Delayed development in Fischer's pygmy fruit bat, Haplonycteris fischeri, in the Philippines

Abstract

Summary. A long delay in post-implantation embryonic development was detected in Fischer's pygmy fruit bats (palaeotropical fruit bats of the suborder Megachiroptera), the first time such a delay has been demonstrated outside the bat suborder Microchiroptera. Samples of bats were obtained from the Philippines over 5 years, and reproductive tracts were preserved and examined using standard histological techniques. Most parous female pygmy bats were impregnated in June, within a few weeks of parturition, and the embryos underwent superficial implantation at the anterior end of the uterus contralateral to the previously gravid uterus. Shortly thereafter, the rate of embryonic growth slowed tremendously for up to 8 months. During the period of delay, the mean length of the embryoblast increased only from 280 \g=m\m to 520 \g=m\m. In March of the following year, the developmental rate increased, and the embryos completed development in the next 3 months. The 8-month delay gives these bats a gestation period of 11\m=.\5 months, the longest known in bats. Most nulliparous females become pregnant at an age of 3\p=n-\5months, and their embryos entered a similar delay that terminated in March or April, after 2\p=n-\6months of delay. Males showed signs of fertility throughout the entire year, but testis volume was highest during May, June and July, at about the time when most females become receptive.

Embryonic diapause: development on hold

“…In rodents and in many other mammalian species (Table 1), the embryo is arrested at the blastocyst stage for variant intervals that are specific to the species and to the environmental conditions. A similar strategy known as delayed development is found in bats, whereby the blastocyst implants superficially, then grows very slowly, re-sulting in long and variable gestation lengths (Heideman, 1989). Although there are some detracting hypotheses, the consensus view of the significance of embryonic diapause as an evolutionary strategy is that it allows the uncoupling of fertilization from birth, thereby ensuring that postnatal development occurs under the most favorable environmental conditions for survival of the offspring (Lindenfors et al, 2003).…”

Formation of reticulated endoderm, Reichert's membrane, and amniogenesis in blastocysts of captive-bred, short-tailed fruit bats,Carollia perspicillata

“…envelopment had been reported for another microchiropteran bat (Glossophaga soricina; Rasweiler, 1974) belonging to the same family and for a megachiropteran bat (Haplonycteris fischeri; Heideman, 1989). It also may occur in the vampire bat (Desmodus rotundus), where it was identified as precociously formed extraembryonic mesoderm (Wimsatt, 1954), the disc-winged bat (Thyroptera tricolor; Wimsatt and Enders, 1980), and several other megachiropterans (Selenka, 1892;Kohlbrugge, 1913;Keibel, 1922;Moghe, 1956).…”

Social structure of a polygynous tent‐making bat,Cynopterus sphinx(Megachiroptera)

“…Why should harem maintenance be a year-round endeavor if opportunites for mating are limited to such sharply defined periods of the annual cycle? One possible explanation is that mating activity is spread over an extended period, so the highly synchronous timing of parturition could be achieved via sperm storage, delayed implantation, or post-implantational delays in embryonic development (Heidemann, 1988(Heidemann, , 1989Heideman, Cummings & Heaney, 1993;Kofron, 1997;Heideman & Powell, 1998). However, seasonally bimodal peaks in spermatogenic activity in males (Krishna & Dominic, 1984;Sandhu, 1988) and the timing of conceptions in females (Krishna & Dominic, 1983;Sandhu, 1984) indicate well-defined periods of mating for C. sphinx in peninsular India.…”