Cytogenetic Characterization of Brown Howler Monkeys, Alouatta guariba clamitans (Atelidae, Platyrrhini): Meiotic Confirmation of an X1X1X2X2X3X3/X1X2X3Y1Y2 Sex Chromosome System

Abstract

For brown howler monkeys (Alouatta guariba clamitans), diploid chromosome numbers varying from 2n = 45 to 2n = 52, with XX/XY, X₁X₁X₂X₂/X₁X₂Y, and X₁X₁X₂X₂X₃X₃/X₁X₂X₃Y₁Y₂ sex chromosome systems have been described by mitotic studies but still await confirmation by meiotic analyses. We analyzed 3 male individuals sampled in the wild (in the municipality of Santa Maria, RS, Brazil) as well as 1 male and 1 female individual in captivity at the São Braz breeding center. Peripheral blood samples and testicular biopsies were taken. We found different diploid numbers for both sexes in somatic cells, 2n = 45,X₁X₂X₃Y₁Y₂ in males and 2n = 46,X₁X₁X₂X₂X₃X₃ in females, with 4 metacentric (9-12), 7 submetacentric (1-6, 8), and 9 acrocentric autosomal chromosome pairs (13-20, 22). X₁ and X₂ were submetacentric chromosomes, while X₃, Y₁, and Y₂ were acrocentric ones. Spermatocyte microspreads were examined for synaptonemal complexes. Pachytene spermatocyte analysis was done to verify the chromosome number and morphologies observed in mitotic karyotypes. Immunodetection was performed using anti-SMC3 and anti-CREST antibodies. The presence of a sex chromosome pentavalent X₁X₂X₃Y₁Y₂ in the males was confirmed by C-banding in metaphase I and by immunodetection in prophase I by the clear identification of 5 centromeres. The G-banded karyotype corresponded to that previously described for A. g. clamitans in the south of Brazil (Curitiba, Parana State, and Blumenau, Santa Catarina State) and for the Misiones Province, Argentina.