On Earth, Foxes and Wolves do not get along very well (even though they are "cousins".) However on Vulpes, the human DNA inside both the fox and wolf makes them compatable.
Male Fox and Female Wolf
This type of relationship is fairly common (especially among 2nd and 3rd Generation male foxes). Since both the fox and wolf are canines their bodies can accomodate each other very nicely. At first when the couple begins to mate it is a loose fit because the penis of the fox is slightly smaller than that of a wolf, however the female will draw tighter until his knot grows inside her. The knot of a male fox is generally between golfball and baseball size. And once the knot is in her it cannot be removed until they were finished mating. The couple remains tied together for about 10 to 20 minutes. Once mating is complete, the female wolf becomes very friendly and the couple will more than likely marry eventually.
After about 2 months, the female wolf gives birth to 3 to 7 pups (both fox and wolf). After birth the fox and wolf couple will be eternally bonded together and they will have a couple more litters together.
Male Wolf and Vixen
This type of relationship is less common, However it is the most common interspecies relationship among vixens. Mating occurs the same way as with a male fox and a female wolf. The only difference is that a male wolf is larger than what a vixen is used to. However, since they are both canines the vixen can accomodate the wolf easily. However the knot of the wolf is much larger than that of a fox (between baseball and cantaloupe-size...to any female of another species this would be very painful and possibly even dangerous. But not to a canine female.) The wolf and vixen will often remain tied together for up to 90 minutes. However, when the male pulls out, some pain is caused because the vixen is not used to accomodating knots of this size.
After 7 to 8 weeks, the vixen gives birth to anywhere from 4 to 8 pups (depending upon the amount of pain she has to deal with as he pulls out of her during mating.) Most male wolf/vixen couples do marry. However, some vixens have to deal with so much pain that the vixen will marry one of her own and they will often split the children evenly.*