Fruit Bats in Africa

A western Woermann's fruit bat Megaloglossus azagnyi clings to the underside of a palm frond, copyright Jakob Fahr.

The diversity of bats often goes under-appreciated. With over 1200 known species around the world (with new ones continuing to be named on a regular basis), they significantly outnumber any of the other traditionally recognised orders of mammals except the rodents. The basal relationships among the bats have been subject to some disagreement in recent years but it is generally agreed that living bats can be divided between three main lineages, one of which is the Pteropodidae, the fruit bats of the Old World. Pteropodids differ in a number of ways from all other bats, the most notable of which being that they mostly do not use echolocation (some do, but not in the same way as other bats: whereas non-pteropodids use sounds produced by their vocal chords for sonar, echolocating pteropodids click with their tongues or clap their wings). Instead, pteropodids use their over-sized eyes to see their way in the dark. The most familiar pteropodids may be the large flying foxes of the genus Pteropus, but they are not the only members of the family.

Not all pteropodids are as large as the flying foxes, either. Megaloglossus is a genus of one or two species of fruit bat found in lowland rain forests in tropical Africa. They are the smallest of Africa's pteropodids (forearm length is about four centimetres, which I'm guessing translates into a wingspan of about a foot?) and differ from other African pteropodids in their slender faces and long, protrusible tongue (the latter feature, of course, explaining the genus name). For a long time, Megaloglossus was classified with other long-tongued pteropodids in a subfamily Kiodotinae, of which it would have been the only African component. However, Bergmans (1997) reclassified it as part of a uniquely African tribe, the Myonycterini, on the basis of features such as partially webbed toes and a ventral collar of thick hair. The 'kiodotines' are now recognised as a polyphyletic assemblage that have evolved their protrusible tongues convergently, presumably to feed on flower nectar.

Woermann's fruit bat Megaloglossus woermanni being handled on a stick by an interfering human, copyright Natalie Weber.

Until recently, only a single species of Megaloglossus was recognised: Woermann's fruit bat M. woermanni, originally named for a specimen from Gabon. A separate subspecies, M. woermanni prigoginei, has been suggested for larger individuals in the eastern part of the larger country now called Congo but Bergmans (1997) noted that the type specimen of the species fell within the size range for 'prigoginei'. A recent molecular study of Myonycterini by Nesi et al. (2013) identified a genetic divide between specimens from Cameroon, Gabon and the Congos on one hand and Liberia and the Côte d’Ivoire on the other, and the authors proposed recognising the latter as a separate species Megaloglossus azagnyi for which they proposed the somewhat awkward vernacular name of 'western Woermann's fruit bat'. However, M. azagnyi is recognised solely on the basis of genetic distance; no morphological distinction has yet been identified between the populations. Nesi et al. (2013) claimed that specimens of M. azagnyi were generally smaller than M. woermanni, but their reported measurement ranges indicate a broad overlap between the two. Bergmans (1997), who examined a greater number of specimens than Nesi et al., suggested a broad cline of increasing size from the west to the east of Megaloglossus' range but no definite gap. Nesi et al.'s division also leaves the status uncertain of populations in intervening regions such as Nigeria. The distribution of Megaloglossus is divided into two by the 'Dahomey gap', a region of dry coastal savannah in Benin, Togo and Ghana that splits the wetter rainforests on either side. However, as noted by Nesi et al. themselves, palaeontological records indicate that the Dahomey gap has not been consistenly present in the past, and it should not be assumed that it corresponds to the division between M. woermanni and M. azagnyi.

REFERENCES

Bergmans, W. 1997. Taxonomy and biogeography of African fruit bats (Mammalia, Megachiroptera). 5. The genera Lissonycteris Andersen, 1912, Myonycteris Matschie, 1899 and Megaloglossus Pagenstecher, 1885; general remarks and conclusions; annex: key to all species. Beaufortia 47 (2): 11–90.

Nesi, N., B. Kadjo, X. Pourrut, E. Leroy, C. P. Shongo, C. Cruaud & A. Hassanin. 2013. Molecular systematics and phylogeography of the tribe Myonycterini (Mammalia, Pteropodidae) inferred from mitochondrial and nuclear markers. Molecular Phylogenetics and Evolution 66: 126–137.