Abstract

Because sequence information is now available for the 648bp barcode region of cytochrome c oxidase 1 (COI) from more than 400,000 animal species, this gene segment can be used to probe patterns of mitochondrial evolution. The present study examines levels of amino acid substitution and the frequency of indels in COI from 4177 species of arachnids, including representatives from all 16 orders and 43% of its families (267/625). It examines divergences at three taxonomic levels—among members of each order to an outgroup, among families in each order and among BINs, a species proxy, in each family. Order Distances vary fourfold (0.10–0.39), while the mean of the Family Distances for the ten orders ranges fivefold (0.07–0.35). BIN Distances show great variation, ranging from 0.01 or less in 12 families to more than 0.25 in eight families. Patterns of amino acid substitution in COI are generally congruent with previously reported variation in nucleotide substitution rates in arachnids, but provide some new insights, such as clear rate acceleration in the Opiliones. By revealing a strong association between elevated rates of nucleotide and amino acid substitution, this study builds evidence for the selective importance of the rate variation among arachnid lineages. Moreover, it establishes that groups whose COI genes have elevated levels of amino acid substitution also regularly possess indels, a dramatic form of protein reconfiguration. Overall, this study suggests that the mitochondrial genome of some arachnid groups is dynamic with high rates of amino acid substitution and frequent indels, while it is ‘locked down’ in others. Dynamic genomes are most prevalent in arachnids with short generation times, but the possible impact of breeding system deserves investigation since many of the rapidly evolving lineages reproduce by haplodiploidy, a mode of reproduction absent in ‘locked down’ taxa.

Highlights

  • With nearly 100,000 known species and perhaps a million awaiting description [1], the arachnids are the most diverse class of arthropods after insects

  • The present study reveals patterns of rate variation congruent with those detected in earlier investigations, but provides further details on its taxonomic localization

  • The present results confirm rate acceleration in the superorder Acariformes, but indicate that it is greater in the Trombidiformes than the Sarcoptiformes

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Summary

Introduction

With nearly 100,000 known species and perhaps a million awaiting description [1], the arachnids are the most diverse class of arthropods after insects. These species are assigned to ten well-accepted orders and to a final lineage, the Acari, whose boundaries are less secure. Amino Acid Variation in COI from Arachnida sequence from their project: Código de Barras de los Arácnidos de México: Ácaros (Arachnida: Acari) asociados a los vertebrados e invertebrados de México, No 122944, funded by Consejo Nacional de Ciencia y Tecnología (the National Council of Science and Technology), http://www.conacyt.mx/. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

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