Biology subjects

Vallon, L.

Publications and source records attributed to Vallon, L..

3 recordsLinked to original sources

bioRxiv2026

From urban runoff to mosquito success : spatiotemporal microbial assembly in larval water habitats under anthropogenic stressors

Urban mosquito habitats are heterogeneous aquatic ecosystems where anthropogenic inputs shape physicochemical conditions and microbial community assembly. However, the combined effects of environmental chemistry and microbial dynamics on mosquito fitness remain poorly understood across space and time. Here, we integrated environmental chemistry, metabarcoding, and experimental assays to investigate how spatiotemporal variation in urban larval habitats influences environmental microbial assembly and the biology of the Asian tiger mosquito, Aedes albopictus. Six stormwater drains were monitored over five months to characterize ions, dissolved gases, micropollutants, and bacterial and fungal communities. Laboratory assays using water from three contrasting habitats were then conducted to evaluate oviposition preference and mosquito performance. Microbial community composition was strongly structured by breeding-site identity and associated with distinct physicochemical signatures. Bacterial communities remained relatively stable over time, whereas fungal assemblages exhibited stronger temporal turnover. These environmental differences translated into marked variation in larval performance, ranging from rapid development and high survival to delayed development, reduced survival, and episodic cohort collapse under environmentally unstable conditions. Adult traits further revealed carry-over effects of larval environment exposure across life stages. Correlation analyses showed that mosquito fitness was associated with both abiotic variables and microbial taxa linked to larval survival, development, emergence, and adult longevity. In contrast, oviposition preference remained consistently high across habitats despite strong differences in offspring performance, indicating a decoupling between habitat attractiveness and suitability. Overall, our results demonstrate that anthropogenic stressors shape microbial assembly in urban larval habitats, with cascading consequences for mosquito fitness and population dynamics.

ecology↗

bioRxiv2025

Friend or foe: A mosquito parasite with mixed transmission mode displays mutualistic traits promoting oogenesis.

Mutualism is often selected in vertically transmitted symbionts due to their fitness interdependence with hosts. However, the evolution of mutualism remains unclear in symbionts using both vertical and horizontal transmission. In this study, we show that Ascogregarina taiwanensis, previously known as a weak horizontally transmitted parasite of the Asian tiger mosquito (Aedes albopictus), exhibits mutualistic traits that enhance mosquito reproduction. The symbiont improves embryogenesis and extends the egg-laying period while most females are pseudo-vertically transmitting symbiont oocysts to their progeny at oviposition sites. Dual transcriptomic analyses reveal that early oogenesis in infected females involves increased nitrogen metabolism in both partners, enhanced detoxification of blood waste, and activation of egg development pathways. These changes lead to improved assimilation of blood proteins essential for egg production. Our findings provide rare empirical evidence of a symbiont displaying both parasitic and mutualistic traits, offering new insights into the evolutionary dynamics of mixed-mode transmission symbioses. Significance StatementHow mutualism evolves from parasitism remains a central question in evolutionary biology, particularly for symbionts that combine vertical and horizontal transmission. We show that Ascogregarina taiwanensis, an Apicomplexan parasite previously known to be costly for developing Aedes albopictus mosquitoes, is also pseudo-vertically transmitted: most females release oocysts into the water during oviposition, exposing their offspring. Surprisingly, infection enhances host reproduction by promoting oogenesis through protein assimilation, leading to the production of larger larvae. Dual transcriptomic analyses reveal coordinated shifts in host and parasite metabolism, especially in nitrogen assimilation. Our findings provide rare evidence that mutualistic traits can emerge in a symbiont with mixed-mode transmission, offering new insights into the evolutionary transitions shaping host-microbe interactions.

evolutionary biology↗

bioRxiv2024

Needle in a haystack: culturing plant-beneficial Helotiales lineages from plant roots

Root-associated Helotiales fungi are increasingly recognized as beneficial fungal partners promoting plant growth under nutrient-limited conditions, particularly in non-mycorrhizal hosts, lacking the ancestral arbuscular mycorrhizal symbiosis. However, the ecology of these fungi is still cryptic as relatively few lineages have been successfully cultivated from roots for further study. Here, we attempted the mass isolation of root endophytic fungi to evaluate the recovery of known plant-beneficial Helotiales lineages using a tailored culture-based approach. We sampled six wild non-mycorrhizal species from the Brassicaceae, Caryophyllaceae, and Cyperaceae, growing in nutrient-limited alpine soils. We isolated 602 root endophytes and compared this culturable diversity with the one observed via fungal ITS2 metabarcoding. Metabarcoding revealed that Helotiales taxa dominated the fungal communities, with 43% of these detected taxa also represented in our collection. Accordingly, most root endophytes in our collection (53%) were Helotiales. These isolates, some with P solubilisation potential, belonged primarily to three Helotialean clades and were phylogenetically related to plant growth-promoting or mycorrhizal-like strains. This analysis highlights that roots of alpine non-mycorrhizal plants are reservoirs of plant-beneficial root-endophytic Helotiales, and the isolates obtained are a promising resource to explore the plant-beneficial mechanisms and ecological traits of these fungi.

microbiology↗