Chromosomal phylogeny and evolution of the African mole-rats (Bathyergidae)

The subterranean African mole-rats (Family Bathyergidae) show considerable variation in their diploid numbers, but there is limited understanding of the events that shaped the extant karyotypes. Here we investigate chromosomal evolution in specimens representative of six genera and an outgroup species, the cane rat Thryonomys swinderianus, using flow-sorted painting probes isolated from the naked mole-rat, Heterocephalus glaber (2n = 60). A chromosomal phylogeny based on the cladistic analysis of adjacent syntenies detected by cross-species chromosome painting was not consistent with that obtained using DNA sequences due, in large part, to the conserved nature of the Bathyergus, Georychus and Cryptomys karyotypes. In marked contrast, the Fukomys and Heliophobius species showed extensive chromosome reshuffling, permitting their analysis by a computational approach that has conventionally been employed in comparative genomic studies for retrieving phylogenetic information based on DNA sequence or gene order data. Using the multiple genome rearrangements (MGR) algorithm and chromosomal rearrangement data detected among F. damarensis, F. darlingi, F. mechowi and the sister taxa B. janetta and Heliophobius argenteocinereus, cytogenetic support for the monophyly of Fukomys and a sister association for F. darlingi + F. damarensis was retrieved, mirroring the published sequence-based topology. We show that F. damarensis, a lineage adapted to arid and climatically unpredictable environments in Southern Africa, is characterized by a large number of fissions the fixation of which has probably been favoured by environmental factors and/or its particular eusocial structure.