Phylogenetic Relationships and Adaptation in Deep-Sea Mussels: Insights from Mitochondrial Genomes.

Kai Zhang,Ting Xu,Jin Sun,Pei-Yuan Qian,Jian-Wen Qiu

doi:10.3390/ijms22041900

Abstract

Mitochondrial genomes (mitogenomes) are an excellent source of information for phylogenetic and evolutionary studies, but their application in marine invertebrates is limited. In the present study, we utilized mitogenomes to elucidate the phylogeny and environmental adaptation in deep-sea mussels (Mytilidae: Bathymodiolinae). We sequenced and assembled seven bathymodioline mitogenomes. A phylogenetic analysis integrating the seven newly assembled and six previously reported bathymodioline mitogenomes revealed that these bathymodiolines are divided into three well-supported clades represented by five Gigantidas species, six Bathymodiolus species, and two “Bathymodiolus” species, respectively. A Common interval Rearrangement Explorer (CREx) analysis revealed a gene order rearrangement in bathymodiolines that is distinct from that in other shallow-water mytilids. The CREx analysis also suggested that reversal, transposition, and tandem duplications with subsequent random gene loss (TDRL) may have been responsible for the evolution of mitochondrial gene orders in bathymodiolines. Moreover, a comparison of the mitogenomes of shallow-water and deep-sea mussels revealed that the latter lineage has experienced relaxed purifying selection, but 16 residues of the atp6, nad4, nad2, cob, nad5, and cox2 genes have underwent positive selection. Overall, this study provides new insights into the phylogenetic relationships and mitogenomic adaptations of deep-sea mussels

Highlights

Mytilidae is a family of highly diverse mussels that are widely distributed from freshwater to marine water and from coastal areas to the deep-sea [1,2]
A previous study has established that Bathymodiolinae split from its shallowwater sister group Modiolinae roughly 110.4 Million years ago (Ma) [4], but given the difficulty in sampling these deep-sea animals, little is known about their biology
Despite the lack of phytoplanktonderived food in the deep-sea, these mussels thrive in the special deep-sea habitats due to their symbiosis with bacteria that are dependent on simple organic molecules, such as methane and hydrogen sulfide, as a source of energy [1,4]

Summary

Introduction

Mytilidae is a family of highly diverse mussels that are widely distributed from freshwater to marine water and from coastal areas to the deep-sea [1,2] This family is currently divided into seven subfamilies. Despite the lack of phytoplanktonderived food in the deep-sea, these mussels thrive in the special deep-sea habitats due to their symbiosis with bacteria that are dependent on simple organic molecules, such as methane and hydrogen sulfide, as a source of energy [1,4] Owing to their ecological importance and remarkable biological characteristics, deep-sea mussels have been considered a suitable animal model for studying adaptation and symbiosis [4,7,8,9,10]

Methods

Results

Discussion

Conclusion