The ‘‘Phoca standard’’: an external molecular reference for calibrating recent evolutionary divergences

• Main Authors: Ulfur Arnason, Xiufeng Xu, Anette Gullberg, Dan Graur
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1996
• Subjects: Arctic; Arctic Harbour; Arctic Basin; Phoca hispida; ringed seal
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.571.2027; http://nsmn1.uh.edu/dgraur/ArticlesPDFs/JME_Phoca.pdf

Abstract. Comparison of the complete mitochondrial DNA (mtDNA) of the high-Arctic ringed seal (Phoca hispida) and the sub-Arctic harbour (P. vitulina) and grey (Halichoerus grypus) seals shows that they are ge-netically equidistant from one another. We relate the evolutionary divergence of the three species to expand-ing glaciation in the Arctic Basin and establish, in con-junction with mtDNA data, a standard reference for cali-bration of recent divergence events among mammalian taxa. In the present study, we apply the ‘‘Phoca stan-dard’ ’ to the dating of divergences within the hominid phylogenetic tree. After determining the relative rates of substitution over all mitochondrial protein-coding genes in the different evolutionary lineages, we estimate that humans and chimpanzees diverged from each other 6.1 Mya (95 % confidence limits: 5.2–6.9 Mya). The corre-sponding lower-limit divergence between common chimpanzee, Pan troglodytes, and pygmy chimpanzee, P. paniscus, occurred 3 (2.4–3.6) Mya, and the primary split within the P. troglodytes complex 1.6 (1.3–2.0) Mya. The analyses suggest that the split between Gorilla and Pan/Homo occurred 8.4 (7.3–9.4) Mya. They also suggest that Pongo (orangutan) and the lineage leading to gorillas, chimpanzees, and humans diverged 18.1 (16.5–19.6) Mya. The present analysis is independent of the hominid paleontological record and inferential mor-phological interpretations and thus is a novel approach to the lower-limit dating of recent divergences.