ABSTRACT
Rhododendron ferrugineum L. (Ericaceae) is a subalpine shrub found throughout the Pyrenees and Alps at elevations of 1600-2200 m. We examined relationships between genetic and geographic distance, using 115 dominant amplified fragment length polymorphism (AFLP) markers to assess genetic structure over a wide range of spatial scales. We sampled 17 sites with distances of 4 km to more than 1000 km between them. At these scales we detected no association between geographic distance and genetic distance between populations. This suggests that genetic drift and gene flow are not in equilibrium for these populations. This pattern could have resulted from recent and rapid postglacial colonization, from more recent human disturbance, or as a function of frequent and random "natural" long-distance colonization. At two of our sites we used transects (two horizontal and two vertical with respect to slope at each site) to sample at distances ranging from 10 m to more than 5000 m. At this scale we observed a positive relationship between genetic and spatial distance along two vertical transects, one at each site. We hypothesize that isolation-by-distance at this smaller scale is a function of restricted gene flow via seed dispersal.
Subject(s)
Genetics, Population , Rhododendron/genetics , Altitude , Analysis of Variance , DNA Primers , Europe , Evolution, Molecular , Geography , Polymorphism, Restriction Fragment Length , Population DynamicsABSTRACT
Ixodes ricinus is considered as the main vector of Lyme Borreliosis in France. The aim of our investigations was to obtain a comprehensive view of the spatial risk linked to the distribution of the species in our country. Previous studies [1] have provided strong evidence that the species populations are widely distributed, so the objective of the present work was to ascertain the bacteriological infection of the tick by the agent of the zoonosis (Borrelia burgdorferi, sensu lato), over the French territory, whatever the ecological conditions may be. For this purpose, we kept the same framework as that used in our acarological investigation, a phytoecological zoning of the territory into 54 geographically separate and ecologically distinct units distributed into three climatic zones. Batches of ticks, picked up in these different phytoecological units (only two thirds of which were sampled), were submitted for bacteriological investigation. A total of 4,673 ticks were examined, individually, for the presence of Borrelia burgdorferi, by immunofluorescence. Percentages of infection according to the various stages of Ixodes ricinus free stages, collected by flagging, were as follows: 4.95% in 3,247 nymphs, 11.2% in 699 males, 12.5% in 727 females. Larvae were ignored. Practically all the tested units harboured the bacterium. The percentage of tick samples (25 ticks or more) absolutely free of Borrelia, wherever they came from, is very low (not exceeding 10 percent of the sampled forests). Our study confirms the assessment of a widespread distribution of the zoonosis in France which was, until now, exclusively based on an approximate distribution of limited human cases observed in the country.
Subject(s)
Arachnid Vectors/microbiology , Borrelia burgdorferi Group/isolation & purification , Ixodes/microbiology , Animals , Ecology , Female , France/epidemiology , Humans , Lyme Disease/epidemiology , Lyme Disease/transmission , Male , Plants , Prevalence , Seasons , Temperature , Zoonoses/microbiologyABSTRACT
The aim of the study was to precise the geographical repartition of Lyme borreliosis in the Rhône-Alpes district, to describe the ecological characteristics of the areas propitious to the disease, and to verify the vectorial competence of I. ricinus. The cases of Lyme disease were located by means of a questionnaire sent to 1156 physicians. The vector role of I. ricinus was studied by two ways: firstly by searching a correlation between the geographical repartition of the tick and that of cases, secondly by proving the Borrelia infection of the tick. Lyme disease is widely spread in the study area, mainly at the foothill level, its repartition is largely coinciding with that of I. ricinus which was found infected by B. burgdorferi (s.l.). However a few cases, located near the Mediterranean area, set an unanswered problem.
