Evolutionary process of deep-sea bathymodiolus mussels

Area of Science:

• Marine Biology
• Evolutionary Biology
• Deep-Sea Ecology

Background:

• Deep-sea chemosynthetic communities harbor unique organisms with unresolved invasion and adaptation strategies.
• Understanding the origin and evolution of dominant deep-sea mussels, such as Bathymodiolus, is crucial for deciphering life in these extreme environments.

Purpose of the Study:

• To investigate the global phylogenetic relationships of deep-sea Bathymodiolus mussels and their relatives.
• To reconstruct the evolutionary history and diversification timing of deep-sea mussels.

Main Methods:

• Phylogenetic analysis using mitochondrial DNA sequences (cytochrome c oxidase subunit I and NADH dehydrogenase subunit 4).
• Molecular clock dating to estimate evolutionary divergence times.
• Comparative analysis of mussel groups from various deep-sea habitats (vents, seeps, whale falls, sunken wood).

Main Results:

• Deep-sea Bathymodiolinae mussels from vents and seeps formed four distinct phylogenetic groups.
• Mussels from sunken wood and whale carcasses (Modiolinae) represented an outgroup, with shallow-water relatives positioned more distantly.
• Diversification of Bathymodiolus mussels initiated in the early Miocene, with further diversification in the early to middle Miocene.

Conclusions:

• Phylogenetic data support the 'Evolutionary Stepping Stone Hypothesis,' suggesting ancestors exploited sunken wood and whale falls for deep-sea adaptation.
• Evolution of symbiosis, from extracellular to intracellular, accompanied nutritional adaptation in whale carcass environments.
• Mytilid ancestors likely exploited whale falls during their adaptation to deep-sea ecosystems.