In climatically seasonal habitats, favourable periods for reproduction may be simply determined by large annual changes in temperature or rainfall. In contrast, in climatically less seasonal habitats, reproductive timing may be determined by a wide variety of seasonal factors. Three hypotheses regarding reproductive timing were tested for a fruit bat, Huplonycteris Jischeri Lawrence, by comparing reproductive timing and climate at four moderately seasonal Philippine sites with differing climates. Bats were sampled in five years on Negros Island (9″22′N, 123″l I'E), and in one to four months on four other islands. Flower and fruit abundance was monitored in two years on Negros. In five years on Negros, parturition and lactation coincided with the time of the average dry-wet season transition and early wct season, but did not vary in response to substantial annual variation in the onset of rains. Reproductive timing did not change in response to annual variations in Rower or fruit abundance; lactation coincided with a peak in fruit abundance in one year, but not in a second, and reproductive success appeared to be reduced when lactation coincided with scarce resources. At a second site with a different pattern of rainfall, reproduction was nevertheless synchronous with Negros. Samples from two of the three remaining localities indicate a two- to three-month lag in reproductive events relative to Negros, despite rainfall patterns remarkably similar to that of Negros. All three hypotheses for reproductive timing were rejected. As an alternative, Huplonycteris may evolve timing patterns in response to local seasonal patterns of resource abundance.
Huplonycteris has an eight-month post-implantation delay 'in embryonic development. Six hypotheses on the adaptive significance of this delay in Huplonyrferis were evaluated. Three were rejected, but the data were consistent with the remaining hypotheses: (1) The delay sets the time of parturition at a particular time of year; (2) the delay allows all females to produce young relatively synchronously; and (3) the delay allows females to resorb or abort defective embryos without losing an opportunity for reproduction.