Absence of Blood Chimerism in Twin Goeldi's Monkeys (<i>Callimico goeldii</i>): Implications for Interpreting Callitrichid Phylogeny

Goeldi's monkey (Callimico goeldii, the lone species in this genus) shows an array of characteristics that are typical for both New World primate families, the Cebidae and the Callitrichidae, and as such their taxonomic classification has remained in question. Based on DNA, the genus Callimico is regarded as a member of the monophyletic group of clawed New World monkeys (Callitrichidae). Callitrichids, as a rule, give birth to twins, which are blood chimeras due to placental blood vessel anastomoses. In contrast, wild and captive Callimico almost exclusively have singleton births, as in all cebids. To address whether Callimico shares chimeric twinning with other callitrichids, we did DNA profiling of the only presently available twin pair of captive Callimico. DNA banding patterns revealed distinct differences between the twins, indicating an absence of blood chimerism. We infer that predominantly single birth in Callimico most likely represents a derived state that evolved independently in this genus, rather than the ancestral callitrichid condition.