Microsatellite Variation in Colonizing and Palearctic Populations of Drosophila subobscura

Abstract

The recent colonization of North America by Drosophila subobscura has provided a great opportunity to analyze a colonization process from the beginning. A comparative study using 10 microsatellite loci was conducted for five European and two North American populations. No genetic differentiation between European populations was detected, indicating that gene flow is high among them and that the microsatellites used in the present work represent neutral markers not subject to differentiation due to selection. Extensive reduction in the number of alleles and a significant decrease in heterozygosity in colonizing populations were detected that could be explained by the founder effect and a subsequent quick but not infinite expansion. Assuming that all alleles present in the colonized area were carried by the sample of colonizers, we estimated that most probably 4-11 individuals expanded in the new area. F(ST) and the chord distance measures reflect the colonization process more accurately, since drift has been the major force in differentiating the Old and New World populations, and thus other measures considering allele size differences, such as Rho(ST) and deltamu2, are less reliable for studying nonequilibrium populations. Finally, our results were consistent with the two-phase microsatellite mutational model, indicating that most alleles are generated by gain or loss of a repeat unit, while some alleles originate by more complex mutations.

Gene flow and gene flux shape evolutionary patterns of variation in Drosophila subobscura

“…An independent origin of this association in both populations seems unlikely and the more parsimonious explanation is gene flow between them. Overall, these results suggest that gene flow between populations of D. subobscura is high, and agree with several studies detecting non-negligible gene flow between natural European populations of this species (Latorre et al, 1992;Pascual et al, 2001;Zivanovic et al, 2007). High gene flow between distant populations could be attributed to migration, both by passive transportation associated to human activities (Pascual et al, 2007) and to the active dispersal capabilities of D. subobscura (Serra et al, 1987).…”

“…However, given that these chromosomal arrangements are under strong selection (Prevosti et al, 1988;Balanyà et al, 2006), gene flow between populations would likely be underestimated using the inversions themselves as makers. Interestingly, low levels of genetic differentiation between European populations of D. subobscura were observed using molecular markers such as restriction fragment-length polymorphisms (Rozas et al, 1995) and microsatellite loci (Pascual et al, 2001). Consequently, gene flow and gene flux could be changing the genetic content of inversions from widely separated populations.…”

Alive and kicking, or, living on borrowed time? – Microsatellite diversity in natural populations of the endangered Ulmus minor Mill. sensu latissimo from Croatia

“…The gene diversity observed (H e ) was compared to the gene diversity expected at mutation-drift equilibrium (H eq ) and calculated from the observed number of alleles under different mutation models: infi nite allele model -IAM (Kimura and Crow 1964), stepwise mutation model -SMM (Ohta and Kimura 1973) and an intermediate twophase model -TPM (Di Rienzo et al 1994). The TPM model was applied assuming 30% -TPM 1 (Pascual et al 2001, Hoelzel et al 2002, Kuehn et al 2003) and 5% multistep changes -TPM 2 (Piry et al 1999). Based on the number of loci in our dataset, the Wilcoxon sign-rank test (Luikart et al 1998) was chosen for the statistical analysis of heterozygote excess or defi ciency as recommended by Piry et al (1999).…”

Climate change and chromosomal inversions in Drosophila subobscura

“…the expansion from Puerto Montt to Santiago within 1 yr points to a dispersal rate of roughly 2.7 km d -1; see Section 2.3). Furthermore, no genetic differentiation between European populations has been detected using microsatellite loci, which suggests that gene flow due to migration is sufficiently high to homogenize the genetic constitution of populations at putatively neutral markers (Pascual et al 2001). Gene flow prevents populations from optimally adapting to their environments (Ronce & Kirkpatrick 2001), but there is no clear amount of migration or gene flow at which point populations can become effectively isolated with respect to their evolutionary dynamics (Rice 2004).…”