Calibrating the molecular clock beyond cytochrome b: assessing the evolutionary rate of COI in birds

LAVINIA, PABLO D.; KERR, KEVIN C. R.; HEBERT, PAUL D. N.; TUBARO, PABLO L.; LIJTMAER, DARÍO A.

Guaruja

Congreso; Evolution 2015; 2015

Society for the Study of Evolution (SSE), Society of Systematic Biologists (SSB) y American Society of Naturalists (ASN)

Estimating the age of species or their component lineages based on sequence data is crucial for many studies in avian evolutionary biology. Although calibrations of the molecular clock in birds have been performed almost exclusively using cytochrome b (cytb), they are commonly extrapolated to other mitochondrial genes. The existence of a large, standardized cytochrome c oxidase subunit I (COI) library generated as a result of the DNA barcoding initiative provides the opportunity to obtain a calibration for this mitochondrial gene in birds. In this study we compare the evolutionary rate of COI relative to cytb across ten different avian orders. We obtained divergence estimates for both genes from nearly 300 phylogenetically independent pairs of species through the analysis of almost 5000 public sequences. For each pair of species we calculated the difference in divergence between COI and cytb. Our results indicate that COI evolves on average 14% slower than cytb, but also reveal considerable variation both among and within avian orders, precluding the use of this value as a standard adjustment for the COI molecular clock for birds. Our findings suggest that thisvariation is partially explained by a clear negative relationship between the difference in divergence in these genes and the age of species. Distancesforcytbarehigher than thosefor COI for closely related species, but the values becomesimilar as the divergence between the species increases. This pattern appears to result from the comparisonof a gene (COI) with a relatively constant rate and one (cytb) with a negatively time-dependent rate, a difference that could be related to lower functional constraints ona small number of sites in cytb that allow it to initially accumulate mutations more rapidly than COI.