Schlüsselwörter
(Englisch)
|
rabies epizootic, Vulpes vulpes, microsatellites, temporal variation, degenerated DNA, genetic differentiation, genetic drift, fragmented landscape
|
Kurzbeschreibung
(Englisch)
|
There are very few long-time studies on the dynamics of natural populations and even more rare are studies describing the genetic structure of populations over a period of several generations. During the rabies epidemic in Switzerland - lasting from 1967-96 - an unique data set of over 27000 individual fox canine teeth were collected at the Swiss Rabies Centre in Bern. Recent advances in molecular methods, in particular the amplification of short tandem repeat markers by means of PCR, make it possible to obtain sufficient genetic information from ancient teeth sample. The aim of this study is to describe the genetic variation in rabies affected and unaffected Swiss fox populations before, during and after the epi-demic. Furthermore, this project should bring a better understanding of the genetic variation in time and space, the migration process between fox populations, the effect of geographical barriers and that transmission rate correlates with genetic relatedness within rabies affected fox populations in a fragmented landscape. For this purpose it is planned to analyse 700 historical and recent fox samples using up to sixteen canine polymorphic microsatellites.
|
Projektziele
(Englisch)
|
a.) In a pilot-study we will test the reliability of amplified genotypes using teeth as a DNA source. Quality and quantity of the extracted DNA will be described and investigated in correlation to the age of the samples. In addition, it will be tested whether the chemical preservation of the museum samples has influ-enced DNA quality and if a different treatment of these samples has to be considered. The level of genotyping errors in relation to the age and source of the samples have to be quantified in order to determine if the error rate is low enough to estimate levels of genetic diversity.
b.) It is our first major aim to assess genetic variability in time and space in a rabies unaffected popula-tion. For this question we plan to use historical teeth samples from the canton Uri, completed by currently provided tissue samples. This fox population is well isolated by a complete mountain range surrounding the canton, can be regarded rather as a demographic island than an open system which will simplify statistical analysis. To estimate mean generation time, the genetic data set will be completed with demographic data by ageing historical and recent samples. Particularly we will test whether the construction of the fenced motorway (N2) all along the valley of Uri will have had considerably affected migration pattern and genetic exchange within the fox population over the last 30 years.
c.) Our second major aim is to describe the genetic diversity in two fox population before, during and af-ter the rabies epidemic. For this study, we will focus on the Fricktal AG and on the canton Glaurs - two areas with a very different topography and a epidemiological history. In both areas sufficient samples were collected in the early 70ies. Due to the expected severe decrease of the population size by the infectious disease, we expect substantial genetic drift leading to changes in allele frequencies, substantial loss of genetic variability and temporary reduced effective population size. By including genetic data from recent fox samples, we will be able to show whether the recent population was only founded by local sur-viving individuals or by additional immigrants.
d.) Additionally to the three previously mentioned areas we will chose a further number of sampling areas to compare prerabies and recent genetic structure within and between populations in relation to the severity of the local rabies epidemic and the advanced fragmentation of the landscape. This approach will give insight to the genetic consequences and the migration processes after a rabies outbreak within and between local fox populations. For this question we will use additional samples from the Natural History Museum of Bern.
We believe that the short generation time of Swiss red foxes - which we estimate to be only between two and three years - will enable detect changes in populations genetic parameters within a time period of 30 years.
|
Abstract
(Englisch)
|
Infectious disease can affect the demography of natural populations and, as a consequence, can alter the genetic variation within and between those populations. This study investigated long-term effects of rabies-induced mortality on the demography and genetic variation in two Swiss red fox populations over ten to fourteen generations. In Switzerland, the last rabies epizootic persisted from 1967 to 1999 and was continuously monitored by collecting fox carcasses throughout the country. Alongside records of rabies tests and post-mortem data, tooth samples were systematically archived for ageing. In this study, DNA from 666 individual teeth was extracted. For 279 extracts, the concentration of nuclear DNA was estimated in a quantitative PCR and found to be negatively correlated with storage time. After excluding samples with insufficient DNA concentration for reliable genotyping, 382 samples were screened using between nine and seventeen canine and red fox specific microsatellites. Tooth samples were completed with 189 modern tissue samples. By assessing the age structure continuously throughout and after the rabies epizootic for the first population, population density and age structure was found to be altered by the high rabies-induced mortality. In contrast, no long-term trends in genetic diversity were identified although a high variation of HO, HE, FIS was discovered both in short-term and longer-term. A strong isolation-by-distance pattern was revealed for the second population by comparing individual pairwise genetic with spatial distances using modern samples. Furthermore, genetic data show that dispersal was sex-biased and altered by the topography of the landscape. When investigating isolation-by-distance patterns within the same population in 1971-73 and 1982-84 at lower population densities, density-dependant dispersal was observed. In conclusion, this study revealed no loss of genetic diversity in red foxes following a rabies epizootic despite a severe population bottleneck, yet highlights population density as an importance factor to determine local spatial genetic structure.
|
Publikationen / Ergebnisse
(Englisch)
|
Wandeler, P., Smith, S., Morin, P.A., Pettifor, R.A., Funk, S.M. (2003). Patterns of nuclear DNA degeneration over time - a case study in historic teeth samples. Molecular Ecology 12: 1087-1093.
Wandeler, P. Spatial and temporal population genetics of Swiss red foxes (Vulpes vulpes) following a rabies epizootic. Doktorarbeit, Cardiff University.
Demographic and temporal population genetics in a red fox population following a rabies epizootic. Population Genetics Group, University of Sussex, December 17-19, 2003.
Temporal population genetics in a red fox population following a rabies epidemic. Workshop for Population Genetics for Animal Conservation, Trento, Italy, September 4-6, 2003.
Wandeler, P., Funk, S. M., Largiadèr, C.R., Gloor, S., Breitenmoser, U. (2003). The city-fox phenomenon: genetic consequences of a recent colonization of urban habitat. Molecular Ecology 12: 647-656.
|
