Why do some fish thrive in oil-polluted water?

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Why do some fish thrive in oil-polluted water?

News Scientists thought guppies in Northern Trinidad could be a rare example of adaptation to crude oil pollution. But they found something else.
PUBLISHED: 26 JAN 2016 When scientists from McGill University learned that some fish were proliferating in rivers and ponds polluted by oil extraction in Southern Trinidad, it caught their attention. They thought they had found a rare example of a species able to adapt to crude oil pollution. At a time when humans are imposing an unprecedented burden on the world's ecosystems, studying how organisms can tolerate pollutants is crucial to understanding the impact of human activities – and to helping to mitigate it in the future. By Melody Enguix When scientists from McGill University learned that some fish were proliferating in rivers and ponds polluted by oil extraction in Southern Trinidad, it caught their attention. They thought they had found a rare example of a species able to adapt to crude oil pollution. At a time when humans are imposing an unprecedented burden on the world's ecosystems, studying how organisms can tolerate pollutants is crucial to understanding the impact of human activities – and to helping to mitigate it in the future. Led by Dr. Gregor Rolshausen, then a postdoctoral researcher at McGill working with Prof. Andrew Hendry, the team went to study the guppy fish living in polluted areas, comparing their morphology and genetic makeup to those of similar guppies from non-polluted parts of Trinidad.

The ability of populations to rapidly adapt to new environments will determine their future in an increasingly human-modified world. Although meta-analyses do frequently uncover signatures of local adaptation, they also reveal many exceptions. We suggest that particular constraints on local adaptation might arise when organisms are exposed to novel stressors, such as anthropogenic pollution. To inform this possibility, we studied the extent to which guppies Poecilia reticulata  show local adaptation to oil pollution in southern Trinidad. Neutral genetic markers revealed that paired populations in oil-polluted versus not-polluted habitats diverged independently in two different watersheds. Morphometrics revealed some divergence (particularly in head shape) between these environments, some of which was parallel between rivers. Reciprocal transplant experiments in nature, however, found little evidence of local adaptation based on survival and growth. Moreover, subsequent laboratory experiments showed that the two populations from oil-polluted sites showed only weak local adaptation even when compared to guppies from oil-free northern Trinidad. We conclude that guppies show little local adaptation to oil pollution, which might result from the challenges associated with adaptation to particularly stressful environments. It might also reflect genetic drift owing to small population sizes and/or high gene flow between environments.