The ability to bite food off hard surfaces, such as coral, evolved about 50 million years ago and led to the rapid formation of new species of fish on coral reefs and similar habitats
Photo Credit: Roy Zeigerman
Scientific Frontline: Extended "At a Glance" Summary: Habitat-Driven Fish Diversification
The Core Concept: Approximately 50 million years ago, the evolutionary adaptation allowing fish to bite and scrape food directly from hard surfaces triggered a rapid acceleration in species diversification across marine and freshwater ecosystems.
Key Distinction/Mechanism: Unlike fish residing in the open water column, which experienced stable evolutionary rates due to a lack of physical structure, lineages that adapted to feed on complex hard surfaces (such as coral reefs and lakebeds) accessed novel ecological niches. This interaction between anatomical innovation and structured habitats drove a 1.5 to 1.7 times increase in speciation rates compared to pelagic counterparts.
Origin/History: This evolutionary pulse began shortly after the Paleocene-Eocene Thermal Maximum (PETM) 56 million years ago, a severe global warming event that turned over marine ecosystems and created a "blank slate" for adaptation. Researchers from UC Davis quantified this phenomenon by analyzing the evolutionary rates of 9,560 fish species over a 350-million-year phylogenetic timeline, with findings recently published in the Proceedings of the National Academy of Sciences.
Major Frameworks/Components:
- Evolutionary Innovation: The anatomical development of biting mechanics enabled specific lineages (such as parrotfish, butterflyfish, and surgeonfish) to exploit previously inaccessible dietary resources like attached algae, snails, and shellfish.
- Habitat Complexity: Highly structured environments provide greater opportunities for behavioral and anatomical divergence compared to uniform, open-water habitats.
- Punctuated Evolution: The study demonstrates macroevolution proceeding in concentrated bursts following major environmental upheavals and the acquisition of novel traits, rather than at a constant, gradual rate.
Branch of Science: Evolutionary Biology, Marine Biology, Ecology, and Ichthyology.
Future Application: Understanding the historical mechanisms that generate biodiversity yields predictive models for how marine ecosystems may reorganize following severe climate shifts. This data directly informs contemporary conservation strategies and ecosystem management for highly vulnerable coral reef habitats.
Why It Matters: This research resolves a fundamental question regarding the uneven distribution of global biodiversity. It explains the evolutionary mechanics that allowed coral reefs to support thousands of distinct fish species, illustrating how the dynamic interplay between a species' traits and its physical environment shapes the natural world.
Why are there so many of species of coral reef fish? According to a new study, it’s because about 50 million years ago, some fish figured out how to bite food from hard surfaces.
Evolution doesn’t proceed at an even pace: Species evolve in jumps and spurts, followed by lulls. These periods of rapid diversification usually occur after a dramatic environmental change or upheaval, or when a lineage develops a new “innovation” that allows them to use a previously inaccessible resource. For fish, the ability to feed from a hard surface was one such innovation.
In a study published Proceedings of the National Academy of Sciences, University of California, Davis, researchers show that fish lineages that acquired the ability to scrape algae, snails and shellfish from hard surfaces evolved in more diverse ways than fish living higher in the water column, where there are no hard surfaces to feed from.
“This is one of the reasons we have so many species of coral reef fish today,” said Nick Peoples, graduate student in the Population Biology graduate group and lead author on the paper. “When we account for the entire evolutionary history of fishes in different habitats, we find that this immense and unparalleled acceleration of diversification happened on coral reefs.”
Why is biodiversity so unevenly distributed?
The study was spurred by Peoples’ desire to understand why fish diversity is so unevenly distributed across different habitats and ecosystems.
“Coral reefs have 6,000-7,000 species of fish, and there’s a lot of diversity in freshwater environments in Africa, but there's comparatively fewer species in the open ocean and deep sea,” said Peoples. “We were interested in what is driving that pattern. The process of diversification is what structures the biodiversity we see today, so understanding that process can give us interesting insights into how biodiversity is generated and maintained.”
Tracking evolution’s pace
To investigate whether differences in the pace of evolution might have led to biodiversity differences between habitats, the researchers estimated the rate of fish evolution over the past 350 million years.
First, they classified 9,560 fish species into seven categories based on where they live: at the bottom of freshwater lakes or oceans; near — but not on — the bottom of freshwater lakes or oceans; higher in the water column; or on coral reefs. Then, they used a pre-existing evolutionary tree to estimate the rates of speciation (the emergence of new species) and extinction for each habitat during 1-million-year intervals.
They showed that, around 50 million years ago, the rate of diversification increased by around 1.5 to 1.7x for fish species living in coral reefs or at the bottom of fresh or marine bodies of water. This acceleration was particularly pronounced for coral reef fish. In contrast, the rate of evolution remained relatively stable for fish that live in open water.
This difference is due to the fact that open water habitats are less complex, the researchers said. With water on all sides, fish that live higher in the water column have fewer opportunities to develop new behaviors or anatomical features compared to fish that live in crowded coral reefs or lakebeds.
“Our results show that the global biodiversity of fishes was shaped by the dynamic interplay between the traits of species and the features of the habitats they occupy,” said Peoples.
Giving fish a clean slate
The jump in fish evolution began shortly after the Paleocene-Eocene Thermal Maximum (PETM), a 200,000-year period of climate warming that occurred approximately 56 million years ago. During the PETM, global temperatures rose by 5◦ to 8◦C, which caused a rapid turnover in species, especially for plankton and corals living in shallow waters.
“We think this reorganization of what fishes could eat was almost like a blank slate for fishes to diversify on,” said Peoples.
When they compared the rate of evolution of corals during the same time period, the researchers didn’t find any evidence for increased coral diversification after the PETM.
“This suggests that the acceleration in fish speciation after the PETM is due to the evolution of the fish themselves and how they're interacting with the environment,” said Peoples.
By comparing diversification rates for different groups of fish, the researchers showed that only specific lineages underwent this pulse of evolution.
“On reefs, it's the fish that eat parts of the reef that really took off and diversified,” said Peter Wainwright, professor in the Department of Evolution and Ecology and senior author on the paper. “The groups that really stand out in our analysis are parrotfish, butterflyfish, angelfish, surgeonfish, rabbitfish and triggerfish. These are all fish that feed by biting the reef, whereas we don't see an increase in speciation in reef fish that feed in mid-water, like snappers, groupers and sea basses.”
The study adds to previous research published by Wainwright’s lab that also investigated the evolution of teeth and biting in fish.
“Biting is a unique mode of feeding that evolved recently in fish,” said Wainwright. “This study shows at the macro level that these unique modes of feeding contributed to the incredible diversity of reef fishes that we see today.”
Funding: The work was supported by the University of California, Davis. Peoples was supported by a University of California, Davis, Dissertation Year Fellowship and the Achievement Rewards for College Scientists (ARCS) Foundation.
Published in journal: Proceedings of the National Academy of Sciences
Title: Habitat-specific temporal variation in the pace of fish diversification
Authors: Nick Peoples, Michalis Mihalitsis, and Peter C. Wainwright
Source/Credit: University of California, Davis | Liana Wait
Reference Number: ebio042826_01
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