Abstract
The BP Deepwater Horizon Oil Disaster was the most catastrophic offshore oil spill in U.S. history, yet we still have a poor understanding of how organisms could evolve in response to the toxic effects of crude oil. This study offers a rare analysis of how fitness‐related traits could evolve rapidly in response to crude oil toxicity. We examined evolutionary responses of populations of the common copepod Eurytemora affinis residing in the Gulf of Mexico, by comparing crude oil tolerance of populations collected before versus after the Deepwater Horizon oil spill of 2010. In addition, we imposed laboratory selection for crude oil tolerance for ~8 generations, using an E. affinis population collected from before the oil spill. We found evolutionary increases in crude oil tolerance in the wild population following the oil spill, relative to the population collected before the oil spill. The post‐oil spill population showed increased survival and rapid development time in the presence of crude oil. In contrast, evolutionary responses following laboratory selection were less clear; though, development time from metamorphosis to adult in the presence of crude oil did become more rapid after selection. We did find that the wild population, used in both experiments, harbored significant genetic variation in crude oil tolerance, upon which selection could act. Thus, our study indicated that crude oil tolerance could evolve, but perhaps not on the relatively short time scale of the laboratory selection experiment. This study contributes novel insights into evolutionary responses to crude oil, in directly examining fitness‐related traits before and after an oil spill, and in observing evolutionary responses following laboratory selection.
Highlights
The BP Deepwater Horizon Oil Disaster of 2010 was the most catastrophic offshore spill in U.S history, with an estimated 4.6 million barrels of oil spilling into the Gulf of Mexico over 86 days (Griffiths, 2012)
We examined evolutionary responses of the populations to the “water-accommodated fraction” of crude oil, which harbors the polycyclic aromatic hydrocarbons (PAHs) and other toxic compounds (Almeda et al, 2013; Faksness, Brandvik, & Sydnes, 2008; Forth, Mitchelmore, Morris, & Lipton, 2017; Liu & Kujawinski, 2015; Melbye et al, 2009)
Our results revealed evolutionary shifts in fitness-related traits in a population of the copepod E. affinis in response to crude oil toxicity, following the Deepwater Horizon oil spill of 2010 in the Gulf of Mexico (Figures 1–3; Tables 1–3)
Summary
The BP Deepwater Horizon Oil Disaster of 2010 was the most catastrophic offshore spill in U.S history, with an estimated 4.6 million barrels of oil spilling into the Gulf of Mexico over 86 days (Griffiths, 2012). We examined evolutionary responses of the populations to the “water-accommodated fraction” of crude oil, which harbors the PAHs and other toxic compounds (Almeda et al, 2013; Faksness, Brandvik, & Sydnes, 2008; Forth, Mitchelmore, Morris, & Lipton, 2017; Liu & Kujawinski, 2015; Melbye et al, 2009) Copepods, with their exceedingly large numbers and relatively short generation times (~15–20 days in E. affinis) are likely to experience significant evolutionary responses to environmental perturbations. Extensive sampling by the Lee lab in March of 2011 (~11 months after the Deepwater Horizon oil spill) revealed a marked absence of E. affinis, and the plankton community in general, in locations where they are typically common, including in Fourleague Bay, Blue Hammock Bayou (29°18′19.15′′N, 91°7′42.48′′W), and Oyster Bayou (29°08′36′′N, 90°43′00′′W), Louisiana, USA The antibiotic Primaxin (20 mg/L) was added at each water change to reduce bacterial growth
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