Gregory, 1915
General characteristics
The subfamily Cheirogaleinae contains three genera: genus Microcebus, genus Cheirogaleus and genus Allocebus. This taxon, formerly grouped at the same generic level as genus Phaner within the family Cheirogaleidae, can be distinguished clearly by numerous anatomical and etho-ecological characters (Petter et al., 1971) as well by its karyotype (Rumpler and Albignac, 1970).
Cytogenetics
The diploid number of chromosomes for Cheirogaleinae is 66, i.e. 64 autosomes and 2 gonosomes. All autosomes are acrocentric and may be split into pairs of regular decreasing size. The largest chromosomes measure about 12 microns in size. The smallest ones are punctiform and are only a few microns large. The X chromosome is submedian and the Y chromosome is acrocentric punctiform.
The compared cytogenetic studies of the Prosimians made it possible to build a distinctive phylogenetic tree for the Malagasy lemurs, based on the chromosome numbers, which are mostly different (Rumpler et al., 1994). The Cheirogaleinae represent an exception however, because Microcebus murinus, Mirza coquereli, Cheirogaleus major, Cheirogaleus medius and Allocebus trichotis all have 2N = 66 chromosomes (Karyo A. trichotis). So far, the ‘banding’ studies of these different species have not been able to show exact differences between them. The method of ‘digesting DNA’, using ‘restriction enzymes’ have shown that, although very few differences exist between the three genera, they are nevertheless distinguishable by means of this method. In addition, Microcebus murinus has more bands in common with Mirza coquereli, which are not found for Cheirogaleus major. From this it may be deduced that the genus Cheirogaleus was first separated during evolution, followed much later by a separation between M. murinus and M. coquereli. The systematic position of Allocebus within the Cheirogaleinae is much more difficult to define. Although the method, which was used to distinguish between M. murinus and M. coquereli, did not give a definite conclusion, it is supposed that Allocebus is much more related to M. murinus than to C. major.