Evaluation of Maternal Features as Indicators of Asynchronous Embryonic Development in Miniopterus natalensis

The timing of early reproductive events for the Natal long-fingered bat, Miniopterus natalensis, was examined during its breeding season (August to December) in its maternity roost at the De Hoop Nature Reserve (South Africa). This migrating species is monoestrous with copulation occurring around April in South African populations. Embryonic development is stalled during hibernation by delayed implantation of the blastocyst. As a result, limb bud stage embryos (CS13) are first noted in other South African populations in mid-September. The timing of these reproductive events for the De Hoop population is similar with bats arriving at the maternity roosts in September and embryos at the limb bud stage (CS13) being noted in this month. Pregnancy was not synchronous in the population with bats dissected on the same day exhibiting differences in the stage of development of their young (CS11 to CS21 being the largest range). Maternal features (progesterone concentration, body mass and abdominal distension) were analysed to determine if they provided a reliable estimate of embryonic stage. The progesterone concentrations of pregnant bats showed a similar profile to the Kwa-Zulu Natal and the Eastern Cape populations. Though progesterone concentration did increase as pregnancy progressed, it was not an accurate predictor of embryonic stage. Maternal body mass did not correlate with the stage of embryonic development. However, abdominal distension determined by palpation is an accurate field based predictor of the stages of pregnancy: no abdominal distension, small to medium abdominal distension and large abdominal distension distinguished between non-pregnant bats and those carrying either early (CS11–CS15) or mid-developmental stages (CS16–CS21), respectively.