Search PubMed⌕ Search

Biomedical subjects

Serge Morand

Publications and source records attributed to Serge Morand.

34 records · Page 2Linked to original sources
PubMed2004

Molecular phylogeny of congeneric monogenean parasites (Dactylogyrus): a case of intrahost speciation.

Dactylogyrus species (Dactylogyridae: Monogenea) are a group of monogenean gill parasites that are highly specific to freshwater fish of the family Cyprinidae. Dactylogyrus species were sampled from 19 cyprinids and one percid collected in Europe. Using partial 18S rDNA and ITS1 sequences, a phylogeny of 51 Dactylogyrus species was reconstructed to investigate the patterns of parasite speciation and diversification. Three main Dactylogyrus lineages were recognized from all phylogenetic trees, that is, analysis of 18S rDNA alone and combined 18SrDNA and ITS1. The first lineage associates the Dactylogyrus species of Cyprinus carpio and Carassius auratus of the Cyprininae; the second associates Dactylogyrus species of the Gobioninae, Pseudorasbora parva of the Rasborinae, and Ctenopharyngodon idella of the Cyprininae; and the third associates Dactylogyrus species of the Leuciscinae and Alburninae and Barbus barbus of the Cyprininae. Our results suggest that the genus Dactylogyrus is of quite recent origin and that these three lineages separated from each other in a very short period of time. Host subfamily mapping onto the parasite tree inferred from analysis of the combined dataset showed that the Cyprininae could be plesiomorphic hosts for Dactylogyrus. Dactylogyrus parasites would have secondarily colonized the Percidae and representatives of the Leuciscinae, Alburninae, Gobioninae, and Rasborinae. Comparison of host and parasite phylogenetic relationships indicated that a very high number of parasite duplications occurred within two of the three Dactylogyrus lineages. Dactylogyrus diversification can be mainly explained by sympatric intrahost speciation events that seem to be correlated to strict host specificity. Moreover, the present study shows that the congeneric parasites speciating within one host tend to occupy niches within hosts differing at least in one niche parameter.

Animals↗
PubMed2003

Correlated evolution between host immunity and parasite life histories in primates and oxyurid parasites.

Maturation time is a pivotal life-history trait of parasitic nematodes, determining adult body size, as well as daily and total fecundity. Recent theoretical work has emphasized the influence of prematurational mortality on the optimal values of age and size at maturity in nematodes. Eosinophils are a family of white blood cells often associated with infections by parasitic nematodes. Although the role of eosinophils in nematode resistance is controversial, recent work has suggested that the action of these immune effectors might be limited to the larval stages of the parasite. If eosinophils act on larval survival, one might predict, in line with theoretical models, that nematode species living in hosts with large eosinophil numbers should show reduced age and size at maturity. We tested this prediction using the association between the pinworms (Oxyuridae, Nematoda) and their primate hosts. Pinworms are highly host specific and are expected to be involved in a coevolutionary process with their hosts. We found that the body size of female parasites was negatively correlated with eosinophil concentration, whereas the concentration of two other leucocyte families-neutrophils and lymphocytes-was unrelated to female body size. Egg size of parasites also decreased with host eosinophil concentration, independently of female size. Male body size was unrelated to host immune parameters. Primates with the highest immune defence, therefore, harbour small female pinworms laying small eggs. These results are in agreement with theoretical expectations and suggest that life histories of oxyurid parasites covary with the immune defence of their hosts. Our findings illustrate the potential for host immune defence as a factor driving parasite life-history evolution.

Animals↗
PubMed2003

Reproductive barriers between congeneric monogenean parasites (Dactylogyrus: Monogenea): attachment apparatus morphology or copulatory organ incompatibility?

Morphometrical parameters of the attachment apparatus and copulatory organs of 52 Dactylogyrus species parasitizing 17 species of cyprinid fishes were analysed to test for the existence of reproductive barriers among congeneric species. The minimal spanning tree (MST) method was applied in the analyses. The position of "real" parasite communities, based on (1) observed infracommunities, (2) a checklist of parasites for a given host in the morphological space, was compared to the position of randomly generated communities using all Dactylogyrus species. The distribution of species similarity within infracommunities (using both attachment and copulatory measurements) was not significantly different from that obtained by simulation, and this trend was similar for both the checklist and observed infracommunities. When real infracommunities were separated according to host specificity (specialists versus generalists), we found differences reflecting similarities in the shapes of attachment and copulatory organs. Within specialists, more similarities in the shape of the attachment apparatus can be found than within generalists, whereas the similarity in copulatory organ shape seems to be random. When generalists are considered, parasite infracommunities with the greater differences in attachment apparatus are also more different in terms of the shape of their copulatory apparatus. We conclude that specialist parasites possess more similarity in attachment apparatus due to specialisation to their host, whereas the species similarity in copulatory organs within infracommunities exhibits a random pattern, but with the copulatory organs being more variable than the attachment apparatus (which may be due to reproductive isolation). The morphology of the copulatory apparatus seems not to be the single factor explaining reproductive isolation among species.

Animals↗
PubMed2003

Descriptions of two new species of the genus Tachygonetria Wedl, 1862 (Nematoda-Pharyngodonidae) and discussion of the relationships among the species of the genus.

Two species of pinworm, parasites of Testudo graeca Linneaus, 1758 from Morocco, are described: Tachygonetria poulini sp. nov. and Tachygonetria settatensis sp. nov. Light and scanning electron microscopy studies revealed morphological differences in the structure of the cephalic end in both sexes, as well as in the structure of the caudal end in the male, which enabled us to differentiate these species from others, and from each other. The relationships among the species of the genus Tachygonetria are discussed.

Animals↗
PubMed2003

A comparison of the structure of helminth communities in the woodmouse, Apodemus sylvaticus, on islands of the western Mediterranean and continental Europe.

We investigated the pattern of helminth species diversity in woodmouse, Apodemus sylvaticus, on western Mediterranean islands. We first performed a survey of the helminth fauna of A. sylvaticus in Sicily. Despite the small sampling effort, parasite species richness in Sicily is large in comparison with parasite species richness on other Mediterranean islands. We tested the nestedness of helminth parasite species from a number of Mediterranean localities using data compiled from epidemiological surveys of the helminth species of A. sylvaticus. We showed a nested pattern for woodmouse helminth species on western Mediterranean islands which suggests that the distribution of parasites on these islands is not the result of a random process. Properties of helminth parasites such as taxonomic group or life cycle and properties of the host population localities such as area size or the stability of the environment (estimated by mammal species diversity) contribute to the nestedness.

Animals↗
PubMed2003

Phylogenies, the comparative method and parasite evolutionary ecology.

A growing number of comparative analyses in the field of parasite evolution and ecology have used phylogenetically based comparative methods. However, the comparative approach has not been used much by parasitologists. We present the rationale for the use of phylogenetic information in comparative studies, and we illustrate the use of several phylogenetically based comparative methods with case studies in parasite evolutionary ecology. The independent contrasts method is the most popular one, but presents some problems for studying co-adaptation between host and parasite life traits. The eigenvector method has been recently proposed as a new method to estimate and correct for phylogenetic inertia. We illustrate this method with an investigation of patterns of helminth parasite species richness across mammalian host species. This method seems to perform well in situations where host and parasite phylogenies are not perfectly congruent, but one might still want to correct for the effects of both. Finally, we present a method recently proposed for variation partitioning in a phylogenetic context, i.e. the phylogenetically structured environmental variation.

Animals↗
PubMed2003

Phylogenetic relationships of the Dactylogyridae Bychowsky, 1933 (Monogenea: Dactylogyridea): the need for the systematic revision of the Ancyrocephalinae Bychowsky, 1937.

Phylogenetic analyses based on partial 18S rDNA sequences of polyonchoinean monogeneans were conducted in order to investigate the relationships between selected families and subfamilies of the Dactylogyrinea, mainly within the Dactylogyridae. We tested the status of the Ancyrocephalidae sensu Bychowsky & Nagibina (1978) and the Ancyrocephalinae sensu Kritsky & Boeger (1989). Within the Dactylogyrinea, the Diplectanidae and Dactylogyridae are well supported by maximum likelihood and maximum parsimony analyses, but their phylogenetic relationship with the Pseudomurraytrematidae remains unresolved. Phylogenetic relationships between the Pseudodactylogyrinae, Ancyrocephalinae, Ancylodiscoidinae and Dactylogyrinae indicate paraphyly of the Ancyrocephalidae sensu Bychowsky & Nagibina (1978). The group of species recently considered as the Dactylogyridae sensu Kritsky & Boeger (1989) comprises two sister groups. The first group includes the freshwater Ancyrocephalinae and the Ancylodiscoidinae. The second group includes the Pseudodactylogyrinae, Dactylogyrinae and the Ancyrocephalinae from the fish species Siganus doliatus and Tetraodon fluviatilis. The non-monophyly of the Ancyrocephalinae (i.e. the non-monophyly of the group of species recently considered as members of Ancyrocephalinae), previously suggested by Kritsky & Boeger (1989) using the morphological characters, indicates that classification of the Dactylogyridae needs to be revised.

Animals↗
PubMed2003

Recognition of two genetic groups in the Klebsiella oxytoca taxon on the basis of chromosomal beta-lactamase and housekeeping gene sequences as well as ERIC-1 R PCR typing.

Whilst searching for a molecular method to identify the different species of Raoultella and Klebsiella oxytoca, it was observed that the OXY-1 and OXY-2 beta-lactamase-producing K. oxytoca isolates displayed two distinguishable enterobacterial repetitive intergenic consensus (ERIC)-1R profiles. It was hypothesized that the two groups of chromosomal beta-lactamases might correspond to two groups of strains in the K. oxytoca taxon. To confirm this hypothesis, clinical isolates and reference strains of K. oxytoca were studied by determination of the sequence of their bla(OXY) genes, and of a partial fragment of their 16S rRNA (387 bp) and rpoB (512 bp) genes. The sequence data were phylogenetically analysed by using the parsimony method. Four clinical isolates possessed a bla(OXY-1) gene and nine possessed a bla(OXY-2) gene. The mean percentage of rpoB and 16S rRNA gene identity was > 99% within each group of strains, whereas it was 96.56 +/- 0.24% for rpoB genes and 97.80 +/- 0.22% for 16S rRNA genes between the group of strains harbouring the bla(OXY-1) gene and the group harbouring the bla(OXY-2) gene. The phylogenetic tree resulting from combined analysis of the 16S rRNA and rpoB datasets showed that the K. oxytoca isolates were monophyletic and separated into two clades; these clades included strains with either the bla(OXY-1) gene or the bla(OXY-2) gene. This result was supported with high bootstrap values of 97 and 99%, respectively. Moreover, the two groups of strains displayed distinct ERIC-1R profiles, with bands characteristic of each profile. Thus, the chromosomal bla(OXY) gene sequence is able to delineate not only two groups of beta-lactamases in K. oxytoca, but also two clades in the K. oxytoca taxon, in a manner similar to the sequence of housekeeping genes. These results suggest that K. oxytoca should be divided into two genetic groups, group OXY-1 represented by K. oxytoca strain SL781 (=CIP 104963) and group OXY-2 by K. oxytoca strain SL91l (= CIP 106098).

Bacterial Typing Techniques↗
PubMed2003

Quantifying phylogenetically structured environmental variation.

Comparative analysis methods control for the variation linked to phylogeny before attempting to correlate the remaining variation of a trait to present-day conditions (i.e., ecology and/or environment). A portion of the phylogenetic variation of the trait may be related to ecology, however; this portion is called "phylogenetic niche conservatism." We propose a method of variation partitioning that allows users to quantify this portion of the variation, called the "phylogenetically structured environmental variation." The new method is applied to published data to study, in a phylogenetic framework, the link between body mass and population density in 79 species of mammals. The results suggest that an important part of the variation of mammal body mass is related to the common influence of phylogeny and population density.

Analysis of Variance↗
PubMed2002

Abundance-prevalence relationship of gill congeneric ectoparasites: testing the core satellite hypothesis and ecological specialisation.

We investigated the abundance-prevalence relationships in monogeneans belonging to the genus Dactylogyrus. A total of 182 dactylogyrid populations representing nine species were collected from the gills of roach ( Rutilus rutilus). Local abundance was found to be strongly positively correlated with prevalence. Two hypotheses were tested to explain this relationship: (1) the core-satellite hypothesis, and (2) the ecological specialisation hypothesis. Abundance was log-normally distributed, and the relationship between mean abundance and variance of abundance followed Taylor's power law prediction. Prevalence showed a negative binomial distribution, which does not confirm the core-satellite hypothesis. The positive relationship between abundance and prevalence was found for both specialists and generalists. However, generalists were found to be more widely distributed among hosts and had higher abundances than specialists, which supports the ecological specialisation hypothesis.

Animals↗
PubMed2002

Investigating patterns may reveal processes: evolutionary ecology of ectoparasitic monogeneans.

We reviewed several published and ongoing studies concerning monogenean communities. Patterns of species richness, host specificity, community structure and host--parasite coevolutionary interaction were carefully analysed, and hypotheses of evolutionary processes are proposed. The structuring of monogenean communities seems to be related to both ecological and historical constraints. The database supports an absence of intra- and interspecific competition in monogeneans. Species richness seems to be more due to host characteristics than to parasite interactions. Monogeneans seem to specialise on large hosts, leading to greater species richness on those hosts. The morphometric evolution of attachment and copulatory organs support the hypothesis of a reproductive segregation among conspecifics parasitising the same host(s). It also suggests the existence of concurrent adaptive and non-adaptive processes. The general absence of a coevolutionary pattern between host and parasites also suggests the constraints of history without dismissing the influences of ecological factors in the structuring of the communities. More generally, we strengthen the need to study the structure of communities in a phylogenetic context.

Animals↗
PubMed2002

Description of Tachygonetria combesi n. sp. and redescriptions of four species of Tachygonetria Wedl, 1862 (Nematoda: Pharyngodonidae), with a new diagnosis of the genus.

The generic diagnosis of Tachygonetria Wedl, 1862 is modified based on the study and redescription of Tachygonetria vivipara Wedl, 1862 (collected from large intestine of Uromastyx acanthinurus Bell, from North Africa) and T. dentata (Drasche, 1883) (collected from large intestine of Testudo graeca Linnaeus in Settat, Morocco and T. hermanni Gmelin in Catalonia, Spain). The following taxa were redescribed: Tachygonetria conica (Drasche, 1883) and T. robusta (Drasche, 1883) (both from the large intestine of Testudo graeca collected in Settat, Morocco); the subspecies Tachygonetria conica nicollei (Seurat, 1918) is suppressed. A new species, T. combesi n. sp. is described from the large intestine of Testudo hermanni, which confirms the revision of the genus. Scanning electron microscopical studies revealed substantial interspecific differences in the structure of the caudal end.

Animals↗
PubMed2002

Coevolution between Lamellodiscus (Monogenea: Diplectanidae) and Sparidae (Teleostei): the study of a complex host-parasite system.

Host-parasite coevolution was studied between Sparidae (Teleostei) fishes and their parasites of the genus Lamellodiscus (Monogenea, Diplectanidae) in the northwestern Mediterranean Sea. Molecular phylogenies were reconstructed for both groups. The phylogenctic tree of the Sparidae was obtained from previously published 16S mitochondrial DNA (mtDNA) sequences associated with new cytochrome-b mtDNA sequences via a "total evidence" procedure. The phylogeny of Lamellodiscus species was reconstructed from 18S rDNA sequences that we obtained. Host-parasite coevolution was studied through different methods: TreeFitter, TreeMap, and a new method, ParaFit. If the cost of a host switch is not assumed to be high for parasites, all methods agree on the absence of widespread cospeciation processes in this host-parasite system. Host-parasite associations were interpreted to be due more to ecological factors than to coevolutionary processes. Host specificity appeared not to be related to host-parasite cospeciation.

Animals↗
PubMed2002

Epizootiology of Syphacia obvelata from a domestic mouse population on the subantarctic Kerguelen Archipelago.

The effects of abundance, age, and sex of feral domestic mice Mus musculus domesticus on infections with the nematode parasite Syphacia obvelata were analyzed during a long-term study of the mouse population on Guillou Island (1.45 km2), a part of the subantarctic Kerguelen Archipelago. The population dynamics of the nematode did not follow the variation in host abundance. However, depending on the year, differences in pinworm abundance were found between the age classes and sex. Such patterns suggest that parasitic infections may have been modulated by host-intrinsic factors, e.g., either by the way of innate or adaptive immunity, rather than extrinsic factors, e.g., host abundance.

Age Factors↗
PubMedDate not supplied

A predator-prey model with predators using hawk and dove tactics.

In this work we present a predator-prey model that incorporates individual behavior of the predators. A classical Lotka-Volterra model with self-limiting prey describes the predator-prey interaction. Predator individuals can use two behavioral tactics to dispute a prey when they meet, the classical hawk and dove tactics. Each individual can use both tactics along its life. The predator behavioral change is described by means of a game dynamic model based upon the replicator equations, where the gain depends on prey density. We assume that the demographic process, predator-prey interactions, acts at a slow time scale in comparison with the evolution of the behavior of the predator population. The existence of two time scales allows studying the complete system from a reduced one, which describes the dynamics of the total predator and prey densities at the slow time scale. The aim of this work is to study the effects of individual predator behavior on the dynamics of the predator-prey system. The main conclusion that emerges from this study is the existence of a relationship between prey density and the strategy adopted by predators: aggressive behavior is connected to high prey and low predator densities, whereas a polymorphism dove-hawk is found at low prey and high predator densities.

Animals↗