Journal of Molecular Evolution

, Volume 86, Issue 2, pp 118–137 | Cite as

Iterative Calibration: A Novel Approach for Calibrating the Molecular Clock Using Complex Geological Events

  • Tzitziki Loeza-QuintanaEmail author
  • Sarah J. Adamowicz
Original Article


During the past 50 years, the molecular clock has become one of the main tools for providing a time scale for the history of life. In the era of robust molecular evolutionary analysis, clock calibration is still one of the most basic steps needing attention. When fossil records are limited, well-dated geological events are the main resource for calibration. However, biogeographic calibrations have often been used in a simplistic manner, for example assuming simultaneous vicariant divergence of multiple sister lineages. Here, we propose a novel iterative calibration approach to define the most appropriate calibration date by seeking congruence between the dates assigned to multiple allopatric divergences and the geological history. Exploring patterns of molecular divergence in 16 trans-Bering sister clades of echinoderms, we demonstrate that the iterative calibration is predominantly advantageous when using complex geological or climatological events—such as the opening/reclosure of the Bering Strait—providing a powerful tool for clock dating that can be applied to other biogeographic calibration systems and further taxa. Using Bayesian analysis, we observed that evolutionary rate variability in the COI-5P gene is generally distributed in a clock-like fashion for Northern echinoderms. The results reveal a large range of genetic divergences, consistent with multiple pulses of trans-Bering migrations. A resulting rate of 2.8% pairwise Kimura-2-parameter sequence divergence per million years is suggested for the COI-5P gene in Northern echinoderms. Given that molecular rates may vary across latitudes and taxa, this study provides a new context for dating the evolutionary history of Arctic marine life.


Molecular dating Clock calibration Echinodermata Bering Strait DNA barcoding 



This work was supported by a graduate scholarship from Consejo Nacional de Ciencia y Tecnología (315757 to TLQ) and by the Natural Sciences and Engineering Research Council of Canada (Discovery Grant 2010-386591 and 2016-06199 to SJA). We also acknowledge the Ontario Ministry of Research Innovation for providing funding to Paul Hebert for the development of BOLD, which was the main resource of data for this project. Special thanks to Teresa J. Crease, Elizabeth G. Boulding, Jonathan D.S. Witt, and Mari Kekkonen for discussion and their valuable feedback on earlier versions of this manuscript. We sincerely thank two anonymous reviewers for their helpful and constructive comments. Finally, we want to acknowledge all the researchers who have made public COI barcode sequences from echinoderms.

Supplementary material

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Supplementary material 1 (XLSX 856 KB)
239_2018_9831_MOESM2_ESM.txt (126 kb)
Supplementary material 2 (TXT 125 KB)
239_2018_9831_MOESM3_ESM.docx (18 kb)
Supplementary material 3 (DOCX 17 KB)


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Authors and Affiliations

  1. 1.Biodiversity Institute of Ontario & Department of Integrative BiologyUniversity of GuelphGuelphCanada

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