The Role of Prolactin in Naked Mole-rat Eusociality

James Gilbert, Queen Mary University of London

 

Aims

The evolutionary shifts of organisms from independent living to high levels of cooperation represents some of the most significant events in the history of life on our planet. The evolutionary benefits of sociality are well characterized, yet the underpinning physiological and behavioural mechanisms and adaptations are poorly understood.

Naked mole-rats are among the most social of all mammals, living in large and highly-cooperative groups. Reproduction is monopolized by a single reproductive pair, with the so-called ‘queen’ exhibiting behaviour that suppresses the onset of puberty in other individuals. These non-breeders form an industrious workforce, with >99% never reproducing throughout their long lives (~30 years).

Previous research suggests prolactin may play a role in stimulating cooperate behaviour and maintaining the permanent (but reversible) pre-pubescent state in non-breeding adults. In the first empirical test of this hypothesis, preliminary observations indicate a positive relationship between prolactin and working behaviour, while also hinting that queens may direct aggression towards individuals with low prolactin.

To confirm this result in a statistically-robust dataset, further hormone analysis is now needed. I am seeking funding that would allow me to measure prolactin in urine samples to confirm the preliminary results.

 

Evaluation

Naked mole-rats have a highly unusual social system that features strict reproductive monopolisation by dominant breeders and a highly prosocial, industrious worker group. Understanding how this system emerged and is maintained is of interest to social and evolutionary biologists.  

Through this project, we explored the hypothesis that the peptide hormone prolactin plays an important role in maintaining the non-reproductive worker phenotype. With support from the Bioscientifica Trust, we used ELISA kits to estimate urinary prolactin levels in individuals from multiple naked mole-rat colonies and looked for a relationship between prolactin and individual behaviour. We found variable levels of prolactin in non-breeders, which may represent part of the mechanism of reproductive suppression. We did not find any relationship between prolactin and working behaviour or aggression. This was an interesting finding and was published in 2022.  

We also attempted to reverse the non-reproductive phenotype by administering a prolactin antagonist drug, cabergoline. We saw no physical or behavioural changes during the 8-week administration period and analysis of urine samples showed cabergoline had not reduced prolactin. This was a surprise as cabergoline has successfully suppressed prolactin in many mammals. Although it was interesting to discover that naked mole-rat prolactin was not sensitive to cabergoline, it was disappointing not to be able to document the behaviour and physiology throughout a period of prolactin suppression in non-breeders.

 

Grant awarded: £1,707.00