Aspects of the biology of the East African root rat, Tachyoryctes splendens (Family: Spalacidae) from Tanzania

Abstract

This thesis investigates a number of aspects of the biology of the East African root rat, Tachyoryctes splendens (Rüppell, 1835) and provides important information currently depauperate in the literature. These aspects include the general burrow architecture with respect to fractal dimension (i.e. exploration efficiency), locomotory activity patterns in relation to specific light cycles, the pattern of reproduction, age structure and population growth characteristics based on craniometrics and body mass data, and genetic population structure based on molecular data. Assessment of burrow architecture revealed higher fractal dimension during the wet compared to the dry season as a consequence of increased soil moisture content promoting efficient excavation. Female burrow systems exhibited greater fractal dimensions than males as a result of increased energy costs for provisioning when female has pup(s). Locomotory activity patterns of the captive East African root rat subjected to different lighting schedules maintained under a constant temperature demonstrated that captive T. splendens displays a higher percentage of activity during the dark than the light phase of all light-dark and dark-light cycles, suggesting that their activity is entrained by light. Under constant darkness, the species concentrated a higher percentage of its activity during subjective night intimating that T. splendens is able to run their activities at the absence of light stimulus (i.e. possesses an endogenous circadian rhythm). An investigation of reproductive biology of the species as determined from post-mortem examination of the gonads and hormone concentrations of specimens collected on a monthly basis in the field revealed a bimodal pattern of reproduction that mirrored the pattern of rainfall. The peaks of both male and female indicators of reproductive markers coincided with peaks of rainfall implying that precipitation is the major factor influencing reproductive activities since rainfall water facilitates the flush of vegetation and enhance food production in the form of forbes, grasses and underground storage organs of geophytes. An assessment of ontogenetic variation and sexual dimorphism based on craniometric data from five relative age classes revealed overall increase in cranial dimensions with increasing age and that males were larger than females from age class 2, a trend that was also reflected in body mass. The molecular results revealed the low genetic distances using cytochrome b (cyt-b) across the sampling range, implying that amongst distinct populations only a single species occurs across the sampled range. The greatest sequence differences at the mitochondrial DNA D-loop was observed both within and among geographically neighbouring populations, while the same haplotypes were sometimes shared across the sampling range that indicate a high molecular diversity within the species.