Age determination in the Cape molerat Georychus capensis

Abstract

An analysis of 92 specimens of Georychus capensis showed them to have a distinct season of birth (October to December) with a maximum of two litters per season. Given this distinct seasonality in breeding, and using the date of capture and the presence or absence of placental scars, the age of non-parous and most nonpregnant females could be determined with an accuracy of about 1,5 months (half the length of the birth period). Six cheek tooth eruption and wear stages were recognized. These, as well as body mass, were significantly positively correlated with age. Tooth characteristics and body mass were therefore used, in conjunction with the date of capture, to determine the age of males and pregnant and multiparous females. The growth characteristics of G. capensis were then investigated: growth in mass appears to continue after reproductive maturity with only a slight levelling off. All body and skull measurements were significantly positively correlated with age (P< 0,001). A semi-log regression model (with age logm transformed) gave the best fit of the data, except in the case of body mass, which was slightly better predicted by a linear model. Skull parameters were generally more strongly correlated with age than was body mass, which in turn was better than linear o body measurements. Lower jaw length, two separate measurements of skull height, and zygomatic width were the individual measurements most strongly correlated with age. No sexual α dimorphism was found in G. capensis.