PHYLOGENETIC ANALYSIS OF G-BANDED KARYOTYPES AMONG THE SOUTH-AMERICANSUBTERRANEAN RODENTS OF THE GENUS CTENOMYS (CAVIOMORPHA, OCTODONTIDAE), WITH SPECIAL REFERENCE TO CHROMOSOMAL EVOLUTION AND SPECIATION
Mo. Ortells, PHYLOGENETIC ANALYSIS OF G-BANDED KARYOTYPES AMONG THE SOUTH-AMERICANSUBTERRANEAN RODENTS OF THE GENUS CTENOMYS (CAVIOMORPHA, OCTODONTIDAE), WITH SPECIAL REFERENCE TO CHROMOSOMAL EVOLUTION AND SPECIATION, Biological Journal of the Linnean Society, 54(1), 1995, pp. 43-70
The chromosomes of subterranean rodents of the South American genus Ct
enomys are highly variable with diploid numbers ranging from 10 to 70.
The phylogenetic relationships of this group have been analysed cladi
stically using G-banded karyotypes as have the chromosomal rearrangeme
nts involved in its karyotypic differentiation. One group, called the
'Corrientes group', has very variable chromosomes but low allozymic an
d morphological differentiation among its members. This group has been
analysed with respect to chromosomal speciation. Using a member of an
other subfamily (Octodontomys gliroides) as an outgroup, the results i
ndicate that karyotypes with low diploid and fundamental numbers are p
lesiomorphic. The range of diploid numbers studied here is between 22
and 70, while the fundamental numbers are between 40 and 86. It was fo
und that the main chromosomal rearrangement that transforms karyotypes
towards higher diploid and fundamental numbers is the acquisition of
new chromosomal material via unknown mechanisms, followed by pericentr
ic inversions that generate new chromosomal arms, centric fusions and
centric fissions. In spite of their low differentiation regarding allo
zymic and morphological features, it was found that the karyomorphs of
the Corrientes group have enough chromosomal differentiation to consi
der them as distinct species. Beside the range of diploid and fundamen
tal numbers of this group (42-70 and and 80-84 respectively), their pa
irwise chromosomal differences are high. The most closely related of t
hem differ in one nonhomologous arm, one Robertsonian change and a who
le chromosome duplication. The most differentiated taxa differ in 20 a
rms with lack of homology, 12 Robertsonian changes (one with monobrach
ial homology), six pericentric inversions and the above mentioned prob
able arm duplication. For these reasons, it is probable that some kind
of chromosomal speciation has occurred in the Corrientes group.