Rev. biol. mar. oceanogr. 49(2): 193-207


Calibrating the chitons (Mollusca: Polyplacophora) molecular clock with the mitochondrial DNA cytochrome C oxidase I gene

Cedar I. García-Ríos1, Nivette M. Pérez-Pérez1, Joanne Fernández-López1 and Francisco A. Fuentes1

1Departamento de Biología, Universidad de Puerto Rico en Humacao, Avenida José E. Aguiar Aramburu, Carretera 908 km 1,2, Humacao, Puerto Rico

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Sister species separated by the Isthmus of Panama have been used to estimate the rate of molecular evolution. A molecular clock calibrated with a well studied geological event can be useful to propose evolutionary history hypotheses. The Isthmus of Panama emerged completely 3.1 million years ago (mya), but fossil evidence has shown that rocky shore and reef mollusks communities were isolated early (5.1-10.1 mya). The divergence of segments of the mitochondrial gene cytochrome oxidase I (COI) was determined for 2 pairs of sister species of chitons. The pair Stenoplax purpurascens of the Caribbean and S. limaciformis of the tropical Eastern Pacific consists of phenotypically similar species. The species of the second pair, Acanthochitona rhodea from the south of the Caribbean and A. ferreirai of the Panama and Costa Rica Pacific coast, were treated as the same species until the recent description of A. ferreirai. Homologous fragments of the COI gene were compared using specimens collected on both coasts of Costa Rica. For the Stenoplax genus pair, a total divergence of 11.4% base pairs (bp) was determined. The Acanthochitona pair showed a divergence of 10.4-10.5% bp. These values allow calculated divergence rates from 3.7% / mya (3.1 mya isolation) to 1.1% / mya (early isolation). This is the first calibration of the COI as a molecular clock for the polyplacophora.

Key words:  Isthmus of Panama, molecular clock, COI, Stenoplax, Acanthochitona