Growth and longevity modulation through larval environment mediate immunosenescence and immune strategy of Tenebrio molitor.

International audienceBackground The Disposable Soma Theory of aging suggests a trade-off between energy allocation for growth, reproduction and somatic maintenance, including immunity. While trade-offs between reproduction and immunity are well documented, those involving growth remain under-explored. Rapid growth might deplete resources, reducing investment in maintenance, potentially leading to earlier or faster senescence and a shorter lifespan. However, rapid growth could limit exposure to parasitism before reaching adulthood, decreasing immunity needs. The insect immunity’s components (cellular, enzymatic, and antibacterial) vary in cost, effectiveness, and duration. Despite overall immunity decline (immunosenescence), its components seem to age differently. We hypothesize that investment in these immune components is adjusted based on the resource cost of growth, longevity, and the associated risk of parasitism. Results We tested this hypothesis using the mealworm beetle, Tenebrio molitor as our experimental subject. By manipulating the larval environment, including three different temperatures and three relative humidity levels, we achieved a wide range of growth durations and longevities. Our main focus was on the relationship between growth duration, longevity, and specific immune components: hemocyte count, phenoloxidase activity, and antibacterial activity. We measured these immune parameters both before and after exposing the individuals to a standard bacterial immune challenge, enabling us to assess immune responses. These measurements were taken in both young and older adult beetles. Upon altering growth duration and longevity by modifying larval temperature, we observed a more pronounced investment in cellular and antibacterial defenses among individuals with slow growth and extended lifespans. Intriguingly, slower-growing and long-lived beetles exhibited reduced enzymatic activity. Similar results were found when manipulating larval growth duration and adult longevity through variations in relative humidity, with a particular focus on antibacterial activity. Conclusion The impact of growth manipulation on immune senescence varies by the specific immune parameter under consideration. Yet, in slow-growing T. molitor , a clear decline in cellular and antibacterial immune responses with age was observed. This decline can be linked to their initially stronger immune response in early life. Furthermore, our study suggests an immune strategy favoring enhanced antibacterial activity among slow-growing and long-lived T. molitor individuals

“Born with a silver spoon in the mouth has bad sides too”: Experimentally increasing growth rate enhances individual quality but accelerates reproductive senescence in females of the mealworm beetle, Tenebrio molitor

International audienceSenescence occurs because of the decline of the strength of selection with age, allowing late-life reduced performances not being counter selected. From there, several phenomena may explain late-life reduced performances, such as the accumulation of deleterious mutations, the expression of pleiotropic genes or the existence of resource trade-offs between early and late performances. This latter phenomenon is at the core of the disposable soma theory of aging, which predicts that growth and early-life reproduction have costs that increase reproductive and actuarial senescence. Whereas the impact of the cost of early reproduction on reproductive and actuarial senescence has been extensively studied, that of the cost of growth remains overlooked and often inconclusive, possibly because of confounding effects associated with the procedures used to manipulate growth rate. Here, we investigated the cost of growth rate and its impact on reproductive senescence and longevity of females of the mealworm beetle, Tenebrio molitor. For this purpose, we generated insects with contrasted growth rates by raising groups of them in conditions below, above and optimal relative humidity (RH: 55, 85 and 70%, respectively) during the larval stage. Theresulting adult females then bred, under the same optimal RH conditions, early in life, then later in life and were followed there until death. We found that larvae grown under the highest relative humidity exhibited the highest larval growth rate, thanks to both shorter growth duration and the achievement of heavier pupae mass. Adult females from this favorable growing condition lived longer, were more fecund early in life, but suffered from lower late-life reproductive investment. Our study shows that growth rate, which is highly dependent on the early-life environment, is an important factor modulating adult reproductive senescence, through the occurrence of early-late life trade-offs

Influential Insider: Wolbachia, an Intracellular Symbiont, Manipulates Bacterial Diversity in Its Insect Host

International audienceFacultative intracellular symbionts like the α-proteobacteria influence their insect host phenotype but little is known about how much they affect their host microbiota. Here, we quantified the impact of infection on the bacterial community of the cabbage root fly by comparing the microbiota of -free and infected adult flies of both sexes. We used high-throughput DNA sequencing (Illumina MiSeq, 16S rRNA, V5-V7 region) and performed a community and a network analysis. In both sexes, infection significantly decreased the diversity of bacterial communities and modified their structure and composition by reducing abundance in some taxa but increasing it in others. Infection by was negatively correlated to 8 bacteria genera ( was the most impacted), and positively correlated to and . We suggest that might antagonize for being entomopathogenic (and potentially intracellular), but would favor and because they might protect the host against chemical plant defenses. Although they might seem prisoners in a cell, endocellular symbionts can impact the whole microbiota of their host, hence its extended phenotype, which provides them with a way to interact with the outside world