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Consistent individual differences in behaviour, also called behavioural types, are often observed in animal populations and can correlate to form behavioural syndromes. Behavioural types and syndromes have consequences in various fields of ecology, from species interactions to ecosystem services, notably through the role they can play in the slow–fast life history continuum. Individuals differ in their life history strategies along this continuum according to their relative investment in reproduction or survival, and the pace-of-life syndrome (POLS) hypothesis predicts a coevolution between these life history strategies and behavioural types linked to risk taking. In this framework, the aim of our study was thus to investigate the existence of behavioural types and their links with life history traits in the parasitoid hymenopteran Venturia canescens . We considered two behaviours, exploration and activity, that are linked to risk taking and resource acquisition, and three life history traits, longevity, egg load and offspring production rate. We found consistent individual differences in both exploration and activity. However, contrary to the predictions of the POLS, the behavioural types did not correlate with each other or with the life history traits tested. We thus found no evidence of a POLS in V. canescens . However, the existence of behavioural types in female parasitoids may be of utmost importance for biological control efficiency.

International audience; The alternation of light and dark periods on a daily or seasonal time scale is of utmost importance for the synchronization of physiological and behavioral processes in the environment. For the last 2 dec- ades, artificial light at night (ALAN) has strongly increased worldwide, disrupting the photoperiod and its related physiological processes, and impacting the survival and reproduction of wild animals. ALAN is now considered as a major concern for biodiversity and human health. Here, we present why insects are relevant biological models to investigate the impact of ALAN. First the phenotypic responses to ALAN and their underpinning mechanisms are reviewed. The consequences for popula- tion dynamics, and the community composition and functioning are described in the second part. Because ALAN provides new and widespread selective pressure, we inventory evolutionary changes in response to this anthropogenic change. Finally, we identify promising future avenues, focusing on the necessity of understanding evolutionary processes that could help stakeholders consider darkness as a resource to preserve biodiversity as well as numerous ecosystem services in which insects are involved.

6 pages; International audience; Ontogeny of animal personality is still an open question. Testing whether personality traits correlated with state variables (e.g. metabolic rate, hormones) and/or life history traits, and which ones are involved, requires more empirical studies. Insects with metamorphosis represent a good opportunity to tackle this question. Because of the various degrees of internal (physiological, nervous) and environmental changes linked to metamorphosis they allow testing whether these modifications drive consistency in personality traits between immature and adult stages. In this review, we establish general predictions for the effects of metamorphosis on personality in insects with complete or incomplete metamorphosis and suffering from a strong or weak niche shift after metamorphosis. We then reviewed the still rare empirical literature and discuss future research axes.

This preprint has been reviewed and recommended by Peer Community In Evolutionary Biology (http://dx.doi.org/10.24072/pci.evolbiol.100047) 1. Sib-mating avoidance is a pervasive behaviour that likely evolves in species subject to inbreeding depression. Laboratory studies have provided elegant demonstrations of sib-mating avoidance, but small-scale bioassays often minimize the costs associated with mate finding and choice, which could lead to spurious findings. 2. We used the hymenopteran parasitoid wasp Venturia canescens as a model organism, because previous laboratory studies revealed that sib-mating led to a 25% decrease in fertile offspring, and that sib-mating was partially avoided. 3. Our study consisted of a mate choice experiment in laboratory cages to determine if kin discrimination occurs in this species. We further performed a field study in which 86 wild-caught males, 155 wild-caught females and their 226 daughters were genotyped at eighteen microsatellite loci. With these data, we reconstructed the genotype of each female ′s mate and estimated the relatedness of each mating pair. 4. Mate choice experiments confirmed that females are capable of discriminating kin. Time to mating depended on the frequency of female encounters with related and unrelated males. Contrary to previously published results, however, no sib-mating avoidance was detected. In the field, the effective rate of sib-mating did not differ from the probability that sibs encounter one other at random, which corroborates the absence of sib-mating avoidance. We also detected a weak but significant male bias in dispersal, which could reduce encounters between sibs. 5. Our results suggest that, despite kin discrimination, V. canescens tolerates sib-mating in the field. The weak male-biased dispersal cannot explain entirely this pattern. This raises the question as to why kin discrimination is maintained in this species. It further calls into question the idea that inbreeding depression occurs in most species with single-locus complementary sex determination.

International audience; Mating failures at low density – a common type of Allee effect – can reduce the per capita reproductive rate and, if severe enough, doom small populations to extinction. Parasitoids frequently undergo low densities triggered by their typically cyclic dynamic and/or the bottlenecks they experience when introduced for the biological control of agricultural pests. However, most parasitoid species belong to the order Hymenoptera and reproduce via arrhenotokous parthenogenesis: unfertilized eggs develop into males. A common belief is therefore that parasitoids are immune to the mate-finding Allee effect because mating failures yields more males, which should in turn restore mating success. Yet, meta-analyses of biological control introductions suggest that hymenopteran parasitoids are as extinctionprone as non-parthenogenetic species. Here we developed a population dynamic model to investigate the advantage of arrhenotokous parthenogenesis for parasitoid species that experience a mate-finding Allee effect. We show that: i) the conditions for which mating failures drive parasitoids to extinction are marginally more restricted for parthenogenetic species than for non-parthenogenetic ones; ii) parthenogenesis increases the resistance of parasitoids to accidental decrease in density and to invasions by a competing species whether or not parthenogenetic; and iii) parthenogenesis favors population establishment in new environments, whether or not already occupied. Hence even if arrhenotokous parthenogenesis is not as effective as expected to limit parasitoid extinctions caused by mating failures, it provides a significant advantage for population establishment and persistence.

International audience; Extinctions have no simple determinism, but rather result from complex interplays between environmental factors and demographic‐genetic feedback that occur at small population size. Inbreeding depression has been assumed to be a major trigger of extinction vortices, yet very few models have studied its consequences in dynamic populations with realistic population structure. Here we investigate the impact of Complementary Sex Determination (CSD) on extinction in parasitoid wasps and other insects of the order Hymenoptera. CSD is believed to induce enough inbreeding depression to doom simple small populations to extinction, but we suggest that in parasitoids CSD may have the opposite effect. Using a theoretical model combining the genetics of CSD and the population dynamics of host‐parasitoid systems, we show that CSD can reduce the risk of parasitoid extinction by reducing fluctuations in population size. Our result suggests that inbreeding depression is not always a threat to population survival, and that considering trophic interactions may reverse some pervasive hypotheses on its demographic impact.

Animals adjust their behaviour in response to changing environmental conditions. This form of plasticity can result from animals’ experience and their capacity to update information about their habitat. In the context of optimal foraging in patchy environments, animals may estimate profitability of patches from different cues to update their estimate of the profitability of the whole habitat. Updating may be achieved by weighting pieces of information obtained at different times. We studied how female parasitoids, Venturia canescens, weight different cues about each host patch profitability they successively encounter to adjust their foraging decisions accordingly. Our results show that parasitoids clearly perceived the profitability of the patches and that their foraging decisions were equally influenced by older and more recent foraging experience. We designed a second experiment to unravel, from three interdependent cues of patch profitability, which information source was mainly used to update the estimate of environmental profitability. The number of eggs laid in previously visited host patches seems to be an integrative cue of environmental profitability. We discuss the adaptive value of the weighting of successive pieces of information and the use of the different information sources in regard to the ecological context in which the wasps thrive.

The ability to adjust resource allocation to the quality of the environment has broad implications for animal reproductive success. Organisms with complex life cycles that may experience various selection pressures during their lifetime are expected to evolve mechanisms to modulate the resource allocation strategies adopted during ontogeny to the conditions encountered by the adult. In the parasitoid Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae), thelytoky appears to have been selected for in anthropogenic habitats, where hosts are relatively numerous and food is absent, and arrhenotoky in natural habitats where hosts are more scarce and food is present. A previous study postulated that during their juvenile stage, females of both reproductive modes adopt strategies of energy allocation in accordance with these conditions, possibly providing a direct short-term advantage to arrhenotokous forms, which partially co-occur with thelytokous forms under natural conditions. To test this assumption, we provided daily adult thelytokous and arrhenotokous females with a small number of hosts together with food. To compare their lifetime resource allocation strategies, we recorded wasp longevities, egg loads, and carbohydrate reserves in wasps of different ages. Our analysis indicates that thelytokous females are able, to a certain extent, to cope with these conditions, because they reached the same longevity as arrhenotokous females. Nevertheless, thelytokous females suffered from a higher degree of time limitation compared with arrhenotokous ones, and arrhenotokous wasps appeared to maintain their energetic advantage over the adult stage. These results provide new insights, and point to the consideration of other activities, such as flight performance and/or ability to reach food and hosts, in the understanding of the role of resource allocation strategies in the maintenance of sex in this species.

Whether to invest in current or future reproduction is an important trade-off in life history evolution. For insect parasitoids, this trade-off is determined, among other factors, by the decision whether to search for hosts (immediate gain of fitness) or food (delayed fitness gains). Although host searching has been well studied, food sources, cues that parasitoids use to search for food and how insects modify their feeding behaviour have not. To address these questions, we investigated the food- and host-searching decisions made by the parasitoid Venturia canescens in both laboratory (olfactometer experiments) and field conditions (choice experiments). The wasps detected chemical cues associated with food, as well as those associated with hosts, and moved towards one or the other according to their nutritional state. Females used as food sources the same fruits that harboured hosts and detected the olfactory cues that would direct them to these fruits. Field results were consistent with those obtained in the laboratory. By integrating responses to infochemicals related to host and food, V. canescens might reduce the costs associated with food searching, so that more time and energy can be allocated to foraging for hosts. This behaviour should result in an adaptive advantage over parasitoids that incur additional costs by searching for hosts and food in different locations.

International audience; In sexual organisms, low population density can result in mating failures and subsequently yields a low population growth rate and high chance of extinction. For species that are in tight interaction, as in host-parasitoid systems, population dynamics are primarily constrained by demographic interdependences, so that mating failures may have much more intricate consequences. Our main objective is to study the demographic consequences of parasitoid mating failures at low density and its consequences on the success of biological control. For this, we developed a deterministic host-parasitoid model with a mate-finding Allee effect, allowing to tackle interactions between the Allee effect and key determinants of host-parasitoid demography such as the distribution of parasitoid attacks and host competition. Our study shows that parasitoid mating failures at low density result in an extinction threshold and increase the domain of parasitoid deterministic extinction. When proned to mate finding difficulties, parasitoids with cyclic dynamics or low searching efficiency go extinct; parasitoids with high searching efficiency may either persist or go extinct, depending on host intraspecific competition. We show that parasitoids suitable as biocontrol agents for their ability to reduce host populations are particularly likely to suffer from mate-finding Allee effects. This study highlights novel perspectives for understanding of the dynamics observed in natural host-parasitoid systems and improving the success of parasitoid introductions.

1. Flight is an energy-demanding behaviour in insects. In parasitic wasps, strategies of nutrient acquisition and allocation, resulting life-history trade-offs and relationships with foraging strategies and resource availability have received much attention. However, despite the ecological importance of dispersal between host and food patches, and the great impact energy diverted to flight should have on lifetime reproductive success, the eco-physiology of flight in parasitoids is poorly understood. 2. The objective of this study is to (i) identify the energetic resources used to fuel flight, and (ii) relate nutrient type and rate of utilisation to selective pressures in terms of resource availability posed by the environment. 3. Using a flight mill and biochemical assays, we compared flight performance and nutrient dynamics during flight between two reproductive modes of the parasitoid Venturia canescens Gravenhorst, which is known to thrive preferentially in contrasted environments (i.e. natural vs. anthropogenic habitat), differing notably in host and food distribution. 4. Biochemical analyses of different nutrient types showed that glycogen is the flight fuel used by this species, yet no significant differences in its dynamics in flight were found between the two reproductive modes. 5. Results suggest that both glycogen quantity and flight performance are related to the diverging ecological conditions experienced by thelytokous and arrhenotokous strains. © 2012 The Royal Entomological Society.

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When foraging partially depleted patches (i.e., a fraction of hosts are already parasitized), female parasitoids must decide: 1—whether to superparasitize, and 2—whether to stay in their current patch (thus missing the opportunity of finding a better patch elsewhere). To make these decisions, parasitoids may rely on different cues, produced both by the environment and by conspecifics. Animals thriving in different environments may differ in cues they use. In the solitary parasitoid Venturia canescens, thelytokous (asexual) and arrhenotokous (sexual) individuals are found in two contrasting environments. Thelytokous females, from anthropogenic conditions, are known to cope with superparasitism in an adaptive way. On the other hand, little is known about superparasitism by arrhenotokous females. We compared the host exploitation strategies of thelytokous and arrhenotokous females in partially depleted patches. Hosts parasitized by thelytokous females were more frequently avoided than those parasitized by arrhenotokous females, suggesting a stronger chemical marking of the former. Only thelytokous females used information from conspecifics for patch-leaving decisions. The conformity of the differences in the behavior of thelytokous and arrhenotokous females with the environmental conditions they experience in their habitat is discussed.

In the hymenopteran parasitoid Venturia canescens, asexual (obligate thelytoky not induced by Wolbachia bacteria) and sexual (arrhenotokous) wasps coexist in field conditions despite the demographic cost incurred due to the production of males by sexual females. Arrhenotoky predominates in field conditions, whereas populations in indoor conditions (mills, granaries) are exclusively thelytokous. These differences in the relative abundance of the two modes of reproduction between environments suggest that the individuals of each reproductive mode may have developed strategies adapted to the conditions prevailing in each kind of habitat. The two environments contrast in temperature variability and in the spatial heterogeneity of host availability. In this study, we considered the combined effect of temperature and host availability on host patch exploitation by thelytokous and arrhenotokous V. canescens. As expected, arrhenotokous females were more sensitive to temperature changes. If the temperature decreased before foraging, they remained longer and exploited patches more thoroughly. This is consistent with the expected behaviour of parasitoids in response to signs of unfavourable conditions that entail increasing risk of time limitation or a reduced probability of attaining further patches. Both arrhenotokous and thelytokous females increased patch exploitation with host availability. However, unexpectedly, we found no difference in the way the two types of wasp responded to differences in host availability. Differences in the strategies adopted under different environmental conditions may indicate divergence of niche-specific life history traits between the two modes of reproduction. Niche displacement may partly account for the coexistence of these two modes of reproduction at a geographical scale.

Endoparasitoid insects have evolved mechanisms to counteract host immune defences. At oviposition, the endoparasitoid Venturia canescens injects virus-like particles (VLPs) together with the egg that interfere with the immune system of the host. These prevent encapsulation of the parasitoid egg. It has been shown that the gene coding for one of the VLP proteins exists in two variants (called Repeat-Plus (RP) and Repeat-Minus (RM)). Previous observations suggested that these variants induce pleiotropic effects on the reproductive biology of the female resulting, in an impeded transfer of eggs from the ovarioles to the oviducts in RM females, and in alterations in the egg laying sequence. We show that RM females from another geographical locality do not exhibit any phenotypic alteration of the reproductive biology. By showing a lack of association between VLP alleles and the reproductive phenotypic characteristics in a given strain, our results do not support the hypothesis of pleiotropic effects. Conversely, the results suggest that different genes code for the VLPs and for the reproductive biology characteristics. Different phenomena such as linkage, the action of pathogens, etc. could explain the association between characters that is observed in some strains.

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Light pollution, defined as the alteration of night natural lighting levels by artificial light sources, is a widespread anthropogenic disturbance that affects almost every ecosystem on Earth. It mainly comes from direct illumination due to public street lighting, but can also take the form of skyglow (i.e. the scattering of upwardly-emitted light into the atmosphere) which extends over hundreds of kilometres around urbanised areas. For a long time, light pollution had received less attention than other types of anthropogenic disturbances such as climate change. However, a growing number of studies have highlighted its numerous biological consequences on a large number of organisms, and at all levels of biological organisation (individuals, populations, ecosystems). Light pollution is therefore now considered as an important driver of global change and a major concern for human health and biodiversity. Studies on light pollution have mainly focused on nocturnal organisms, which are more likely to be disturbed by the presence of light at night. This is particularly true for insect, as evidenced by numerous studies that investigated the attractiveness of artificial light sources on moths or the modification of flashing activities in fireflies exposed to light pollution. On the contrary, very little is known about consequences of light pollution on diurnal insects. The aim of my thesis was therefore to investigate experimentally the changes induced by light pollution in a diurnal parasitoid, the wasp Venturia canescens. To do this, I studied behavioural, life-history and physiological traits of female wasps exposed to various intensities of light pollution. My work was divided in two parts. The first part dealt with changes in behavioural traits related to parasitic efficiency and lifetime reproductive success, in relation to energy reserves, at the intra- and trans-generational levels. I demonstrated that light pollution led diurnal wasps to become active and search for food and hosts at night. In addition, I showed that light at night, depending on its intensity, also modified wasps’ daytime foraging behaviour, but without affecting their energy reserves. Indeed, there was an increased preference for host searching in wasps exposed to low intensity light pollution. However, light at night does not seem to have a strong effect on the lifetime reproductive success of Venturia canescens. Finally, light pollution also acted at trans-generational level, influencing offspring feeding behaviour and development time. In the second part of my work, I focused on a physiological trait, the production of melatonin. Melatonin is a key hormone involved in the regulation of circadian rhythm in organisms. It is also known to be strongly impacted by the presence of light at night. This hormone is therefore likely to play a major role in the phenotypic changes observed in organisms exposed to light pollution. Melatonin has been well studied in vertebrates, especially mammals, but knowledge of its synthesis and circadian rhythm in insect is scarce. I therefore developed two methods for quantifying melatonin in Venturia canescens, in order to describe its dynamics over a 24-hour cycle in the absence of light pollution. This work could thus serve as a basis for future studies to experimentally test the effect of light pollution on melatonin synthesis in Venturia canescens.; La pollution lumineuse, définie comme la modification des niveaux naturels de lumière nocturne par des sources lumineuses artificielles, est une perturbation anthropique très répandue qui touche quasiment tous les écosystèmes sur Terre. Elle provient principalement de l'éclairage public, mais peut également prendre la forme du « skyglow », un halo lumineux dû à la diffusion de la lumière par les particules présentes dans l'atmosphère qui s'étend sur des centaines de kilomètres autour des zones urbanisées. Pendant longtemps, la pollution lumineuse a été moins étudiée que d'autres perturbations anthropiques telles que le changement climatique. Cependant, un nombre croissant d'études a mis en évidence ses nombreuses conséquences biologiques sur un grand nombre d'organismes à tous les niveaux d’organisation biologique (individus, populations, écosystèmes). La pollution lumineuse est donc désormais considérée comme un acteur important du changement global, et représente une préoccupation majeure pour la santé humaine et la biodiversité. Les études sur la pollution lumineuse se sont surtout intéressées aux organismes nocturnes, plus susceptibles d'être perturbés par la présence de lumière pendant la nuit. Ce constat est particulièrement vrai pour les insectes, comme l'attestent de nombreuses études s’intéressant à l’attractivité des lumières artificielles sur les papillons de nuit ou à la modification du comportement de signalement par flash lumineux chez les lucioles en présence de pollution lumineuse. Au contraire, les conséquences de la pollution lumineuse sur les insectes diurnes sont peu connues. L’objectif de ma thèse était donc d'étudier expérimentalement les changements causés par la pollution lumineuse chez un parasitoïde diurne, Venturia canescens. Pour cela, je me suis intéressée à différents traits comportementaux, physiologiques et d’histoire de vie de femelles exposées à différentes intensités de pollution lumineuse. La première partie de mon travail porte sur les modifications de traits comportementaux liés à l'efficacité parasitaire et au succès reproducteur, en lien avec les réserves énergétiques, aux niveaux intra et transgénérationnels. J'ai démontré que la pollution lumineuse conduisait les femelles à être actives et à chercher de la nourriture et des hôtes la nuit. De plus, j'ai montré que la lumière nocturne, selon son intensité, modifiait également le comportement d’approvisionnement des femelles parasitoïdes pendant la journée, sans affecter leurs réserves énergétiques. En effet, une préférence accrue pour la recherche d'hôtes a été constatée chez les femelles exposées à une pollution lumineuse de faible intensité. Cependant, la pollution lumineuse ne semble pas avoir un fort effet sur le succès reproducteur de Venturia canescens. Enfin, la pollution lumineuse agit également au niveau transgénérationnel, en influençant le comportement alimentaire ainsi que le temps de développement des descendants. Dans la seconde partie de mon travail, je me suis intéressée à un trait physiologique, la production de mélatonine. La mélatonine est une hormone clé impliquée dans la régulation du rythme circadien des organismes. On sait de plus qu’elle est fortement influencée par la présence de lumière pendant la nuit. Cette hormone est donc susceptible de jouer un rôle majeur dans les changements phénotypiques observés chez les organismes soumis à la pollution lumineuse. La mélatonine a été bien étudiée chez les vertébrés, en particulier les mammifères, mais les connaissances sur sa synthèse et son rythme circadien chez les insectes sont rares. J'ai donc développé deux méthodes de quantification de la mélatonine chez Venturia canescens, afin de décrire sa dynamique sur un cycle de 24 heures en l'absence de pollution lumineuse. Ces travaux pourront ainsi servir de base à de futures études souhaitant tester expérimentalement l'effet de la pollution lumineuse sur la synthèse de mélatonine chez Venturia canescens.