Effects of daily fluctuating temperatures on the Drosophila–Leptopilina boulardi parasitoid association

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Differentiation of thermal reaction norms between marginal and core populations of a northward expanding parasitoid

Abstract Understanding the speed of and the type of mechanisms that species use to adapt to rapid change is a central question in evolutionary biology. Classically, the two mechanisms denoted in the literature that allow individuals to address these environmental changes are either phenotypic plasticity or rapid evolutionary changes. However, phenotypic plasticity itself can evolve rapidly. In this study, we investigated the genetic differentiation between marginal and core populations of a high-trophic level insect, Leptopilina boulardi , a Drosophila parasitoid, which has exhibited a very rapid progression northward of its geographical range. Several life history traits have been investigated in different populations according to four fluctuating thermal regimes that mimic the thermal conditions in the field. We found that at low developmental temperature, the two northern marginal populations that have to face a colder winter, survive longer than the two core populations. In addition, the northernmost populations exhibit a higher potential fecundity, a higher starvation resistance and a larger amount of energy at low temperatures. These significant genetic differentiations with genotype-by-environment interactions show that a rapid genetic differentiation of the shape of thermal reaction norms is possible when populations have to cope with new environments

Local adaptation of a Drosophila parasitoid: habitat-specific differences in thermal reaction norms

International audienceLocal climate is an important source of selection on thermal reaction norms that has been well investigated in cline studies, where populations sampled along altitudinal or latitudinal gradients are compared. Several biotic factors vary with climate, but are rarely integrated as alternative agents of selection to climatic factors. We tested the hypothesis that habitat may select for thermal reaction norms and magnitude of phenotypic plasticity in a drosophila parasitoid, independently of the climate of origin. We sampled populations of Leptopilina boulardi, a Drosophila parasitoid in two different habitats, orchards and forests. Orchards offer laying opportunities over small distances for parasitoids, with a low variability in the number of hosts per patch, while forests offer more dispersed and more variable patches. The sampling was realized in a temperate and a Mediterranean climate. We measured egg load, volume of eggs, longevity and lipid content for parasitoids reared at two temperatures. Reaction norms were opposite for populations from forests and orchards for investment in reproduction, independently of the climate of origin. The maximal investment of resources in reproduction occurred at the lower temperature in orchards and the higher temperature in forests. Host distribution differences between habitats may explain these opposite reaction norms. We also observed a flatter reaction norm for egg load in forests than in orchards. This relative canalization may have been selected in response to the higher variability in laying opportunities observed in forests. Our results demonstrate the potential role of resource distribution in evolution of thermal plasticity

Scanning the European corn borer (<em>Ostrinia</em> spp.) genome for adptive divergence between host-affiliated species

International audienceIt has recently been shown that the European corn borer, a major pest of maize crops, is actually composed of two genetically differentiated and reproductively isolated taxa, which are found in sympatry over a wide geographical range in Eurasia. Each taxon is adapted to specific host plants: Ostrinia nubilalis feeds mainly on maize, while O. scapulalis feeds mainly on hop or mugwort. Here, we present a genome scan approach as a first step towards an integrated molecular analysis of the adaptive genomic divergence between O. nubilalis and O. scapulalis. We analysed 609 AFLP marker loci in replicate samples of sympatric populations of Ostrinia spp. collected on maize, hop and mugwort, in France. Using two genome scan methods based on the analysis of population differentiation, we found a set of 28 outlier loci that departed from the neutral expectation in one or the other method (of which a subset of 14 loci were common to both methods), which showed a significantly increased differentiation between O. nubilalis and O. scapulalis, when compared to the rest of the genome. A subset of 12 outlier loci were sequenced, of which 7 were successfully re-amplified as target candidate loci. Three of these showed homology with annotated lepidopteran sequences from public nucleotide database

The French touch in entomological biology : synthesis of the "16th Colloque Biologie de l'Insecte"

Pas de résumé, pas de mots clés,pas de doi.International audience

The rapid northward shift of the range margin of a Mediterranean parasitoid insect (Hymenoptera) associated with regional climate warming

Aim Many species are undergoing range shifts to higher latitudes in response to global warming. Whereas several studies of insects have examined causes of variability in the rate of range expansions, few studies have investigated species occupying higher trophic levels, where the effects of climate change are predicted to be particularly strong. Here, we analyse changes in the geographical range of Leptopilina boulardi, a small parasitoid of Drosophila larvae, in relation to temperature changes in the study area. Location The Rhone-Saone Valley in south-eastern France. Methods A survey of L. boulardi and its two Drosophila host species was conducted in 16 localities at the northern margin of the L. boulardi range over a period of 9years. A generalized linear mixed model was used to explain the occurrence of the parasitoid in the study area and its northward progression. We also developed linear mixed-effects models to determine the temperature changes in the studied area. Results Leptopilina boulardi was found to be moving very rapidly northwards, with an average rate of range expansion of 90 km decade-1, exceeding previously observed rates for small insects. We recorded significant warming (+1.57 degrees C, on average from 1979 to 2011), with a considerable temperature increase of 4 degrees C in the spring. Leptopilina boulardi range expansion is not limited by host availability, and we suggest that this northward range expansion is primarily a direct response to climate warming. Main conclusions In south-eastern France, a very rapid progression northwards, which coincides with a marked increase in temperature, was observed for a higher-trophic-level insect