Lurking males lead to hard-to-fertilize mouse eggs

Mixed-sex society raises females’ resistance to sperm

FERTILIZED  The egg of a common house mouse (a fertilized one shown) is likely to be tougher to fertilize if the mouse grew up around a lot of males.

R.C. Firman

How much male company a female mouse sniffs and sees as she grows up affects how easy her eggs will be for sperm to fertilize.