REPRODUCTIVE CHARACTERISTICS AND GROWTH IN THE EUSOCIAL ZAMBIAN COMMON MOLE-RAT (CRYPTOMYS SP., BATHYERGIDAE)

A large data set on reproduction, growth, and juvenile mortality in ca ptive eusocial Zambian common mole-rats (Cryptomys sp.) has been stati stically evaluated. The gestation length was 98 days (range 84-112 day s). The mean litter size was 2.4 (SD = 0.9; range 1-5; n = 102). Large r litters (4 and 5) were generally rare but rather frequent in two mul tiparous females. The mean neonate weight was 7.9 g (ranging from 5.7 g to 10.7 g) and was negatively correlated with the litter size. The n eonate and suckling mortality was about 34% and was higher in males; s o that the sex ratio (male/female) of sucklings eight weeks after birt h was 0.7:1 (n = 159). The growth within the first 20 weeks of age was linear (at a rate of about 0.27 g/day) and independent of gender, lit ter size or family size. The growth constants calculated according to the Gompertz equation were very low (K = 0.006; n = 17). The predictio n of the aridity hypothesis of eusociality in mole-rats that the first litters born to pairs should grow faster than litters born to establi shed families was not supported by the evaluation of a larger sample s ize. Pregnant and at the same time lactating females restricted their investment to embryos and fetuses but not to sucklings. The growth and developmental rate in Zambian mole-rats seems to be a conservative ra ther than a plastic trait. We may assume (or at least we cannot exclud e) that the slow developmental rate is one of the causes rather than a consequence of (eu)sociality.