Nouvelles données sur la cytogénétique et la spéciation des Leggada (Mammalia-Rodentia-Muridae)

Summary

To the 237 pigmy-mice studies in his previous papers, the author brings new data concerning the cytogenetics of 25 Leggada. One first set of 12 mice from Nigeria belongs to the same polymorphic series containing themusculoides from the Ivory Coast and the Central African Republic.

A small sample from Ippy (Central African Republic), although the individuals are morphologically all alike and referable tomusculoides, shows an amazing diversity: ♂/259.2N=28, N.F.=36, sex chromosomes of the translocated type (TR). We meet here a new robertsonian combination in the polymorphic series, 34/33/32/31 ... 28/... 22/... 19/18.

♀/260.2N=32, N.F.=36, sex chromosomesTR. Both big biarmed autosomes are metacentric — submetacentric with a centromeric index of about 0.25 by the typicalmusculoides having the same diploid number.

♂/261.2N=19, N.F.=36, sex chromosomesX/Y ₁ Y ₂. The first occurrence of such sex chromosomes by the Leggada. By themusculoides from Rhodesia we were dealing with the typeX ₁ X ₂ /Y. ♀/262.2N=18, N.F.=36, sex chromosomesX/X. Very likely the female of ♂/261.

In the complexminutoides-musculoides, we meet many different caryotypes and it is obvious that the chromosomal mutations play here the part of a primary factor of isolation, previous to the gene mutations which later will allow the taxonomic determination of the species actually ‘in statu nascendi’.