I have a solo male in my community tank of tetras and guppies. He's a male, but his mate didn't last the cycle and/or the Ich; I never bothered to get another...?
He does okay, but I think he likes my female Guppy, but then again, she'll accept any attention!
LOL - You know, I actually Googled this behavior and even though they are different species I came across a few (unverified) articles of Molly-Guppy coupling.
The Mollie is easily 2x the size of the smaller male Guppies and is always chasing them off. So far though, all of the frys are "normal"!
I think it extremely unlikely, but if horses and donkeys can do it...?