5.1 Evolution of eusociality in mole-rats  (Page 5/8)

Why shove your colony mates?

Jacobs and Jarvis (1996) looked at shoving in H. glaber , the naked mole-rat, testing a hypothesis that it occurs because of a conflict between a queen and her non-breeding colony members. The work-conflict hypothesis supposes that non-breeders withhold aid because they may become breeders or because it gives them more inclusive fitness, so the queen shoves them to encourage work. The effect of shoving, then, would be an increase in work. The actual results, however, were quite different. They found no relationship between relatedness and shove rate, so the queen shows no kin bias in her shoving. She is however, more likely to shove her larger workers than smaller ones. More importantly, shoving does not increase work rates. In addition, larger colony members work less than smaller members even though they are shoved more often, and non-breeders occasionally shove other non-breeders (Jacobs and Jarvis 1996). The fact that non-breeders shove each other suggests that shoving can be used to assert dominance. The larger workers are likely members of the dispersal caste found by O’Riain et al. (1996) and Braude (2000). The queen shoves them more often because they pose more of a threat to her dominance, and possibly, shoving helps ensure their reproductive suppression.

Kin recognition

In order to maximize inclusive fitness, mole-rats must ensure that their aid is given only to relatives and not to outsiders who exploit them. As a result, they must have some way to identify relatives. As O’Riain and Jarvis (1997) point out, direct determination of relatedness in mole-rats will not work too well since relatedness in colonies is high. It is not surprising, then, that mole-rats identify colony members instead of kin. Colony members are generally highly related, and mole-rats are unlikely to encounter many foreigners inside their burrows. The probable mechanism used by mole-rats to identify foreigners and colony members is odor familiarity (O’Riain and Jarvis 1997). However, in common mole-rats and naked mole-rats, odor familiarity must be continually reinforced. If a mole-rat is removed from its colony for long enough (at least twelve hours), upon reintroduction it is viewed as foreign since it has lost the distinctive scent of the burrow (Burda 1995, O’Riain and Jarvis 1997).

Another result of kin recognition, in naked mole-rats at least, is that patrollers can identify intruders and start an alarm to get rid of them. Colony members want to keep foreign naked mole-rats out of the colony because the intruder reduces their chance at eventually gaining breeding rights (O’Riain and Jarvis 1997), especially given that breeders prefer outbreeding to inbreeding.