Human cultural practices can affect evolution in wildlife populations, researchers have found.
A religious ceremony held by the indigenous Zoque people of southern Mexico has led to evolutionary change in a local fish species.
A report, published this month by the journal Biology Letters, discovered that populations of Atlantic Molly (Poecilia mexicana) exposed to the toxin rotenone, as part of annual religious ceremony, have evolved significant resistance to the toxin.
The Zoque people release toxic barbasco root into the water as part of an annual ritual.
The ritual
For centuries the Zoque people have walked deep in to a cave of the Cueva del Azufre system to carry out a fertility ceremony, asking the gods to end the dry season and allow crops to grow. As part of the ceremony, barbasco plant root-containing the fish toxin rotenone- is released into the cave’s waters. Paralysed fish, seen as a gift from the gods, are collected and eaten until the crops are ready for harvest.
The team of researchers led by Dr. Michael Tobler, an evolutionary ecologist at Oklahoma State University, and Dr. Gil Rosenthal, a biology professor at Texas A&M decided to investigate the effects of barbasco root after witnessing the ceremony in 2007.
Lab work
“We wanted to do a lab experiment where we exposed fish from different parts of the creek to barbasco,” Tobler says. “Some of these fish had been more exposed than others.”
The laboratory work discovered fish populations annually exposed during the ceremony could tolerate the poisonous water for twice as long as other populations.
Dr. Tobler believes this demonstrates that human cultural practices have led to the evolution of tolerance through natural selection.
“The cool thing is that this ceremony has gone on a long time and that the fish responded to it evolutionarily,” Tobler says. “Lots of species couldn’t live with these changes. It highlights how nature is affected by human activity.”
Several examples of evolution in response to human-induced environmental change exist, including the evolution of dark colouration of the peppered moth, which provided camouflage in areas where the moth’s habitat had been darkened by soot from nearby factories.
Scientists believe this latest research demonstrates that human-induced evolution can occur in a small population of an endangered species, a process which was previously thought to be unlikely.
Future of the Zoque
Since inspiring this research in 2007 the Zoque people have been forced to abandon their ceremony due to pressure from the Mexican government to protect the endangered fish. Tobler and Rosenthal, however, are keen to protect both the fish and the cultural practices of the Zoque people.
“We need to understand what the impact really is on these fish rather than eliminate the ceremony completely,” Tobler says. “We want to hopefully find a balance between the cultural practices of these people and the ecosystem.”
Click here to read the full paper.
William McLennan 