Caryotypes de quelques hybrides interspécifiques dePitymys (Mammalia,Rodentia)

Summary The Robertsonian polymorphism ofPitymys subterraneus involves only 1 pair of metacentric autosomes. The crosses of forms with 52, 53 and 54 chromosomes do not show any differences in their reproductive rate. So a single autosome trivalent does not affect the fecondity. Many hybrids have been obtained betweenP. subterraneus (2N=52 or 54) andP. multiplex (2N=48) with 50 or 51 chromosomes, respectively. Even with a heterogenous karyotype they are not entirely sterile. 2 progeny were produced from back-crosses. The 2 parental species seem to result from recent speciation. Only fecondation or embryogenesis occurs in crossingP. duodecimcostatus withP. subterraneus orP. multiplex. The chromosome complement of 1 hybrid embryo ofP. duodecimcostatus (2N=62)×P. multiplex (2N=48) has been studied showing 55 chromosomes.P. duodecimcostatus appears to belong to a more distant evolutionary group.