Hierarchical analyses of genetic differentiation in a hybrid zone of Sorex araneus (Insectivora: Soricidae)

Abstract

Microsatellites are used to unravel the fine‐scale genetic structure of a hybrid zone between chromosome races Valais and Cordon of the common shrew (Sorex araneus) located in the French Alps. A total of 269 individuals collected between 1992 and 1995 was typed for seven microsatellite loci. A modified version of the classical multiple correspondence analysis is carried out. This analysis clearly shows the dichotomy between the two races. Several approaches are used to study genetic structuring. Gene flow is clearly reduced between these chromosome races and is estimated at one migrant every two generations using R‐statistics and one migrant per generation using F‐statistics. Hierarchical F‐ and R‐statistics are compared and their efficiency to detect inter‐ and intraracial patterns of divergence is discussed. Within‐race genetic structuring is significant, but remains weak. FST displays similar values on both sides of the hybrid zone, although no environmental barriers are found on the Cordon side, whereas the Valais side is divided by several mountain rivers. We introduce the exact G‐test to microsatellite data which proved to be a powerful test to detect genetic differentiation within as well as among races. The genetic background of karyotypic hybrids was compared with the genetic background of pure parental forms using a CRT–MCA. Our results indicate that, without knowledge of the karyotypes, we would not have been able to distinguish these hybrids from karyotypically pure samples.

Restricted Gene Flow at Specific Parts of the Shrew Genome in Chromosomal Hybrid Zones

“…4). The genetic structure values measured in this study are globally similar to what Lugon-Moulin et al (1999a) and Brü nner et al (2002b) observed in the same hybrid zones using only seven microsatellite loci. This implies that the set of 10 loci added in this study carry similar information to the first seven loci.…”

“…Data collection, sizing of the bands, and analysis were done using the GeneScan software (Applied Biosystems). The individuals already genotyped at some loci (L9, L16, L57, L62, and L69) in other studies (Lugon-Moulin et al 1999a;Brü nner et al 2002b) were not analyzed again for this study.…”

“…Genetic analyses of both hybrid zones showed that the species-specific status is the main cause of genetic divergence among populations, with the effect of distance or geographic barriers being weak (Lugon-Moulin et al 1999a;Brü nner et al 2002b). However, comparing these genetically very similar but karyotypically very different hybrid zones, Brü nner et al (2002b) was unable to discriminate between reproductive barriers caused only by genetic factors or in combination with chromosomal differences.…”

Microsatellite polymorphism in the edaphic spruce, Picea asperata, originating from the mountains of China

“…However, microsatellite mutations are known to deviate from an ideal SMM or GSM (Estoup and Angers 1998, Ellegren 2000, Xu et al 2000. A comparison of the values of F ST under a random mutation process and R ST under a strict stepwise mutation model, computed using the same data, can provide valuable insights into phylogenetic inferences, i.e., the importance of mutation vs. genetic drift or gene flow for population differentiation (Michalakis and Veuille 1996, Ross et al 1997, Estoup et al 1998, Lugon-Moulin et al 1999). …”

Genetic differentiation in populations of the cestode Bothriocephalus acheilognathi (Cestoda, Pseudophyllidea) as revealed by eight microsatellite markers

“…Each allele in each locus was standardized prior to the R st calculations in order to minimize the variance due to differences in sample sizes. Slatkin's R st , which is a Wright's (1951) F stanalogue assuming a stepwise mutation model (SMM, Kimura & Crow, 1964), appears to better reflect true differentiation in highly structured populations (see Lugon-Moulin et al 1999, for a review). R st CALc software was also used to calculate N m values and du 2 genetic distance as defined by Goldstein et al (1995).…”