Is the highveld mole‐rat Cryptomys hottentotus pretoriae (Rodentia: Bathyergidae) an induced or spontaneous ovulator?

Abstract

The highveld mole-rat Cryptomys hottentotus pretoriae is a social subterranean rodent that exhibits seasonal reproduction. Non-reproductive females remain anovulatory whilst in the confines of the natal colony. However, during the southern hemisphere summer, dispersal of non-reproductive females from the natal colony occurs with subsequent pairing with unrelated males. This study investigates whether the dispersing female highveld mole-rat is an induced or spontaneous ovulator. Eight non-reproductive females were removed from their natal colonies during the breeding season and housed individually for 5 weeks. Urine was collected every second day during the next 5 weeks of isolation. After this initial period, isolated females underwent one of three trials: two females were kept isolated without a male, three females were individually placed in chemical but not physical contact with unvasectomized males, while each of the remaining three females were allowed full contact with a vasectomized male. Urine was again collected every second day for a further 5 weeks, after which the females were killed. Both urinary progesterone profiles and histology of the ovaries revealed that the female highveld mole-rat is an induced ovulator. Females in physical contact with vasectomized males exhibited a significant increase in urinary progesterone concentration as well as the presence of corpora lutea in their ovaries, both indicative of ovulation. The act of coitus is necessary for ovulation to take place even though the males were not capable of fertilization. This is the first time induced ovulation has been shown in bathyergid rodents.

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

“…The two sexes from this species meet very briefly for procreation. It has been speculated upon that the common mole-rat, Cryptomys hottentotus hottentotus [31] may be an induced ovulator, while studies on the highveld mole-rat, C. hottentotus pretoriae and the Natal mole-rat, C. hottentotus natalensis, have revealed that females tend to undergo induced ovulation [6] and [7]. In marked contrast, the naked mole-rat is a spontaneous ovulator [8].…”

“…In social, seasonally breeding bathyergids occurring in environments where rainfall is predictable, dispersing females of the highveld mole-rat, Cryptomys hottentotus pretoriae [6] and Natal mole-rat, Cryptomys hottentotus natalensis [7] also exhibit induced ovulation. This is in marked contrast to the eusocial naked mole-rat, Heterocephalus glaberwhich occurs in ecologically constrained environments where rainfall often fails or is sporadic and spontaneous ovulation is the modus operandi [8].…”

Plasticity and constraints on social evolution in African mole-rats: ultimate and proximate factors

“…Thus, strong selective pressure for both seasonal reproduction and induced ovulation, where mating triggers ovulation, reducing the latency from pairing to conception, has led to the evolution of these traits in solitary species of mole-rats inhabiting regions with a predictable and seasonal rainfall (Georychus and Bathyergus) [38,40,68 -70]. This is mirrored in Cryptomys, where induced ovulation occurs in the cooperatively breeding highveld mole-rat, Cryptomys hottentotus pretoriae, and the Natal mole-rat, Cryptomys hottentotus natalensis [71,72]. A common characteristic of these species, apart from the Natal mole-rat, is that they are all either seasonally breeding and or dependable on regular and predictable but short lived mating opportunities.…”

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

“…Indeed, in the tuco tucos, the presence of spines may also facilitate lock during mating and the removal of copulatory plugs, thus facilitating sperm competition (Ramm, Parker and Stockley 2005). Induced ovulation has been found in both solitary and cooperatively breeding species (van Sandwyk and Bennett, 2005, Malherbe et al 2004and Jackson and Bennett, 2005. A characterstic feature of these taxa is that they are either seasonally breeding or ar depemdent on short lived mating encounters.…”

“…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.…”