Sex makes them sleepy: host reproductive status induces diapause in a parasitoid population experiencing harsh winters

When organisms coevolve, any change in one species can induce phenotypic changes in traits and ecology of the other species. The role such interactions play in ecosystems is central, but their mechanistic bases remain underexplored. Upper trophic level species have to synchronize their life-cycle to both abiotic conditions and to lower trophic level species’ phenology and phenotypic variations. We tested the effect of host seasonal strategy on parasitoid diapause induction by using a holocyclic clone of the pea aphid Acyrthosiphon pisum producing asexual and sexual morphs that are viviparous females (i.e. laying embryos) and oviparous females (laying eggs), respectively, the latter being only present at the end of the growing season. Aphidius ervi parasitoids from populations of contrasted climatic origin (harsh vs. mild winter areas) were allowed to parasitize each morph in a split-brood design and developing parasitoids were next reared under either fall-like or summer-like temperature-photoperiod conditions. We next examined aspects of the host physiological state by comparing the relative proportion of forty-seven metabolites and lipid reserves in both morphs produced under the same conditions. We found that oviparous morphs are cues per se for diapause induction; parasitoids entered diapause at higher levels when developing in oviparous hosts (19.4 ± 3.0%) than in viviparous ones (3.6 ± 1.3%), under summer-like conditions (i.e., when oviparous aphids appear in the fields). This pattern was only observed in parasitoids from the harsh winter area since low diapause levels were observed in the other population, suggesting local adaptations to overwintering cues. Metabolomics analyses show parasitoids’ response to be mainly influenced by the host’s physiology, with higher proportion of polyols and sugars, and more fat reserves being found in oviparous morphs. Host quality thus varies across the seasons and represents one of the multiple environmental parameters affecting parasitoid diapause. Our results underline strong coevolutionary processes between hosts and parasitoids in their area of origin, likely leading to phenological synchronization, and we point out the importance of such bottom-up effects for trait expression, and for the provision of ecosystem services such as biological control in the context of climate change

Rising temperature reduces divergence in resource use strategies in coexisting parasitoid species.

International audienceCoexistence of species sharing the same resources is often possible if species are phylogenetically divergent in resource acquisition and allocation traits, decreasing competition between them. Developmental and life-history traits related to resource use are influenced by environmental conditions such as temperature, but thermal trait responses may differ among species. An increase in ambient temperature may, therefore, affect trait divergence within a community, and potentially species coexistence. Parasitoids are interesting models to test this hypothesis, because multiple species commonly attack the same host, and employ divergent larval and adult host use strategies. In particular, development mode (arrested or continued host growth following parasitism) has been recognized as a major organiser of parasitoid life histories. Here, we used a comparative trait-based approach to determine thermal responses of development time, body mass, egg load, metabolic rate and energy use of the coexisting Drosophila parasitoids Asobara tabida, Leptopilina heterotoma, Trichopria drosophilae and Spalangia erythromera. We compared trait values between species and development modes, and calculated trait divergence in response to temperature, using functional diversity indices. Parasitoids differed in their thermal response for dry mass, metabolic rate and lipid use throughout adult life, but only teneral lipid reserves and egg load were affected by developmental mode. Species-specific trait responses to temperature were probably determined by their adaptations in resource use (e.g. lipogenesis or ectoparasitism). Overall, trait values of parasitoid species converged at the higher temperature. Our results suggest that local effects of warming could affect host resource partitioning by reducing trait diversity in communities

Divergent life history strategies in congeneric hyperparasitoids

peer reviewedLife histories can reveal important information on the performance of individuals within their environment and how that affects evolutionary change. Major trait changes, such as trait decay or loss, may lead to pronounced differences in life history strategies when tight correlations between traits exist. Here, we show that three congeneric hyperparasitoids (Gelis agilis, Gelis acarorum and Gelis areator) that have diverged in wing development and reproductive mode employ markedly different life history strategies. Potential fecundity of Gelis sp. varied, with the wingless G. acarorum maturing a much higher number of eggs throughout life compared with the other two species. Realized lifetime fecundity, in terms of total offspring number was, however, highest for the winged G. areator. The parthenogenic G. agilis invests its resources solely in females, whilst the sexually reproducing species both invested heavily in males to reduce competitive pressures for their female offspring. Longevity also differed between species, as did the direction of the reproduction-longevity trade-off, where reproduction is heavily traded off against longevity only in the asexual G. agilis. Resting metabolic rates also differed between the winged and wingless species, with the highest metabolic rate observed in the winged G. areator. Overall, these geline hyperparasitoids showed considerable divergence in life history strategies, both in terms of timing and investment patterns. Major trait & Bertanne Visse

Overwintering strategies of a guild of cereal aphid parasitoids along a climatic gradient

227 p.Los insectos como pequeños ectotermos viven en una amplia gama de ambientes térmicos y tienen que adoptar diferentes estrategias para resistir condiciones desfavorables tales como: migración, entrar en diapausa o permanecer activos. A lo largo de esta Tesis, se han explorado diferentes impulsores ecológicos en parasitoides de áfidos a lo largo de un gradiente latitudinal en el valle centro-sur de Chile. Se evaluó si las condiciones ambientales a lo largo de este gradiente llevaron a una mayor incidencia de diapausa en latitudes altas (más frías) en comparación con latitudes bajas (más cálidas). Además, exploramos si la diapausa está regulada por estímulos bióticos (es decir, efecto del hospedero, disponibilidad del hospedero y la competencia materna). Se observó una ausencia de un claro gradiente de temperatura latitudinal norte-sur. Según la intensidad del invierno, las localidades muestreadas se clasificaron como áreas de invierno frío, templado o cálido. Se observaron niveles bajos de incidencia de diapausa a lo largo de todo el gradiente latitudinal. Sin embargo, observamos cambios en la composición de las especies de áfidos y parasitoides, ya que sus niveles de abundancia relativa variaron entre las áreas climáticas, mostrando que la mayoría de los individuos adultos dentro del gremio de parasitoides están activos durante el invierno. Además, la diapausa en los parasitoides de áfidos estuvo influenciada por la especie hospedera atacada y por la percepción de escasez de hospederos en la diapausa de invierno. Asimismo, la competencia intraespecífica directa entre hembras de parasitoides en condiciones de verano se tradujo en un aumento de la descendencia en diapausa, sin embargo, este efecto no se observó en condiciones de invierno. Por lo tanto, la plasticidad del desarrollo y las respuestas evolutivas observadas ofrecen una explicación mecánica para la variación adaptativa de la historia de vida en los parasitoides de áfidos, lo que sugiere que el éxito de los parasitoides como agentes naturales depende en gran medida de la densidad del hospedero y el momento de las actividades estacionales. // ABSTRACT: Insects as small ectotherms are known to live in a wide range of thermal climates and have to adopt different strategies to resist unfavorable conditions such as: migration, enter in diapause or remain active. Throughout this Thesis, different ecological drivers have been explored in aphid parasitoids along a latitudinal gradient in the central‒south valley of Chile. We tested whether environmental conditions along this gradient led to a higher diapause incidence on high latitudes (colder) compared to low latitudes (warmer). In addition, we explored whether diapause is regulated by biotic stimulus (i.e., host effect, host availability, and maternal competition). We found an absence of a clear north-south latitudinal temperature gradient. Based on the intensity of winter, the sampled localities were categorized as either cold, mild, or warm winter areas. Low levels of diapause incidence were observed along the whole latitudinal gradient. Nevertheless, we observed changes in the compositions of aphid and parasitoid species, as their levels of relative abundance varied among the climatic areas, showing that most adult individuals within the parasitoid guild are active during winter. In addition, diapause in aphid parasitoids was influenced by the attacked host species and from the perception of host scarcity in winter diapause. Likewise, direct intraspecific competition among female parasitoids in summer conditions has been translated into an increase of the diapause offspring, however, this effect was not observed in winter conditions. Thus, developmental plasticity and the observed evolutionary responses offer a mechanistic explanation for adaptive life-history variation in aphid parasitoids suggesting the success of parasitoids as natural agents depends strongly on host density and timing of seasonal activities

Scientists' warning on climate change and insects

Climate warming is considered to be among the most serious of anthropogenic stresses to the environment, because it not only has direct effects on biodiversity, but it also exacerbates the harmful effects of other human-mediated threats. The associated consequences are potentially severe, particularly in terms of threats to species preservation, as well as in the preservation of an array of ecosystem services provided by biodiversity. Among the most affected groups of animals are insects—central components of many ecosystems—for which climate change has pervasive effects from individuals to communities. In this contribution to the scientists' warning series, we summarize the effect of the gradual global surface temperature increase on insects, in terms of physiology, behavior, phenology, distribution, and species interactions, as well as the effect of increased frequency and duration of extreme events such as hot and cold spells, fires, droughts, and floods on these parameters. We warn that, if no action is taken to better understand and reduce the action of climate change on insects, we will drastically reduce our ability to build a sustainable future based on healthy, functional ecosystems. We discuss perspectives on relevant ways to conserve insects in the face of climate change, and we offer several key recommendations on management approaches that can be adopted, on policies that should be pursued, and on the involvement of the general public in the protection effort

Effect of environmentally realistic doses of pesticides on tritrophic interactions in grass strips

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