The Naked Mole Rat presents a oddity in many of its reproductive behaviors when compared to other African Mole Rats.
The breeding female of a colony of
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But perhaps the most interesting part divergence of
The non breeding females and males of a colony of
Non-breeding females have what appear to be prepubescent ovaries and within the ovaries primordial follicles.11 Tests have also shown that non-breeding females have low urinary progestrone and estrogen levels. Ovulation appears to be inhibeted because of inadequete lutenizing hormone being secreted from the anterior pituitary. In tests, secretions of lutenizing hormone have been low or non-existant.12 The levels of the other pituitary gonadotrophin, follicle stimulating hormone, are unknown.
Scientists have theorized that these hormonal differences are caused by an insensitivity to GnRH. When tested, it was shown that the senstivity of GnRH receptors was quite low.13 However GnRH has been shown to be a self-regulating hormone whereby its receptors become more sensitive as more GnRH is released. Researchers showed that periodic injections of GnRH every four hours caused the sensitivity of GnRH receptors to up regulate.14
Furthermore, females who are suppressed are not permanently so. When removed from a colony a female
Between breeding males and non-breeding males there are significant differences in body weight, and there are fewer cells that secrete testosterone in non-breeding males.16 Dissection of the testis have also revealed that non-breeding males have many fewer sperm. In half the testis of a Breeding male 8.6 million sperm were found, while in the non-breeding male only 1.8 million sperm were revealed. Furthermore, the sperm that were found in non-breeding males were non-motile.17
Non-breeders also evince lower urinary testosterone levels, and lower basal levels of lutenizing hormone.18 Exogenous administration of GnRH also had less of an effect upon non-breeding males. However, the testosterone levels in breeding males is variable and closely in sync with the ovarian cycle of the breeding female. The breeding male's testosterone levels peak right during the follicular stage of the ovarian cycle, right before estrus. Thus at different times in the breeding cycle non breeding males will actually have higher levels of lutenizing hormone than the breeding males.19
Finally, like the females, the suppression of sexuality is not permanent, and within five days of being removed from their home colony non-breeding males will undergo hormonal changes so that their levels are equivalent to those of breeding males and their testis will enlarge.20
It is currently unknown what cues are responsible for the morphological and hormonal changes that happen to sexually suppressed mole rats. It was once thought that primer pheromones in the urine of the reproductive might act as chemical cues causing the hormonal changes in the non-breeders. Since the mole rats share a communal bathing area, such cues might be spread to all the members of the colony.21 Furthermore, it was shown that removing the breeding female from physical but not olfactory contact was not enough to maintain the suppression on the non-breeding females in the colony.22 However, other tests with soiled bedding suggested that pheromones in the urine were also not responsible for the hormonal changes.23 Currently researchers hypothesize that direct contact with the female, including harassment may be responsible for the hormonal and behavioral changes. How this would transmit itself through the endocrine system is unknown.24
The only evidence of direct aggressive behavior in mole rats is shoving that happens between the queen and worker mole rats. It is currently unclear what this shoving is for, but there are two dominant theories. One suggests that aggression from the female indicates her reproductive dominance and willingness to fight, reducing the threat of colony members challenging her for breeding status 25. The other hypothesis is that the shoving is aimed at workers who aren't working hard enough, and work activity levels seem to vary inversely with the individuals relatedness to the breeding female. However, studies have not been able to suggest a link between work level and relatedness as predicted by the second hypothesis.26 Large animals, regardless of their relatedness to the female worked less. Furthermore, it was found that workers were more likely to be shoved when already working, rather than when resting in the nest.27 This preliminary evidence would thus suggest that the second hypothesis is incorrect.