What can we deduce about the reproductive condition of spinifex hopping mice (Notomys alexis) from external examination?

Abstract

Field studies often use external examination of the vagina or the swelling of the scrotum to make deductions about the reproductive condition of rodents. In this study we sought to determine what information on reproductive condition could be gained from external examination of the reproductive anatomy of spinifex hopping mice (Notomys alexis) using individuals from a captive colony. Female N. alexis with perforate vaginae had a significantly larger mean uterine mass and larger mean maximum ovarian follicle diameter than non-perforate females. Corpora lutea were recorded in two perforate animals but were not present in females with a ‘pinhole’-size perforate or non-perforate vagina. In male hopping mice scrotal bulge size was unrelated to testes mass, ventral prostate mass or presence/absence of sperm in the cauda epididymides. Males with dark scrotal pigmentation had a significantly smaller mean testes mass than males with light or no pigmentation. However, there was no relationship between scrotal pigmentation and ventral prostate mass or sperm presence in the cauda epididymides. Our study suggests that vaginal perforation is an acceptable indicator of sexual maturity in female hopping mice, but scrotal bulge size and scrotal pigmentation should not be used to predict reproductive condition of males.

Female reproductive suppression in an Australian arid zone rodent, the spinifex hopping mouse

“…The proportion of females with a perforate vagina at pastoral sites was almost 10 times the proportion found in reserve sites. Vaginal perforation correlates with sexual maturity and potential ovulation in laboratory colonies of N. alexis (Berris et al ., 2020) and imperforate females of adult body mass are in anoestrus (Breed & Leigh, 2011; Berris et al ., 2020). There was a high proportion of adult females with non‐perforate vaginae in the high‐density reserve population, despite suitable conditions for breeding at nearby pastoral sites.…”

“…To determine sexual maturity and/or reproductive activity, adult females had their vaginal appearance classified as either perforate, slightly perforate (with a pinhole‐sized opening) or imperforate. Females with a fully perforate vagina were assumed to be sexually mature and/or reproductively active, and adult females with an imperforate or slightly perforate vagina were considered reproductively suppressed (Berris, Breed & Carthew, 2020). To assess whether females were currently breeding, the teats of adult females were examined to determine whether they were extended, and if they were then attempts were made to express milk to determine whether they were currently, or had recently been, lactating.…”