Sex and the Single Island Fox

When it comes to reproduction, island foxes are not your typical canine. 

A female dog will go into heat and become reproductively receptive even if there is no male dog nearby. Dogs have spontaneous ovulation, they have a determined reproductive cycle which includes a spike of hormone to release the ovum or egg into the female's reproductive tract. Not so with island foxes. 

Captive breeding occurred from 2000 - 2008

During the period of captive breeding to increase island fox populations, it was discovered that female island foxes, without access to a male partner, did not show the elevated hormone patterns signaling they had ovulated. These single females did not go into heat.

A similar reproductive behavior occurs in members of suborder Feliformia, or the cat branch of carnivores (cats, otters, wolverines, ferrets, etc.), and in bears. These species have induced ovulation–some physical or hormonal stimulus from the male is required to stimulate or initiate ovulation.

To date island foxes are the only canine observed to have this reproductive trait. However, research on this facet of reproduction is minimal. It is unknown if gray foxes, the ancestor of island foxes, are induced ovulators. 

Gray foxes (Urocyon cinereoargenteus) are an ancient species. Some sources consider them the most basal or closest to the root of the canine family tree. In Decline and Recovery of the Island Fox the authors suggest induced ovulation may be a primitive trait shared between these ancient canines and other carnivores, like cats and bears. Spontaneous ovulation may have evolved later in the branches of the canine family tree that gave rise to red foxes and wolves. Compare gray fox and island fox.

The single female island fox? 

Well, she just doesn't waste her reproductive energy if there is no eligible mate at hand. 

What other animals are known to have induced ovulation? rabbits and camels