Cytosystematics, sex chromosome translocations and speciation in African mole-rats (Bathyergidae: Rodentia)
Date
2008-03
Authors
Deuve, Jane Lynda
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The Bathyergidae are subterranean rodents endemic to Africa south of the Sahara.
They are characterised by divergent diploid numbers that range from 2n=40 in
Fukomys mechowi to 2n=78 in F. damarensis. In spite of this variation there is
limited understanding of the events that shaped the extant karyotypes and in an
attempt to address this, and to shed light on the mode and tempo of chromosomal
evolution in the African mole-rats, a detailed analysis of both the autosomal and sex
chromosome components of the genome was undertaken. In addition to G- and Cbanding,
Heterocephalus glaber (2n=60) flow-sorted painting probes were used to
conduct cross-species chromosome painting among bathyergids. This allowed the
detection of a balanced sex chromosome-autosome translocation in F. mechowi that
involved a complex series of rearrangements requiring fractionation of four H. glaber
autosomes and the subsequent translocation of segments to sex chromosomes and to
the autosomal partners. The fixation of this rare rearrangement has probably been
favoured by the presence of an intercalary heterochromatic block (IHB) that was
detected at the boundary with the translocated autosomal segment. Male meiosis in
Cryptomys, the Fukomys sister clade, was investigated by immunostaining of the
SCP1 and SCP3 proteins involved in the formation of the synaptonemal complex.
This allowed confirmation of a Y-autosome translocation that is shared by C.
hottentotus subspecies. We discuss reduced recombination between Y and X2 that
seems to be heterochromatin dependent in the C hottentotus lineage, and the
implications this holds for the evolution of a meiotic sex chromosome chain such as
has been observed in platypus. By extending cross-species chromosome painting to
Bathyergus janetta, F. damarensis, F. darlingi and Heliophobius argenteocinereus,
homologous chromosomal regions across a total of 11 species/subspecies and an
outgroup were examined using cladistic and bioinformatics approaches. The results
show that Bathyergus, Georychus and Cryptomys are karyotypically highly conserved
in comparison to Heterocephalus, Heliophobius and Fukomys. Fukomys in particular
is characterised by a large number of rearrangements that contrast sharply with the
conservative Cryptomys. The occurrence and fixation of rearrangements in these
species has probably been facilitated by vicariance in combination with life history
traits that are particular to these mammals.
Description
Thesis (PhD (Botany and Zoology))--University of Stellenbosch, 2008.
Keywords
African mole-rats, Cytosystematics, Sex-autosome rearrangements, Dissertations -- Zoology, Theses -- Zoology, Bathyergidae -- Cytogenetics, Bathyergidae -- Speciation, Translocation (Genetics)