Naked Mole-Rats or How I Learned to Stop Reproducing and Love the Queen

Apologies to those who took ecology last semester, but I love these creatures and refuse to shut up about them. Naked mole-rats (and their closely related cousins, Damaraland mole rats) are the only examples of eusociality in the mammalian world. Eusociality is a level of social organization defined by Wilson as having three features: reproductive division of labor, overlapping generations and cooperative care of young. Although eusocial organization is commonly associated with order Hymentopera, these  two mammalian species have been described.

Just like bees and ants, naked mole-rats form colonies underground, and most naked mole-rats are non-reproductive workers. There’s one queen who is physically larger and reproductive, while the other mole-rats perform tasks like guarding and digging.

Naked Mole-Rat

Cute little gal, huh?

The existence of these highly eusocial mammals suggests that kin selection alone cannot explain the evolution of eusociality, as naked-mole rats are not haplodiploid. Why would an individual naked mole-rat give up all attempts to reproduce and pass on its own genetic lineage when it’s at very best only 50% related to its brothers and sisters?

Close study of naked mole-rats reveals intriguing facts about their social structure and biology. First, naked mole-rats are physiologically sterile – the females’ vaginas are imperforate – due to urinary chemosignals during development, suggesting a form of social reproductive suppression that has some similarity to other rodent social structures. The suppression is not permanent, however:  the death or removal of a queen will result in females  quickly regaining reproductivity in as little as two weeks (1)

In fact, the flexibility underlying a seemingly rigid and unforgiving social structure provides clues for its evolution.  Based upon observational study, researchers developed a model that suggests that eusociality in the mole-rats came about due to ecological stress, and that such eusociality evoled independently in the Damaraland mole-rats and naked mole-rats. Faulkes et al. measured the genetic relatedness of the many species of mole-rats using 12s rRNA homology, then scored the habitat of each species against factors that could drive the species towards reproductive skew such as aridity and food density. They found that the highest levels of reproductive skew – eusociality – correlated with extreme aridity and paucity of food – essentially, the reproductive success of the individual is increased even if it does not reproduce (after all, some genes are shared between it and its fellow workers) (2).

Naked mole-rats also provide evidence for how social organization is regulated neurologically. Species of voles that are solitary or social have different levels of oxytocin receptors in different areas of their brains, and have for a long time been used as model animals for understanding social behavior. Last year, a study was published in the Journal of Comparative Neurology that showed that naked mole-rats show similar patterns of oxytocin receptor sites as social voles – suggesting that oxytocin is a major regulator of social organization in rodents (3).

Did I mention that naked mole-rats don’t feel pain (or at least show a normal response to pain agonists like capsaicin) and resist cancer (4,5)? They’re pretty cool animals! Reed has a great website on them if you’re interested (6). Given that their range is limited to Ethiopia and the Horn of Africa, however, they might be a bit too far away to observe this semester.

(1) Faulkes, C. G., D. H. Abbot, J. U. M. Jarvis. 1990. Social suppression of ovarian cyclicity in captive and wild colonies of naked mole-rats, Heterocephalus glaber. J. Reprod. Fert. 88:559-568.

(2) Faulkes, C. G., N. C. Bennett, M. W. Bruford, H. P. O’Brien, G. H. Aguilar and J. U. M. Jarvis. 1997. Ecological constraints drive social evolution in the African mole-rats. Proc. R. Soc. B 246:1619-1627.

(3)Kalamatianos T., C. G. Faulkes, M. K. Oosthuizen, R. Poorun, N. C. Bennett, C. W. Coen. 2010. Telencephalic Binding Sites for Oxytocin and Social Organization: A Comparative Study of Eusocial Naked
Mole-Rats and Solitary Cape Mole-Rats. J. Comp. Neurol. 518:1792-1813.




Published in: on January 28, 2011 at 11:23 pm  Comments (2)  

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    • I could not hit approve fast enough

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