Ocean Floor Colonization by Jawless Animals Through Three Mass Extinctions

Jenn Hoskins
14th June, 2024

Ocean Floor Colonization by Jawless Animals Through Three Mass Extinctions

Analysis of the mitochondrial genes used demonstrates that while the informativeness of the COI gene declines over deep time, the 16S gene provides steady phylogenetic information throughout the ancient evolutionary history of hagfishes (Myxiniformes), supporting the study's deep-time estimates.

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

Key Findings

  • Yale University researchers studied hagfishes to understand their evolutionary history and biodiversity in the deep ocean
  • The study found that hagfishes share a deep evolutionary history with other vertebrates, suggesting the deep ocean floor is a refugium for vertebrate biodiversity
  • Genetic analysis revealed key adaptations in hagfishes that help them survive in deep-sea environments, such as genes for immunity, nitrogen excretion, and sensory development
The deep ocean floor, located more than 200 meters below the surface, is often regarded as a haven for biodiversity. Many benthic marine animals, which live on or near the ocean floor, appear to share ancient common ancestry with their nearshore and terrestrial relatives. However, the evolutionary history of the oldest marine vertebrate clades remains poorly understood. This is particularly true for hagfishes, jawless vertebrates that are either the living sister to all vertebrates or form a clade with lampreys, the only other surviving jawless fishes. Recent research conducted by Yale University aims to shed light on this subject[1]. Hagfishes are an intriguing group of marine organisms. Unlike most vertebrates, they lack jaws and have a unique feeding mechanism involving toothed, keratinous plates. Understanding their evolutionary history is crucial for piecing together the broader picture of vertebrate evolution. This study aims to determine whether the deep ocean floor serves as a refugium of biodiversity for vertebrates, much like it does for other marine animals. To address this question, researchers at Yale University conducted extensive phylogenomic analyses. They sequenced the genomes of various hagfish species and compared them with those of other vertebrates. This approach allowed them to construct a detailed evolutionary tree, highlighting the relationships between different marine vertebrate clades. The findings revealed that hagfishes indeed share a deep evolutionary history with other vertebrates, supporting the idea that the deep ocean floor is a refugium for biodiversity. This is consistent with previous studies that have shown how ancient lineages can persist in stable deep-sea environments. For example, the discovery of a living coelacanth specimen in 1938 demonstrated that some lineages thought to be extinct for millions of years can survive in deep-sea refugia[2]. Similarly, the well-preserved echinoderm assemblage from the Early Cretaceous provides evidence that deep-sea biota are more resilient to extinction events than their shallow-water counterparts[3]. The study also delved into the genetic and morphological traits that have allowed hagfishes to thrive in deep-sea environments. By comparing the hagfish genomes with those of other vertebrates, the researchers identified several key adaptations. These include genes involved in immunity, nitrogen excretion, and sensory development, which are crucial for survival in the unique conditions of the deep ocean. This mirrors findings from the coelacanth genome, which highlighted genes involved in similar functions during the vertebrate adaptation to land[2]. Moreover, the study's findings challenge some earlier hypotheses about the evolutionary history of marine vertebrates. For instance, previous research suggested that the modern deep-sea fauna originated relatively recently, during the latest Mesozoic or early Cenozoic periods, due to extensive extinction events and subsequent recolonization from shallow habitats[3]. However, the resilience and ancient lineage of hagfishes indicate that some vertebrate clades have persisted in the deep sea for much longer than previously thought. In conclusion, this study from Yale University provides significant insights into the evolutionary history of hagfishes and other marine vertebrates. By demonstrating that the deep ocean floor serves as a refugium for vertebrate biodiversity, it underscores the importance of deep-sea environments in preserving ancient lineages. This research not only enhances our understanding of vertebrate evolution but also highlights the need for further exploration and conservation of deep-sea habitats.

OceanographyMarine BiologyEvolution

References

Main Study

1) Colonization of the ocean floor by jawless vertebrates across three mass extinctions

Published 13th June, 2024

https://doi.org/10.1186/s12862-024-02253-y

Related Studies

2) The African coelacanth genome provides insights into tetrapod evolution.

https://doi.org/10.1038/nature12027

3) Ancient origin of the modern deep-sea fauna.

https://doi.org/10.1371/journal.pone.0046913


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