Extensive Independent Amplification of Platy-1 Retroposons in Tamarins, Genus Saguinus .

Platy-1 retroposons are short interspersed elements (SINEs) unique to platyrrhine primates. Discovered in the common marmoset ( Callithrix jacchus ) genome in 2016, these 100 bp mobile element insertions (MEIs) appeared to be novel drivers of platyrrhine evolution, with over 2200 full-length members across 62 different subfamilies, and strong evidence of ongoing proliferation in C. jacchus . Subsequent characterization of Platy-1 elements in Aotus , Saimiri and Cebus genera, suggested that the widespread mobilization detected in marmoset (family Callithrichidae) was perhaps an anomaly. Two additional Callithrichidae genomes are now available, a scaffold level genome assembly for Saguinus imperator (tamarin; SagImp_v1) and a chromosome-level assembly for Saguinus midas (Midas tamarin; ASM2_v1). Here, we report that each tamarin genome contains over 11,000 full-length Platy-1 insertions, about 1150 are shared by both Saguinus tamarins, 7511 are unique to S. imperator , and another 8187 are unique to S. midas . Roughly 325 are shared among the three callithrichids. We identified six new Platy-1 subfamilies derived from Platy-1-8, with the youngest new subfamily, Platy-1-8c_ Saguinus , being the primary source of the Saguinus amplification burst. This constitutes the largest expansion of Platy-1 MEIs reported to date and the most extensive independent SINE amplification between two closely related species.