Morphological and allozyme variation of Eidolon helvum (Mammalia : Megachiroptera) in the islands of the Gulf of Guinea

Morphological and genetic variation is evaluated among populations of the b at, Eidolon helvum, in the islands of the Gulf of Guinea (Central Africa). The populations from the islands of Bioko, Principe, and Sao Tome do not sh ow significant phenetic differentiation, although a trend towards a reducti on of size is found in the latter two islands. The low genetic distances be tween populations, as well as their values of Wright's fixation indexes, su ggest that gene flow has hampered differentiation on these islands. In cont rast, the population from Annobon, the smallest and farthermost island, sho ws remarkable morphological and genetic differentiation. On the mainland, E . helvum displays unique migratory and dispersal behaviours, but migratory behaviour was not found in any of the island populations. The combination o f selective forces in harsher oceanic environments and restricted gene flow among populations appears to have favoured the high degree of morphologica l differentiation of E. helvum on Annobon. Due to the extended length of th e dry season in Annobon, an earlier achievement of sexual maturity-and cons equently smaller size-may be advantageous in the absence of migration. The differentiation is more marked among females, which also suggests that sele ction may be linked to the reproductive pattern. The population of the isla nd of Annobon is herein described as a new subspecies, Eidolon helvum annob onensis subsp. nov. (C) 2000 The Linnean Society of London.