Phylogeography of the southern African vlei rat, Otomys irroratus, inferred from chromosomal and DNA sequence data

[摘要] ENGLISH ABSTRACT: This study examines the phylogeography of the southern African vlei rat, Otomysirroratus using the mtDNA cyt b gene and chromosomal data derived using G-, and C-banding,Ag-NOR staining and fluorescence in situ hybridization (FISH using flow sorts of Myotomysunisulcatus). A total of N = 102 specimens were used from the Western Cape, Eastern Cape,Northern Cape, Free State, Mpumalanga and KwaZulu-Natal provinces of South Africa. Of theN = 102, N = 55 comprised fresh material while N = 47 comprises museum material obtainedfrom the Durban Natural Science Museum of South Africa.Cytogentic analysis of N = 55 specimens collected from seven localities in South Africarevealed intra-specific variation resulting from two rearrangements, namely pericentric inversionsand heterochromatin variation. Of the 55 specimens that were analyzed 47% containedinversions or centromeric shifts on four autosomes (OIR1, OIR4, OIR6 and OIR10) which werepresent singly in specimens (i.e. none of the specimens contained all four inversionsconcurrently). These inversions were present in both homozygous and heterozygous state over awide geographic range suggesting that they are floating polymorphisms. Given the potential roleof inversions in post-mating isolation (through production of aneuploid gametes), the prevalenceof inversions as floating polymorphisms in the vlei rats suggest that they are probably retained inthe population through suppression of recombination in the inverted regions of the chromosomes.In addition, differences between populations is due to the presence or absence of heterochromaticarms (and not inversions), which cause variation in the NFa (40 – 49) and supernumerary Bchromosomes, resulting in the variation in diploid number (2n = 28 – 32). Analysis of N = 55specimens revealed Ag-NORs on 7 autosomal pairs 1, 2, 5, 7, 8 and 9 proximal to the centromereon the short arm of the chromosome. Pair 8 also displayed Ag-NOR at the distal end of the longarm of the chromosome in individuals from the Free State province. Pair 3 showed two Ag-NORs occurring proximal to the centromere on the short arm and on the terminal end of the longarm, respectively.I obtained 953bp of mtDNA cyt b from fresh material and 400bp from museum material.Using maximum parsimony and Bayesian inference two main clades were retrieved. Clade Aspecimens occur mainly in the Western and Eastern Cape provinces of South Africa. Clade Bspecimens occur in the Eastern Cape, Free State, KwaZulu-Natal, Northern Cape andMpumalanga provinces of South Africa. The mean sequence divergence between the main clades(A and B) is 7.0% and between sub-clades comprising clade B is 4.8%, while within clade A thesequence divergence was 1.91%. Nested clade analysis revealed allopatric fragmentation withinO. irroratus. Chromosomal characters also support the two evolutionary lineages as clade A haspericentric inversions which occur as floating polymorphisms which are absent in clade B. CladeB in turn is fixed for a complex tandem fusion rearrangement which is absent from clade A.Divergence date estimates indicate that the two clades separated around 1.1 MYA, whichcoincides with climate changes since the late Pliocene/Pleistocene epochs. Cladogenesis withinthis species complex could therefore have been influenced by habitat fragmentation. A fulltaxonomic review of O. irroratus is therefore warranted by this study.

[发布机构] Stellenbosch University