No abstract

Metric features and modular and laminar distributions of intrinsic projections of area 17 were studied in Cebus apella. Anterogradely and retrogradely labeled cell appendages were obtained using both saturated pellets and iontophoretic injections of biocytin into the operculum. Laminar and modular distributions of the labeled processes were analyzed using Nissl counterstaining, and/or cytochrome oxidase and/or NADPH-diaphorase histochemistry. We distinguished three labeled cell types: pyramidal, star pyramidal and stellate cells located in supragranular cortical layers (principally in layers IIIa, IIIb α, IIIb ß and IIIc). Three distinct axon terminal morphologies were found, i.e., Ia, Ib and II located in granular and supragranular layers. Both complete and partial segregation of group I axon terminals relative to the limits of the blobs of V1 were found. The results are compatible with recent evidence of incomplete segregation of visual information flow in V1 of Old and New World primates.

Different kinds of constitutive heterochromatin variation were observed in 72 specimens of Cebus apella, belonging to five distinct subspecies, captured in four geographic regions of South America. One particular chromosome type, affecting pair 19, was found to be exclusive of one subspecies (Cebus apella paraguayanus) and to have a distribution significantly different from that expected at equilibrium. Conversely, some other chromosome polymorphisms were more widespread, with distributions compatible with equilibrium. Other variant types, probably resulting from paracentric inversions involving both heterochromatin and euchromatin, were rarer and restricted to single specimens. Finally, a distinctive chromosome type 11 was found to be exclusive of one subspecies (Cebus apella xanthosternos), where it appeared as a fixed trait.

We analyzed the molecular divergence of 2 separate populations of Cebus apella paraguayanus, recently considered a junior synonym of Cebus cay, and estimated its time of separation from C. apella. Cytochrome b DNA from 23 C. cay from Brazil and 9 from Paraguay showed 24 haplotypes (20 and 4, respectively), accounting for 29 variable sites (19 transitions and 10 transversions), with 40.0%, 26.7%, and 33.0% replacements at first, second, and third codon positions, respectively. Genetic distance between haplotypes averaged 0.5%, with 1.1% between C. cay populations. Phylogenetic reconstructions and median joining separated C. cay from Brazil and Paraguay. Neighbor joining showed C. cay and C. apella as sister groups, although C. cay and C. apella collapsed in maximum parsimony and maximum likelihood topologies. Analysis of molecular variance showed the highest variance component between C. cay populations, and mismatch distribution indicated that this species suffered a recent demographic expansion. Divergence time estimates suggested that the 2 populations of C. cay split in the Pleistocene, a period of repeated glaciation events leading to drastic changes in the vegetation composition of different biomes.