Do dispersing non-reproductive female Damaraland mole-rats, Cryptomys damarensis (Rodentia: Bathyergidae) exhibit spontaneous or induced ovulation?

Abstract

The Damaraland mole-rat is a eusocial, subterranean rodent that exhibits a seasonal breeding. Non-reproductive females show physiological suppression of reproduction whilst in the confines of the natal colony. This study set out to investigate whether dispersing female Damaraland mole-rats exhibit induced or spontaneous ovulation. Fifteen non-reproductive females were removed from their natal colonies and housed individually for a period of 6 weeks. During this period urine was collected from all animals every second day. After this initial period the animals were divided into 3 groups. Females were subjected to 1 of 3 trials: a control group housed separately without a male, allowed non-physical contact, or placed in direct physical contact with vasectomized males. Urine was collected for a further 5 weeks, and urinary progesterone profiles established. All three groups showed a significant difference in urinary progesterone concentrations between the two treatment periods indicating initiation of follicular development in all animals following removal from the colony. Histological results further revealed that at least one animal in the control group and five of the six animals in the vasectomized group had corpora lutea present in the ovaries showing that ovulation has taken place. All groups had similar numbers of Graafian follicles, indicating that all females were likely to ovulate in the near future. This finding suggests that females are capable of spontaneous ovulation, but the act of coitus may advance the onset of ovulation in this arid dwelling mole-rat. Article Outline

Breeding status and social environment differentially affect the expression of sex steroid receptor and aromatase mRNA in the brain of female Damaraland mole-rats

“…All samples were run in one assay, respectively. The progesterone assay had previously been validated for F. damarensis [18]. The antiserum is highly specific for progesterone with a low cross reactivity to all other naturally occurring steroids except for 20-α-dihydroprogesterone and 11-deoxycortisol with a cross reactivity of 2% and 2.4% respectively.…”

“…This blockade results from an inhibition of ovulation, which is caused by a disruption in the normal GnRH secretion from the hypothalamus [16]. These females start to ovulate spontaneously when removed from the presence of the queen [17,18]. …”

Pattern of ovulation in the East African root rat (Tachyoryctes splendens) from Tanzania: induced or spontaneous ovulator?

“…A characterstic feature of these taxa is that they are either seasonally breeding or ar depemdent on short lived mating encounters. In contrast, the two eusocial species of mole-rat, the Damaraland mole-rat and the naked mole-rat are both spontaneous ovulators and are non seasonal, breeding throughout the year and have regular mating encounters (Faulkes et al 1990;Snyman et al 2006). …”

“…There was no significant difference in progesterone concentration between the extracted and nonextracted pools and as a consequence we used the neat urine to measure native progesterone. The use of non-extracted urine to investigate patterns of ovulation has been succesfully used in other roednet moles (Malherbe et al 2004;Jackson and Bennett 2005;van Sandwyk and Bennett 2005;Snyman et al 2006;Faulkes et al 2010). We spiked the standard curve with 6 samples at a dilution of 1:16 from a pool of urine of low concentration to these 50μL of progesterone in increasing concentrations (0.3, 1.6, 6.4, 31.8, 63.6 and 127.2 nmols/l) whucg were subsequently assayed in dupicate.…”

An Example of Burrow System Architecture of Dispersing Damaraland Mole-Rats

“…Dispersal constitutes the opportunity to escape from social suppression and to subsequently pair with an unrelated male to form a new colony (Jarvis & Bennett 1993). Indeed, experimental removal of those females from the confines of their natal colony in captivity lifts this physiological suppression as evident by the occurrence of spontaneous ovulation (Molteno & Bennett 2000;Snyman et al 2006).…”