Study of male-mediated gene flow across a hybrid zone in the common shrew (Sorex araneus) using Y chromosome.

Despite many studies, the impact of chromosome rearrangements on gene flow between chromosome races of the common shrew (Sorex araneus Linnaeus, 1758) remains unclear. Interracial hybrids form meiotic chromosome complexes that are associated with reduced fertility. Nevertheless comprehensive investigations of autosomal and mitochondrial markers revealed weak or no barrier to gene flow between chromosomally divergent populations. In a narrow zone of contact between the Novosibirsk and Tomsk races hybrids are produced with extraordinarily complex configurations at meiosis I. Microsatellite markers have not revealed any barrier to gene flow, but the phenotypic differentiation between races is greater than may be expected if gene flow was unrestricted. To explore this contradiction we analyzed the distribution of the Y chromosome SNP markers within this hybrid zone. The Y chromosome variants in combination with race specific autosome complements allow backcrosses to be distinguished and their proportion among individuals within the hybrid zone to be evaluated. The balanced ratio of the Y variants observed among the pure race individuals as well as backcrosses reveals no male mediated barrier to gene flow. The impact of reproductive unfitness of backcrosses on gene flow is discussed as a possible mechanism of the preservation of race-specific morphology within the hybrid zone.

Natural tick-borne encephalitis virus infection among wild small mammals in the southeastern part of western Siberia, Russia.

Infestation of small mammals, including common shrews Sorex araneus L., field mice Apodemus agrarius Pallas, and red voles Clethrionomus rutilus Schreber, with immature Ixodes persulcatus ticks and their infection with tickborne encephalitis virus (TBEV) were studied in the forest-steppe habitat in the vicinity of Novosibirsk, Russia. Larval ticks parasitize all three host species, but virtually all nymphs were found only on field mice and red voles. Detection of the viral RNA using reverse transcription (RT) with subsequent nested polymerase chain reaction (nPCR) and of viral antigen using enzyme-linked immunosorbent assay (ELISA) revealed a high prevalence of TBEV-positive animals in both the summer and winter. The proportion of small mammals with hemagglutination inhibition (HI) antibodies was significantly lower than with ELISA-detected antibodies. Taken together, the data suggest that small mammals may maintain TBEV as a persistent infection throughout the year.