Abstract
This study investigated the effects of isolation of subordinate naked mole rats from natal colonies on their reproductive success. Naked mole rat is one of the known mammals that exhibit eusociality. It has been noted that naked mole rats have their reproduction restricted to one queen and less than three males; the rest of the animals within the colony remain sterile. The study aimed at establishing whether the reproductive suppression in subordinate naked mole rats is the outcome of social stress exerted by breeding female in the colony or other unknown environmental factors within the colony set-up. Experimental period was 20 weeks and it involved two stages, acclimatization and isolation. Before acclimation, 2 female subordinate naked mole rats were sacrificed. Blood samples were collected and appropriately preserved for later analysis. On the 2nd, 4th and 6th weeks of acclimatization, 2 female mole rats were sacrificed at each stage and blood samples were harvested for analysis. On week 7, eighteen subordinate females were isolated and randomly assigned into two groups of 9 animals each in two separate cages for 14 weeks. One week 8, 2 subordinate females from each group were randomly selected, sacrificed and blood samples collected for analysis. The same procedure was repeated on week 12 and 20 of study. Hormonal analysis was done using ELISA technique. The Statistical analysis done using student t-test at 95% confidence level and significance level was set at P < 0.05. Results showed increase in cortisol levels only in singly isolated females which were the greatest on week 8 (from 35.5 ng/ml to 123.4 ng/ml). Mean estradiol in singly isolated females was 18 ± 2.52 pg/ml while females paired with males had 19.0 ± 3.0 pg/ml hence no significant difference (paired t = -1.73, P = 0.23). Conclusively, the observed reproductive suppression among subordinate naked mole rats in natal colonies is probably due to presence of queen or other reproductive aspects that may not be directly related to stress.
Highlights
Naked mole rats (Heterocephalus glaber) are found in many parts of Makueni and Kitui Counties, in Kenya
The increase in mean cortisol levels in singly isolated females (SIF) was greatest at the time of isolation from 35.5 ng/ml to 123.4 ng/ml compared to levels between week 8 and week 12, whereby the hormone increased from 123.4 to 130.2 ng/ml
The lower mean serum estradiol levels in female subordinate naked mole rats between day 1 to week 6 compared to the levels measured during isolation period agree with the previous studies [6] where female naked mole rats exhibited increased estradiol and progesterone levels immediately after one month of removal from their colony
Summary
Naked mole rats (Heterocephalus glaber) are found in many parts of Makueni and Kitui Counties, in Kenya. Their reproduction is restricted to one queen and less than three males; the rest of the animals within the colony remain sterile. The factors underlying reproductive inhibition among subordinate female naked mole rats in a natal colony remain obscure. The present study, interfered with the natal colony set up in order to explore the possibility that reproductive suppression on the female subordinate naked mole rats could be a form of stressor that impairs cyclicity, reproductive hormone synthesis and secretion and, reproductive success. The findings of this study would provide the basis for studying variations in reproductive hormones which could be applicable to human beings when exposed to stress and how these contribute to trade-offs with reproduction
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