Fig 5. Male introgression and nuclear swamp.

The proto-M. arctoides population is characterized by a black mitochondrial genome (mt), and black sex chromosomes (XY) and autosomes (auto). The M. mulatta population covers a grey mitochondrial (mt), grey sex chromosomes (XX), and autosome. (1) Given male migration and female philopatry, the males from population proto-M. arctoides invade population M. mulatta and produce hybrid offspring carrying grey mt but a half black sex chromosome and autosome. (2) The female hybrids from population M. mulatta backcrossed with males of population proto-M. arctoides. (3) If this continued over generations, the frequency of population M. mulatta genetic signals on the grey sex chromosome and autosome would significantly decrease. The grey nuclear genome will be swamped by black nuclear genome until it is completely replaced. In contrary, the grey mitochondrial genome will remain in population M. mulatta. (4) The extant M. arctoides population only has one grey mitochondrial haplotype and one black nuclear genome. The black mitochondrial genome (dotted line in the square) disappeared probably due to bottleneck during glaciations period. (The Fig imitates Zinner et al. [75]).