Many of us are familiar with anglerfishes, though we may not be aware that that’s what they are called, or that more than one type exists. Frequently depicted in popular culture with giant heads, large mouths, sharp teeth and a lightbulb appendage on top, this is indeed a real type of anglerfish that occupies the deep sea (think Finding Nemo), but it’s just one of more than 200 species of anglerfish.
Working with specimens from the Burke Museum and NOAA, Elizabeth Miller, a former National Science Foundation Postdoctoral Fellow at the University of Washington School of Aquatic and Fishery Sciences (SAFS), was captivated by the great diversity of shapes of anglers, which was at odds with how the species is often depicted. Inspired by the world-renowned anglerfish research that has taken place at SAFS and the Burke Museum under Curator Emeritus Ted Pietsch – who wrote the book on the diversity of anglerfishes – Elizabeth set out to build a family tree of anglerfishes and delve into the evolution of new shapes, such as body elongation.
In a new study published in Nature Ecology & Evolution in November 2024, Elizabeth (now a postdoctoral scholar at University of California, Irvine) worked with SAFS Associate Professor and Curator of Fishes, Luke Tornabene, and a multinational team including scientists from Scripps Institution of Oceanography, The University of Oklahoma, and Rice University, to combine genetic material that has been collected and stored from anglerfishes over many years by agencies such as NOAA and museums like the Burke. Much like humans build their family trees by sending in DNA and tracing their lineage online, anglerfish phylogeny is also based on genetic similarity, but over a much longer timescale. “Think millions of years instead of a few hundred,” Elizabeth said.
The team then paired this family tree with measurements of body and skull shape to ask how the diversity of anglerfishes evolved over time. This is where specimen collections such as those housed in The UW Fish Collection are so important, because they preserve fish species as a snapshot in time to when they were collected from often very hard to reach places, such as the deep ocean. The measurements were taken from over 400 anglerfish specimens, with a quarter of these also CT scanned at Friday Harbor Labs (FHL). CT scans provide three-dimensional images of the skeleton and skull of preserved specimens without damaging them, an important tool for preserving very rare museum specimens. These images were used to quantify the shape of anglerfishes, which the team then used to infer how shape evolved using phylogenetic approaches.
What they learned was that the evolution of new shapes is very fast in deep-sea anglerfishes, especially in association with body elongation. “In evolutionary biology, we call a lineage like this an adaptive radiation, meaning a lineage that evolves a lot of different shapes associated with different ecological niches or ways of living,” Elizabeth said. “Adaptive radiations are well known on land and shallow water, but I had never heard of an adaptive radiation in the deep-sea. I was excited to see if anglerfish fit that mold.” Which they did. The researchers found that the deviation away from the archetypical globose shape is especially associated with rapid evolution.
How exactly do they know this? This is where the family tree comes in handy. It showed that elongated anglers, such as the wolftrap angler, are closely related to “blobby” ones such as the footballfish. As they share a recent common ancestor, that means there was a short amount of time in between the blobby ancestor and that elongated shape they have today. “A high evolutionary rate implies a lot of change in a short amount of time,” Elizabeth said.
“This study is a great example of how new technology is allowing us to look at museum specimens in ways no one imagined when they were collected decades ago,” said Katherine Maslenikov, Ichthyology Collections Manager at UW. “Anglerfishes are rare and delicate so there has historically not been a lot of research into their anatomy. Genetics has allowed us to build powerful data sets that help us construct the family trees of organisms, but it is the museum specimens that then let us examine their anatomy to try to understand the ecology and behavior in evolutionary terms. Micro CT scanning allows for non-destructive imaging of the specimens, so we are now able to see the delicate skeletons of these rare species and be inspired to ask new questions.”
The name anglerfish applies to all members of the order Lophiiformes, which has five groups: frogfishes, batfishes, monkfishes, sea toads, and the bathypelagic anglers. Most picture the bathypelagic group when they hear the word anglerfish (suborder Ceratioidei). There are 350 species in Lophiiformes, with roughly half in the bathypelagic ceratioid lineage, the group that this paper is focused on.
“As to why rapid evolution over a quick time frame happens in the deep sea? It is hard to know, but we have some hypotheses,” Elizabeth added. “Anglerfish don’t really swim – they just float and wait for prey to come to them, drawn by their lures. This means the body can take on different forms and not negatively impact the fish, such as a blobby shape increasing drag in the water.” Some elongated shapes may have evolved as an increased surface area in a dark environment enhances sensation. “But all of these are just hypotheses right now – fruit for future research!” Elizabeth said.