How do crustaceans become a crab?

Researchers found five independent carcinomas in both true and false cancers and at least seven cases of removal of carcinomas.

Credit: Courtesy of Joanna M. Wolf.

Cancers have been living the meme on social media lately. The memes laugh that in the end everything will look like a crab. But it is actually based on some truth.

The crab shape has evolved many times, with evolutionary biologist LA Borradaile coining the term carcinogenesis in 1916 to describe the convergent evolutionary process in which crustaceans evolve into a crab-like form from a non-cancer-like form. The crabs are the infrared Decapodal crustacean of Brachyura and are considered “real crabs,” and most are carcinogenic. “False crabs” are from the infrared Anomura. This group evolved plans for a cancer-like body three or more times from an ancestor that did not develop cancer.

In a paper published March 11 in Biological categories, A team of researchers led by Harvard University found that the cancer-like plan of the body evolved at least five times independently in both true (Brachyura) and pseudo-carcinomas (Anomura). They also discovered that a crab-like body plan was lost at least seven times in a process called crab removal.

The team, led by first author Joanna M. Wolf, a postdoctoral researcher in the Department of Organic and Evolutionary Biology (OEB) at Harvard University, examined a composite of phylogenetic data for crabs. They pooled morphological data from major fossils and live crab populations as well as data from behavior, natural history, functional morphology and evolution, all from the authors’ previous studies.

Wolf said that building comprehensive data sets, including fossil and surviving species, that represent all lobster families is critical to identifying the key characters that define what a lobster is. “This will allow us to solve the multiple origins and losses of ‘crab’ body shapes over time and determine the timing of the origin of major evolutionary developments and the body’s plans.”

Carcinogenesis is characterized by the presence of a flat, broad carapace (hard upper shell) and a folded wing (abdomen or tail). The pleon is largely hidden under the body of the crab, in contrast to the pleon of the crab which can be seen. In de-bullying, the shield is elongated and narrow. The side is not curved and is usually visible or even elongated. De-progeny is an example of a group re-developing a lost morphology, which is thought to be a rare event in evolution.

Chief researcher Heather D. Bracken-Grissom, Associate Professor at Florida International University: “Biologists want to know how to” predict “whether the phenotype, or morphology, will evolve in a group.” “Cancer evolution screening provides a significant evolutionary time range from 250 million years ago, for which, with sufficient genetic and epigenetic data, we might be able to predict the morphology that will produce.”

Wolff agreed, “Carcinogenesis also allows us to compare the convergent evolution in fossil morphology with that of living organisms, which has not been done commonly thus far.”

Researchers are not completely sure but they hypothesize that it is possible that the common ancestor of Brachura and Anomura was not carcinogenic. “This evidence indicates that carcinogenicity did indeed evolve independently in these groups,” said co-author Javier Luque, postdoctoral researcher, OEB, Harvard University and the Smithsonian Institution of Tropical Research.

Wolff is currently working with Associate Professor Javier Ortega Hernandez, OEB, Harvard University, to test the hypothesis that carcinogenesis can be quantified by measuring the shapes of crab specimens found from the collections of Harvard University’s Museum of Comparative Zoology.


This work was supported by the National Science Foundation DEB # 1856679, DEB # 1856667, and a Postdoctoral Fellowship from the National Council for Research, Science, and Engineering of Canada (NSERC).

Details of the article and the author

Joanna M Wolf, Javier Locke, Heather D. Volcanoes-Grissom. 2021. How to Become a Crab: Typical Constraints of a Repetitive Body Plan. Biological categories DOI: 10.1002 / bies.202100020

Author (s) Correspondents

Joanna Wolf [email protected]

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