Abstract
BackgroundDifferences among species and among years in reproductive seasonality (the tendency for clusters of events to fall at approximately the same point in each year) and synchrony (amount of clustering of events within a year) have been intensively studied in bats, but are difficult to assess. Here, we use randomization methods with circular statistics to test for synchrony and seasonality of reproduction in three species of nectarivorous megachiropteran bats on Negros Island in the central Philippines.ResultsIn Rousettus amplexicaudatus, estimated dates of birth were both highly synchronous and highly seasonal. In Macroglossus minimus, estimated births were seasonal and significantly clustered within years, but within each year births occurred over a broad period, indicating a low level of synchrony. In Eonycteris spelaea, estimated births were also seasonal and had statistically significant synchrony, with birth periods within years intermediate in synchrony between R. amplexicaudatus and M. minimus. All three species had a similar seasonal pattern, with two birth periods in each year, centered on March or April and August or September. In one species, R. amplexicaudatus, primigravid females (in their first pregnancy) produced their young in June and July, a birth period significantly different in timing from the two birth periods of older adult females. This more conservative pattern of young females may allow higher survival of parents and offspring at cost of a lost reproductive opportunity. There was weak evidence that in some years primigravid females of M. minimus might differ in timing from older adults. There were few significant differences in reproductive timing among different years, and those differences were generally less than two weeks, even during a severe drought in the severe el Niño of 1983.ConclusionThe results suggest that these species follow an obligately seasonal pattern of reproductive timing with very little phenotypic plasticity. The resampling methods were sensitive to differences in timing of under two weeks, in some cases, suggesting that these are useful methods for analyses of seasonality in wild populations of bats.
Highlights
IntroductionDifferences among species and among years in reproductive seasonality (the tendency for clusters of events to fall at approximately the same point in each year) and synchrony (amount of clustering of events within a year) have been intensively studied in bats, but are difficult to assess
Differences among species and among years in reproductive seasonality and synchrony have been intensively studied in bats, but are difficult to assess
If selection favors a pattern of reproductive timing that maximizes fitness, fitness trade-offs from these factors may affect the degree of synchrony and seasonality of reproduction
Summary
Differences among species and among years in reproductive seasonality (the tendency for clusters of events to fall at approximately the same point in each year) and synchrony (amount of clustering of events within a year) have been intensively studied in bats, but are difficult to assess. The selective pressure favoring seasonal reproduction is the reduction in reproductive success during the harsher seasons [2]. If selection favors a pattern of reproductive timing that maximizes fitness, fitness trade-offs from these factors may affect the degree of synchrony and seasonality of reproduction. Seasonal and highly synchronous reproduction should be favored if there is a single, narrow window offering optimum conditions for reproduction [4]. The degree of both synchrony and seasonality may be affected by such factors as temporal peaks in resources, predator satiation, advantages of intra-specific cooperation (e.g., clustering of juveniles for warmth), or intra/interspecific competition. There is a broad range of temporal reproductive strategies among mammals both within and among species [1,2], which may indicate that there are many potential solutions to these trade-offs
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