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Human Appetite Driving Evolution of Smaller Conch Size

Update Date: Mar 19, 2014 06:25 PM EDT

The human appetite for seafood has been linked to the evolution of smaller conch size, according to a new study.

The latest research suggests that the Caribbean fight conch living in the lagoons of Panama's Bocas del Toro 7,000 years ago had 66 percent more meat than their modern descendents.

Scientists explain that the persistent harvesting of the largest conchs made it advantageous for conchs to evolve to mature at a smaller size.

Researchers said this kind of human-driven evolution of wild animals is called "unnatural selection" and has only been documented under scenarios of high-intensity harvesting, like industrialized fishing.

"These are the first evidence that low-intensity harvesting has been sufficient to drive evolution," said lead author Aaron O'Dea of the Smithsonian Tropical Research Institute. "The reason may be because the conch has been subjected to harvesting for a long period of time." 

Researchers compared mature shell sizes before human settlement to those excavated from human trash heaps.

After analyzing the size of shells and the thickness of lips in fossil, scientists found that size at sexual maturity in conchs declined during the past 1,500 years in concert with human harvesting.

Researchers explained that the fighting conch Strombus pugilis lives hidden in the muddy sediments of lagoons. The conch only emerges when it reaches sexual maturity, which it has thickened up its out lip as protection against predators, to compete for mates.

Researchers said the latest findings reveal the effects of long-term subsistence harvesting on an important marine resource. Researchers said the latest findings also suggest that declining yields may not be the only detrimental effects of an evolutionary change to mature at smaller size. They believe that the ability of the conchs to reproduce, their quality of offspring and other important traits can be damaged by size-selective evolution.

"There is a glimmer of hope that the evolutionary trend toward smaller size can be halted or reversed," archeologist Thomas Wake of UCLA's Cotsen Institute of Archeology said in a statement. He notes that some modern sites prohibit the harvesting of the largest conchs.

"Marine protected areas not only serve to protect biodiversity, they can also help maintain genetic diversity. This study shows that such genetic diversity is critical to sustain value of marine resources for the millions of humans that rely upon subsistence harvesting around the world," he concluded.

The findings are published in the journal Proceedings of the Royal Society B.

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