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First genome of an Antarctic notothenioid fish sequenced

by Greg St. Martin

North­eastern pro­fessor H. William Det­rich is part of an inter­na­tional research team that has sequenced the first genome of an Antarctic notothe­nioid fish. The break­through, he said, will shed light on the animal’s unique evo­lu­tionary adap­ta­tion to freezing waters and will help reveal how the fish will respond to rising water tem­per­a­tures pro­jected over the next two cen­turies due to cli­mate change.

Det­rich, a pro­fessor of marine mol­e­c­ular biology and bio­chem­istry at Northeastern’s Marine Sci­ence Center, col­lab­o­rated with researchers at sev­eral insti­tu­tions in South Korea and Aus­tralia as well as in Oregon. Their work was pub­lished recently in the journal Genome Biology.

Det­rich, who co-​​authored the paper, noted that the notothe­nioid fishes, a group of approx­i­mately 100 species, have adapted over the past 40 mil­lion years to Antarctic Ocean water tem­per­a­tures that dropped by more than 20 degree Cel­sius to the freezing point of sea­water. While many other fish species fled to warmer waters, the notothe­nioids remained behind. With less com­pe­ti­tion for food, the group’s pop­u­la­tion and number of species grew, a process referred to as adap­tive radiation.

By sequencing the genome of the Antarctic Bull­head notothen, the researchers found that the notothe­nioids adapted to freezing waters in part through changes to many pro­teins that func­tion in mito­chon­dria, the power plants of cells. Pre­vi­ously described evo­lu­tionary phe­nomena, including the acqui­si­tion of genes that pro­duce pro­tein antifreezes to pre­vent body fluids from freezing, were also con­firmed in the genome.

We’re pro­viding the first global snap­shot into the changes in notothe­nioid fish genomes that allowed the group to suc­cess­fully exploit its envi­ron­ment,” Det­rich said. “The genome is like a time cap­sule that records the evo­lu­tionary events asso­ci­ated with cold adaptation.”

Det­rich has been trav­eling to Palmer Sta­tion in Antarc­tica for the past 30 years to study the cold-​​loving notothe­nioids. He recently col­lected 162 tissue sam­ples from at least 10 dif­ferent species of notothe­nioid fish that will be added to Ocean Genome Legacy, a public and rare biorepos­i­tory of DNA sam­ples from marine life. OGL re-​​located last year to Northeastern’s Marine Sci­ence Center, and these new sam­ples will sig­nif­i­cantly bol­ster the OGL’s col­lec­tion of Antarctic fish DNA sam­ples for marine sci­en­tists to access.

The next step is to sequence more notothe­nioid fish genomes so that com­par­isons can be made between dif­ferent species to under­stand how they adapted to dif­ferent niches in their envi­ron­mental, Det­rich said. For example, some notothe­nioid species have evolved skele­tons that are calcium-​​poor, which makes them lighter and enables them to swim easily throughout the water column in search of food, whereas others have retained heavy skele­tons and feed pri­marily near the seafloor. By com­paring genomes from light and heavy species, researchers might be able to under­stand the process leading to reduced bone min­er­al­iza­tion, which could poten­tially inform the devel­op­ment of ther­a­peu­tics for humans with osteo­porosis, he said.

The ice­fishes, a sub­group of the notothe­nioids, have also lost the capacity to make the oxygen-​​transporting pro­tein hemo­globin as well as the red blood cells that carry hemo­globin through the cir­cu­la­tion. Com­paring ice­fish genomes to those of their red-​​blooded rel­a­tives should reveal how this fas­ci­nating “adap­ta­tion” occurred and per­haps lead to new treat­ments for human ane­mias, he said.

This work, Det­rich said, can also shed light on how the notothe­nioids might adapt to rising water tem­per­a­tures due to cli­mate change; cur­rent pro­jec­tions indi­cate a 2–5 degree Cel­sius increase over the next two centuries.

The first ques­tion is, can they do it based on the genetic con­tents of their cur­rent genomes? The second is whether evo­lu­tion can act over such a short time period to restore their ability to live at unnat­u­rally warm tem­per­a­tures,” Det­rich said.

While under­standing the fish’s genome will help the researchers answer these ques­tions with greater cer­tainty, Det­rich said the notothe­nioids face an uphill battle. For one, they will have a much shorter time period to adjust to a warming ocean than they had to adapt to freezing waters. In addi­tion, the hemo­glo­bin­less ice­fishes will undoubt­edly be chal­lenged as they deal with the lower oxygen levels that come with rising ocean tem­per­a­tures. Can they do it?

The Korea Polar Research Insti­tute, the U.S. National Insti­tutes of Health, and the U.S. National Sci­ence Foun­da­tion sup­ported this research.

Originally published in news@Northeastern on November 10, 2014

Photo courtesy William Detrich

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