The Gulf killifish of Galveston Bay, Texas, was both nearly doomed to local extinction by humans transforming its home to a toxic soup, and also rescued by humans - through their accidental introduction of an invasive fish genetically armed with pollution-resistant traits. Following gene exchange with this invader, the Gulf killfish developed the ability to persist in polluted waters in a region of the Gulf of Mexico that's been contaminated by industrial activity for approximately 60 years. This is an example of how inter-species connectivity and a gene exchange process called hybridization play important roles in adaptation to rapid environmental changes. Increasingly, studies show that some species can rapidly adapt to a fast-changing climate. Hybridization between species is being recognized as a crucial source of genetic variation that can fuel this adaptation, but it can also reduce population fitness and cause species to collapse. "Given that many species now confront the threat of newly introduced species into their habitat, hybridization's role as a creative force, as opposed to a destructive one, is a controversial issue of pressing importance," writes Karin Pfenning in a related Perspective. To better understand if hybridization has rescued declining populations by facilitating rapid adaptation to a novel human threat, researchers here focused on a heavily polluted bay along the gulf coast of Texas, rife with industrial chemicals known to cause heart deformations in fish. In this region, the Gulf killifish (Fundulus grandis) appear to have evolved an adaptive resistance over recent decades. Elias Oziolor and colleagues used experimental and population genomic analyses to better understand the molecular nature of these adaptations. They identified variation in genes known to be associated with toxic resistance, and their analyses further suggest that these adaptations were likely enabled by the recent accidental hybridization of genetic material from the Atlantic Killifish (Fundulus heterolitus). Because the nearest population of Atlantic Killifish is found more than 2,500 kilometers away, they were likely brought to the region by human activity, possibly ship ballast water or baitfish transport. Apart from the benefit shown here, hybridization with invasive species also carries risks, emphasizes Pfenning. "Ultimately we still need to clarify the conditions under which hybridization diminishes versus enhances biodiversity in a rapidly changing world," she writes.
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