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An indigenous religious ritual selects for resistance to a toxicant in a livebearing fish


Human-induced environmental change can
affect the evolutionary trajectory of populations.
In Mexico, indigenous Zoque people annually
introduce barbasco, a fish toxicant, into the
Cueva del Azufre to harvest fish during a religious
ceremony. Here, we investigated tolerance
to barbasco in fish from sites exposed and unexposed
to the ritual. We found that barbasco
tolerance increases with body size and differs
between the sexes. Furthermore, fish from sites
exposed to the ceremony had a significantly
higher tolerance. Consequently, the annual ceremony
may not only affect population structure
and gene flow among habitat types, but the
increased tolerance in exposed fish may indicate
adaptation to human cultural practices in a
natural population on a very small spatial scale.