Different Selection Levels of Mitogenomes: New Insights into Species Differentiation of the <i>Triops longicaudatus</i> (LeConte, 1846) Complex (Branchiopoda: Notostraca)

Abstract

Lineages of the Triops longicaudatus (LeConte, 1846) complex, originally endemic to the Americas, have been able to successfully colonize extreme environments such as temporary aquatic systems through shifts in their reproductive modes. To gain insights into their stress adaptations and species differentiation, we explored the genetic diversity of populations of the T. longicaudatus complex and constructed their haplotype networks. Using maximum likelihood and Bayesian analyses, we analyzed the complete mitogenome sequences of seven Triops species to infer their phylogenetic relationships. To identify the possible role of mtDNA evolution in stress adaptation, the evolutionary rates and molecular signatures of natural selection for all 13 PCGs were investigated using multiple approaches of selection tests. The results showed that signals of relaxed purifying selection and positive selection were found in specific genes of complexes I, IV, and V, indicating that mitogenomes in the T. longicaudatus complex have undergone adaptive evolution. Different patterns of selection in the mitochondrial genes between the hermaphroditic and gonochoric branches imply that functional constraints have played a significant role in the evolution of T. longicaudatus complex mitogenomes, which was essential for survival in extreme environments.

Keywords

• mitochondrial genome
• phylogeny
• reproductive mode
• purifying selection
• positive selection