Litter sizes and mammary numbers of naked mole-rats: Breaking the one-halfrule

Among mammals generally and rodents particularly mean litter sizes usually are about one-half the number of mammae, and maximum litter sizes approxima te mammary numbers. Naked mole-rats (Heterocephalus glaber: Bathyergidae) a re exceptions to both generalizations. Field-caught Litters averaged 11.3 y oung +/- 6.2 SD (n = 82), and captive-born Litters averaged 11.4 +/- 5.6 yo ung (n = 190). Similarly, numbers of mammae on breeding females averaged 11 .6 +/- 1.1 (n = 43) in the field and 11.5 +/- 2.0 (n = 29) in captivity. Ma ximum litter sizes were 28 in the held and 27 in captivity, whereas the max imum number of mammae was 15. More than one-half of field-caught and captiv e males and females had different numbers of mammae on the two sides of the ir body. Neither total numbers of mammae nor fluctuating asymmetries in mam mary numbers differed significantly between males and females, nor between breeders and nonbreeders. There was no relationship between litter sizes an d numbers of mammae or fluctuating asymmetries in mammary numbers. Breeding female naked mole-rats can bear and successfully rear litters that are far more numerous than their mammae because, on a proximate level, young take turns nursing from the same mammary and, on an ultimate level, breeding fem ales are fed and protected by colony mates, enabling them to concentrate th eir reproductive efforts on gestation and lactation.