Growth and reproduction in the fruit bat Epomophorus wahlbergi.

Abstract

This study was carried out on the Natal South Coast between 30° 12' S and 30° 19' S, where 1085 Epomophorous wahlbergii were caught by mist-netting, and a captive breeding colony was kept between June 1977 and February 1982. Age determination techniques were developed using three criteria; linear growth measurements to obtain the age of animals prior to the attainment of the growth asymptote, tooth eruption to determine the age of animals prior to the attainment of a full permanent dentition, and tooth wear in combination with birth-pulse timing to obtain the age of animals after the growth asymptote and full permanent dentition had been reached. Stevens asymptotic growth curve, performed on forearm length, eye-nose distance and zygomatic width, observations of tooth eruption in cage born bats and linear regression of tooth height data provided the basis for age predictions. Age structure of the population indicated that the greatest percentage of losses occurred between the 5-10 and 10-15 month age group in both sexes. A maximum ecological longevity of nine years is suggested. A killed sample of 81 males and one live caged male provided the basis for the male reproductive study. Puberty onset occurred at eight months and sexual maturity attainment at 13-17 months. Sperm was present throughout the year and no seasonal variations in testicular or gonadial parameters occurred. However, seasonality was shown in body mass, blood testosterone levels, epaulette hair length, calling and testes position. The unusual and constant presence of spermatocytes/spemlatids in the epididymis cauda was observed and meiotic abnormality suggested as an explanation. Epaulettes have an attractive function for females during the mating period, and calling probably acts as a means of year-round territory maintenance. Lek mating is considered possible and a seasonal change in behaviour during the mating season from male groups to individual callers may occur. Five hundred and fifty three captured and released females and a killed sample of 111 females provided the basis for the female reproductive investigation. Puberty commenced at 2,5 months and sexual maturity was attained at six months. The first proestrus onset took place at a mean age of 5,6 months and first conception at 6,2 months. The species exhibits a seasonally polyoestrous pattern with an extended season. Conceptions occur from May to December, the peak months being May, June and July. Births occur from October to June with the peak birth season in November and December. The majority of females undergo one pregnancy per year terminating in November/December with a small percentage terminating around April. Primordial, primary, secondary and early vesicular follicles were present in the ovary year round. The presence of intermediate and late vesicular follicles however followed a seasonal pattern covering April to November. Increased uterine epithelial height and endometrial gland numbers followed a bimodal pattern. Oestrus can occur in the absence of a male and conception peaks coincided with shortest daylength, lowest rainfall, temperature and humidity. Fruiting and rainfall are suggested as ultimate causes of breeding as the peak in lactation coincided with rainfall and fruiting maxima. A series of timetables showing variations in the timing of the annual reproductive cycle with one and two pregnancies is presented. A precaution against abortion and preparation for a postpartum pregnancy were used to explain the presence of intermediate and late vesicular follicles in the non-luteal ovary at the beginning and end of pregnancy. Ovaries and uterine horns showed a functional dextral dominance although anatomically left and right appear symmetrical. Alternation of ovarian function between left and right may occur in those animals undergoing two annual pregnancies. A localized endometrial reaction may occur but was not confirmed. No transovular migration takes place. The corpus luteum reached maximum size at the beginning of pregnancy and was absent at the end. E. wahlbergi was found not to fit into the usual pattern of autumn conceptions and spring births. The species showed a high fecundity rate for a monotocous species and the gestation period was long for its body size. Parturition, lactation, maternal care and juvenile behaviour were observed in the captive colony. A method for inducing birth, using Prostaglandin E(2) and Oxytocin was applied. Births took place during daylight hours. The labour posture was head down and delivery occurred after three hours of labour. Fetal presentation was head first and placental delivery was delayed until approximately two hours after birth. Placentophagia was observed. The infant is born dorsally furred, with eyes closed and large muzzle, weighing up to 20,3 % of the mother's postpartum mass. Mother/infant behaviour and juvenile behaviour up to flight initiation is described. Competent flight takes place at a mean age of 81,1 days. Milk is higher in carbohydrate content and lower in protein content than previously studied insectivorous bat milk. A correlation is suggested between head first delivery presentation, delay in placental delivery, appearance of the infant at birth and those species which carry their young in flight instead of leaving than behind in a nursery.