A flying what? Symbiosis retracts paper claiming new species arise from accidental mating

In 2009, Donald Williamson made what many biologists said was an extraordinary claim: The reason caterpillars become butterflies is that two different species accidentally mated with one another. As Brendan Borrell explained at the time in Scientific American:

In the current issue of Proceedings of the National Academy of Sciences (PNAS), Donald Williamson, a wheelchair-bound 87-year-old zoologist from the University of Liverpool in England, suggests that the ancestors of modern butterflies mistakenly fertilized their eggs with sperm from velvet worms, also known as onychophorans. “People have been trying to find one solution that covers all of metamorphosis,” Williamson says. “I say it’s a change in taxon during development.”

One of the biologists Borrell spoke to said the paper was “better suited for the ‘National Enquirer than the National Academy.'” In a letter published a few months later in PNAS, one scientist wrote:

Perhaps the most amazing thing from this article is not the bold proposal, but the fact that the author believes that there is a research program behind his claims: “As an initial trial, it should be possible to attach an onychophoran spermatophore to the genital pore of a female cockroach and see if fertilized eggs are laid” (1). I am not sure this can be taken seriously.

Now, a journal has retracted a related paper, in Symbiosis, “Larval genome transfer: hybridogenesis in animal phylogeny:

This article has been published OnlineFirst, but is withdrawn due to significant duplication of previously published material and lack of balance. 

We hadn’t seen “lack of balance” cited as a reason for a retraction before, so we wanted to learn more. Williamson tells Retraction Watch he did not agree to the retraction:

I don’t think that I am any more biased towards larval transfer than Charles Darwin was biased towards natural selection.

In a separate statement, he added:

This review paper was accepted by Symbiosis and published on-line on 20 January 2011.  M. W. Hart and R. K. Grosberg then made representations to the editor and the publisher, and, on 24 March 2011, the paper was “withdrawn due to significant duplication of previously published material and lack of balance.”

My paper is a review of previously published material.  I draw attention to Hart and Grosberg’s misuse of C-values of DNA in their 2009 paper, and I am happy to let readers judge whether I show lack of balance.

In the 2009 paper to which he refers, published in the PNAS, Hart and Grosberg refute Williamson’s claims:

The evolution and loss of distinctive larval forms in animal life cycles have produced complex patterns of similarity and difference among life-history stages and major animal lineages. One example of this similarity is the morphological forms of Onychophora (velvet worms) and the caterpillar-like larvae of some insects. Williamson [(2009) Proc Natl Acad Sci USA 106:15786–15790] has made the astonishing and unfounded claim that the ancestors of the velvet worms directly gave rise to insect caterpillars via hybridization and that evidence of this ancient “larval transfer” could be found in comparisons among the genomes of extant onychophorans, insects with larvae, and insects without larvae. Williamson has made a series of predictions arising from his hypothesis and urged genomicists to test them. Here, we use data already in the literature to show these predictions to be false. Hybridogenesis between distantly related animals does not explain patterns of morphological and life-history evolution in general, and the genes and genomes of animals provide strong evidence against hybridization or larval transfer between a velvet worm and an insect in particular.

Indeed, in the now-retracted Symbiosis paper — we’ve made a PDF available here, since the journal has removed the article from its site completely, instead of just marking it as retracted — Williamson writes:

Recent articles by Hart and Grosberg (2009) and Minelli (2009) claim that genome sizes undermine my thesis that caterpillars evolved from onychophorans by hybridogenesis (Williamson 2009). Both of these critical articles, however, are based on C-values of DNA (weights in picograms) (Gregory 2009), but these weights lump together coding and non-coding DNA and include repetitive sequences.

Hart told us the case doesn’t have much in common with other cases we tend to cover:

Dr. Williamson sent me a copy of his Symbiosis paper after it had been accepted and published in the journal’s on-line system in advance of print publication. I pointed out to the Symbiosis editors that Dr. Williamson’s Symbiosis paper had many of the same flaws in scholarship and logic as in his 2009 PNAS paper (which generated a lot of controversy). I also pointed out that the Symbiosis paper shared many illustrations (not data graphics) and ideas in common with his previous essays in other journals. This wasn’t a case of publishing the same data twice, just very weak scholarship and lack of originality.

The editor of Symbiosis, David Richardson, wrote by email:

I am not willing to discuss this matter except to say that it did not involve any matter of wrong-doing by the author, simply that  a significant amount of the information in the paper closely duplicated that published earlier without sufficiently addressing previous concerns  about the significance of particular findings.

Williamson said that a slightly shorter version of the paper will be published next year as “The origins of larvae and the demise of Haeckelian zoology” in a book called Evolution from the Galapagos: Two centuries after Darwin.

Hat tip: Brendan Borrell