Anglerfish are among the ocean’s most bizarre creatures. This group of deep-sea dwellers is best known for the bioluminescent lures that dangle from their foreheads to attract predators, but they have also developed some traits that have helped them defy evolutionary odds. They likely adapted larger jaws, smaller eyes and more compressed body shapes to survive in the ocean’s harsh bathypelagic zone – 3,300 to 4,000 feet below the ocean’s surface. The findings are detailed in a study published Nov. 27 in the journal Nature ecology and evolution.
“Frogfish are a perfect example of how life can innovate under extreme constraints,” study co-author and Rice University evolutionary biologist Kory Evans said in a statement.
These strange and spiky creatures have that perfected the art of deep sea fishing with their dangling locks, but also open a window into how evolution works in such an inhospitable and unexplored place.
In the studya team of biologists studied how anglerfish – or Lophiiformes–transitioned from seabed habitats to the open waters of the deep sea. They used museum specimens to analyze their DNA and created 3D images to build the anglerfish’s evolutionary tree. Ultimately, they used the genetic data of 132 species, representing approximately 38 percent of the described anglerfish species. The genetic data was supplemented with fossils that were analyzed using micro-CT scans. These images and family trees allowed the team to identify the physical changes and innovations that allowed these animals to thrive in one of the most inhospitable locations on Earth.
The team discovered that the deep-sea pelagic anglerfish is called ceratioids–comes from an ancestor who lived on the seabed. This ancestor lived at the bottom of the ocean’s continental slope before it merged into the open waters of the bathypelagic zone. This step then set the stage for rapid evolutionary change. The ceratioids subsequently developed features such as larger jaws, smaller eyes, and laterally compressed bodies. These adaptations are all tailored to living in a place with limited food sources and no sunlight.
Despite these changes, ceratioids also showed a large Variation in body shapes. They range from the more familiar round and bulbous anglerfish to the long ‘wolf bustard’ ceratioid with a trap-like jaw. According to the teamThis diversity of body shapes was the most surprising part of the study, because the rugged bathypelagic zone did not constrain evolution as expected, despite the lack of ecological diversity among other living things in this zone. On the contrary, these ceratioids look very different from their bottom-dwelling relatives. This suggests that ceratioids are rather limited by the environmental challenges of the deep sea explored new evolutionary possibilities by diversifying their body shapes and the way they hunt.
“With their unique features, such as bioluminescent lures and large oral openings, deep-sea anglerfish may be one of the few documented examples of adaptive radiation in the resource-limited bathypelagic zone,” Evans said. “These traits likely gave anglerfish an advantage in exploiting scarce resources and navigating the extreme conditions of their environment, although we do not have strong evidence that this diversity is directly linked to this type of resource specialization.”
According to Evansthe study also leaves room for the possibility that other non-adaptive forces, such as random mutations, also contributed to the observed variability in anglerfish.
[Related: This rare ‘Finding Nemo’ fish mysteriously washed up on a California beach.]
When the team compared anglerfish clades – a group of organisms believed to have evolved from a common ancestor – in different habitats, they found even more unexpected results. They looked at coastal species such as frogfishthat live in coral reef environments with their deep-sea counterparts. The coastal devilfish had much lower evolutionary changes than their relatives that lived in the deeper sea.
“The idea that a homogeneous, low-resource environment – like being surrounded on all sides by nothing but water – would produce diverse body and skull plans is really counterintuitive in this field,” study co-author and postdoctoral researcher at the University of California, Irvine. Rose Faucher said in a statement. “If fish have different features that allow them to communicate, such as corals and plants in shallow water or sand and rocks on the seabed, then we expect fish to have a lot of variation in shape. Instead, we see it in these deep-sea fish, which have nothing but water to communicate with.”
According to the teamthis study provides valuable insights into how all life – not just anglerfish – can adapt to extreme environments. The deep sea is one of the least understood ecosystems on Earth, but plays a crucial role in the planet’s biodiversity and carbon cycle. A better understanding of how organisms survive under these conditions can help scientists predict how life elsewhere might respond to environmental changes. The research also shows that even low-resource environments, such as the bathypelagic zone, can trigger significant evolutionary changes, opening new avenues for studying evolution. Or more simply: life finds a way.
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