Life history traits of free-living bush Karoo rats (Otomys unisulcatus) in the semi-arid Succulent Karoo

Abstract

Life history traits are adaptations to specific environmental conditions but are also phylogenetically constrained. We studied life history traits of free-living bush Karoo rats (Otomys unisulcatus) that are endemic to the semi-arid regions of South Africa. They show behavioural, rather than physiological, adaptations to arid environments, which might affect life history traits compared to their mesophyllic otomyine relatives. We studied the reproduction and lifespan of bush Karoo rats over 2 and a half years. The mean litter size was 1.7 and was not dependent on the month of birth. Males were larger and had higher disappearance rates than females. Age and mass at reproductive maturity did not differ between the sexes. Individuals born earlier (May to July) in the breeding season reached reproductive maturity in the year of their birth, whereas those born later (August to November) reached maturity in the following year. Mass at maturity was dependent on timing of birth; individuals born earlier were lighter than those born later. The growth rate of all males was double that of all females, and male post-weaning growth rates were greater than that of females but not affected by the timing of birth. Lifespan, which was shorter in males than females, was not dependent on timing of birth. Compared to other members of the tribe Otomyini, bush Karoo rats had a slow pace of life, possibly because of the energy constraints in their arid habitat. Litter size, mass at maturity and lifespan are assumed to be phylogenetically constrained in the tribe Otomyini.