Tips and nodes are complementary not competing approaches to the calibration of molecular clocks.
Molecular clock methodology provides the best means of establishing evolutionary timescales, the accuracy and precision of which remain reliant on calibration, traditionally based on fossil constraints on clade (node) ages. Tip calibration has been developed to obviate undesirable aspects of node calibration, including the need for maximum age constraints that are invariably very difficult to justify. Instead, tip calibration incorporates fossil species as dated tips alongside living relatives, potentially improving the accuracy and precision of divergence time estimates. We demonstrate that tip calibration yields node calibrations that violate fossil evidence, contributing to unjustifiably young and ancient age estimates, less precise and (presumably) accurate than conventional node calibration. However, we go on to show that node and tip calibrations are complementary, producing meaningful age estimates, with node minima enforcing realistic ages and fossil tips interacting with node calibrations to objectively define maximum age constraints on clade ages. Together, tip and node calibrations may yield evolutionary timescales that are better justified, more precise and accurate than either calibration strategy can achieve alone.
School of Earth Sciences, University of Bristol, Life Sciences Building, Bristol BS8 1TQ, UK joe.oreilly@bristol.ac.uk.
Joseph E
http://orcid.org/0000-0001-9775-253X
JE
O'Reilly
School of Earth Sciences, University of Bristol, Life Sciences Building, Bristol BS8 1TQ, UK phil.donoghue@bristol.ac.uk.
Philip C J
http://orcid.org/0000-0003-3116-7463
PC
Donoghue
D000818:Animals; D002138:Calibration; D019143:Evolution, Molecular; D005580:Fossils; D006927:Hymenoptera / Q000145:classification; D010163:Paleontology; D010802:Phylogeny; D013997:Time Factors; D035501:Uncertainty
Hymenoptera; calibration; molecular clock; node; tip