Phylogeographic Patterns in Mitochondrial DNA of the Ostrich (Struthio camelus)

Abstract

We assayed restriction-site differences in mitochondrial DNA (mtDNA) within and among populations of the Ostrich (Struthio camelus) throughout much of its African distribution. Little genetic diversity was evident among samples drawn from localities throughout southern Africa (S.c. australis), while deep divisions in the mtDNA gene tree exist between representatives of the eastern (S.c. molybdophanes and S.c. massaicus) and northern African subspecies (S.c. camelus). The low mtDNA variability within australis and the presence of widespread mtDNA genotypes in this subspecies suggest considerable his- torical interconnectedness among populations, either through gene flow and/or recent col- onization from smaller source populations. The strong phylogeographic structuring evident in eastern and northern Africa aligns with the currently accepted subspecies designations. Data indicate that the Ethiopian system of the Great Rift Valley has been effective in disrupting east-west gene flow between molybdophanes and camelus, while ecological differences and behavioral/reproductive cues have contributed to maintaining the genetic and phenotypic discreteness of molybdophanes and massaicus in east Africa. Although contemporary Ostrich populations are effectively divided into southern and northern populations by a belt of Brachystegia woodland, arid-corridor links in the recent evolutionary past appear to have allowed for periodic contact between australis and massaicus populations. Consequently, the development of subspecific differences between these two taxa has occurred within the context of shallow evolutionary separation. Received 28 July 1992, accepted 25 November 1992. THE OSTRICH (Struthio camelus) is currently re- garded as comprising four extant subspecies separated by fairly marked phenotypic differ- ences; a fifth, S.c. syriacus, whose range once reportedly extended into Arabia, is now con- sidered extinct (Brown et al. 1982). As presently understood, the species' natural range is re- stricted to the African continent, generally south of the Sahara. This distribution is disrupted by a belt of Brachystegia (miombo) woodland in south-central Africa (Hamilton 1982) that effec- tively divides the Ostrich into northern and southern populations with the former incor- porating S.c. camelus, S.c. molybdophanes and S. c. rnassaicus, while S.c. australis is confined to