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Heredity (Edinb)
2019 May 01;1225:513-524. doi: 10.1038/s41437-018-0141-7.
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Is molecular evolution faster in the tropics?
Orton MG
,
May JA
,
Ly W
,
Lee DJ
,
Adamowicz SJ
.
Abstract
The evolutionary speed hypothesis (ESH) suggests that molecular evolutionary rates are higher among species inhabiting warmer environments. Previously, the ESH has been investigated using small numbers of latitudinally-separated sister lineages; in animals, these studies typically focused on subsets of Chordata and yielded mixed support for the ESH. This study analyzed public DNA barcode sequences from the cytochrome c oxidase subunit I (COI) gene for six of the largest animal phyla (Arthropoda, Chordata, Mollusca, Annelida, Echinodermata, and Cnidaria) and paired latitudinally-separated taxa together informatically. Of 8037 lineage pairs, just over half (51.6%) displayed a higher molecular rate in the lineage inhabiting latitudes closer to the equator, while the remainder (48.4%) displayed a higher rate in the higher-latitude lineage. To date, this study represents the most comprehensive analysis of latitude-related molecular rate differences across animals. While a statistically-significant pattern was detected from our large sample size, our findings suggest that the EHS may not serve as a strong universal mechanism underlying the latitudinal diversity gradient and that COI molecular clocks may generally be applied across latitudes. This study also highlights the merits of using automation to analyze large DNA barcode datasets.
2016-06199 Gouvernement du Canada | Natural Sciences and Engineering Research Council of Canada (Conseil de Recherches en Sciences Naturelles et en Génie du Canada)
Fig. 1. Sister lineages discovered for (a) Echinodermata (n = 56), (b) Perciformes (n = 54), and (c) Hymenoptera within North America (n = 517) separated by a minimum of 20 degrees in median absolute latitude and 0.02–0.15 sequence divergence, presented as examples of the total pairings analyzed in this study (n = 8037; see Fig. S7 for plots for all taxa). The point for each Barcode Index Number (BIN) included in a pair is plotted according to its median latitude and median longitude on Kavrayskiy VII map projections using the data visualization software plotly (https://plot.ly/). Pairings of lineages were color and symbol coded by the difference in median absolute latitude
Fig. 2. Linear regression analysis of standardized, phylogenetically independent contrasts (PICs) for all pairings of latitude-separated sister lineages belonging to Arthropoda (n = 7900), whereby each point represents one sister pair and the fitted regression line is forced through the origin. (a) PICs in median latitude vs. signed PICs in branch length (positive sign = larger branch length at lower latitude) (slope of regression = 5.36E-06). (b) PICs in median temperature vs. signed PICs in branch length (slope of regression = 6.73E-06). Each pairing of lineages is separated by a minimum of 20 degrees in median absolute latitude and 0.02–0.15 sequence divergence. Each pairing of lineages is color/symbol coded differently according to major insect order or gray/plus symbol for remaining orders within Arthropoda using the data visualization software plotly (https://plot.ly/)
