IUCN / SSC Cat Specialist Group - Digital Cat Library |
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| Nussberger, B. | |
| Assessing introgression between European wildcats (_Felis silvestris silvestris_) and domestic cats (_Felis silvestris catus_) | |
| 2013 Full Book | |
Introgression is an important issue in evolutionary biology. It is defined as the flow of genes between taxa through hybridization beyond the first generation. Introduced genes of a closely related taxon may serve as raw material for rapid adaptive evolutionary change. On the other hand, introgression could lead to reduced fitness in hybrids, i.e. outbreeding depression, if the newly mixed traits are maladapted to the environment or if, on the genomic level, co-adapted gene complexes are disrupted. In conservation biology, introgression is often seen as a threat to genetic integrity by genome swamping and as especially relevant when hybridization is human-induced. This is the case for the European Wildcat (_Felis silvestris silvestris_), which is hybridizing with the domestic cat (_Felis silvestris catus_), potentially since over 2500 years. Hence, assessing the impact of introgression by monitoring free-ranging cat populations is crucial for wildcat conservation. However, introgression is difficult to detect. In wildcats, neither morphological nor genetic methods allowed accurate recognition of introgression so far. In the present thesis, I aimed to provide the basic knowledge necessary to investigate the effects of introgression on wildcats by 1) developing genetic markers able to disclose introgression; 2) establishing a genotyping method for non-invasive samples that allow monitoring a wildcat population based on hair samples; 3) assessing the introgression rate in the wildcat population of the Jura region; and 4) describing hybridization patterns in wildcats from France, Germany and Switzerland. Chapter 1 describes the development of single nucleotide polymorphism (SNP) markers, which allow reliable recognition of individual levels of introgression in wildcats, domestic cats and their admixed progeny. Chapter 2 shows how I optimized a SNP genotyping method to yield reliable genotypes of single hairs. I developed a 96.96 Fluidigm SNP genotyping array (SNP chip), based on the nuclear diagnostic SNPs described in chapter 1 and on published mitochondrial (mtDNA) SNPs. In chapter 3, this optimized genotyping method was then applied to non-invasively and systematically collected hair samples of the cat population of the Swiss Jura, to assess its rate of introgression. Twenty one percent of the sampled wildcats were introgressed, based on the nuclear diagnostic markers. This corresponds to a migration rate from domestic cats to wildcats of 0.02 migrants per generation. In contrast, migration rate from wildcats into domestic cats was negligible, suggesting a directional introgression. Haphazard sampling of the same wildcat population, mostly via road kills, led to similar results. Hybridization was found to occur between wildcat male and domestic cat female as well as vice versa and, based on the occurrence of backcrosses, both female and male F1-hybrids seemed viable and fertile. The hybridization patterns observed in chapter 3 were confirmed in chapter 4, where I estimated introgression rates in a large set of free-ranging wildcats of France, Switzerland and Germany. I found 53 hybrids (11%) out of 491 samples, corresponding to a migration rate from domestic cat to wildcat of 0.02 migrants per generation. Migration rate from wildcat into domestic cat was lower. Maternally inherited markers were more often introgressed than paternally inherited ones. Furthermore, hybrids seemed to concentrate at wildcat distribution edges. In addition, I found some evidence that the wildcat population of the Franco-Swiss Jura is possibly expanding. |
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