The 14/15 association as a paradigmatic example of tracing karyotype evolution in New World monkeys

Fluorescence in situ hybridization (FISH), chromosome painting in particular, has been extensively exploited in the phylogenetic reconstruction of primate evolution. Although chromosome painting is a key method to map translocations it is not effective in detecting chromosome inversions which may be up to four times more frequent than other chromosomal rearrangements. BAC-FISH can economically delineate marker order and reveal intrachromosomal rearrangements. However, up to now BAC-FISH has only been rarely used to study the chromosomes of New World monkeys partly due to technical difficulties. In this paper we used BAC-FISH to disentangle the complex evolutionary history of the ancestral 14/15 association in NWMs, beginning from the squirrel monkey (Saimiri boliviensis). To improve the hybridization efficiency of BAC-FISH in NWMs, we “translated” the human BACs into Callithrix jacchus (CJA) BACs, which yielded a much higher hybridization efficiency to other NWM species than human BACs. Our results disclosed 14 synteny blocks in squirrel monkeys, 7 more than with chromosome painting. We then applied a subset of CJA BACs on 6 other NWM species. The comparison of the hybridization pattern of these species contained phylogenetic information to discriminate their evolutionary relationship. Of note, Aotus was found to share an inversion with Callithrix, thus definitely assigning the Aotus genus to Cebidae. The present study can be seen as a paradigmatic approach to investigate the phylogenetics of NWMs by molecular cytogenetics.