The African mole-rats exhibit the broadest spectrum of social structure of any of the seven families or subfamilies of subterranean rodents. Jarvis, in Advances in the Study of Behavior, 1999 VII SUMMARY Finally, despite their apparent long history of inbreeding, which is expected to have purged recessive deleterious alleles from naked mole-rat populations, inbreeding depression, in the form of greater susceptibility to disease due to low genetic diversity at the individual and colony level (i.e., loss of heterosis), has been observed ( Ross-Gillespie et al., 2007). Presumably, the costs of avoiding inbreeding would be lower than this figure for the Damaraland mole rats, but higher for the naked mole rats. The latter estimate is comparable to our high estimate for the outbred subsocial spiders. In other rodents, as in prairie dogs, no evidence of inbreeding depression on five measures of reproductive success was found ( Hoogland, 1992), while in deer mice a 0.44 depression in percent survival was detected (reviewed in Crnokrak and Roff, 1999). We are not aware of estimates of inbreeding depression in outbred African mole rats. Finally, the much larger litter sizes of the naked mole rat (average 14 pups), which probably coevolved with its social and breeding system, might provide somewhat of a shelter against inbreeding depression (e.g., Stockley and Macdonald, 1998) when compared to a species with much smaller litter sizes, as are the Damaraland mole rats (average three pups). 1) may be more limited in the Damaraland mole rats given their monogamous mating system (i.e., О” N mВ =В О” N fВ в‰…В 1), while multiple males (i.e., О”N fВ <В 1) may be present in naked mole-rat colonies. Additionally, the region of inbreeding tolerance ( Fig. In fact, 8% of Damaraland mole rats achieve reproductive status upon dispersal compared to 0.1% in naked mole rats ( Jarvis and Bennett, 1993), a difference we suspect it is related to the smaller size of their colonies, closer proximity in space, and greater frequency with which Damaraland mole-rat colonies are established. Again, although it is difficult to tease cause and effect apart, that the Damaraland mole rats have maintained the ancestral outbred system of species in their genus may be a result of their larger body size and their apparently greater chances of achieving reproduction upon dispersal. Thus, notwithstanding the findings that a rare disperser morph exists ( Braude, 2000 O'Riain et al., 1996) and that, given a choice, outbreeding is preferred ( Ciszek, 2000), costs of avoiding inbreeding are likely to be close to prohibitive in the naked mole rat or any ancestral species moving into its ecological niche. Further, the fact that their colonies are widely distributed in space ( Jarvis and Bennett, 1993) should make it difficult for dispersing males to locate a foreign nest. up to 41 in the Damaraland mole rats) and primary mode of colony reproduction by budding ( Jarvis et al., 1994 but see Braude, 2000), suggest that naked mole rats would have limited chances for successful independent breeding. 131В g) and poikilothermic nature of the naked mole rats, along with their much larger colony sizes (up to 295 vs. Although it is difficult to tease cause and effect apart, the smaller body size (30 vs.

The species, however, exhibit important differences that may influence their costs of avoiding inbreeding through rejection of related mates and/or dispersal to establish an independent nest. Both species also form long-lived stable colonies with typically a single breeding female and nonbreeding colony members ( Jarvis and Bennett, 1993 Jarvis et al., 1994).

Both species live in extremely arid environments with patchily distributed resources that can only be located during short and unpredictable periods of strong rainfalls when the hard rock soils in which they live soften enough for digging ( Jarvis et al., 1994). In both cases, it is suggested that eusociality may have evolved due to high costs of dispersal, constraints on independent breeding, and benefits of colonial living. Mole rats are of special interest as they have given rise to two eusocial species, one highly inbred-the naked mole rat-and one outbred-the Damaraland mole rat ( Burland et al., 2002 Jarvis et al., 1994 O'Riain and Faulkes, 2008 Reeve et al., 1990). Leticia AvilГ©s, Jessica Purcell, in Advances in the Study of Behavior, 2012 A Mole Rats

G force mole rat