Widespread introgression of the Mus musculus musculus Y chromosome in Central Europe

According to Haldane’s rule, sex chromosomes should harbour more incompatibilities than autosomes. As a consequence, transmission of sex-linked genes across a genetic barrier is expected to be hampered. A remarkable example of a contradiction of this assumption was reported from the hybrid zone between two house mouse subspecies in western Czechia and south-eastern Germany where unidirectional east→west Y chromosome introgression was observed. Since the phenomenon was coupled with differences in sex ratio, this was hypothesised to be caused by a genetic conflict between sex-specific genes on sex chromosomes or elsewhere in the genome. Here we capitalise on a large material consisting of almost 7500 mice collected across a vast area from the Baltic Sea to the Alps embracing a ~900 km long portion of the zone with the aim to (i) detect its exact course and (ii) reveal the extent and pattern of the Y chromosome introgression in Central Europe. We show that the path of the zone is quite tortuous even at the global scale and the introgression is rather a rule than an exception. We also show that although sex ratio perturbations described in our previous study appear also in other introgression areas, they may not be ubiquitous. Finally, we reveal that although not all Y chromosome types are associated with the introgression, it is not restricted to a single ‘winning’ haplotype.

X Chromosome Introgression and Recombination in the cephus Group of Cercopithecus Monkeys

A representative of Cercopithecus erythrotis was surveyed at a 9.3-kb region of the X chromosome. The data were compared against homologous sequences of closely related Cercopithecus monkeys including C. cephus, a species recently shown to have 2 polymorphic X-chromosomal lineages. Direct sequence comparisons and subsequent phylogenetic analyses revealed that synapomorphies in the first 4.3 kb cluster C. erythrotis with one C. cephus lineage, while synapomorphies in the latter 5.0 kb join it with the second C. cephus lineage. This pattern very likely reflects an ancestral episode of introgression from C. cephus into C. erythrotis followed by a recombination event. Similar groups of synapomorphies occur at different phylogenetic depths within the C. erythrotis/C. cephus/C. ascanius radiation and reveal new details in the evolutionary history of this 3-species clade.