Assessment of Stress on Serum Estradiol and Cortisol Levels in Female Subordinate Naked Mole Rats Following Isolation from Natal Colony

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.