5.1 Evolution of eusociality in mole-rats

Author: Sheena Shah-Simpson

Introduction

Mole-rats (family Bathyergidae) are a type of rodent found in Africa. They live underground in burrows made up of different chambers for their nests, latrines, food storage areas, alongside chambers for foraging, in which they dig with their incisors and foreclaws. They eat roots, tubers, and bulbs. Most species of mole-rat are solitary, coming together only for mating. A few species, though, form colonies where many mole-rats live together in large complex burrows they have dug because it makes it easier to gather food and reduces predation risks.

Of the species that live in colonies, eusociality has evolved independently at least twice, in Heterocephalus glaber , the naked mole-rat ( [link] ), and separately in Cryptomys damarensis , the Damaraland mole-rat (Allard and Honeycutt 1992, Jarvis and Bennett 1993, Walton et al. 2000, Faulkes et al. 2004). Colonies in both species have three morphologically distinct castes. The first caste is made up of the breeders, usually one female “queen” and her one to three mates, who breed and encourage the workers in their daily tasks. The second caste is formed by the workers, usually mole-rats who are highly related to the queen. These workers are reproductively suppressed by their own hormones that are secreted due to social cues from the queen, keeping them working instead of reproducing. They take care of the offspring, forage for food, and patrol the burrows. The final caste is the dispersal caste, made up of mole-rats of a slightly larger build who act as workers until they leave the colony to either found or join another. The dispersal caste is virtually the only form of gene flow in these mole-rat populations since the colonies are usually separated by a large distance that is dangerous for mole-rats to cross above ground.