Geographical variation of chromosomal number in Alouatta fusca clamitans (Primates, Atelidae)

A variation in the karyotype of Alouatta fusca clamitans from different geo graphical ranges is presented. Blood samples of six captive specimens from different States of Brazil were analyzed. Distinct diploid numbers were fou nd: 2n=52, 2n=45 and 46. The odd number was due to Y-autosome translocation . The comparison of the G-banding patterns with previous published reports of 2n=49 and 50 allowed us to identify Robertsonian rearrangements and peri centric inversions as the most important chromosomal rearrangements involve d in the differentiation of the observed cytotypes. The finding of specific cytotypes associated to different geographical ranges suggests a northern- southern division of Alouatta fusca clamitans, due to a possible reproducti ve isolation between different chromosomal complements. The fixation of suc h rearrangements could have occurred during the existence of the quaternary refuges, when the populations have been disrupted in smaller demes.