Absence of germ cell nests in most adult females and aging-associated depletion of ovarian reserve in northern common mole-rats of genus Fukomys

Abstract The reproductive span of female mammals is largely determined by the size of the ovarian reserve - the number of follicles present in the ovaries. Each follicle contains an oocyte, a female germ cell. The naked mole-rat has been shown to exhibit protracted female fertility, with females being fertile for their entire lifespan, attributed to the large number of primordial follicles and the unusual presence of germ cell nests in adult ovaries – in other mammals, nests were shown to break down and form primordial follicles by early postnatal stages. In this study, we revealed that in closely related African mole-rats of the genus Fukomys , the reproductive span matches the lifespan in approximately half of the females. While the size of the ovarian reserve is similar to that of the naked mole-rat, primarily due to the equally large number of primordial follicles, adult ovaries of the giant mole-rat ( Fukomys mechowii ) are devoid of germ cell nests in most females. In anecdotal observations of adult congeners such as Mashona mole-rat ( Fukomys darlingi ) and Ansell’s mole-rat ( Fukomys anselli ), no germ cell nests were found. Our results also indicate that the ovarian reserve decreases with age and is largely depleted in aged females. In addition, we developed a novel approach of computational quantification of oocytes using histological sections, substantially decreasing the time needed for data analysis while preserving the accuracy of manual quantification.