocompétence, en fonction de la richesse parasitaire enregistrée dans différentes populations continentales et insulaires dans le bassin méditerranéen occidental. Les faunes parasitaires insulaires des micromammifères et du mulot sylvestre montrent une diminution de leurs richesses spécifiques. La colonisation des îles n'est pas un processus aléatoire. L'investissement dans la défense immune n'est pas lié à la différence de pression parasitaire entre les localités. L'étude de l'exon 2 du locus DQA de classe II montre un polymorphisme important avec une diminution de la diversité génétique en condition insulaire. La diversité parasitaire pourrait être une des forces de sélection maintenant le polymorphisme du CMH dans les populations en plus des forces neutres. Les résultats de cette étude ne soutiennent pas le parasitisme comme facteur responsable du syndrome d'insularité du mulot sylvestre dans les îles méditerranéennes.A decrease in species diversity is the main characteristic of island fauna. Moreover, island populations show modifications of their life histories traits in comparison with their mainland counterparts (insular syndrome). Several hypotheses proposed to explain these island manifestations have never taken into account parasitism pressure. Furthermore, parasite selective pressure on host life histories traits and on maintenance of genetic diversity is poorly studied considering parasite diversity as parasite pressure. The aim of this study is to show that parasite diversity could affect genetic diversity of a selected gene and could modify life history traits due to changes in investment in immune defences. Parasite diversity in island populations was studied on micromammals and in particular Rattus rattus, Mus musculus and Apodemus sylvaticus. This last species was used for studying genetic diversity at the second exon of the class II Mhc-DQA locus and variation in investment in the immune response with the measure of immunocompetence in comparison with parasite species richness recorded in eight island and mainland populations in the west Mediterranean area. Micromammals and woodmouse parasite fauna show a decrease in parasite species richness on islands. Island colonisation is not a random process. Immune investment in island and mainland populations of woodmouse is not related to differences in parasite diversity. The second exon of the MHC-DQA locus revealed a large polymorphism with a decrease of genetic diversity in island populations. Parasite diversity could be one of the main selective pressures maintaining MHC polymorphism in addition with neutral forces. This study does not support parasitism as a responsible factor of woodmouse insular syndrome in the Mediterranean area.PERPIGNAN-BU Sciences (661362101) / SudocSudocFranceF

Murine Cytomegalovirus Is Not Restricted to the House Mouse Mus musculus domesticus: Prevalence and Genetic Diversity in the European House Mouse Hybrid Zone

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Evolution and trans-species polymorphism of MHC class IIbeta genes in cyprinid fish.

The polymorphism of DAB genes encoding MHC IIbeta was investigated in 11 cyprinid species from central Europe. The species belonged to four subfamilies: Cyprininae, Tincinae, Gobioninae and Leuciscinae. Two paralogous groups of sequences, DAB1 and DAB3, were recognised according to the similarity of their nucleotide and amino-acid sequences and from phylogenetic analyses using either partial exon 2 or partial exon 3 sequences. A high allelic variability among species was found for exon 2, indicating extensive MHC polymorphism. Time divergence estimation supports the separation of DAB1 and DAB3 groups predating the separation into fish subfamilies, and a cyprinid origin of the DAB genes. Phylogenetic trees using exon 2 support the hypothesis of trans-species polymorphism, which appears to be limited to the subfamily level, i.e. the presence of sequences from different species in the same allelic group was more often recognised within subfamilies Cyprininae and Leuciscinae than between them. Phylogenetic trees using exon 3 reflect the phylogenetic patterns previously found for Cyprinidae systematics. Specific nucleotides and amino-acids in exon 3 that separate both subfamilies, as well as the species within the Cyprininae subfamily were observed. A lack of segregation in leuciscin species was recognised and the alleles of different leuciscin species tend to share similar motifs in exon 3. This could be explained by the ancient and complicated dispersion history of Cyprininae and the radiation of Leuciscinae. The effects of selective pressures were investigated: (1) within species, (2) among lineages, and (3) among sites. From intraspecific analyses, exon 2 sequences were identified as the targets of diversifying selection, whilst the evolution of exon 3 seems to be under the influence of purifying selection. The analyses among lineages indicate positive selection in many branches when using exon 2, therefore confirming trans-species polymorphism, whilst the DAB lineages of exon 3 are potentially submitted to purifying selection to some extent. Moreover, our results suggest the secondary acquisition of function of DAB1 group after duplication. The analyses among sites reveal that exon 2 exhibits sites under positive selection mostly corresponding to the putative PBR sites involved in the alpha-helix structure of the protein