Led by Ralph Brinster, professor of physiology at Penn Vet, the researchers speculated that the females' effect on the environment of the spermatogonial stem cells likely occurs through the male's endocrine and nervous systems.
However, they said that the process could also involve other systems as well.
The change amounts to a reduction of fertility six months earlier in "lonely" mice as compared to those who have female companionship.
The results have significant implications for the maintenance of male fertility in wildlife, livestock and even human populations.
For the study, the researchers housed male mice with and without female companions for 16-32 months-each male was placed with two novel females at two-month intervals to test its ability to impregnate the females.
They found that males housed with females did not show a drop in fertility until 32 months of age, a six-month increase in fertility over males housed alone.
However, the researchers also observed that once male fertility began to decrease, the rate of decrease was the same for both those that lived with females and those that did not.
Apparently, the decline in fertility could be partly due to defects in the sperm-production process.
"It appears that housing females with a male mouse delays the decline of reproductive processes at the cellular level by somehow affecting the cells surrounding the stem cells that produce spermatozoa in the testes. Whether this female influence occurs in other species is not known," said Brinster.
This research continues 10 years of study on the relationship between the stem cell environment, called the "niche" and spermatogonial stem cells, or SSCs.
The researchers said that the female is just one of many environmental cues that may influence the niche and cells, and thereby fertility, of the male.
However, what is not known is whether this female influence occurs in other species, but the researchers know that the female profoundly modifies a variety of responses in males in many areas of male physiology and psychology.
The study was reported online in the journal Biology of Reproduction.