The integration of multiple independent data reveals an unusual response to Pleistocene climatic changes in the hard tick Ixodes ricinus
ABSTRACT In the last few years, improved analytical tools and the integration of genetic data with multiple sources of information have shown that temperate species exhibited more complex responses to ice ages than previously thought. In this study, we investigated how Pleistocene climatic changes affected the current distribution and genetic diversity of European populations of the tick Ixodes ricinus, an ectoparasite with high ecological plasticity. We first used mitochondrial and nuclear genetic markers to investigate the phylogeographic structure of the species and its Pleistocene history using coalescent-based methods; then we used species distribution modelling to infer the climatic niche of the species at last glacial maximum; finally, we reviewed the literature on the I. ricinus hosts to identify the locations of their glacial refugia. Our results support the scenario that during the last glacial phase, I. ricinus never experienced a prolonged allopatric divergence in separate glacial refugia, but persisted with interconnected populations across Southern and Central Europe. The generalist behaviour in host choice of I. ricinus would have played a major role in maintaining connections between its populations. Although most of the hosts persisted in separate refugia, from the point of view of I. ricinus, they represented a continuity of 'bridges' among populations. Our study highlights the importance of species-specific ecology in affecting responses to Pleistocene glacial-interglacial cycles. Together with other cases in Europe and elsewhere, it contributes to setting new hypotheses on how species with wide ecological plasticity coped with Pleistocene climatic changes.
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ABSTRACT: AimTo investigate the phylogeography of the aposematic wood tiger moth (Parasemia plantaginis) across its Holarctic distribution and to explore how its genetic structure relates to geographical differences in hindwing warning coloration of males and females. Males have polymorphic hindwing coloration, while female hindwing coloration varies continuously, but no geographical analyses of coloration or genetic structure exist.LocationThe Holarctic.Methods We sequenced a fragment of the mitochondrial cytochrome c oxidase subunit I gene (COI) from 587 specimens. We also examined more current population structure by genotyping 569 specimens at 10 nuclear microsatellite loci. Species distribution modelling for present conditions and the Last Glacial Maximum (LGM) was performed to help understand genetic structure. Geographical patterns in hindwing warning coloration were described from 1428 specimens and compared to the genetic analyses.ResultsWe found only two instances of genetic divergence that coincided with distinct, yet imperfect, shifts in male hindwing coloration in the Caucasus region and Japan. A shift in female hindwing colour did not appear to be associated with genetic structure. A change from sexual monomorphism to sexual dimorphism was also observed. Mitogenetic (mtDNA) structure does not show the influence of glacial refugia during the LGM. Climate shifts following the LGM appear to have isolated the red Caucasus populations and other southerly populations. Populations at opposite ends of the moth's distribution showed high levels of differentiation in the microsatellite data analysis compared to the shallow mitogenetic structure, supporting a more recent divergence.Main conclusionsParasemia plantaginis populations appeared to have been historically well connected, but current populations are much more differentiated. This raises the possibility that incipient speciation may be occurring in portions of the species' distribution. Some changes in colour align to genetic differences, but others do not, which suggests a role for selective and non-selection based influences on warning signal variation.Journal of Biogeography 04/2015; DOI:10.1111/jbi.12513 · 4.97 Impact Factor
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ABSTRACT: AimThe pine processionary moth (PPM) is a species complex containing two congeneric taxa, namely Thaumetopoea pityocampa and Thaumetopoea wilkinsoni, with a circum-Mediterranean distribution and a strong geographical structure. We developed comparative phylogeographies for two of the main natural enemies of the PPM, the egg parasitoids Baryscapus servadeii and Ooencyrtus pityocampae, to determine to what extent their Quaternary histories were parallel and mirrored that of their host.LocationPine and cedar forests around the Mediterranean Basin.Methods Egg masses of the PPM were sampled from its whole range and parasitoids allowed to emerge in the laboratory. We sequenced one mitochondrial fragment from 303 individuals of B. servadeii and 239 of O. pityocampae, and the nuclear ITS2 for a subset of the samples. The distribution of genetic diversity, network of alleles and AMOVAs were analysed to decipher the phylogeographical structures, and PPM and host plant effects.ResultsResults differed drastically between the two parasitoid species. We found 87 haplotypes and five ITS alleles for B. servadeii, which showed a strong phylogeographical structure over its distribution range. We identified four divergent clades, one of them further forming four haplogroups. Refugial areas were similar to those of the host. AMOVA showed that over 40% of the variance could be explained by the insect host structure. In contrast, O. pityocampae showed 16 closely related haplotypes, one corresponding to 60% of the individuals. PPM structure explained only 15% of the variance. The effects of the pine host were limited in both parasitoid species.Main conclusionsBaryscapus servadeii probably survived Quaternary climatic oscillations in long-term refugia where the PPM host was also continuously present. Although not strictly parallel, its history showed high degrees of similarity with that of the host. Conversely, results suggest that O. pityocampae had different climatic requirements and experienced severe bottleneck(s) during the Quaternary. Yet, it efficiently recolonized its main host range, probably helped by its parthenogenetic reproduction and possibly also by local host shifts.Journal of Biogeography 02/2015; DOI:10.1111/jbi.12495 · 4.97 Impact Factor
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ABSTRACT: In insects, ABC transporters have been shown to contribute to defence/resistance to insecticides by reducing toxic concentrations in cells/tissues. Despite the extensive studies about this detoxifying mechanism, the temporal patterns of ABC transporter activation have been poorly investigated. Using the malaria vector Anopheles stephensi as a study system, we investigated the expression profile of ABC genes belonging to different subfamilies in permethrin-treated larvae at different time points (30 min to 48 h). Our results showed that the expression of ABCB and ABCG subfamily genes was upregulated at 1 h after treatment, with the highest expression observed at 6 h. Therefore, future investigations on the temporal dynamics of ABC gene expression will allow a better implementation of insecticide treatment regimens, including the use of specific inhibitors of ABC efflux pumps.