Researchers have just discovered that mole rats, previously believed to follow a caste system, are actually more similar to cooperative animals such as meerkats. Mole rats aren’t simply born into roles, their behaviors and roles change with age. The findings are in a paper just published in the journal Proceedings of the National Academy of Sciences.
Damaraland mole rats, the species used in the study, are burrowing rodents native to southern Africa. They live in colonies that consist of a breeding queen, a breeding male, and workers. The workers are responsible for tasks such as digging tunnels, finding food, and defending their home. If a mole rat finds food, the food is shared with the entire colony. Damaraland mole rats are one of two known “eusocial” vertebrate species, the other being another mole rat species (naked mole rats). Eusocial animals have high levels of social organization with dedicated cooperative roles. Only one breeding pair reproduces, the rest of the group supports the pair.
Researchers from the Department of Zoology at the University of Cambridge built an artificial tunnel system to study Damaraland mole rats. The tunnels were built in a laboratory based in the Kalahari Desert, the mole rats’ natural habitat. The research team set up multiple colonies and then observed them over the next three years. They tracked individual mole rats to see if their behaviors changed with age or other factors.
The team found that the mole rats didn’t have a true caste system, as had been previously suggested in past studies. Instead, age was a better predictor of behavior, with an increase in cooperative behaviors as the mole rats aged. The mole rats were mostly generalists, performing different roles as needed. This is in contrast to insects such as termites and ants, in which individuals are born into specific roles. In insects, these roles are static. The mole rats showed more flexibility, with roles changing as they aged.
These findings show that true caste systems may have only evolved in eusocial invertebrates. The only known eusocial vertebrates, mole rat species, change roles as they age. Mole rats, previously thought to stay in static roles, are generalists and perform more cooperative duties as they get older. The study provides new insights into mole rat colonies and eusocial behaviors.
Zöttl, M et al. Differences in cooperative behavior among Damaraland mole rats are consequences of an age-related polyethism. Proceedings of the National Academy of Sciences (2016).