Partial support for the classical ring species hypothesis in the Chaerephon pumilus species complex (Chiroptera: Molossidae) from southeastern Africa and western Indian Ocean islands

We examined phylogenetic and phylogeographic relationships (cyt b, control region, Rag2) among members of the Chaerephon pumilus species complex from islands in the western Indian Ocean, and eastern and southeastern Africa. The sampling also includes material from the topotype of C. naivashae, holotypes of C. elphicki and C. langi, and syntypes of C. limbatus, all considered junior synonyms of C. pumilus. We found that the nominate C. pumilus sensu stricto (s.s.) from Massawa, Eritrea, is specifically distinct from the following taxa/samples, all of which form part of the C. pumilus species complex defined by Goodman et al. (2010):C. pumilus from southeastern Africa, the syntype of C. limbatus, the holotypes of C. elphicki and C. langi, and the topotype of C. naivashae. The conclusions relating to the type material are based on only 57 informative sites present within the 206 nucleotides of cytochrome b sequence obtainable. Chaerephon pumilus s.s. (Eritrea and Yemen) diverged from the other members of the C. pumilus species complex about 6.24 million years ago (MYA); Chaerephon atsinanana diverged approximately 5.01 MYA from a well-supported but unresolved clade comprising subclades, which appear to have arisen between 0.88 and 2.39 MYA and include: C. pusillus (Comoros and Aldabra); C. leucogaster (western Madagascar, Pemba, Zanzibar, Comoros); C. pumilus s.l. (southeastern Africa); and C. pumilus s.l. (Tanzania). There is evidence of introgression of both C. pusillus and C. pumilus s.l. (southeastern Africa) mitochondrial control region haplotypes into C. leucogaster. Clade B1 (network 7) of the C. pumilus species complex has several attributes of a ring species, but appears to differ from this model in several aspects. We propose that a source population on mainland Africa may have migrated in two directions across the Mozambique Channel, a potential barrier to gene flow, differentiating into C. pusillus on the Comoros and into C. leucogaster on Madagascar. Chaerephon leucogaster may then have migrated to the Comoros, where it occurs in sympatry with C. pusillus, completing the ring. In support of the hypothesis, there is evidence of isolation by distance around the ring, although there is also a relatively high degree of genetic structure and limited gene flow. It appears that the island-based component species may have differentiated in allopatry, with some gene flow by over water dispersal, whereas the African mainland species may have differentiated through isolation by distance.