Oral presentation- Open Session 12th International Mammalogical Congress

The spiny mouse (Acomys cahirinus) – a menstruating rodent (#239)

Nadia Bellofiore 1 , jemma evans 1 , Peter Temple-Smith 2 , Hayley Dickinson 1
  1. Hudson Institute of Medical Research, Clayton, VICTORIA, Australia
  2. Obstetrics and Gynecology, Monash University, Clayton, Victoria, Australia

Menstruation, is the cyclical shedding of the decidualised endometrium in the absence of pregnancy. Menstruation is limited to 78 higher-order primates (human beings and Old World monkeys), 4 species of bat, and the elephant shrew. This represents only ~1.5% of the known ~5502 mammalian species. We recently made the unexpected discovery of menstruation in a rodent, the spiny mouse (Acomys cahirinus), a desert-adapted rodent native to the Middle East.

 Virgin female spiny mice aged 12-16 weeks were studied for 2 consecutive reproductive cycles. Mean menstrual cycle length was 8.7 ± 0.4 days with red blood cells observed in the vaginal lavage fluid over 3.0 ± 0.2 days. Cyclic endometrial shedding and blood in the vaginal canal after each infertile cycle was confirmed in all virgin females. The endometrium was thickest during the luteal phase, when plasma progesterone peaked and the optical density for prolactin immunoreactivity was strongest. The spiny mouse undergoes spontaneous decidualization, demonstrating for the first-time natural menstruation in a rodent (Bellofiore, 2017, AJOG).

The unprecedented discovery of menstruation in a rodent species suggests that this reproductive feature was overlooked by previous investigators because of the dogma that rodents are not menstruating mammals. There is a need to consider the possibility of other menstruating species. The peripheral position of Acomyinae in most rodent phylogenies suggests a need to broaden phylogenetic analysis of this and related genera.