Monogamy vs. Polygamy – only a small difference?

Is it possible that only a small difference between two similar animals can cause one animal to be faithful and another to be a player?

The vole is a small rodent, and there are two varieties: the mountain vole and the prairie vole.

The prairie vole has been shown to be monogamous – they make a pair and remain bonded for life. In fact, if one of the partners dies, the other partner may die soon afterwards. (awwww)

Mountain voles are polygamous – they will mate with quite a few different partners throughout a lifetime.

By the current definition of species, these animals belong to different species. However, they are fairly similar.

It turns out that the main difference between the two animals revolves around oxytocin, the “bonding hormone”. The polygamous mountain voles bond less, it seems, because of a lessened sensitivity to oxytocin. (See link below.)

It is always interesting to observe two species which are closely related, who differ only slightly and in a measurable way. The implications are that accidental variations in an organism’s makeup can make huge differences in how they interact with the world.

http://www.thefreelibrary.com/Brain+receptor+shapes+voles’+family+values.-a012488361