Biology subjects

Ansart, A.

Publications and source records attributed to Ansart, A..

7 recordsLinked to original sources

bioRxiv2025

How does urbanization shape shell phenotype, behaviour and parasite prevalence in the snail Cornu aspersum?

Urbanization is a complex and multivariate environmental change, leading to e.g. habitat fragmentation and loss, changes in local climate, soil imperviousness, pollution, etc. This is likely to exert pressures simultaneously on various dimensions of organisms multivariate phenotypes, leading to trait shifts with potential ecological consequences. However, responses to urbanization are often studied one (type of) trait at a time. In this context, we studied how, in the brown garden snail Cornu aspersum, shell phenotype (shell size and colour/reflectance), behaviour (food intake, mobility) and metazoan parasite prevalence respond to urbanization. Within an urbanization gradient spanning the French city of Rennes, we found that snails from more urbanized sites closer to the urban centre were smaller, whereas urbanization had no detectable effect on shell reflectance, parasite prevalence or behaviour. Larger snails and snails with paler shells were more likely to be infected by trematode metacercariae and sexually-transmitted nematodes (Nemhelix bakeri), respectively. Snails harbouring trematode sporocysts ate typically less, while those infected by N. bakeri moved more slowly. We discuss the decrease of snail size along the urbanization gradient in relation with the Urban Heat Island effect and the potential decrease of resource quality and availability in urban sites. The absence of detectable effects of urbanization on shell reflectance, mobility and parasite prevalence may be due to scale mismatches between how urbanization is measured and how snails experience microhabitats. We propose further experimental and field studies to decipher interactions between urbanization effects, shell phenotype, life-history traits and parasitism.

ecology↗

bioRxiv2022

Morph-dependent effect of nematode infection on host movement in the land snail Cepaea nemoralis (Mollusca, Gastropoda)

Host behaviour can be influenced by parasitic risk and infection through a variety of direct and indirect mechanisms. We can expect individuals expressing different phenotypes to also differ in the ways their behaviour is altered by parasites. We used the land snail Cepaea nemoralis, a species with various shell colour morphs differing in behaviour and physiology, as a model to study the link between parasite response and individual behaviour variation. We analysed metazoan parasite abundance and its relation to behaviour (movement and food intake) in snails from three shell morphs (from light unbanded to darker five-banded) and from two neighbouring populations from contrasted environments. Snails were parasitized by mites, trematodes and nematodes, from rarest to most frequent. We confirm that terrestrial gastropods can defend against infection by trapping parasitic nematodes in their shell. We show that nematode encapsulated in shells can uncover past infections even when a snail population is currently nematode-free, possibly due to parasite seasonality. We present new observations suggesting that not only nematodes but also mites might be encapsulated in shells. Infection levels varied between morphs, with darker snails harbouring fewer nematodes. Behaviour (movement and food intake) was linked to nematode, but not trematode infection. Individuals with higher nematode load ate less, irrespective of morph and population. The most-infected morph (unbanded snails) showed reduced activity in the nematode-infected population compared to the one that was nematode-free at sampling time. As a result, parasites may cancel previously described behavioural differences between morphs. We discuss the possible mechanisms explaining morph-dependent responses to parasites, and how parasite risk may be an unseen force shaping C. nemoralis morph variation in space and time. We conclude on the possible ecological consequences of the link, mediated by shell colour, between thermal and immune responses.

ecology↗

bioRxiv2020

Increased population density depresses activity but does not influence dispersal in the snail Pomatias elegans

Dispersal is a key trait linking ecological and evolutionary dynamics, allowing organisms to optimize fitness expectations in spatially and temporally heterogeneous environments. Some organisms can either actively disperse or reduce activity in response to challenging conditions, and both responses may be under a trade-off. To understand how such organisms respond to changes in environmental conditions, we studied emigration (the first step of dispersal) and activity behaviour in the gonochoric land snail Pomatias elegans, a litter decomposer that can reach very high local densities, over most of the range of ecologically relevant densities. We found that crowding had no detectable effect on emigration tendency in this species, contrary to previous results in many hermaphroditic snails. Pomatias elegans is nonetheless able to detect population density; we show they reduce activity rather than increase dispersal in response to crowding. We propose that limiting activity may be more advantageous than moving away in species with especially poor movement abilities, even by land mollusc standards, like P. elegans. Interestingly, emigration and activity were positively correlated independently of density; this dispersal syndrome may reflect an underlying pace-of-life syndrome, and is compatible with a dispersal-dormancy trade-off, which would require further investigation. Additionally, we found snails with heavier shells relative to their size tended to be less mobile, which may reflect physical and metabolic constraints on movement and/or survival during inactivity. We finally discuss how the absence of density-dependent dispersal may explain why P. elegans is often found at very high local densities, and the possible consequences of this behaviour for ecosystem functioning and litter decomposition.

ecology↗

bioRxiv2019

Boldness and exploration are linked to shell morph but not environmental context in the snail Cepaea nemoralis

Understanding the maintenance of among-individual behavioral variation in populations, and predicting its consequences, are key challenges in behavioral ecology. Studying the association between repeatable behaviors and other traits under selection may shed light on the underlying selective pressures. We used the model snail Cepaea nemoralis to examine whether individual behavior is associated with shell morph, a key trait that has been extensively studied in the context of thermal tolerance and predator avoidance, and which is known to be under strict genetic control in this species. We quantified proxies of boldness and exploration in snails of three morphs coming from two habitats with different thermal contexts. We show that both behaviors were repeatable at the among-individual level (within-state Rboldness = 0.22 [95% credible interval: 0.15, 0.29]; Rexploration = 0.20 [0.15, 0.25]). Behavior was associated with shell morph, with the darker morph (five-banded) being consistently shyer and slower to explore. There was no evidence that thermal environment of origin influenced behavior. Snails became faster when test temperature increased; we found no evidence morphs differed in their thermal response. Boldness and exploration were correlated among individuals, forming a syndrome (r = 0.28 [0.10, 0.46]). We discuss what these results may tell us about the type of selection exerted by predators. We also detail how our results hint to a genetic link between shell morph and behavior, and the evolutionary implications of such a link. Finally, we discuss how our findings combined with decades of evolutionary research make C. nemoralis a very valuable model to study the evolution of behavior in response to environmental changes.

ecology↗

bioRxiv2018

Dispersers are more likely to follow mucus trails in the land snail Cornu aspersum

Dispersal, i.e. movement leading to gene flow, is a fundamental although costly life history trait. The use of indirect social information may help mitigate these costs, yet in many cases little is known about the proximate sources of such information, and how dispersers and residents may differ in their information use. Land gastropods, which have a high cost of movement and obligatorily leave information potentially exploitable by conspecifics during movement (through mucus trails), are a good model to investigate links between dispersal costs and information use. We used Y-mazes to see whether dispersers and residents differed in their trail-following propensity, in the snail Cornu aspersum. Dispersers followed mucus trails more frequently than expected by chance, contrary to non-dispersers. Ignoring dispersal status during tests would lead to falsely conclude to no trail-following for the majority of ecologically realistic scenarios. Trail following by dispersers may reduce dispersal costs by reducing energy expenditure and helping snails find existing patches. Finally, we point that ignoring the potential for collective dispersal provided by trail-following abilities may lead to wrong inferences on the demographic and genetic consequences of dispersal.

ecology↗

bioRxiv2017

Bottom-up and top-down control of dispersal across major organismal groups: a coordinated distributed experiment

Organisms rarely experience a homogeneous environment. Rather, ecological and evolutionary dynamics unfold in spatially structured and fragmented landscapes, with dispersal as the central process linking these dynamics across spatial scales. Because dispersal is a multi-causal and highly plastic life-history trait, finding general drivers that are of importance across species is challenging but highly relevant for ecological forecasting.\n\nWe here tested whether two fundamental ecological forces and main determinants of local population dynamics, top-down and bottom-up control, generally explain dispersal in spatially structured communities. In a coordinated distributed experiment spanning a wide range of actively dispersing organisms, from protozoa to vertebrates, we show that bottom-up control, that is resource limitation, consistently increased dispersal. While top-down control, that is predation risk, was an equally important dispersal driver as bottom-up control, its effect depended on prey and predator space use and whether dispersal occurred on land, in water or in the air: species that routinely use more space than their predators showed increased dispersal in response to predation, specifically in aquatic environments. After establishing these general causes of dispersal, we used a metacommunity model to show that bottom-up and top-down control of dispersal has important consequences for local population fluctuations as well as cascading effects on regional metacommunity dynamics. Context-dependent dispersal reduced local population fluctuations and desynchronized dynamics between communities, two effects that increase population and community stability.\n\nOur study provides unprecedented insights into the generality of the positive resource dependency of dispersal as well as a robust experimental test of current theory predicting that predator-induced dispersal is modulated by prey and predator space use. Our experimental and theoretical work highlights the critical importance of the multi-causal nature of dispersal as well as its cascading effects on regional community dynamics, which are specifically relevant to ecological forecasting.

ecology↗

bioRxiv2017

Individual boldness is life stage-dependent and linked to dispersal in a hermaphrodite land snail

Both individual variation in dispersal tendency and animal personalities have been shown to be widespread in nature. They are often associated in personality-dependent dispersal, and both have major but underappreciated consequences for ecological and evolutionary dynamics. In addition, personalities are not stable over time and changes can appear through ontogeny, leading to life stage-dependent behaviours. We investigated relationships between dispersal, life stage and boldness in an invertebrate with between- and within-life stages variation in dispersal tendency, the land snail Cornu aspersum. Latency to exit the shell following a simulated attack was repeatable, indicating boldness is a personality trait in Cornu aspersum. Subadults were bolder and more dispersive than adults. Dispersers were bolder than non-dispersers, independently of boldness changes between life stages. We discuss how these results can be explained in relation with life history strategies in this hermaphrodite species, in particular risk management in the context of reproductive investment.

ecology↗