Reproduction, seasonal morphology, and juvenile growth in three Malagasy fruit bats

Abstract

The island nation of Madagascar is home to three endemic species of Old World Fruit Bat in the family Pteropodidae: Pteropus rufus, Eidolon dupreanum, and Rousettus madagascariensis, all three of which are IUCN Red Listed under some category of threat. To inform conservation efforts to model population viability for these threatened species, as well understand the mechanisms underpinning persistence of several potentially zoonotic pathogens hosted by these bats, we here define the seasonal limits of a staggered annual birth pulse across the three species. Our field studies in central-eastern Madagascar indicate that this annual birth pulse takes place in September/October for P. rufus, November for E. dupreanum, and December for R. madagascariensis. Juvenile development periods vary across the three Malagasy pteropodids, resulting in near-synchronous weaning of pups for all species in late January-February at the height of the fruiting season for Madagascar, a pattern characteristic of most mammalian frugivores on the island. We here document the size range in morphological traits for the three Malagasy fruit bat species; these traits span the range of those known for pteropodids more broadly, with P. rufus and E. dupreanum among the larger of recorded species and R. madagascariensis among the smaller. All three species demonstrate subtle sexual dimorphism in observed traits with larger-bodied males vs. females. We explore seasonal variation in adult body condition by comparing observed body mass with body mass predicted by forearm length, demonstrating that pregnant females add weight during staggered gestation periods and males lose weight during the nutritionally-deficit Malagasy winter. Finally, we quantify forearm, tibia, and ear length growth rates in juvenile bats, demonstrating both faster growth and more protracted development times for the largest P. rufus species. The longer development period for the already-threatened P. rufus further jeopardizes this species’ conservation status as human hunting of bats for subsistence is particularly detrimental to population viability during reproductive periods. The more extreme seasonal variation in the mass to forearm relationship for P. rufus may also modulate immune function, an important consideration given these bats’ roles as reservoir hosts for several high profile viral families known to cause severe disease in humans. Our work highlights the importance of longitudinal field studies in collecting critical data for mammalian conservation efforts and human public health alike.