Patterns of variation of mutation rates of mitochondrial and nuclear genes of gastropods

BackgroundAlthough mitochondrial DNA (mtDNA) of many animals tends to mutate at higher rates than nuclear DNA (nuDNA), a recent survey of mutation rates of various animal groups found that the gastropod family Bradybaenidae (suborder Helicina) shows a nearly 40-fold difference in mutation rates of mtDNA (mu (m)) and nuDNA (mu (n)), while other gastropod taxa exhibit only two to five-fold differences. To determine if Bradybaenidae represents an outlier within Gastropoda, I compared estimated values of mu (m)/mu (n) of additional gastropod groups. In particular, I reconstructed mtDNA and nuDNA gene trees of 121 datasets that include members of various clades contained within the gastropod subclasses Caenogastropoda, Heterobranchia, Patellogastropoda, and Vetigastropoda and then used total branch length estimates of these gene trees to infer mu (m)/mu (n).ResultsEstimated values of mu (m)/mu (n) range from 1.4 to 91.9. Datasets that exhibit relatively large values of mu (m)/mu (n) (i.e., >20), however, show relatively lower estimates of mu (n) (and not elevated mu (m)) in comparison to groups with lower values. These datasets also tend to contain sequences of recently diverged species. In addition, datasets with low levels of phylogenetic breadth (i.e., contain members of single genera or families) exhibit higher values of mu (m)/mu (n) than those with high levels (i.e., those that contain representatives of single superfamilies or higher taxonomic ranks).ConclusionsGastropods exhibit considerable variation in estimates of mu (m)/mu (n). Large values of mu (m)/mu (n) that have been calculated for Bradybaenidae and other gastropod taxa may be overestimated due to possible sampling artifacts or processes that depress estimates of total molecular divergence of nuDNA in groups that recently diversified.

Automated summary

The study demonstrated variation in estimates of mu (m)/mu (n) among gastropod groups, with the Bradybaenidae family showing a significantly higher mutation rate compared to other groups. Data sets containing sequences of recently diverged species tended to exhibit higher values of mu (m)/mu (n).