The male chromosome of an Eastern European house mouse has infiltrated Western Europe, creating a hybrid strain of “supermice” with extra-high sperm counts.
Normally, hybridization, when two subspecies mate to produce offspring, results in decreased sperm strength in the offspring. But when the western mouse Mus musculus domesticus picks up a male, or Y, chromosome from the eastern mouse Mus musculus musculus, the result is a strain of mice with higher-than-normal sperm counts that now thrives in the Czech Republic and the Bavarian region of Germany. Read full article.