François Lefebvre - Academia.edu (original) (raw)

Papers by François Lefebvre

Research paper thumbnail of Actes du Séminaire national Gallaselle

Research paper thumbnail of Étude et protection des Gallaselles et de leurs habitats aquatiques souterrains en Poitou-Charentes

Research paper thumbnail of Life history constraints on the evolution of abbreviated life cycles in parasitic trematodes

Journal of Helminthology, 2005

Abbreviations of the complex life cycle of trematodes, from three to two hosts, have occurred rep... more Abbreviations of the complex life cycle of trematodes, from three to two hosts, have occurred repeatedly and independently among trematode lineages. This is usually facultative and achieved via progenesis: following encystment in the second intermediate host, the metacercaria develops precociously into an egg-producing adult, bypassing the need to reach a definitive host. Given that it provides relatively cheap insurance against a shortage of definitive hosts, it is not clear why facultative progenesis has only evolved in a few taxa. Here a comparative approach is used to test whether progenetic trematodes are characterized by larger body size and egg volumes, two traits that correlate with other key life history features, than other trematodes. These traits may constrain the evolution of progenesis, because precocious maturation might be impossible when the size difference between the metacercaria and a reproductive adult is too large. First, trematode species belonging to genera i...

Research paper thumbnail of Stratégies de reproduction chez les crustacés isopodes terrestres

Merci tout d'abord au professeur Jean-Pierre Mocquard, pour m'avoir accueilli dans son laboratoir... more Merci tout d'abord au professeur Jean-Pierre Mocquard, pour m'avoir accueilli dans son laboratoire, pour avoir accepté d'être le directeur officiel de ma thèse et pour m'avoir initié aux joies de la statistique. Je rends hommage à cet homme, puits de science et de bon sens. Je ne trouve pas les mots pour remercier ici Gilbert Martin, actuel directeur du laboratoire. Je remercie tous les membres du jury pour avoir accepté de juger ce travail : Merci à Colette Rivault (Chargée de recherche, Rennes 1) d'avoir accepté la lourde tâche d'être rapporteur. Nous avons en commun de travailler sur d'infimes vermines ; vous les blattes, moi les cloportes. Merci à Karl Eduard Linsenmair (professeur, Institut Theodor Boveri de Würzburg) que je ne connaissais que par papiers interposés et qui a su, grâce à ses travaux sur Hemilepistus, apporter un peu de dimension évolutive à l'étude du comportement des isopodes terrestres. Merci également d'avoir accepté d'être rapporteur. Merci à Noëlle Bru (docteur en statistiques, Université de Grenoble), pour avoir accepté de revoir les méthodologies employées dans ce travail. Merci à cet oeil naïf sur ce petit monde de la reproduction du cloporte. Merci à Frank Cézilly (professeur, Université de Dijon) pour m'avoir fait découvrir la discipline dans laquelle je voulais orienter mes recherches. Merci pour ce que tu fais aujourd'hui pour l'écologie comportementale en France ; le terme d'école Cézilly n'est pas usurpé. Merci à Michel Veuille (professeur, Paris). Que ce manuscrit lui rappelle aux bons souvenirs de son travail de thèse sur les crustacés Jaera. Merci Didier pour avoir co-encadré la fin du travail. Ton aide et ton soutien m'ont été précieux. Tes remarques toujours pertinentes. Merci à toi, Yves, pour tout. Pour m'avoir accepté en DEA, puis fait confiance pour un doctorat. Merci pour cette totale liberté d'initiative et d'exécution dans mes recherches. Ce fut certes parfois un peu dur, mais ô combien formateur. Merci de ta patience face à cet esprit un tantinet libertin. Remerciements également à Françoise Mead que je n'ai jamais eu le plaisir de rencontrer, mais qui, à travers sa thèse, a écrit la bible française en matière de reproduction du cloporte. Les recherches exposées dans ce manuscrit ont été effectuées au sein de l'unité « Génétique et Biologie des

Research paper thumbnail of Silvering of female eels (Anguilla anguilla) in two sub-populations of the Rhone Delta

Bulletin Français de la Pêche et de la Pisciculture

The eel population of the Camargue lagoon system can be divided into two subunits living in two d... more The eel population of the Camargue lagoon system can be divided into two subunits living in two distinct biotopes (freshwater and brackish water) and characterised by different population structures and especially growth patterns. The sub-population living in the Fumemorte canal (average salinity: 0.9 g/l) is a freshwater population type (81.6% females, maximum ages observed=9-11 years, slow growth (annual gain 46 mm)) whereas that of the Vaccares lagoon (average salinity: 9.7 g/l over the same period) is typical of a lagoon (45.6% females, maximum ages 5-6 years, fast growth (annual gain 90 mm)). In each sub-population, Gonadosomatic Index (GSI) and OI (Ocular Index) were measured on female eels over a sampling period that started in January 1997 and ended in December 2000. In both types of habitat, and in agreement with previous studies, we observed a threshold value of GSIgreater than or equal to1.4% characterising the silver stage (MARCHELIDON et al., 1999). The increase in eye ...

Research paper thumbnail of Anguillicolosis Among Silver Eels: A 2-YEAR Survey in 4 Habitats from Camargue (Rhône Delta, South of France)

Bulletin Français de la Pêche et de la Pisciculture, 2003

We have investigated the spread of the infection by Anguillicola crassus among the silver phase o... more We have investigated the spread of the infection by Anguillicola crassus among the silver phase of the European eel Anguilla anguilla in the Rhône delta. We reported values of prevalence, mean intensity and abundance in 4 habitats and we revealed negative relationships between these parasitic parameters and values of salinity (prevalence from 52 % in brackish waters to 77 % in fresh waters). We have also assessed the health state of the infected organ, i.e. the swimbladder. This may be a way to check the parasitic history of individuals throughout their continental phase. In silver eels free from parasites, the proportion of past infected individuals was ranged between 40 % and 78 %. When adding individuals showing worms at the autopsy with those showing signs of past infection(s), we highlighted a great proportion of silver eels really affected by anguillicolosis (from 71 % to 95 %, with a negative relationship in respect to salinity values). So, considering the spread of the infection, and its potential impairments on body condition, gas exchanges, hydrostatic abilities, etc., one may legitimately question about the proportion of silver eels that may get back to the Sargasso sea and reproduce.

Research paper thumbnail of Recrutement Des Civelles (Anguilla Anguilla) Sur La Cote Mediterraneenne Française : Analyse Comparee Des Caracteristiques Biometriques et Pigmentaires Des Saisons 1974-75 et 2000-01

Bulletin Français de la Pêche et de la Pisciculture, 2003

Une campagne d'échantillonnage des civelles Anguilla anguilla a été menée de novembre 2000 à mai ... more Une campagne d'échantillonnage des civelles Anguilla anguilla a été menée de novembre 2000 à mai 2001 au grau de la Fourcade (Saintes-Maries-de-laMer , côte méditerranéenne française). Des civelles ont été capturées sur toute la période d'échantillonnage, mais les maxima d'abondance se situent en janvier-février et, dans une moindre mesure, en avril. Afin d'optimiser le recrutement dans les lagunes littorales intérieures, la mesure de gestion proposée est donc de favoriser l'ouverture des martelières au milieu de l'hiver. Le suivi des proportions mensuelles des différents stades pigmentaires (de V A à VI A 4) permet de conclure à un vieillissement généralisé des civelles en recrutement de novembre à mars, puis à l'arrivée d'un deuxième flux de civelles jeunes en avril. Parallèlement, il est observé une diminution très nette des masses et des longueurs moyennes mensuelles, et ce, même en ne considérant qu'un stade pigmentaire donné (en l'occurrence V B). Ces résultats sur l'évolution des caractéristiques biométriques et pigmentaires sont en accord avec les deux séries de travaux déjà menés sur la façade méditerranéenne française (années 30 et 70), ainsi qu'avec les données publiées en différents points de la façade atlantique. L'analyse comparée de ces données avec celles issues de la dernière étude en date sur la côte méditerranéenne française (Bages-Sigean, Languedoc-Roussillon, campagne 1974-75 ; LECOMTE-FINIGER, 1976) montre une composition pigmentaire mensuelle totalement différente, et révèle une diminution significative de la longueur des civelles, de l'ordre de 5 % en 25 ans.

Research paper thumbnail of Spatial and temporal variation in Anguillicola crassus counts: results of a 4 year survey of eels in Mediterranean lagoons

Diseases of Aquatic Organisms, 2002

We present the results of a survey of anguillicolosis in the Rhône River delta. From January 1997... more We present the results of a survey of anguillicolosis in the Rhône River delta. From January 1997 to December 2000, a total of 13 319 eels (Anguilla anguilla from elver to silver phase) were examined, in which we found 22 227 swimbladder nematodes (Anguillicola crassus adults and preadults). A generalised linear model (GLM) framework was used to explore the relative contribution of various factors to the occurrence, intensity and abundance of the parasite. We reveal a major influence of the month of sampling, and we document the existence of a seasonal pattern with regular peaks in early summer and late winter. In contrast, the year of sampling is of secondary importance, and no particular trend in the development of the infection can be detected. More than a decade after the first record of A. crassus in the Rhône River delta, anguillicolosis has thus attained a constant infection rate of nearly 50%, with a mean number of 3 or 4 macroscopic lumen worms per infected eel. The eel length strongly influences the intensity and the abundance of the nematode, but has little if any effect on the probability of being infected. There exists a linear relationship between eel size and the number of parasites, but not between eel size and prevalence. We observe a decrease in the proportion of infected individuals among elver eels. We discuss this result in relation to the possible mortality of heavily infected individuals and/or a change in the eels' alimentary diet.

Research paper thumbnail of An evaluation of indices of gross pathology associated with the nematode Anguillicoloides crassus in eels

Journal of Fish Diseases, 2011

This study compares two alternative indices for quantifying the gross pathology of the swimbladde... more This study compares two alternative indices for quantifying the gross pathology of the swimbladder of eels, Anguilla anguilla (L.), infected with the nematode Anguillicoloides crassus. Two observers recorded twice the scores obtained by the two indices on the same set of 71 wild caught eels (from elver to silver eels, French Mediterranean lagoons). The Length Ratio Index (LRI), performed better than the Swimbladder Degenerative Index (SDI), in three of four predefined criteria of decision. First, the LRI better correlated with an estimate of the swimbladder volume reduction, a functional consequence of the infection (representativeness). Also, the LRI was less prone to subjectivity (inter-observer variability) and more precise (intra-observer variability), although less easy to generate (time needed for measurement/ assessment). Using a sub-sample of 32 unaffected eels (showing minor if any swimbladder damage and no living worms at autopsy), we ascertained a linear relationship between the swimbladder length and the total body length, a prerequisite of isometric growth, to definitively accept the new ratio index as a valid alternative to the SDI. Also, because the LRI can be recorded on live specimens with radio-imagery (non-invasive method), we recommend its use, and provide a graph of correspondence between the SDI scores, the LRI scores and the estimated proportion of gas loss in the swimbladder.

Research paper thumbnail of Female-extended control over their reproductive investment: the role of early mating interactions on oocyte maturation in the terrestrial crustacean Armadillidium vulgare (Latreille, 1804)

Invertebrate Reproduction & Development, 2010

View related articles Citing articles: 3 View citing articles Currently working as an independent... more View related articles Citing articles: 3 View citing articles Currently working as an independent researcher, in scientific association with the Natural History Museum of London, UK *

Research paper thumbnail of Epidemiology and

577Lefebvre et al.—Anguillicolosis in the short-finned eel

Research paper thumbnail of Progenesis in digenean trematodes: a taxonomic and synthetic overview of species reproducing in their second intermediate hosts

Parasitology, 2005

Precocious egg production, i.e. progenesis, has been documented for a number of species in scatte... more Precocious egg production, i.e. progenesis, has been documented for a number of species in scattered reports throughout the trematode literature. The last 2 extensive studies on the subject date from Buttner in the early 1950s (in French) and from Tang in the early 1980s (in Chinese). Overall, 43 species were then known for their ability to produce eggs at the metacercarial stage while still in the second intermediate host. Here, we update the list, and document the existence of progenesis in a total of 79 digenean trematode species, for which we provide information on the taxonomy of the hosts, the facultative or obligate character of progenesis, relevant references, as well as some other pertinent biological information. We then review the subject by asking 7 questions of fundamental evolutionary importance. These include: What favours progenetic development? What are the associated costs and benefits? How are progenetic eggs released from the host? While exposing the various opin...

Research paper thumbnail of Alternative life-history and transmission strategies in a parasite: first come, first served?

Parasitology, 2005

Alternative transmission strategies are common in many parasitic organisms, often representing di... more Alternative transmission strategies are common in many parasitic organisms, often representing discrete phenotypes adopted in response to external cues. The facultative truncation of the normal 3-host life-cycle to a 2-host cycle in many trematodes provides an example: some individuals mature precociously, via progenesis, in their intermediate host and produce eggs without the need to reach a definitive host. The factors that determine how many and which individuals adopt the truncated life-cycle within a parasite population remain unknown. We investigated the occurrence of progenesis in the trematode Stegodexamene anguillae within its fish intermediate host. Location within the host was a key determinant of progenesis. Although the size and egg output of progenetic metacercariae encysted in host gonads did not differ from those of the few progenetic metacercariae in other host tissues, the likelihood of metacercariae becoming progenetic was much higher for those in the gonads than ...

Research paper thumbnail of Anguillicolosis: dynamics of the infection over two decades

Diseases of Aquatic Organisms, 2004

The dynamics of the infection of the European eel Anguilla anguilla L. by the Asian nematode Angu... more The dynamics of the infection of the European eel Anguilla anguilla L. by the Asian nematode Anguillicola crassus Kuwahara, Niimi and Itagaki, 1974 (i.e. anguillicolosis) was monitored over 2 decades in an oligohaline canal in southern France (Camargue, Mediterranean coast). Since the first mention of the parasite in this canal in 1985, which was also the first record in France, prevalence of pre-adult and adult forms has risen from 32 to 73%. However, during the last 7 yr (1997 to 2003), prevalence seems to have stabilized around values of 60 to 70% and parasite load, though inter-annual variation is substantial, shows no sign of increase (intensity for the last 5 yr: min. = 3.70, max. = 9.66, mean = 6.01). Our results thus confirm the dynamic pattern observed elsewhere in Europe, i.e. a rapid spread following the introduction of the parasite in a water system and then stabilization around ceiling levels. We review possible mechanisms that may explain such a leveling off in the infection spread. We particularly document the possibility that repetitive infections may render the infected organ, i.e. the swimbladder, unsuitable for further A. crassus establishment. In support of this hypothesis, we showed that the infection rate is lower among eels with severely damaged swimbladders.

Research paper thumbnail of On the origin of Anguillicoloides crassus, the invasive nematode of anguillid eels

The nematode Anguillicoloides crassus is one of the many threats hanging over anguillid eels, now... more The nematode Anguillicoloides crassus is one of the many threats hanging over anguillid eels, now known to infect six Anguilla species worldwide. It was first described in Japan, in 1974, and is commonly thought to natively stem from East Asia. Here our primary objective was to critically evaluate this long-held statement. We first retraced the factual history of this global invader, to later investigate the pros and cons for an East Asian origin. After exploring the alternative scenarios for the joint origin of the two anguillicolid parasites occurring in this area, we concluded that the geographic zone covering the natural range of the local eel A. japonica is still the most probable origin (in the absence of another identified candidate host and area). However, we cannot exclude that A. crassus may have been previously introduced along with exotic eel species, at some early stages of aquaculture in Japan. We call for caution when dealing with the native origin of this and other parasitic invaders in provenance of East Asia, a region to be regarded as a major crossroads for fish and parasites of the world. We finally identified the need for a possible resolution of the question, which includes a deeper sampling effort in the Indo-Pacific zone and the further development of molecular phylogeographic studies of all five anguillicolid species and their hosts.

Research paper thumbnail of Differing trophic niches of three French stygobionts and their implications for conservation of endemic stygofauna

Aquatic Conservation: Marine and Freshwater Ecosystems

Research paper thumbnail of Mass drives mating success in Armadillidium vulgare (Crustacea, Oniscidea)

Research paper thumbnail of Levebvre et al. 2013

Research paper thumbnail of Is the continental life of the European eel Anguilla anguilla affected by the parasitic invader Anguillicoloides crassus?

Proceedings of the Royal Society B: Biological Sciences, 2013

Quantifying the fitness cost that parasites impose on wild hosts is a challenging task, because t... more Quantifying the fitness cost that parasites impose on wild hosts is a challenging task, because the epidemiological history of field-sampled hosts is often unknown. In this study, we used an internal marker of the parasite pressure on individual hosts to evaluate the costs of parasitism with respect to host body condition, size increase and reproductive potential of field-collected animals for which we also determined individual age. In our investigated system, the European eel Anguilla anguilla and the parasitic invader Anguillicoloides crassus, high virulence and severe impacts are expected because the host lacks an adaptive immune response. We demonstrated a nonlinear relationship between the severity of damage to the affected organ (i.e. the swimbladder, our internal marker) and parasite abundance and biomass, thus showing that the use of classical epidemiological parameters was not relevant here. Surprisingly, we found that the most severely affected eels (with damaged swimbladder) had greater body length and mass (þ11% and þ41%, respectively), than unaffected eels of same age. We discuss mechanisms that could explain this finding and other counterintuitive results in this host-parasite system, and highlight the likely importance of host panmixia in generating great inter-individual variability in growth potential and infection risk. Under that scenario, the most active foragers would not only have the greatest size increase, but also the highest probability of becoming repeatedly infected-via trophic parasite transmission-during their continental life.

Research paper thumbnail of On the male-effect in the terrestrial Crustacean Armadillidium vulgare (Latreille, 1804)

Invertebrate Reproduction & Development, 1999

In the terrestrial Crustacean Armadillidium vulgare, the onset of female reproduction can be sped... more In the terrestrial Crustacean Armadillidium vulgare, the onset of female reproduction can be sped up by a male-induced stimulation. This male-effect is mainly characterized by a shortening of the vitellogenesis period, which occurs during the preparturial intermoult. The determinism of this phenomenon, for the first time reported by Jassem in 1982, was investigated here by both experimental and ethological approaches.

Research paper thumbnail of Actes du Séminaire national Gallaselle

Research paper thumbnail of Étude et protection des Gallaselles et de leurs habitats aquatiques souterrains en Poitou-Charentes

Research paper thumbnail of Life history constraints on the evolution of abbreviated life cycles in parasitic trematodes

Journal of Helminthology, 2005

Abbreviations of the complex life cycle of trematodes, from three to two hosts, have occurred rep... more Abbreviations of the complex life cycle of trematodes, from three to two hosts, have occurred repeatedly and independently among trematode lineages. This is usually facultative and achieved via progenesis: following encystment in the second intermediate host, the metacercaria develops precociously into an egg-producing adult, bypassing the need to reach a definitive host. Given that it provides relatively cheap insurance against a shortage of definitive hosts, it is not clear why facultative progenesis has only evolved in a few taxa. Here a comparative approach is used to test whether progenetic trematodes are characterized by larger body size and egg volumes, two traits that correlate with other key life history features, than other trematodes. These traits may constrain the evolution of progenesis, because precocious maturation might be impossible when the size difference between the metacercaria and a reproductive adult is too large. First, trematode species belonging to genera i...

Research paper thumbnail of Stratégies de reproduction chez les crustacés isopodes terrestres

Merci tout d'abord au professeur Jean-Pierre Mocquard, pour m'avoir accueilli dans son laboratoir... more Merci tout d'abord au professeur Jean-Pierre Mocquard, pour m'avoir accueilli dans son laboratoire, pour avoir accepté d'être le directeur officiel de ma thèse et pour m'avoir initié aux joies de la statistique. Je rends hommage à cet homme, puits de science et de bon sens. Je ne trouve pas les mots pour remercier ici Gilbert Martin, actuel directeur du laboratoire. Je remercie tous les membres du jury pour avoir accepté de juger ce travail : Merci à Colette Rivault (Chargée de recherche, Rennes 1) d'avoir accepté la lourde tâche d'être rapporteur. Nous avons en commun de travailler sur d'infimes vermines ; vous les blattes, moi les cloportes. Merci à Karl Eduard Linsenmair (professeur, Institut Theodor Boveri de Würzburg) que je ne connaissais que par papiers interposés et qui a su, grâce à ses travaux sur Hemilepistus, apporter un peu de dimension évolutive à l'étude du comportement des isopodes terrestres. Merci également d'avoir accepté d'être rapporteur. Merci à Noëlle Bru (docteur en statistiques, Université de Grenoble), pour avoir accepté de revoir les méthodologies employées dans ce travail. Merci à cet oeil naïf sur ce petit monde de la reproduction du cloporte. Merci à Frank Cézilly (professeur, Université de Dijon) pour m'avoir fait découvrir la discipline dans laquelle je voulais orienter mes recherches. Merci pour ce que tu fais aujourd'hui pour l'écologie comportementale en France ; le terme d'école Cézilly n'est pas usurpé. Merci à Michel Veuille (professeur, Paris). Que ce manuscrit lui rappelle aux bons souvenirs de son travail de thèse sur les crustacés Jaera. Merci Didier pour avoir co-encadré la fin du travail. Ton aide et ton soutien m'ont été précieux. Tes remarques toujours pertinentes. Merci à toi, Yves, pour tout. Pour m'avoir accepté en DEA, puis fait confiance pour un doctorat. Merci pour cette totale liberté d'initiative et d'exécution dans mes recherches. Ce fut certes parfois un peu dur, mais ô combien formateur. Merci de ta patience face à cet esprit un tantinet libertin. Remerciements également à Françoise Mead que je n'ai jamais eu le plaisir de rencontrer, mais qui, à travers sa thèse, a écrit la bible française en matière de reproduction du cloporte. Les recherches exposées dans ce manuscrit ont été effectuées au sein de l'unité « Génétique et Biologie des

Research paper thumbnail of Silvering of female eels (Anguilla anguilla) in two sub-populations of the Rhone Delta

Bulletin Français de la Pêche et de la Pisciculture

The eel population of the Camargue lagoon system can be divided into two subunits living in two d... more The eel population of the Camargue lagoon system can be divided into two subunits living in two distinct biotopes (freshwater and brackish water) and characterised by different population structures and especially growth patterns. The sub-population living in the Fumemorte canal (average salinity: 0.9 g/l) is a freshwater population type (81.6% females, maximum ages observed=9-11 years, slow growth (annual gain 46 mm)) whereas that of the Vaccares lagoon (average salinity: 9.7 g/l over the same period) is typical of a lagoon (45.6% females, maximum ages 5-6 years, fast growth (annual gain 90 mm)). In each sub-population, Gonadosomatic Index (GSI) and OI (Ocular Index) were measured on female eels over a sampling period that started in January 1997 and ended in December 2000. In both types of habitat, and in agreement with previous studies, we observed a threshold value of GSIgreater than or equal to1.4% characterising the silver stage (MARCHELIDON et al., 1999). The increase in eye ...

Research paper thumbnail of Anguillicolosis Among Silver Eels: A 2-YEAR Survey in 4 Habitats from Camargue (Rhône Delta, South of France)

Bulletin Français de la Pêche et de la Pisciculture, 2003

We have investigated the spread of the infection by Anguillicola crassus among the silver phase o... more We have investigated the spread of the infection by Anguillicola crassus among the silver phase of the European eel Anguilla anguilla in the Rhône delta. We reported values of prevalence, mean intensity and abundance in 4 habitats and we revealed negative relationships between these parasitic parameters and values of salinity (prevalence from 52 % in brackish waters to 77 % in fresh waters). We have also assessed the health state of the infected organ, i.e. the swimbladder. This may be a way to check the parasitic history of individuals throughout their continental phase. In silver eels free from parasites, the proportion of past infected individuals was ranged between 40 % and 78 %. When adding individuals showing worms at the autopsy with those showing signs of past infection(s), we highlighted a great proportion of silver eels really affected by anguillicolosis (from 71 % to 95 %, with a negative relationship in respect to salinity values). So, considering the spread of the infection, and its potential impairments on body condition, gas exchanges, hydrostatic abilities, etc., one may legitimately question about the proportion of silver eels that may get back to the Sargasso sea and reproduce.

Research paper thumbnail of Recrutement Des Civelles (Anguilla Anguilla) Sur La Cote Mediterraneenne Française : Analyse Comparee Des Caracteristiques Biometriques et Pigmentaires Des Saisons 1974-75 et 2000-01

Bulletin Français de la Pêche et de la Pisciculture, 2003

Une campagne d'échantillonnage des civelles Anguilla anguilla a été menée de novembre 2000 à mai ... more Une campagne d'échantillonnage des civelles Anguilla anguilla a été menée de novembre 2000 à mai 2001 au grau de la Fourcade (Saintes-Maries-de-laMer , côte méditerranéenne française). Des civelles ont été capturées sur toute la période d'échantillonnage, mais les maxima d'abondance se situent en janvier-février et, dans une moindre mesure, en avril. Afin d'optimiser le recrutement dans les lagunes littorales intérieures, la mesure de gestion proposée est donc de favoriser l'ouverture des martelières au milieu de l'hiver. Le suivi des proportions mensuelles des différents stades pigmentaires (de V A à VI A 4) permet de conclure à un vieillissement généralisé des civelles en recrutement de novembre à mars, puis à l'arrivée d'un deuxième flux de civelles jeunes en avril. Parallèlement, il est observé une diminution très nette des masses et des longueurs moyennes mensuelles, et ce, même en ne considérant qu'un stade pigmentaire donné (en l'occurrence V B). Ces résultats sur l'évolution des caractéristiques biométriques et pigmentaires sont en accord avec les deux séries de travaux déjà menés sur la façade méditerranéenne française (années 30 et 70), ainsi qu'avec les données publiées en différents points de la façade atlantique. L'analyse comparée de ces données avec celles issues de la dernière étude en date sur la côte méditerranéenne française (Bages-Sigean, Languedoc-Roussillon, campagne 1974-75 ; LECOMTE-FINIGER, 1976) montre une composition pigmentaire mensuelle totalement différente, et révèle une diminution significative de la longueur des civelles, de l'ordre de 5 % en 25 ans.

Research paper thumbnail of Spatial and temporal variation in Anguillicola crassus counts: results of a 4 year survey of eels in Mediterranean lagoons

Diseases of Aquatic Organisms, 2002

We present the results of a survey of anguillicolosis in the Rhône River delta. From January 1997... more We present the results of a survey of anguillicolosis in the Rhône River delta. From January 1997 to December 2000, a total of 13 319 eels (Anguilla anguilla from elver to silver phase) were examined, in which we found 22 227 swimbladder nematodes (Anguillicola crassus adults and preadults). A generalised linear model (GLM) framework was used to explore the relative contribution of various factors to the occurrence, intensity and abundance of the parasite. We reveal a major influence of the month of sampling, and we document the existence of a seasonal pattern with regular peaks in early summer and late winter. In contrast, the year of sampling is of secondary importance, and no particular trend in the development of the infection can be detected. More than a decade after the first record of A. crassus in the Rhône River delta, anguillicolosis has thus attained a constant infection rate of nearly 50%, with a mean number of 3 or 4 macroscopic lumen worms per infected eel. The eel length strongly influences the intensity and the abundance of the nematode, but has little if any effect on the probability of being infected. There exists a linear relationship between eel size and the number of parasites, but not between eel size and prevalence. We observe a decrease in the proportion of infected individuals among elver eels. We discuss this result in relation to the possible mortality of heavily infected individuals and/or a change in the eels' alimentary diet.

Research paper thumbnail of An evaluation of indices of gross pathology associated with the nematode Anguillicoloides crassus in eels

Journal of Fish Diseases, 2011

This study compares two alternative indices for quantifying the gross pathology of the swimbladde... more This study compares two alternative indices for quantifying the gross pathology of the swimbladder of eels, Anguilla anguilla (L.), infected with the nematode Anguillicoloides crassus. Two observers recorded twice the scores obtained by the two indices on the same set of 71 wild caught eels (from elver to silver eels, French Mediterranean lagoons). The Length Ratio Index (LRI), performed better than the Swimbladder Degenerative Index (SDI), in three of four predefined criteria of decision. First, the LRI better correlated with an estimate of the swimbladder volume reduction, a functional consequence of the infection (representativeness). Also, the LRI was less prone to subjectivity (inter-observer variability) and more precise (intra-observer variability), although less easy to generate (time needed for measurement/ assessment). Using a sub-sample of 32 unaffected eels (showing minor if any swimbladder damage and no living worms at autopsy), we ascertained a linear relationship between the swimbladder length and the total body length, a prerequisite of isometric growth, to definitively accept the new ratio index as a valid alternative to the SDI. Also, because the LRI can be recorded on live specimens with radio-imagery (non-invasive method), we recommend its use, and provide a graph of correspondence between the SDI scores, the LRI scores and the estimated proportion of gas loss in the swimbladder.

Research paper thumbnail of Female-extended control over their reproductive investment: the role of early mating interactions on oocyte maturation in the terrestrial crustacean Armadillidium vulgare (Latreille, 1804)

Invertebrate Reproduction & Development, 2010

View related articles Citing articles: 3 View citing articles Currently working as an independent... more View related articles Citing articles: 3 View citing articles Currently working as an independent researcher, in scientific association with the Natural History Museum of London, UK *

Research paper thumbnail of Epidemiology and

577Lefebvre et al.—Anguillicolosis in the short-finned eel

Research paper thumbnail of Progenesis in digenean trematodes: a taxonomic and synthetic overview of species reproducing in their second intermediate hosts

Parasitology, 2005

Precocious egg production, i.e. progenesis, has been documented for a number of species in scatte... more Precocious egg production, i.e. progenesis, has been documented for a number of species in scattered reports throughout the trematode literature. The last 2 extensive studies on the subject date from Buttner in the early 1950s (in French) and from Tang in the early 1980s (in Chinese). Overall, 43 species were then known for their ability to produce eggs at the metacercarial stage while still in the second intermediate host. Here, we update the list, and document the existence of progenesis in a total of 79 digenean trematode species, for which we provide information on the taxonomy of the hosts, the facultative or obligate character of progenesis, relevant references, as well as some other pertinent biological information. We then review the subject by asking 7 questions of fundamental evolutionary importance. These include: What favours progenetic development? What are the associated costs and benefits? How are progenetic eggs released from the host? While exposing the various opin...

Research paper thumbnail of Alternative life-history and transmission strategies in a parasite: first come, first served?

Parasitology, 2005

Alternative transmission strategies are common in many parasitic organisms, often representing di... more Alternative transmission strategies are common in many parasitic organisms, often representing discrete phenotypes adopted in response to external cues. The facultative truncation of the normal 3-host life-cycle to a 2-host cycle in many trematodes provides an example: some individuals mature precociously, via progenesis, in their intermediate host and produce eggs without the need to reach a definitive host. The factors that determine how many and which individuals adopt the truncated life-cycle within a parasite population remain unknown. We investigated the occurrence of progenesis in the trematode Stegodexamene anguillae within its fish intermediate host. Location within the host was a key determinant of progenesis. Although the size and egg output of progenetic metacercariae encysted in host gonads did not differ from those of the few progenetic metacercariae in other host tissues, the likelihood of metacercariae becoming progenetic was much higher for those in the gonads than ...

Research paper thumbnail of Anguillicolosis: dynamics of the infection over two decades

Diseases of Aquatic Organisms, 2004

The dynamics of the infection of the European eel Anguilla anguilla L. by the Asian nematode Angu... more The dynamics of the infection of the European eel Anguilla anguilla L. by the Asian nematode Anguillicola crassus Kuwahara, Niimi and Itagaki, 1974 (i.e. anguillicolosis) was monitored over 2 decades in an oligohaline canal in southern France (Camargue, Mediterranean coast). Since the first mention of the parasite in this canal in 1985, which was also the first record in France, prevalence of pre-adult and adult forms has risen from 32 to 73%. However, during the last 7 yr (1997 to 2003), prevalence seems to have stabilized around values of 60 to 70% and parasite load, though inter-annual variation is substantial, shows no sign of increase (intensity for the last 5 yr: min. = 3.70, max. = 9.66, mean = 6.01). Our results thus confirm the dynamic pattern observed elsewhere in Europe, i.e. a rapid spread following the introduction of the parasite in a water system and then stabilization around ceiling levels. We review possible mechanisms that may explain such a leveling off in the infection spread. We particularly document the possibility that repetitive infections may render the infected organ, i.e. the swimbladder, unsuitable for further A. crassus establishment. In support of this hypothesis, we showed that the infection rate is lower among eels with severely damaged swimbladders.

Research paper thumbnail of On the origin of Anguillicoloides crassus, the invasive nematode of anguillid eels

The nematode Anguillicoloides crassus is one of the many threats hanging over anguillid eels, now... more The nematode Anguillicoloides crassus is one of the many threats hanging over anguillid eels, now known to infect six Anguilla species worldwide. It was first described in Japan, in 1974, and is commonly thought to natively stem from East Asia. Here our primary objective was to critically evaluate this long-held statement. We first retraced the factual history of this global invader, to later investigate the pros and cons for an East Asian origin. After exploring the alternative scenarios for the joint origin of the two anguillicolid parasites occurring in this area, we concluded that the geographic zone covering the natural range of the local eel A. japonica is still the most probable origin (in the absence of another identified candidate host and area). However, we cannot exclude that A. crassus may have been previously introduced along with exotic eel species, at some early stages of aquaculture in Japan. We call for caution when dealing with the native origin of this and other parasitic invaders in provenance of East Asia, a region to be regarded as a major crossroads for fish and parasites of the world. We finally identified the need for a possible resolution of the question, which includes a deeper sampling effort in the Indo-Pacific zone and the further development of molecular phylogeographic studies of all five anguillicolid species and their hosts.

Research paper thumbnail of Differing trophic niches of three French stygobionts and their implications for conservation of endemic stygofauna

Aquatic Conservation: Marine and Freshwater Ecosystems

Research paper thumbnail of Mass drives mating success in Armadillidium vulgare (Crustacea, Oniscidea)

Research paper thumbnail of Levebvre et al. 2013

Research paper thumbnail of Is the continental life of the European eel Anguilla anguilla affected by the parasitic invader Anguillicoloides crassus?

Proceedings of the Royal Society B: Biological Sciences, 2013

Quantifying the fitness cost that parasites impose on wild hosts is a challenging task, because t... more Quantifying the fitness cost that parasites impose on wild hosts is a challenging task, because the epidemiological history of field-sampled hosts is often unknown. In this study, we used an internal marker of the parasite pressure on individual hosts to evaluate the costs of parasitism with respect to host body condition, size increase and reproductive potential of field-collected animals for which we also determined individual age. In our investigated system, the European eel Anguilla anguilla and the parasitic invader Anguillicoloides crassus, high virulence and severe impacts are expected because the host lacks an adaptive immune response. We demonstrated a nonlinear relationship between the severity of damage to the affected organ (i.e. the swimbladder, our internal marker) and parasite abundance and biomass, thus showing that the use of classical epidemiological parameters was not relevant here. Surprisingly, we found that the most severely affected eels (with damaged swimbladder) had greater body length and mass (þ11% and þ41%, respectively), than unaffected eels of same age. We discuss mechanisms that could explain this finding and other counterintuitive results in this host-parasite system, and highlight the likely importance of host panmixia in generating great inter-individual variability in growth potential and infection risk. Under that scenario, the most active foragers would not only have the greatest size increase, but also the highest probability of becoming repeatedly infected-via trophic parasite transmission-during their continental life.

Research paper thumbnail of On the male-effect in the terrestrial Crustacean Armadillidium vulgare (Latreille, 1804)

Invertebrate Reproduction & Development, 1999

In the terrestrial Crustacean Armadillidium vulgare, the onset of female reproduction can be sped... more In the terrestrial Crustacean Armadillidium vulgare, the onset of female reproduction can be sped up by a male-induced stimulation. This male-effect is mainly characterized by a shortening of the vitellogenesis period, which occurs during the preparturial intermoult. The determinism of this phenomenon, for the first time reported by Jassem in 1982, was investigated here by both experimental and ethological approaches.