Assessing age related morphological variations of Rousettus aegyptiacus (E. Geoffroy St.-Hilaire, 1810) in Durba, Democratic Republic of Congo, and Ga Mafefe, South Africa

Abstract

Postnatal growth studies give a better understanding of age related characteristics that form an essential part of mammalian research concerned with population demographics, species management and conservation, and disease investigations. For bats, few studies have focused on their postnatal growth patterns, with this reported in about 5% of the over 1400 species. This thesis assessed age determination in Rousettus aegyptiacus (Mammalia: Pteropodidae) of unknown age from two sites in Central and Southern Africa. A large museum collection of R. aegyptiacus from Durba in the Democratic Republic of Congo was used to examine and relate non-invasive methods that are applicable in field and museum situations, to a destructive, albeit reportedly more accurate, ageing method. The non-destructive methods included linear morphological measurements, cranial bone and dental development (Chapter 2), and micro computed tomography (μCT) scanning, a method not previously studied on Pteropodids, whilst the destructive method was dental cementum annuli ageing (Chapter 3). Five growth development stages based on cranial suture fusion and degree of second molar eruption were related to morphological measurements of forearm length (FAL), total skull length (TSL) and mastoid breadth (MB). The measurements showed a positive linear growth pattern in relation to the development stages, where smaller individuals were associated with the younger stages 1, 2 and 3, and larger individuals with the older stages 4 and 5. Cementum annuli ages for some of the measured individuals identified that smaller, younger bats (stages 1, 2, and 3) were less than two years old and larger, older individuals (stages 4 and 5) were aged two to ten years old. Of the skull and μCT variables assessed, liner modelling outputs gave the closest age predictions to cementum annuli age when using skull mass (Chapter 3). Information on morphological measurements (FAL, head length-HL and ear to ear width-EEW), epiphyseal fusion and reproductive characteristics was further collected from live R. aegyptiacus individuals of the same subspecies (R. a. leachii) as the DRC population, at Ga Mafefe in South Africa as part of a broader disease study. Relating the morphological measurements to the characteristics revealed that no older individuals in the two or more-year age range had unfused epiphysis. In comparison, no younger individuals in the age range of less than two years were scrotal, pregnant or had previously been pregnant. This investigation of age-related morphological variation in R. aegyptiacus linked age obtained from a destructive method (cementum annuli) to identify non-destructive linear measurements (FAL, TSL), skull mass and μCT-derived markers (sutura sagittalis and skull volume) that can be used in age determination. Given the importance of age determination in conservation and disease studies of bats, this knowledge can be applied in field and museum situations to estimate R. aegyptiacus age with quantitative inference.