Deep-Sea Adaptation Revealed by Mitochondrial DNA of Two Sea Cucumbers

Greg Howard
16th May, 2025

Deep-Sea Adaptation Revealed by Mitochondrial DNA of Two Sea Cucumbers

The complete mitochondrial gene maps of the deep-sea sea cucumbers Deima validum and Oneirophanta mutabilis illustrate the distribution of 37 genes across positive and negative strands, revealing a novel gene arrangement in D. validum that contributes to understanding the adaptive evolution of the family Deimatidae.

Image adapted from: Mu et al. / CC BY (Source)

Key Findings

  • *In the South China Sea, scientists decoded the DNA of two deep-sea sea cucumbers to understand their survival strategies.*
  • *They discovered unique genetic arrangements, indicating these species have evolved distinct traits for extreme deep-sea conditions.*
  • *Specific energy-related genes showed adaptations that help the cucumbers thrive in low-oxygen, high-pressure environments.*
Deep-sea environments represent some of the most extreme and least understood ecosystems on Earth. Characterized by high pressure, low temperatures, complete darkness, and limited food sources, these habitats pose significant challenges for the organisms that live there. Recent research by the Chinese Academy of Sciences[1] has shed light on how deep-sea sea cucumbers adapt to such harsh conditions at the molecular level. The study focused on two species of sea cucumbers, Deima validum and Oneirophanta mutabilis, collected from the South China Sea. These species belong to the family Deimatidae, and their mitochondrial genomes—the DNA found in mitochondria, the energy-producing structures within cells—were sequenced for the first time. Mitochondria play a crucial role in energy metabolism and oxygen usage, making their genomes essential for understanding how organisms adapt to environments with limited energy and oxygen. Both species' mitochondrial genomes contain 13 protein-coding genes (PCGs), two ribosomal RNA (rRNA) genes, and 22 transfer RNA (tRNA) genes, consistent with other sea cucumbers. Notably, there are duplications of the trnS and trnL tRNA genes, and the genes are distributed between the positive and negative strands of the DNA. The arrangement of these genes is important for understanding evolutionary relationships and adaptations. When comparing these genomes to those of other sea cucumbers, the researchers discovered a unique gene arrangement in Deima validum, suggesting a distinct evolutionary path within the deep-sea Deimatidae clade. Phylogenetic analysis, which examines the evolutionary relationships between species, showed that Deima validum and Oneirophanta mutabilis cluster together, reinforcing their classification within the deep-sea Deimatidae group. This grouping aligns with previous findings on deep-sea biodiversity, where unique patterns emerge compared to shallower marine environments[2]. Specifically, deep-sea species like these sea cucumbers show maximum biodiversity at higher latitudes and in regions with high carbon export flux and proximity to continental margins. These areas provide more stable and sufficient food sources, which are critical in energy-poor deep-sea ecosystems. The study went further to analyze individual genes within the mitochondrial genomes to identify signs of positive selection—changes that enhance an organism’s ability to survive in its environment. Three sites in the nad2 gene and one site in the nad5 gene exhibited high posterior probabilities of positive selection. These genes are involved in the mitochondrial respiratory chain, which is essential for energy production. By comparing these features with those of shallow sea cucumbers, the researchers suggest that variations in nad2 and nad5 may play a key role in the deep-sea adaptation of Deimatidae sea cucumbers. This research builds on previous understanding of mitochondrial genomics, which has been instrumental in studying genome evolution and inferring evolutionary relationships[3]. Mitochondrial gene arrangements are particularly useful because rearrangements are rare and unlikely to occur independently in separate lineages, making them reliable markers for evolutionary studies. By presenting novel gene arrangements and identifying specific genes under positive selection, the study provides valuable insights into the molecular mechanisms that enable deep-sea organisms to thrive in their extreme environments. Furthermore, this study complements earlier research on deep-sea biodiversity patterns[2]. While previous studies focused on the broader distribution and environmental drivers of biodiversity in deep-sea ecosystems, this research dives into the genetic adaptations that facilitate the survival of specific deep-sea species. The integration of genomic data with ecological patterns offers a more comprehensive understanding of how life persists in the deep ocean. The findings from the Chinese Academy of Sciences not only expand our knowledge of mitochondrial genomics in deep-sea organisms but also establish a foundation for future conservation efforts. Understanding the genetic adaptations that allow species to survive in extreme conditions is crucial for predicting how these ecosystems might respond to environmental changes, such as those driven by climate change or human activities. In conclusion, the sequencing of mitochondrial genomes from Deima validum and Oneirophanta mutabilis provides important insights into the evolutionary adaptations of deep-sea sea cucumbers. By identifying unique gene arrangements and signs of positive selection in key mitochondrial genes, the study advances our understanding of how life can adapt to some of the most challenging environments on Earth. This research not only highlights the intricate relationship between genetics and environmental adaptation but also underscores the importance of conserving the deep-sea ecosystems that host such unique and resilient life forms.

GeneticsMarine BiologyEvolution

References

Main Study

1) Characterization of the complete mitochondrial genomes of two sea cucumbers, Deima validum and Oneirophanta mutabilis (Holothuroidea, Synallactida, Deimatidae): Insight into deep-sea adaptive evolution of Deimatidae

Published 15th May, 2025

https://doi.org/10.1371/journal.pone.0323612

Related Studies

2) Deep-sea diversity patterns are shaped by energy availability.

https://doi.org/10.1038/nature17937

3) Animal mitochondrial genomes.

Journal: Nucleic acids research, Issue: Vol 27, Issue 8, Apr 1999


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