Summary. The reproductive tracts of 112 female little bulldog bats collected around the onset of a breeding season in the Cauca Valley of Colombia were examined histologically. Of the 88 females with luteinizing/luteinized follicles or new CL, 72 carried tubal ova or uterine blastocysts and 16 were non-pregnant. In 14 of the latter follicle rupture had apparently failed to occur, and the oocyte or a collapsed zona pellucida was found within a luteinizing or luteinized follicle. These structures appeared to be functional because most of the affected bats demonstrated preferential stimulation of the ipsilateral oviduct and/or uterine horn. Two of these animals also had a second, older luteinized follicle which contained the remnants of an oocyte. None of these 14 bats exhibited the uterine modifications thought to be associated with a previous pregnancy or had prominent mammary glands. Such reproductive features were, in contrast, frequently demonstrated by other females in the population. These observations suggest that the luteinization of unruptured follicles may have occurred in prepubertal members of the population and reflect immaturity of the hypothalamopituitary—ovarian axis in these individuals.
J. J. Rasweiler IV
Summary. In nearly all animals from a laboratory breeding colony that were examined (85/86) the right ovary was significantly larger than the left. Although primordial follicles were present in both ovaries, Graafian follicles and CL were noted only in the right ovary. The left ovary usually had a much less prominent intraovarian vascular supply, and it is suggested that this may play a central role in limiting the ability of follicles to grow on that side. Many of the bats examined very soon after the introduction of stud males had well-developed CL, sometimes of 2–3 different ages, and uteri that had probably been subjected to stimulation by luteal hormones. Such observations made on females that had been housed with a stud male only for 24 h indicate that the black mastiff bat is a spontaneous ovulator with a functional luteal phase. It was common to observe an extended period after the introduction of a stud male during which spermatozoa were present in the vaginal smears from a female almost every day. Most of the ovulations that resulted in pregnancies appear to have occurred during this period. Of the 72 bats with CL, 11 possessed 2 or more CL of the same age, indicating that multiple ovulations can sometimes take place. The right ovaries of all females examined during advanced pregnancy had non-atretic, vesicular or Graafian follicles in addition to the CL of pregnancy.
Keywords: black mastiff bat; ovarian asymmetry; ovulation
J. J. Rasweiler IV
Summary. Observations were made on the reproductive biology of black mastiff bats maintained in a laboratory colony. Many of the females were inseminated within 24 h after the introduction of the males, and most exhibited a period of 10–50 days during which spermatozoa were present in their vaginal smears almost every day. The frequency of sperm-positive smears began to fall off around the time of implantation, but some smears taken much later in pregnancy were positive. The extent to which spermatozoa in the smears came from reservoirs in the female tract could not be thoroughly investigated, but evidence was obtained that the females have more than a limited period of oestrus. Female courtship behaviour and new copulations were sometimes observed many days after the start of the breeding activity. Also, histological studies of the reproductive tracts of females which had recently mated revealed that many were not in a periovulatory condition. Intact spermatozoa were usually found in the uterine horns and distal oviducts of preovulatory bats and those carrying tubal ova. Spermatozoa were absent from the oviducts of animals bearing early uterine embryos, and were much less abundant in the uterine horns after the start of implantation. Many of the excess spermatozoa appeared to have been expelled into the upper cervix where phagocytic leucocytes were commonly observed in the lumen. Some sperm components were also taken up by epithelial cells in the oviducts and uterine horns.
J. J. Rasweiler IV
Summary. Female long-tongued bats which had been maintained in sexually segregated groups in captivity for more than 8 months were bred and killed at various intervals between Days 1 and 25 post coitum. Their reproductive tracts were then examined histologically.
In 20 of the 28 bats carrying tubal embryos the remnants of 1–4 other ova were also observed in the oviductal ampullae. These remnants consisted of intact zonae pellucidae containing cellular debris, empty zonae, and/or zona fragments. Since long-tongued bats are monovular, the remnants had apparently been retained in the oviducts from previous, non-fertile reproductive cycles. In 27 of the 31 bats carrying implanting blastocysts, zonae pellucidae probably shed by the embryos had been retained in the oviducts. The remnants of 1–3 ova were also observed in the oviductal ampullae of 22 of the 31 bats carrying uterine blastocysts. In at least 14 of these bats the embryos had by-passed ovum remnants in the oviducts on their way to the uterus. No evidence of such remnants was found in the oviducts of 17 animals with tubal or uterine embryos, although old, as well as new, CL were present in the ovaries.
J. J. RASWEILER iv
The reproductive biology of the neotropical bat, Glossophaga soricina, was investigated histologically using 103 animals removed from an experimental laboratory colony at daily intervals during their cycle, as determined by vaginal smears, or following mating.
The animals were polyoestrous, with 22- to 26-day cycles (mode = 24). Ovulation was spontaneous and was followed by a functional luteal phase, terminated by menstruation. Cyclic changes in the oviducal epithelium were pronounced and included an unusual vacuolation of the secretory cells with material that was PAS-, Alcian blue- and Azure A-(pH 4·5) negative.
One oviduct usually exhibited evidence of preferential stimulation, particularly of the epithelium. Oestrual dilatation of the ampulla was restricted to the side of ovulation. The unilateral oviduct reaction may have resulted from hormones diffusing directly across points of 'fusion' of the ovary with the oviduct and mesosalpinx.
The tubal journey of the single fertilized ovum was prolonged. The blastocyst stage was reached on Days 9 to 10 and loss of the zona pellucida occurred in the oviduct on Days 11 to 12. The ovum entered the uterotubal junction between Days 12 and 14. Degenerating ova and free zonae could not pass the ampullary-isthmic junction. Implantation occurred before Day 15 within the uterotubal junction. The lengthy tubal journey of the ovum is presumably related to the fact that menstruation in this species occurs in close temporal proximity to ovulation.
J. J. Rasweiler IV
Most recent research on early mammalian development has been focused upon a select group of laboratory and farm animals. To a certain extent such a concentration of effort has been healthy, since it has provided us with a detailed understanding of early pregnancy in these species. It must be kept in mind, however, that the resulting picture often may not be representative of events occurring in other mammals. Comparative studies can help us to distinguish between the processes and underlying regulatory mechanisms which are common to many species and those which are restricted to a few. The comparative approach is also valuable because it occasionally draws attention to animals which are more ideally suited than the common experimental species for the investigation of specific problems. The purpose of the present paper is to review some of the major features of early pregnancy in bats, one of the largest but most inadequately studied groups of mammals.
F. QUINTERO H. and J. J. RASWEILER IV
Ovarian function and early development of the embryo was investigated histologically in vampire bats removed at timed intervals after mating from a laboratory colony. Both ovaries were equally functional, but a single ovum only was released at each oestrus. The preovulatory follicle or new CL was in the opposite ovary from the old CL in most bats possessing old CL. Large preovulatory follicles were observed as late as Day 5 (Day 1 = first day of sperm-positive vaginal smears). Early cleavage stages were recorded on Days 3 to 8. Advanced morulae and early blastocysts sometimes lacking zonae pellucidae were observed in the oviducts on Days 15 and 16.
J. J. Rasweiler IV and H. de Bonilla
Summary. Uterine function was assessed histologically in Carollia spp. removed from a laboratory breeding colony. The uteri of periovulatory bats examined on days 1–3 post coitum varied considerably depending upon whether regressing corpora lutea were present. In females lacking such corpora lutea, the endometrium was shallow and proliferative. In most of the bats having regressing corpora lutea, the endometrium was thicker and necrotic portions of the superficial lamina functionalis were being sloughed off with associated bleeding (i.e. in the form of a true menstrual process). The presence of regressing corpora lutea and well-developed endometria in these animals indicated that short-tailed fruit bats are spontaneous ovulators with a functional luteal phase to their cycles. Menstruation was also observed in some females that were not periovulatory, or that lacked regressing corpora lutea. The endometrium was not vascularized by spiral arterioles, but it did contain distinctive granulocytes similar to those observed in catarrhine primates and other menstruating bats. Most endometrial growth occurred after ovulation and, in pregnant animals, was associated with retention of the embryos in the oviducts for approximately 13–16 days. Carollia perspicillata normally produces one young at a time, after a gestation period of about 4 months, and is a seasonal breeder in the wild. Menstruation probably provides this bat with an efficient mechanism for eliminating a well-developed endometrium from its simplex uterus in the event of fertilization failure or early embryonic loss. This may give the female another chance to establish a pregnancy and produce an infant at a reasonably opportune time during the same breeding season.
Keywords: fruit bat; menstruation; reproductive cycle; uterus; Carollia
J. J. Rasweiler IV and N. K. Badwaik
Pregnancy was studied in short-tailed fruit bats, Carollia perspicillata, both maintained in a captive breeding colony and collected from a reproductively synchronized wild population on the island of Trinidad. Gestation periods for captive females that successfully reared their young varied as follows: mated at a regular oestrus during their first year in captivity (105–178 days) (mean ± sd: 145 ± 19 days); mated at a postpartum oestrus during their first year in captivity (110–158 days) (133 ± 16 days); mated during their second year in captivity (113–169 days) (127 ± 12 days); females born and mated in captivity (113–159 days) (119 ± 9 days). Most females in the last group had gestation periods of 113–119 days; this may represent the normal (nondelayed) gestation period for the species. Histological studies established that most of the observed variation in duration of gestation was due to delays occurring after the completion of implantation. It seems likely that stress, rather than age, was responsible for the prolongation of pregnancy in some animals, because this occurred less frequently in both younger and older females. There may be stressful situations in the wild (for example, lack of sufficient food or roosting sites) in which the ability to delay pregnancies would be of considerable adaptive value. Evidence was obtained that under some circumstances Carollia can extend gestation even further. Many wild-caught females successfully gave birth at 160–229 days after being isolated from breeding males in captivity. These had been captured at the time of year when, based upon subsequent histological studies of field collected specimens, most adult females should have been in early pregnancy. The field studies have also provided evidence that females in the wild population exhibit a seasonal prolongation of pregnancy.
N. K. Badwaik, J. J. Rasweiler IV and F. Muradali
Histological and immunocytochemical studies of gravid reproductive tracts obtained from the white-winged vampire bat (Diaemus youngi) and the black mastiff bat (Molossus ater) have established that both species develop unusually invasive trophoblast. This is released by the developing discoidal haemochorial placenta, expresses both cytokeratins and vimentin, and invades the myometrium and adjacent tissues (including the ovaries) via interstitial migration within the walls of maternal blood vessels. Hence, this trophoblast is noteworthy for the extent to which it undergoes an epithelial–mesenchymal transformation. In Molossus, it originates from the cytotrophoblastic shell running along the base of the placenta, is mononuclear, and preferentially invades maternal arterial vessels serving the discoidal placenta. This trophoblast may have a role in dilatation of these vessels when the discoidal placenta becomes functional. In Diaemus, the highly invasive trophoblast appears to originate instead from a layer of syncytiotrophoblast on the periphery of the placenta, is multinucleated, and vigorously invades both arterial and venous vessels. During late pregnancy, it becomes extensively branched and sends attenuated processes around many of the myometrial smooth muscle fibres. In view of its distribution, this trophoblast could have important influences upon myometrial contractility and the function of blood vessels serving the gravid tract. Other aspects of intermediate filament expression in the uteri and placentae of these bats are also noteworthy. Many of the decidual giant cells in Molossus co-express cytokeratins and vimentin, while the syncytiotrophoblast lining the placental labyrinth in Diaemus late in pregnancy expresses little cytokeratin.