Differential growth patterns between successive litters of the eusocial Damaraland mole-rat, Cryptomys damarensis, from Namibia



Differential mean rates of growth were calculated for successive litters of mole-rats born to genetically unrelated pairs of C. damarensis. The Logistic equation provided the closest fit to the growth data.

Both intra- and inter-colonial variation in mean maximum growth rate between successive litters incorporated into the natal colonies were determined.

The mean asymptote (A), growth rate constant (K) and inflection time (I) were modelled for the first five litters of pups born to pairs of mole-rats. Inter-colonial analysis of recruitment to colonies revealed litters 1, 2, and 5 to grow faster than litters 3 and 4. Litters 1 and 2 had significantly higher asymptotes and inflection times than litters 3, 4, and 5 (P < 0.001). All litters were assimilated into their natal colonies. There were no significant differences between males and females for the asymptote, growth rate constant, or inflection time (P < 0.05).

Intra-colonial variation of litters 1 to 4 born to a single colony revealed comparable results to that obtained for inter-colonial comparisons. Multiple comparisons showed litters 1 and 2 to have a significantly higher absolute growth rate than litters 3 and 4. The lowest rate of growth being for litter 4.

The patterns of mean differential growth are discussed in the light of the social organization of the colony. It is postulated that growth rates in litters 1, 2, and 3 are more rigid since they constitute the main functional unit of colony organization. Litters 4 and 5 show a greater plasticity in growth; it is speculated that these colony members become incorporated into the various worker and defender groupings which are characteristic of C. damarensis colonies.