Research traces evolution of anglerfishes’ famed fishing-rod lures
University of Kansas
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The Anglerfish species Bufoceratias wedli from the Field Museum of Natural History.
view moreCredit: Photo courtesy Matthew Davis
LAWRENCE — Anybody who has seen “Finding Nemo” knows about those captivating monsters of the sea: anglerfishes. Variously horrific- or alien-looking, many female anglerfishes sport long, protruding lures used for enticing prey or signaling during mating.
What’s more, the dizzying variety in lures doesn’t just include motion-based ones. Some anglerfish species have bioluminescent lures, while others have lures that release chemicals to attract prey or signal potential mates.
Now, open-access research from the University of Kansas appearing in the peer-reviewed journal Ichthyology & Herpetology is giving new detail to the evolutionary history of anglerfishes’ lures, studying more than 100 species to see how the lures evolved.
“Anglerfishes probably have as many species as turtles and tortoises on the planet right now,” said lead author Alex Maile, a doctoral student with KU’s Biodiversity Institute and Natural History Museum. “The really interesting thing is they’re found across the planet in different oceans and habitats. They’re in coral reefs, continental shelves, deep-sea habitats, floating on giant algae mats in the middle of the ocean. All of them are doing this really cool thing using this lure in so many ways.”
Maile said anglerfishes’ lures are an evolutionary modification of the dorsal fin spine on a typical fish, used essentially as a fishing rod.
“The conventional idea was they’re using this to attract prey,” he said. “We think it’s actually serving a dual purpose, especially in the deep sea, where you’re taking a lure, adding a glowing element to it, and now you can attract food, but you can also attract a potential mate.”
Lead author Maile collaborated with co-author Matthew Davis, a professor of biology at St. Cloud State University who earned his doctorate at KU, to trace the evolutionary history of the lures.
They analyzed anglerfish specimens from natural history collections, mapped lure varieties onto an evolutionary tree, dated when changes likely occurred using fossil evidence, and used computer modeling to assess how lure design is tied to behavior, habitat and species diversification.
“For this particular group of fishes, there’s limited observational data on how they use their lures,” Davis said. “Many have never even been filmed or observed alive. This gives us a sense of what kinds of luring strategies exist for open-ocean glowing anglerfishes versus those more inshore. We found specific patterns associated with how the ‘tackle box’ for anglerfishes has changed depending on habitat and selective pressures.”
The researchers determined the original anglerfish lure developed in the common ancestors of today’s variety about 72 million years ago. It was only motion-based.
Then, during the Oligocene, about 34-23 million years ago, glowing lures appeared in certain deep-sea groups, along with an explosion in diversity among anglerfishes, likely because bioluminescence could also be used to communicate with potential mates.
“What we see is a higher rate of speciation in anglerfishes with glowing lures, similar to other fishes using bioluminescence to attract mates or signal to a mate,” Maile said. “We see this pattern with other deep-sea groups like lanternfishes, hatchetfishes and dragonfishes. They use light to say ‘here I am’ to communicate within their species. There have been hypotheses that they’re using the lure to communicate with males. The males have really big noses and relatively big eyes. The lure has adaptations like a little window shutter. They can contract muscle fibers around it and modulate the light in patterns.”
Simultaneously, Davis said their research revealed an elongation of lures in species with bioluminescence.
“The bioluminescence can hang farther in front of the fish, probably in a way that doesn’t light up the fish so prey can’t see it,” he said. “We have the evolutionary tree as a roadmap and can say this evolved one time as we transitioned into pelagic habitats. Along with that transition, we get elongation of the lure.”
The investigation also considered the development of chemical lures, finding they may have evolved independently at different times in two different groups of anglerfishes: batfishes, about 49 million years ago, and frogfishes about 5 million years ago.
“In batfishes, the lure is inside the neurocranium,” Maile said. “They can move it like a slide whistle in and out. They feed on invertebrates like clams, mussels and worms in sandy substrate. Videos show them shooting the lure out and excreting chemicals towards the substrate. Invertebrates are sensitive to these chemicals. The batfishes use their rostrum or blow water with their mouth to clear substrate or dig canals, then eat the prey. X-rays show them full of these hard-shelled invertebrates. Frogfishes hang above a current and secrete chemicals, letting the current carry them. Prey follow up the current, and the frogfish ambush them.”
Yet chemical luring in anglerfishes remains little understood. Maile suggested chemical luring is a likely area for future research.
“Frogfishes likely have more widespread chemical luring,” he said. “On the deep-sea side, we need to investigate the mechanisms of how males perceive bioluminescent signals and what patterns females use with light. That interaction deserves more attention — how males find or detect females.”
Southern seadevil, or the anglerfish species Ceratias tentaculatus, from the Natural History Museum of Los Angeles County.
Credit
Photo: Alex Maile
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