Evolutionary journey of crabs reveal surprising number of land adventures

SEATTLE: A recent study, published in Systematic Biology on November 6, has unveiled intriguing insights into the evolutionary journey of true crabs, a group known as Brachyura, comprising around 7,600 species.

According to media reports, the research challenges past notions and reveals that crabs have transitioned between land and sea on numerous occasions, unlike most terrestrial animals that made a single migration from the ocean.

Kristin Hultgren, an invertebrate zoologist at Seattle University, highlights the significance of this study in creating the most comprehensive evolutionary tree for true crabs, shedding light on their complex journey across different habitats. Unlike well-documented animals like birds and mammals, crabs lacked a unified tree of life until now.

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Joanna Wolfe, an evolutionary biologist at Harvard University, explains that past research treated marine, freshwater, and land crabs as distinct groups, missing the continuum that exists among them.

The study, however, presents a holistic view, emphasizing the need to examine their evolution collectively.

Wolfe and her colleagues gathered genetic data from 333 species of true crabs, combining it with fossils to construct a detailed evolutionary tree.

The findings suggest that true crabs diverged from other crustacean lineages around 230 million years ago during the Triassic Period, refining previous estimates.

The study reveals the astonishing adaptability of crabs to terrestrial life, with as many as 17 independent shifts from the ocean to land. Notably, some crabs reverted to a marine lifestyle after an extended period on land.

Katie Davis, an evolutionary paleobiologist at the University of York, applauds the combination of molecular biology, fossils, and modern numerical techniques, describing it as a fantastic approach to previously unanswerable questions.

The research also offers clues about early arthropods, hinting at the possible adaptations of insects that shared a common aquatic ancestor with crabs. By studying crabs’ successful transition to land, scientists can infer the potential requirements for early insects making a similar journey.

In essence, this study not only unravels the remarkable evolutionary saga of true crabs but also opens windows into the mysterious past of other land-dwelling arthropods.