PNAS retraction weakens theory that fish travel with siblings

In 2016, researchers at Oregon State University published a paper in PNAS that surprised the research community. They showed that certain fish species travel with their siblings — even fighting against the currents of the Pacific Ocean to stay together.

Needless to say, the research community was skeptical, given how difficult a feat this would be. And their skepticism appears to have been warranted.

Recently, the authors — led by Su Sponaugle — retracted the paper, saying a re-analysis of their data using newly developed research tools has erased their confidence in the results. According to Sponaugle, the quick reversal was thanks to the new technology and open data sharing, which led their findings to be successfully challenged within months of publication. She said her team conducted the study with the “best available knowledge we had at the time,” including what they thought were the most advanced tools available to them: 

We followed all the right scientific steps.

While she and her co-authors pulled the paper, believing it was the right thing to do, she told us she wishes the scientific record would show more of the behind-the-scenes discussions that led to the decision.

Sisterhood of the travelling snapper

In November 2016, Sponaugle and her colleagues published “Long-term aggregation of larval fish siblings during dispersal along an open coast,” which said that a certain species of fish — splitnose rockfish a.k.a. Pacific snapper — is able to fight the currents of the Pacific Ocean and stick together with its siblings as it disperses along the coast.

The paper’s main finding ran counter to the prevailing ideas of how young fish moved in the open water. Carlos Garza, a researcher at the National Oceanic and Atmospheric Administration Southwest Fisheries Science Center, told us:

The idea [that siblings could stick together] for long periods of time in this ecosystem is hard to reconcile with the physics of the system, without some previously undescribed active behavior. It required invoking some fairly extraordinary mechanisms that would be game changers for the field.

It’s not the dominant hypothesis and that’s why it was a PNAS paper.

Garza, along with his NOAA colleague Eric Anderson (both researchers also have appointments at the University of California, Santa Cruz), were able to show within a matter of months that the dataset released alongside the PNAS article didn’t support the so-called “sibling dispersal” hypothesis. The NOAA researchers, who also work with rockfish species in California’s Monterey Bay and elsewhere, have developed new species identification tools using next-generation DNA sequencing; with the help of the OSU team, who provided the original biological samples, the two demonstrated that the fish, thought to be siblings, were actually two different species.

PNAS retracted the paper on Dec. 18, at the request of the authors. In the notice, the authors wrote:

Given these new findings, we conclude that our estimates of relatedness were inflated within dyads containing individuals from the same species. Thus, while it is still possible that siblings may travel together in the pelagic ocean, we currently do not have evidence to support this hypothesis.

Everyone involved said that the episode was close to a best-case scenario, as far as retractions go. Anderson told us the OSU team made an “honest mistake” — one he had made himself in his own research — and described their interaction as “collegial.” The teams even worked closely on a letter to PNAS, sent in July, outlining what the re-analysis had found. Anderson noted that he has previously collaborated with one member of the OSU team and plans to continue to do so.

James Estes, the subject matter editor at PNAS who edited the original paper (he’s also a professor at UC Santa Cruz) told us:

After looking carefully at Anderson and Garza’s results, the authors opted to retract the paper… People behaved professionally and science worked as it is supposed to work.

A matter of perspective

While Sponaugle and her colleagues described their interaction with Garza and Anderson in the retraction notice, she felt it wasn’t enough.

I think if it had stretched out over years, it wouldn’t have led to a [retraction], it would have led to a publication. [Garza and Anderson’s analysis] would have been just another paper…

We would like the debate to be visible, rather than us just having to take our paper away. And people should learn from it.

In fact, she says she tried to offer PNAS a different option: Publish a “Perspectives” piece from the OSU team to provide more detail on the use of the new species identification tool. However, PNAS declined to allow that and asked the OSU team to either make a correction or a retraction. Perspectives pieces can only be submitted at the invitation of the editorial board, PNAS says on its website.

But Estes, the PNAS editor, told us:

That option was off the table almost from the beginning.

He added:

I think the OSU group was trying to identify a way forward to resolve the mistakes… PNAS told me that this did not appear to be appropriate for a Perspective in PNAS. Given that the authors and Garza/Anderson agreed on the data interpretation, we subsequently identified two options — a correction and a retraction. After discussing with the authors, they decided on a retraction. I thought this was the right thing to do and told them so.  

The time spent going back and forth with the journal kept the paper in the literature, with an incorrect finding right in the title. The paper has been cited twice, according to Clarivate Analytics’ Web of Science, once in July (when the two teams submitted the critical letter to the journal) and once in October.

Sponaugle told us her team will continuing monitoring rockfishes along the Oregon coast. Now that she’s aware of the new technique to identify species, she’s hopeful that future research will ultimately prove them right. There’s a body of work that has shown siblings of other types of sea creatures, like mollusks, to move around together. And rockfish have exhibited complex behavior not often seen in other fishes, like sexual selection. She told us:

The problem is finding funding to do next-generation sequencing. We’ll continue collect data and seek funds to do it someday, maybe even collaborate with Eric and Carlos.

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