Nav: Home

How the herring adapted to the light environment in the Baltic Sea

August 26, 2019

The evolutionary process that occurs when a species colonizes a new environment provides an opportunity to explore the mechanisms underlying genetic adaptation, which is essential knowledge for understanding evolution and the maintenance of biodiversity. An international team of scientists, led by researchers from Uppsala University, Uppsala, Sweden, reports that a single amino acid change in the light-sensing rhodopsin protein played a critical role when herring adapted to the red-shifted light environment in the Baltic Sea. Remarkably about one third of all fish living in brackish or freshwater carry the same change. The study is published today in PNAS.

"The Atlantic and Baltic herring are excellent models for evolutionary studies for two reasons", explains Dr. Leif Andersson from Uppsala University and Texas A&M University who led the study. "Firstly, their enormous population sizes allow us to study the effects of natural selection without the disturbing stochastic changes in the frequency of gene variants that happens in small populations. Secondly, the colonization of the brackish Baltic Sea by herring within the last 10,000 years (following the most recent glaciation) provides an opportunity to study what happens when a species adapts to a new environment."

"We have examined the entire genome in many populations of Atlantic and Baltic herring and find that a single amino acid change in the protein rhodopsin, in which phenylalanine has been replaced by tyrosine, played a critical role during the adaptation to the Baltic Sea," says Jason Hill, scientist at Uppsala University in Uppsala, Sweden, and first author on the paper. This makes a lot of sense since rhodopsin is a light-sensitive receptor in the retina and satellite data show that the Baltic Sea has a red-shifted light environment compared with the Atlantic Ocean, because dissolved organic material absorbs blue light.

"A careful genetic analysis of our data shows that the evolutionary process must have been very rapid. We estimate that the rhodopsin gene variant found in Baltic herring increased in frequency to become the most common variant within only a few hundred years," says scientist Mats Pettersson at Uppsala University.

The amino acids phenylalanine and tyrosine are structurally very similar and only differs by the presence of a hydroxyl (-OH) moiety in tyrosine, so could this change really be so important?

"In fact, the crystal structure of rhodopsin shows that residue 261 is located in the vicinity of the chromophore retinal where light absorption occurs. The presence of tyrosine in Baltic herring rhodopsin makes light absorption red-shifted by about 10 nanometer and can thereby catch more photons in the red-shifted light environment in the Baltic Sea," says Dr. Patrick Scheerer at Charité - Universitätsmedizin Berlin, in Berlin, Germany, and one of the co-authors of the study.

When the scientists analysed the rhodopsin sequence from more than 2,000 fish they found that about one third of all species occurring in brackish or freshwater carry exactly the same genetic change as the Baltic herring whereas nearly all fish living in marine waters have a rhodopsin gene variant with phenylalanine like the Atlantic herring. "It is remarkable that we find the same mutation occur independently and at least 20 times across thousands of fish species, this provides a really striking example of convergent evolution at the molecular level," says Erik Enbody, co-author and post-doctoral fellow at Uppsala University.

"Our hypothesis is that this change in rhodopsin is particularly important during the juvenile stage and that the Baltic herring variant allows fish larvae to better utilise the light environment in the Baltic Sea when searching for food or avoiding predators", explains Leif Andersson. This hypothesis is supported by their finding that both Atlantic salmon and brown trout that always spawn in freshwater but may live most of their life in marine water have tyrosine 261 in rhodopsin like a freshwater fish. In contrast, the European and Japanese eel which both are born in marine waters but live most of their adult lives in freshwater carry phenylalanine 261 like the great majority of marine fish.
-end-
Jason Hill et al. (2019) "Recurrent convergent evolution at amino acid residue 261 in fish rhodopsin," 2019-08332, in PNAS Latest Articles, http://www.pnas.org/cgi/doi/10.1073/pnas.1908332116

For more information contact:

Professor Leif Andersson, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala in Sweden, and Texas A&M University, USA. phone: +46-18-471 4904, +46-70-425 0233, e-mail: leif.andersson@imbim.uu.se

Uppsala University

Related Science Articles:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.
Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.
Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.
Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.
Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.
World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.
PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.
Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.
Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.
Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.
More Science News and Science Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Clint Smith
The killing of George Floyd by a police officer has sparked massive protests nationwide. This hour, writer and scholar Clint Smith reflects on this moment, through conversation, letters, and poetry.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Nina
Producer Tracie Hunte stumbled into a duet between Nina Simone and the sounds of protest outside her apartment. Then she discovered a performance by Nina on April 7, 1968 - three days after the assassination of Dr. Martin Luther King Jr. Tracie talks about what Nina's music, born during another time when our country was facing questions that seemed to have no answer, meant then and why it still resonates today.  Listen to Nina's brother, Samuel Waymon, talk about that April 7th concert here.