DNA evidence on the phylogenetic systematics of New World monkeys: support for the sister-grouping of Cebus and Saimiri from two unlinked nuclear genes.

Previous inferences from epsilon-globin gene sequences on cladistic relationships among the 16 extant genera of Ceboidea (the New World monkeys) were tested by strength of grouping and bootstrap values for the clades in the most parsimonious trees found: for this epsilon data set enlarged with additional Cebus and Saimiri orthologues; for another nuclear DNA sequence data set consisting of IRBP (interstitial retinol-binding protein gene) intron 1 orthologues; and for tandemly combined epsilon and IRBP sequences. Different ceboid species of the same genus always grouped strongly together as demonstrated by results on Cebus (capuchin monkeys), Saimiri (squirrel monkeys), Callicebus (titi monkeys), Aotus (night monkeys), Ateles (spider monkeys), and Alouatta (howler monkeys). Other strong groupings that could be represented as monophyletic taxa in a cladistic classification were: Cebuella (pygmy marmoset) and Callithrix (marmoset) into subtribe Callitrichina; Callitrichina, Callimico (Goeldi's monkey), Leontopithecus (lion tamarin), and Saguinus (tamarin) into subfamily Callitrichinae; Callitrichinae, Aotus, Cebus, and Saimiri into family Cebidae; Cacajao (uakari monkey) and Chiropotes (saki) into subtribe Chiropotina; Chiropotina and Pithecia (bearded saki) into tribe Pitheciini; Pitheciini and Callicebus into subfamily Pitheciinae; Brachyteles (woolly spider monkey), Lagothrix (woolly monkey), and Ateles into tribe Atelini; and Atelini and Alouatta into subfamily Atelinae. In addition the epsilon and IRBP results congruently grouped (but at lesser strengths) Brachyteles and Lagothrix into subtribe Brachytelina within Atelini, and also Cebus and Saimiri into subfamily Cebinae within Cebidae. Because the IRBP results weakly grouped Pitheciinae with Cebidae, whereas the epsilon results weakly grouped Pitheciinae with Atelinae, the present evidence is best represented in an interim cladistic classification of ceboids by dividing the superfamily Ceboidea into three families: Atelidae, Pitheciidae, and Cebidae.