Lanternfish provide evidence for controversial evolutionary process | Polarjournal
Lanternfish like this ice lanternfish are small deep-sea dwelling fish that can produce light themselves. With about 250 known species worldwide, they are one of the most diverse groups and are the main food source for many polar species. Image: iNaturalist App

For most people, krill is considered the most important food source in polar regions. But in fact, in the twilight of the Arctic and Antarctic deep sea, another group has emerged almost unrecognized as a keystone species, lanternfish. A British-Australian research group has now investigated how this ecologically important group evolved to this point in the first place and have uncovered the first evidence of a previously controversial evolutionary process.

Instead of geographic isolation, other, as yet unknown, factors appear to have been responsible for the evolution of the ancestors of today’s lanternfishes into the more than 250 different known species. This is the sensational result of a broad study by researchers from the Universities of Bristol and Western Australia and the British Antarctic Survey BAS. With their findings, they are fueling a controversial debate, namely that biodiversity does not only evolve through geographic isolation, but that other biological processes may also play a role in the formation of new species. The team published their work in the journal Global Ecology and Biogeography.

The graph shows the global distribution of ecoregions, of which 33 are known. The colors thereby combine the different lanternfish communities. Genetic analyses thereby show that the polar species had indeed evolved separately from the other populations due to geographic conditions. In contrast, however, overlaps have been discovered in temperate and tropical regions, suggesting that species without isolations had formed there. Graphic: Freer et al (2022)

For the study, the research team led by Dr. Jennifer Freer, a marine ecologist at BAS, examined the genetic information of lanternfish and created a distribution map . In addition, the team studied the relationships of the different species and discovered that species that are closely related to each other are also geographically close. Until now, however, it was assumed that new species form when populations of a species are separated by geographic conditions and thus there is no longer any contact between populations. Over time, new genetically determined adaptations develop and two new species are thus created from one species. In the case of lanternfish, these would be, for example, the formation of the Antarctic Convergence Line, which was formed when the land bridge between South America and Antarctica broke up. This was also evident in the team’s analysis. But for temperate and tropical regions, no isolation could explain speciation. “This is a really exciting and important finding because it is the first global evidence to support the idea of speciation without strict geographic isolation in these fishes,” Dr. Freer explains. And Professor Martin Genner of the University of Bristol adds, “This idea remains a controversial biological process, so the insights provided by lanternfish are extremely valuable to our understanding of evolution.”

The team had focused their study on lanternfish because this group represents one of the most diverse families of fish. The approximately 250 species are distributed around the globe and are also ecologically very important. Some species are also native to the polar regions, where they provide food for other animal groups such as whales and seals. In the Southern Ocean, beyond the Antarctic Convergence, they even form the main food source for king and emperor penguins. Because Antarctic lanternfish feed primarily on krill, they are one of the main reasons for the huge king penguin colonies on South Georgia. There the fish find everything they need, including isolation from their now distant relatives in the north. At least for now, because with the increasing warming and thus the border of the convergence line becoming more fragile, a visit of the northern kin could be quite possible. Whether this is in the sense of the fish?

Dr Michael Wenger, PolarJournal

Link to study: Freer J. et al (2022) Glob Ecol Biogeo Epub Global phylogeography of hyperdiverse lanternfishes indicates sympatric speciation in the deep sea; https://doi.org/10.1111/geb.13586

Contributed image: lanternfish Electrona antarctica (C) NOAA

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