Abstract:
In eusocial invertebrates and obligate cooperative breeders, successful reproduction is dependent on assistance from non-breeding
group members. Although naked (Heterocephalus glaber) and Damaraland mole-rats (Fukomys damarensis) are often described as eusocial
and their groups are suggested to resemble those of eusocial insects more closely than groups of any other vertebrate, the extent
to which breeding individuals benefit from the assistance of non-breeding group members is unclear. Here we show that, in wild
Damaraland mole-rats, prospective female breeders usually disperse and settle alone in new burrow systems where they show high
survival rates and remain in good body condition—often for several years—before being joined by males. In contrast to many obligate
cooperative vertebrates, pairs reproduced successfully without non-breeding helpers, and the breeding success of experimentally
formed pairs was similar to that of larger, established groups. Though larger breeding groups recruited slightly more pups than
smaller groups, adult survival was independent of group size and group size had mixed effects on the growth of non-breeders. Our
results suggest that Damaraland mole-rats do not need groups to survive and that cooperative breeding in the species is not obligate
as pairs can—and frequently do—reproduce without the assistance of helpers. While re-emphasizing the importance of ecological
constraints on dispersal in social mole-rats, the mixed effects of group size in our study suggest that indirect benefits accrued through
cooperative behavior may have played a less prominent role in the evolution of mole-rat group-living than previously thought.
