Biology subjects

Roux, O.

Publications and source records attributed to Roux, O..

8 recordsLinked to original sources

bioRxiv2026

Microplastic exposure alters immune-related gene expression in Culex quinquefasciatus mosquitoes and larval microbiota diversity

Background: Microplastics have been detected in many freshwater ecosystems, including stagnant waters where mosquito larvae develop. Larvae are therefore exposed to microplastic pollution, which may affect their life history traits or microbiota along with immune gene expression. However, these effects have never been tested in mosquitoes, despite their major public health importance as vectors of numerous pathogens. Method: We exposed mosquito larvae, from hatching to adult emergence, to four concentrations of polyethylene microplastics (MPs): 0, 60, 200, and 600 MPs/mL. Fourth-instar larvae and newly emerged adult females were collected for each treatment. To investigate the effects of MPs on gene expression and bacterial microbiota, RNA sequencing and 16S metabarcoding approaches were performed on three biological replicates for each developmental stage. Results: Microplastic exposure induced a non-monotonic dose-dependent transcriptomic response. In larvae, only a limited number of genes were differentially expressed (five to eight per concentration), with immune-related genes downregulated at both low and high concentrations. In adult females, the intermediate concentration (200 MPs/mL) elicited the strongest response with 14 differentially expressed genes (DEGs). Regarding the microbiota, microplastic exposure reduced bacterial diversity in larvae, with the lowest diversity observed at the highest concentration. However, no significant changes were detected in the microbiota of adult females. Conclusion: Overall, this study shows that adult females are affected by larval exposure to MPs (i.e. differential expression in immune-related genes) and warrants further studies in this field. This includes: 1) investigating further the effects of MPs on mosquitoes' populations (e.g. through multi-generational studies), 2) gaining more environmentally relevant knowledge on MP effects (i.e. using MPs with a biofilm and/or adsorbed pollutants) and 3) focusing on the effects of MPs on mosquitoes' vectorial capacities.

ecology↗

bioRxiv2024

The complex swarming dynamics of malaria mosquitoes emerges from simple minimally-interactive behavioral rules

Swarming is a widespread collective behavior in animals, often thought to emerge from complex interactions among individuals. Here, we show that mating swarms of malaria mosquitoes can emerge from simple behavioral rules with minimal interaction between individuals. We analyzed two published experimental datasets with three-dimensional flight tracks of Anopheles coluzzii mosquitoes swarming above a visual marker under simulated sunset conditions. We found that individuals alternate between straight flight and rapid turning maneuvers known as saccades. These saccades are triggered at the edge of the swarm, and their directions are biased along the sunset direction. This behavior was found consistent between both datasets and across swarm sizes, including solitary individuals, indicating that inter-individual interactions play a limited role within the studied size range. We developed a simple agent-based model incorporating three behavioral rules: attraction to the swarm center, alignment normal to the sunset horizon, both driven by environmental cues, and repulsion through short-range collision avoidance. The model reproduced key features of natural mosquito swarms, including looping flight paths, central density peaks, and directional alignment. Even in the absence of direct inter-individual interactions, the model generated realistic emergent swarm dynamics, demonstrating that social coordination is not required for swarm emergence. Our findings suggest that mosquito swarming is primarily guided by environmental perception rather than social interaction. This minimal framework offers a new perspective on insect swarming and may apply broadly to the many other insect species that form mating swarms. Understanding these rules could inform strategies for vector control and improve the effectiveness of interventions targeting mosquito reproduction. Author SummaryMosquito swarms are a familiar sight in many parts of the world, but the rules that govern their movement have remained mysterious. In our study, we investigated how male malaria mosquitoes behave in mating swarms. Using high-speed videography and computer simulations, we discovered that these swarms do not rely on complex social interactions. Instead, each mosquito follows a few simple rules based on visual cues from the environment, like the position of the sunset and a ground marker. These rules are enough to produce the looping flight patterns and dense swarms observed in nature. Surprisingly, even a single mosquito can perform this behavior in isolation. This minimal approach challenges the idea that swarming requires strong social coordination. It also opens new possibilities for controlling malaria mosquito populations by targeting the environmental factors that influence mating behavior. Since many insects rely on swarming to reproduce, our findings may help explain similar behaviors across species and inform broader strategies for insect population management.

animal behavior and cognition↗

bioRxiv2024

Multisensory integration in Anopheles mosquito swarms: The role of visual and acoustic information in mate tracking and collision avoidance

Male mosquitoes form aerial aggregations, known as swarms, to attract females and maximize their chances of finding a mate. Within these swarms, individuals must be able to recognize potential mates and navigate the dynamic social environment to successfully intercept a mating partner. Prior research has almost exclusively focused on the role of acoustic cues in mediating the ability of male mosquitoes to recognize and pursue flying females. However, the role of other sensory modalities in this behavior has not been explored. Moreover, how males avoid collisions with one another in the dense swarm while pursuing females remains poorly understood. In this study, we combined free-flight and tethered flight simulator experiments to demonstrate that swarming Anopheles coluzzii mosquitoes integrate visual and acoustic information to track conspecifics and avoid collisions. Our tethered experiments revealed that acoustic stimuli gated mosquito steering responses to visual objects simulating nearby mosquitoes, especially in males that exhibited attraction to visual objects in the presence of female flight tones. Additionally, we observed that visual cues alone could trigger changes in wingbeat amplitude and frequency of mosquitoes. These findings were corroborated by our free-flight experiments, which revealed that mosquitoes modulate their flight responses to nearby conspecifics in a similar manner to tethered animals, allowing for collision avoidance within swarms. Together, these results demonstrate that both males and females integrate multiple sensory inputs to mediate swarming behavior, and for males, the change in flight kinematics in response to multimodal cues allows them to simultaneously track females while avoiding collisions.

neuroscience↗

bioRxiv2024

Spatial and temporal characteristics of laboratory-induced Anopheles coluzzii swarms: shape, structure and flight kinematics

Anopheles mosquitoes mate at sunset in aerial swarms. The development of mating-based methods for effective malaria vector control requires a good knowledge of the flight behaviour of Anopheles species in mating swarms. However, the process of how swarms are formed and maintained remains poorly understood. Here, we characterized the three-dimensional spatial and temporal flight kinematics of Anopheles coluzzii males swarming above a ground marker. We observed that the location, shape and volume of swarms were highly stereotypic, consistent over the swarming duration, regardless of the number of individuals in the swarm. The swarm had an elliptical cone shape, and we observed a differential spatial distribution of flight kinematics parameters within the swarm volume. Among these parameters, only swarm density varied with swarm size. Using a sensory system-informed model, we show that swarm location and shape can accurately be modelled based on visual perception of the marker. To control swarm height, swarming individuals maintain an optical angle of the marker ranging from 24{degrees} to 55{degrees}. Limiting the viewing angle deviation to 4.5% of the maximum value results in the observed elliptical cone swarm shape. We discuss the implications of these finding in mating success, speciation and for vector control.

animal behavior and cognition↗

bioRxiv2021

Behavioural measurements of hearing-sensitivity in swarming Anopheles coluzzii mosquitoes reveal an unprecedentedly low threshold

Mosquitoes of many species mate in station-keeping swarms. Mating chases ensue as soon as a male detects the flight tones of a female with his auditory organs. Previous studies of hearing thresholds have mainly used electrophysiological methods that prevent the mosquito from flying naturally. The main aim of this study was to quantify behaviourally the sound-level threshold at which males can hear females. Free-flying male Anopheles coluzzii were released in a large arena (~2 m high x 2 m x 1 m) with a conspicuous object on the ground that stimulates swarming behaviour. Males were exposed to a range of natural and synthetic played-back sounds of female flight. We monitored the responses of males and their distance to the speaker by recording changes in their wingbeat frequency and angular speed. We show that the mean male behavioural threshold of particle-velocity hearing lies between 13-20 dB SVL (95%-CI). A conservative estimate of 20 dB SVL (i.e., < 0.5 m/s particle velocity) is already 12 to 26 dB lower than most of the published electrophysiological measurements from the Johnstons organ. In addition, we suggest that 1) the first harmonic of female flight-sound is sufficient for males to detect her presence, 2) males respond with a greater amplitude to single-female sounds than to the sound of a group of females and 3) the response of males to the playback of the flight sound of a live female is the same as that of a recorded sound of constant frequency and amplitude.

animal behavior and cognition↗

bioRxiv2020

Mosquito 'mate-seeking' at long-range: are male swarms loud enough to be located by females?

Given the unsurpassed sound-sensitivity of mosquitoes among arthropods and the sound-source power required for long-range hearing, we investigated the distance over which female mosquitoes detect species-specific cues in the sound of station-keeping mating swarms. A common misunderstanding, that mosquitoes cannot hear at long-range because their hearing organs are particle-velocity receptors, has clouded the fact that particle-velocity is an intrinsic component of sound whatever the distance to the sound source. We exposed free-flying Anopheles coluzzii females to pre-recorded sounds of male An. coluzzii and An. gambiae s.s. swarms over a range of natural sound-levels. Sound-levels tested were related to equivalent distances between the female and the swarm for a given number of males, enabling us to infer distances over which females might hear large male-swarms. We show that females do not respond to swarm sound up to 48 dB SPL and that louder SPLs are not ecologically relevant for a swarm. Considering that swarms are the only mosquito sound-source that would be loud enough to be heard at long-range, we conclude that inter-mosquito acoustic communication is restricted to close-range pair interactions. We also showed that the sensitivity to sound in free-flying males is much enhanced compared to that of tethered ones.

ecology↗

bioRxiv2020

No evidence for long-range male sex pheromones in two malaria mosquitoes

AO_SCPLOWBSTRACTC_SCPLOWCues involved in mate seeking and recognition prevent hybridization and can be involved in speciation processes. In malaria mosquitoes, females of the two sibling species Anopheles gambiae s.s. and An. coluzzii mate in monospecific male swarms and hybrids are rare. Long-range sex pheromones driving this behavior have been debated in literature but to date, no study has proven their existence or their absence. Here, we attempted to bring to light their existence. To put all the odds in our favor, we used different chemical ecology methods such as behavioral and electrophysiological assays as well chemical analyses, and we worked with mosquitoes at their optimal physiological mating state i.e. with swarming males during their natural swarming windows. Despite all our efforts, our results support the absence of long-range sex pheromones involved in swarm detection and recognition by females. We briefly discuss the implications of this finding in ecology, evolution and for control strategies.

ecology↗

bioRxiv2019

Larviposition site selection mediated by volatile semiochemicals of larval origin in Glossina palpalis gambiensis

Tsetse flies (Diptera: Glossinidae) are the cyclical vectors of trypanosomes, the causative agents of African animal trypanosomosis or nagana in animals and human African trypanosomosis or sleeping sickness in humans. Tsetse flies are K-strategist species with the deposition of a single larva at 10 days intervals in specific sites. As larviposition site selection will strongly impact reproductive success, it is obvious that the selection of larviposition sites is not random and is under strong selective processes, probably mediated by specific cues as suggested by the existence of an aggregation factor in the Morsitans and Fusca groups. This study aimed to highlight the existence of an aggregation effect in the Palpalis group and to test for its chemical nature. We studied the larviposition site selection of Glossina palpalis gambiensis according to the presence of conspecific and heterospecific larvae buried in substrates in different settings. Three sets of experiments were performed with either individual or grouped (n = 50) gravid females, and with physical access to substrate or not. In both individual and grouped larviposition experiments, females selected significantly more often trays conditioned by larvae (P<0.005), either conspecific or heterospecific even in the absence of physical contact with the substrate. These results highlight the first evidence for larviposition site selection mediated by volatile semiochemicals of larval origin in Glossina palpalis gambiensis. However, these compounds seem not to be species-specific and therefore offer new avenues for the behavioural manipulation of these vectors and for the development of new vector control tools targeting gravid females.\n\nAuthor summaryLarviposition site selection in tsetse flies is govern by several biotic and abiotic factors that lead to an aggregation effect of larvae. Among those, larvae are suspected to produce chemicals that drive females to breeding site but little information is available. This study aimed to highlight the existence of an aggregation effect of larval origin in the Palpalis group and to test for its chemical nature. Through behavioural larviposition choice experiments, we showed that females of Glossina palpalis gambiensis deposit their larvae significantly more often in trays conditioned either by conspecific or heterospecific larvae, even in the absence of physical contact with the substrate. These results highlight the first evidence for aggregation effect in Glossina palpalis gambiensis mediated by volatile semiochemicals of larval origin. Isolation and identification of these chemicals should offer new avenues for the behavioural manipulation of these vectors and for the development of new vector control tools targeting gravid females.

animal behavior and cognition↗