Capacité des pucerons à résister aux parasitoïdes et aux stress abiotiques : rôle du symbiote bactérien Hamiltonella defensa en association avec un nouveau symbiote facultatif du puceron du pois

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2009-2010La résistance aux endoparasitoïdes hyménoptères chez les pucerons est un phénomène complexe impliquant des insectes et des symbiotes bactériens. Il est ainsi maintenant accepté que les symbiotes bactériens facultatifs du puceron du pois Acyrthosiphon pisum, plus particulièrement le symbiote Hamiltonella defensa, jouent un rôle primordial dans la capacité qu'a l'hôte de résister à son principal parasitoïde, Aphidius ervi. Par ailleurs, il a également été démontré que la chaleur pouvait avoir un impact majeur sur la résistance en réduisant celle-ci de manière significative, suggérant du même coup une thermosensibilité des symbiotes. Cette étude va plus loin en abordant l'impact de stress thermiques et UV sur le mécanisme de la résistance d'A. pisum au parasitoïde A. ervi, en lien avec différents types de symbiotes bactériens facultatifs, incluant un nouveau symbiote facultatif désigné sous le nom de PAXS (pea aphid X-type symbiont)

Physical self-concept and participation in physical activity in college students

Introduction: The purpose of this study was to test for reciprocal relations between physical self-concept (PSC) and participation in physical activity (PA). We hypothesized specific bidirectional relations between PSC dimensions (i.e., perceived endurance, sport competence, and strength and body attractiveness) and participation in corresponding types of PA (i.e., aerobic exercise, team or individual sports, and strength training). Methods: Data were gathered from a questionnaire administered to 386 college students on two occasions (3-month interval) to assess PSC and participation in PA. Results: Structural equation modeling revealed significant paths between each PSC dimension and a corresponding type of PA. Students reported more frequent participation in a specific PA when their PSC concerning the activity was high. However, participation in a given PA did not predict subsequent PSC in the corresponding PA, suggesting unidirectional effects of previous PSC on subsequent participation in PA. Conclusions: These results suggest that strategies that contribute to reinforce PSC are primordial and should be targeted as key components for designing effective PA behavior change interventions among college students

Survival to parasitoids in an insect hosting defensive symbionts: a multivariate approach to polymorphic traits affecting host use by its natural enemy.

Insect parasitoids and their insect hosts represent a wide range of parasitic trophic relations that can be used to understand the evolution of biotic diversity on earth. Testing theories of coevolution between hosts and parasites is based on factors directly involved in host susceptibility and parasitoid virulence. We used controlled encounters with potential hosts of the Aphidius ervi wasp to elucidate behavioral and other phenotypic traits of host Acyrthosiphon pisum that most contribute to success or failure of parasitism. The host aphid is at an advanced stage of specialization on different crop plants, and exhibits intra-population polymorphism for traits of parasitoid avoidance and resistance based on clonal variation of color morph and anti-parasitoid bacterial symbionts. Randomly selected aphid clones from alfalfa and clover were matched in 5 minute encounters with wasps of two parasitoid lineages deriving from hosts of each plant biotype in a replicated transplant experimental design. In addition to crop plant affiliation (alfalfa, clover), aphid clones were characterized for color morph (green, pink), Hamiltonella defensa and Regiella insecticola symbionts, and frequently used behaviors in encounters with A. ervi wasps. A total of 12 explanatory variables were examined using redundancy analysis (RDA) to predict host survival or failure to A. ervi parasitism. Aphid color was the best univariate predictor, but was poorly predictive in the RDA model. In contrast, aphid host plant and symbionts were not significant univariate predictors, but significant predictors in the multivariate model. Aphid susceptibility to wasp acceptance as reflected in host attacks and oviposition clearly differed from its suitability to parasitism and progeny development. Parasitoid progeny were three times more likely to survive on clover than alfalfa host aphids, which was compensated by behaviorally adjusting eggs invested per host. Strong variation of the predictive power of intrinsic (body color) and extrinsic traits (symbionts, host plant), indicate that host variables considered as key predictors of outcomes strongly interact and cannot be considered in isolation

Precision feeding of lactacting sows: development of a decision support tool to handle variability

Nutritional requirements of lactating sows mainly depend on milk yield and greatly vary across individuals. Moreover, because the same diet is generally fed to all sows, and feed intake is low and highly variable, nutrient supplies are often insufficient to meet the requirements, especially those of primiparous sows. Conversely, sows with high appetite may be fed nutrient in excess. Acquiring data on sows and their environment at high-throughput allows the development of new precision feeding systems with the perspective of improving technical performance and reducing feeding cost and environmental impact. The objective of this study was thus to design a decision support tool that could be incorporated in automated feeding equipment. The decision support tool was developed on the basis of InraPorc® model. The optimal supply for a given sow is determined each day according to a factorial approach considering all the information available on the sow (i.e. parity, litter size, milk production, body condition…) or predicted from real-time data (i.e. expected feed intake). The approach was tested using data from 817 lactations. Precision feeding (PF) with the mixing of two diets with different nutritional values was then simulated in comparison with conventional feeding (CF) with a single diet. In sows fed in excess PF reduced average digestible lysine excess from 10.9 to 2.7 g/d, whereas in deficient sows the deficiency was reduced from -5.7 to -2.1 g/d. Overall, PF reduced average lysine intake by 6.8%. At the same time, with PF, lysine requirement was met for a higher proportion of sows, especially in younger sows, and a lower proportion of sows, especially older sows, received excessive supplies. PF also reduced average phosphorus intake while limiting the occurrence of excess and deficiency. This study confirms the potential of precision feeding in order to better achieve nutritional requirements of lactating sows and reduce their nutrient intake and excretion. This project has received funding from the European Union’s Horizon 2020 research and innovation program, grant agreement no. 633531

Predictive power of explanatory variables used in RDA models of parasitism of aphid <i>Acyrthosiphon pisum</i> by <i>Aphidius ervi</i>.

<p>Variable aphid color appears as best predictor when tested alone in univariate RDA, but is poorly predictive in multivariate model because of colinearity.</p

Explanatory variables examined to predict outcomes of challenges involving 100 <i>Aphidius ervi</i> wasps on 600 <i>Acyrthosiphon pisum</i> individuals belonging to 10 field-collected clones from either alfalfa or red clover.

<p>Behaviors are listed with their% occurrence recorded for both wasps (<i>wsp.</i>) and aphids (<i>aph.</i>). Behaviors <i>wsp.mve</i> and <i>aph.exc</i> were excluded to take into account colinearity imposed by observation time being limited to 5 min. See text for details.</p

Experimental aphid clones classified by source crop plant, aphid color morph and screened symbiotic bacteria.

<p>Clone IDs are unique numbers from field samples followed by letters: first capital letter (A or C) is for alfalfa or clover crop; lowercase letter (g or p) is for green or pink; last letter is for aphid symbiont, T for <i>Hamiltonella defensa</i>, U for <i>Regiella insecticola</i>, or 0 for none of the symbionts tested for (see text for details). In <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060708#pone-0060708-g001" target="_blank">Figure 1</a>, wasp x clone interactions are identified as e.g. interaction ‘Aw_52Ag0’ where an ‘Aw’ <i>A. ervi</i> wasp interacts with individuals (n = 6) of the clone ‘52Ag0’.</p