Patterns of microsatellite variability among X chromosomes and autosomes indicate a high frequency of beneficial mutations in non-African D. simulans.
We analyzed microsatellite variability at 42 X-linked and 39 autosomal loci from African and European populations of Drosophila simulans. The African D. simulans harbored significantly more microsatellite variability than the European flies. In the European population, X-linked polymorphism was more reduced than autosomal variation, whereas there was no significant difference between chromosomes in the African population. Previous studies also observed a similar pattern but failed to distinguish between a demographic event and a selection scenario. We performed extensive computer simulations using a wide range of demographic scenarios to distinguish between the two hypotheses. Approximate summary likelihood estimates differed dramatically among X chromosomes and autosomes. Furthermore, our experimental data showed a surplus of X-linked microsatellites with a significantly reduced variability in non-African D. simulans. We conclude that our data are not compatible with a neutral scenario. Thus, the reduced variability at X-linked loci is most likely caused by selective sweeps associated with the out-of-Africa habitat expansion of D. simulans.
Schöfl
Gerhard
G
Institut fur Tierzucht und Genetik, Veterinarmedizinische Universitat, Vienna, Austria.
Schlötterer
Christian
C
D000220:Adaptation, Biological / Q000235:genetics; D000818:Animals; D004330:Drosophila / Q000235:genetics*; D018895:Microsatellite Repeats / Q000235:genetics*; D009154:Mutation / Q000235:genetics; D011110:Polymorphism, Genetic; D014960:X Chromosome / Q000235:genetics*