Modeling and evaluating human-mediated dispersal mechanisms at landscape scale: a study of road network and invasion parameters for Lasius neglectus ants invasive species

International audienceAnts invasive species Biological invasions are considered, right after climate and land use changes, to be one of the principal causes of biodiversity erosion. This phenomenon is related to global change, since climate and land use modifications affect environmental conditions, and are partly responsible for the introduction and proliferation of exotic species into new environments. Furthermore, human-mediated dispersal acts as a dispersal vector for many exotic species, both at the introduction and secondary spread stages. On the one hand, introduction stage is a consequence of human-mediated long distance dispersal, due to human activities (and especially commercial exchanges), and is known to happen at large spatial scales (continental or global scales). On the other hand, secondary spread occurs at smaller spatial and time scales (like landscape scale) and can be provided by natural and human-mediated dispersal mechanisms, once the introduction had brought the exotic species into a novel environment, and after it has succeeded in establishing itself (i.e. survive and reproduce). Few works have pointed out the role of these second stages in small-scale invasive species spread. And yet, a lot of invasive species are susceptible to be partly or completely dispersed by local human processes happening at local spatial and time scales (materials transportation, for example). The lack of consideration for this potential important mode of dispersal seems to be the consequence of multiple factors: human-mediated dispersal is generally considered as a long distance dispersal process, more responsible for invasive species introduction than for secondary spread, it is difficult to qualify and quantify this mode of dispersal because of the multiplicity of potentially involved human activities being its vector, for a given organism that can disperse naturally, it is complicated to distinguish between natural and human-mediated dispersal, as they may occur at similar scale.In this paper, we study the spreading pattern of Lasius neglectus, an invasive ant species originated from Anatoly, which invaded Europe in the last decades and which is currently present in the Rhône valley, in France. We present a numerical model enabling the estimation of multiple human-mediated dispersal parameters, based on ground-truth sampling and minimizing a priori

Land-cover and climate factors contribute to the prevalence of the ectoparasitic fungus Laboulbenia formicarum in its invasive ant host Lasius neglectus

International audienceUnderstanding the distribution of parasites is crucial for biodiversity conservation. Here, we studied the distribution of the ectoparasitic fungus Laboulbenia formicarum in native and invasive Lasius ants in a 2000 km2 area. We screened over 16,000 ant workers in 478 colonies of five different species. We found that Lab. formicarum was rare in native Lasius species but infected 58% of the colonies of the invasive species Las. neglectus. At landscape scale, Lab. formicarum presence could not be explained by geographic and genetic distances between Las. neglectus colonies but was associated with hotter and dryer climatic conditions and its prevalence in colonies increased with urbanization. Within infected colonies, fungal prevalence varied from 0 to 100 percent within meters and was negatively correlated with impervious ground cover. In a changing world, our findings emphasize the importance of land-use and climatic factors in shaping the distribution and prevalence of fungal parasites

The observed link between urbanization and invasion can depend on how invasion is measured

Aim Cities are thought to promote biological invasions because invasive species are more often introduced in urban areas and because they are more successful in disturbed environments. However, the association is not as strongly supported by the literature as is generally assumed and might depend on how urbanization and invasion are measured. In this study, we test if the type of data used to assess the link between urbanization and invasion can affect a study's conclusions. Location Europe and middle Rhône valley (~5000 km2 in south-eastern France). Method We studied the spatial distribution of the invasive garden ant Lasius neglectus in its current introduced range in Europe and tested its association with urbanization using three measures of invasion (presence-only, presence–absence and population area) and two measures of urbanization (urban/nonurban land cover classification and proportion of impervious surfaces (buildings, road) per spatial unit). Results Based on presence-only data across Europe, L. neglectus occurred in urban areas 10 times more often than expected from a random geographical distribution. However, when controlling for spatial bias in sampling effort with presence–absence data (1870 sampling locations in the middle Rhône valley, France), the occurrence of the species was independent of urbanization. Moreover, the surface occupied by L. neglectus populations was negatively correlated with urbanization. Main conclusions These findings show that the type of occurrence data used to test the link between urbanization and invasion can strongly affect the conclusion of a study. This is particularly concerning because invasion studies often use presence-only data that are likely biased towards cities. Future urban invasions studies must be carefully designed to avoid this pitfall.Peer reviewe

Mesure de la pollution lumineuse nocturne in natura et étude du rythme circadien de la sécrétion de mélatonine chez des têtards d’amphibiens soumis à la pollution lumineuse

La pollution lumineuse est un phénomène d’origine anthropique associé au développement de l’urbanisation et des activités humaines qui ne cesse de s’étendre à travers le monde, impactant tous les écosystèmes terrestres et aquatiques. La pollution lumineuse est actuellement reconnue comme une pollution environnementale majeure menaçant la biodiversité. En effet, le niveau de lumière ambiante est l’un des facteurs majeurs qui régule de nombreux phénomènes biologiques. Toute altération des cycles naturels de la lumière va avoir un effet sur les mécanismes physiologiques ou comportementaux, et ainsi sur la fitness (valeur sélective) des individus. A plus long terme, la dynamique des populations pourrait être modifiée. Plusieurs études ont été menées afin d’évaluer les niveaux de pollution lumineuse à l’échelle planétaire ou sur certains écosystèmes terrestres ou marins. En revanche, les zones humides d’eaux douces, véritables réservoirs de la biodiversité, ont été très peu étudiées dans ce contexte de pollution lumineuse. Grâce à des capteurs de lumière autonomes « Jasondark » et des cartes de radiance satellites, nous avons réalisé une étude à la fois spatiale et temporelle sur une zone humide majeure, la Dombes, à proximité de la métropole lyonnaise. Nous avons ainsi montré que l’ensemble du territoire de la Dombes est soumis à la pollution lumineuse. La présence de nuages augmente considérablement les niveaux de pollution lumineuse et altère d’autant plus les patrons de variations de la luminosité naturelle. Pour les études sur la pollution lumineuse à visée écologique, il nous parait donc important de ne pas se baser uniquement sur les cartes de pollution lumineuse réalisée à partir des données satellites mais également de réaliser un suivi temporel des niveaux de luminosité nocturne au niveau du sol afin de préciser les risques. Par ailleurs, nous avons également choisi d’étudier un mécanisme physiologique altéré par la pollution lumineuse chez de nombreux taxons, la synthèse de la mélatonine. La mélatonine, sécrétée uniquement la nuit en l’absence de lumière, est l’un des principaux régulateurs des rythmes circadiens. Cette neurohormone régule également de nombreuses fonctions physiologiques telles que l’immunité, le stress oxydant et la reproduction. Les amphibiens appartiennent au 2ème groupe qui contient le plus grand nombre d’espèces nocturnes chez les vertébrés (93%), ce qui rend ce groupe potentiellement très vulnérable à la pollution lumineuse. Nous avons étudié l’expression des 2 enzymes majeures impliquées dans la voie de synthèse de la mélatonine, AANAT et ASMT, ainsi que ces 3 récepteurs chez les têtards de 2 espèces, R. dalmatina et B. bufo, sur 24h. Le groupe exposé à la pollution lumineuse était soumis à une lumière nocturne de 5 lux pendant 23 jours. La rythmicité de l’expression des gènes AANAT et ASMT n’est pas modifiée par une exposition à une lumière nocturne. Pour les récepteurs, nous avons observé une altération de l’expression des récepteurs de la mélatonine chez R. dalmatina mais pas chez B. bufo. L’ensemble de ces résultats montrent l’importance des études expérimentales en écologie de la conservation

Multiple mating in the context of interspecific hybridization between two Tetramorium ant species

International audienc

Modeling and evaluating human-mediated dispersal mechanisms at landscape scale: a study of road network and invasion parameters for Lasius neglectus ants invasive species

International audienceAnts invasive species Biological invasions are considered, right after climate and land use changes, to be one of the principal causes of biodiversity erosion. This phenomenon is related to global change, since climate and land use modifications affect environmental conditions, and are partly responsible for the introduction and proliferation of exotic species into new environments. Furthermore, human-mediated dispersal acts as a dispersal vector for many exotic species, both at the introduction and secondary spread stages. On the one hand, introduction stage is a consequence of human-mediated long distance dispersal, due to human activities (and especially commercial exchanges), and is known to happen at large spatial scales (continental or global scales). On the other hand, secondary spread occurs at smaller spatial and time scales (like landscape scale) and can be provided by natural and human-mediated dispersal mechanisms, once the introduction had brought the exotic species into a novel environment, and after it has succeeded in establishing itself (i.e. survive and reproduce). Few works have pointed out the role of these second stages in small-scale invasive species spread. And yet, a lot of invasive species are susceptible to be partly or completely dispersed by local human processes happening at local spatial and time scales (materials transportation, for example). The lack of consideration for this potential important mode of dispersal seems to be the consequence of multiple factors: human-mediated dispersal is generally considered as a long distance dispersal process, more responsible for invasive species introduction than for secondary spread, it is difficult to qualify and quantify this mode of dispersal because of the multiplicity of potentially involved human activities being its vector, for a given organism that can disperse naturally, it is complicated to distinguish between natural and human-mediated dispersal, as they may occur at similar scale.In this paper, we study the spreading pattern of Lasius neglectus, an invasive ant species originated from Anatoly, which invaded Europe in the last decades and which is currently present in the Rhône valley, in France. We present a numerical model enabling the estimation of multiple human-mediated dispersal parameters, based on ground-truth sampling and minimizing a priori

Effects of traffic noise on tree frog stress levels, immunity, and color signaling

International audienceDuring the last decade, many studies have focused on the detrimental effects of noise pollution on acoustic communication. Surprisingly, although it is known that noise exposure strongly influences health in humans, studies on wildlife remain scarce. In order to gain insight into the consequences of traffic noise exposure, we experimentally manipulated traffic noise exposure as well as the endocrine status of animals to investigate physiological and phenotypic consequences of noise pollution in an anuran species. We showed that noise exposure increased stress hormone level and induced an immunosuppressive effect. In addition, both traffic noise exposure and stress hormone application negatively impacted H. arborea vocal sac coloration. Moreover, our results suggest profound changes in sexual selection processes because the best quality males with initial attractive vocal sac coloration were the most impacted by noise. Hence, our study suggests that the recent increases in anthropogenic noise worldwide might affect a broader range of animal species than previously thought, because of alteration of visual signals and immunity. Generalizing these results to other taxa is crucial for the conservation of biodiversity in an increasingly noisy world

MoRIS: Model of Routes of Invasive Spread. Human-mediated dispersal, road network and invasion parameters

International audienceHuman-mediated dispersal acts as a vector for many exotic species, both at the introduction and secondary spread stages. The introduction stage is a consequence of human-mediated long distance dispersal and is known to happen at continental or global scales. Secondary spread occurs at smaller spatial and time scales (e.g. landscape), and can result from natural or human-mediated dispersal . Despite the importance of local goods and materials (e.g. for landscaping, construction, or road-building) transport for the spread of invasive species, few studies have investigated short distance human-mediated dispersal. This lack of consideration seems to be the consequence of multiple factors: human-mediated dispersal is generally considered as a long distance dispersal process, more important for invasive species introduction than for secondary spread, it is difficult to qualify and quantify this mode of dispersal because of the multiplicity of potentially involved human activities, for organisms that can disperse naturally, it is complicated to distinguish between natural and human-mediated dispersal, as they may occur at similar scales. Even though a range of methodologies are available for describing population spread by natural dispersal, only few models have been developed to describe and predict human-mediated dispersal consequences at small scales, and none of them take into account the topology of the transport infrastructure (roads, waterways).Therefore, in order to fill this gap and provide new insights into invasion dynamics, we combined ecological (invasive species occurrence data) and geographical (transportation network topology) data and used a computer modeling and simulation approach to provide estimate frequencies and distances of materials transportations through landscapes.In the present work, we studied the spreading pattern of Lasius neglectus, an invasive ant species originating from Turkey, which spread into Europe in the last decades. In this species, no mating or dispersal flights are performed, its spread is therefore solely ensured by the transport of soil materials in which individuals are present. We present a numerical model enabling the estimation of multiple human-mediated dispersal parameters, based on ground-truth sampling and a priori minimizing. The first step of this work was to build a model of the landscape-level spreading process taking explicitly into account the topology of the road network. Subsequently, initializing our model with field data, we localized the most probable sites of introduction, the number of jump events, as well as parameters of jump distances linked to the road network. Our model is also able to compute presence probability map, and can be used to calibrate sampling campaigns, explore invasion scenarios, and more generally perform invasion spread predictions. It could be applied to all the species that can be disseminated at local to regional scales by human activities through transportation networks