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Evolutionary theory predicts that vertically transmitted symbionts are selected for low virulence, as their fitness is directly correlated to that of their host. In contrast with this prediction, the Wolbachia strain wMelPop drastically reduces its Drosophila melanogaster host lifespan at high rearing temperatures. It is generally assumed that this feature is maintained because the D. melanogaster-wMelPop symbiosis is usually not exposed to environmental conditions in which the symbiont is virulent. To test this hypothesis, we submitted wMelPop-infected D. melanogaster lines to 17 generations of experimental evolution at a high temperature, while enforcing late reproduction by artificial selection. The fly survival was measured at different time points, as well as two traits that have been proposed to be causally responsible for wMelPop virulence: its relative density and the mean number of copies of octomom, an 8-genes region of the Wolbachia genome. We hypothesised that these conditions (high temperature and late reproduction) would select for a reduced wMelPop virulence, a reduced wMelPop density, and a reduced octomom copy number. Our results indicate that density, octomom copy number and virulence are correlated to each other. However, contrary to our expectations, we could not detect any reduction in virulence during the course of evolution. We discuss the significance of our results with respect to the evolutionary causes of wMelPop virulence.

The effects of density are key in determining population dynamics, since they can positively or negatively affect the fitness of individuals. These effects have great relevance for polyphagous insects for which immature stages develop within a single site of finite feeding resources. Drosophila suzukii is a crop pest that induces severe economic losses for agricultural production; however, little is known about the effects of density on its life‐history traits. In the present study, we (i) investigated the egg distribution resulting from females' egg‐laying strategy and (ii) tested the immediate (on immatures) and delayed (on adults) effects of larval density on emergence rate, development time, potential fecundity, and adult size. The density used varied in a range between 1 and 50 larvae. We showed that 44.27% of the blueberries used for the oviposition assay contained between 1 and 11 eggs in aggregates. The high experimental density (50 larvae) has no immediate effect in the emergence rate but has effect on larval developmental time. This trait was involved in a trade‐off with adult life‐history traits: The time of larval development was reduced as larval density increased, but smaller and less fertile females were produced. Our results clearly highlight the consequences of larval crowding on the juveniles and adults of this fly. [ABSTRACT FROM AUTHOR]

It is now acknowledged that mating system is a dynamic characteristic within species or populations. Indeed, behavioural characteristics shaping the mating system can vary at the inter‐individual level, providing raw material for sexual and natural selections, and at the intra‐individual level, because of phenotypic plasticity and ontogeny of individual behaviours. Social environment is an additional source of variation in sexual behaviours. By focusing on males of the parasitoid wasp Venturia canescens, we assessed how sexual behaviours (courtship and mating) vary between and within individuals, considering males' size as inter‐individual source of variation, and age and mating experience as intra‐individual sources of variation. Consequences of the variations in sexual behaviours at the individual level are appraised by quantifying the costs in longevity and offspring production incurred by (repeatedly) mated males. At the population level, we tested the "agility hypothesis" predicting that smaller males win the male–male competition to access females, resulting in a non‐random assortative mating by size and a negative sexual selection on body size. We showed that V. canescens males are polygynous and that mating incurred longevity cost. Old males had a higher probability to court females, but no mating advantage. Smaller males tended to have a higher mating probability, but size was not under sexual selection and there was a random mating pattern according to individual size. Male–male competition intensity did not influence pairing pattern but tended to influence mating dynamic. Overall, our results suggest that sexual behaviours tended to vary at the inter‐ and intra‐individual levels and the effect of social environment remains to be more precisely described. These variations may impact individuals' reproductive success with potential ecological and evolutionary consequences that are discussed. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2010.03.003 Byline: Marie Metzger (a), Deborah Fischbein (b), Alexandra Auguste (c), Xavier Fauvergue (c), Carlos Bernstein (a), Emmanuel Desouhant (a) Abstract: In many animals, mating takes place after natal dispersal. Consequently, use of reliable information is required to increase the probability of encounters between the sexes. Most of the studies on mate finding in parasitoid insects have focused on the role of a single information source: a sex pheromone. Other sources have been mostly ignored. We studied the nature of olfactory information used for mate finding by the parasitoid Venturia canescens both at a distance and at host patch level, and investigated how this information is used. We tested which sex attracts the other and whether mate location is improved by combining different sources of information. We found that males simultaneously used two types of olfactory cues to find their mate: information directly related to females and an environmental cue provided by hosts. Male efficiency in locating virgin females was enhanced threefold by the association of females with hosts, whereas host patches, on their own, were unattractive to males. Our results also suggest that females emit a volatile pheromone. At the host patch level, males used chemical marks left by females foraging for hosts. These results led us to consider the distinction between signals and cues and we suggest that the volatile pheromone emitted by the females, always described as a signal, could rather be a cue. Although evidence for a volatile sex pheromone is pervasive in parasitoids, our study stresses the role of other cues in mate-finding strategies. Author Affiliation: (a) CNRS, UMR 5558, Laboratoire de Biometrie et Biologie Evolutive, Universite Lyon 1, France (b) Laboratorio de Ecologia de Insectos Forestales INTA EEA Bariloche, Argentina (c) UMR INRA-UNSA-CNRS 1301 'Interactions Biotiques et Sante Vegetale', France Article History: Received 24 July 2009; Revised 26 October 2009; Accepted 2 March 2010 Article Note: (miscellaneous) MS. number: 09-00498R