Abstract
Human activity has caused a deterioration in the health and population size of riverine species; thus, public policies have been implemented to mitigate the anthropogenic impacts of water use, watercourse transformation, and pollution. We studied the Maipo River Basin, one of the most polluted with untreated wastewater in Chile, for a period of 12 years (2007‐2019). Since the implementation of new public policies, including the operation of a wastewater collector (2012), the Maipo River Basin is currently much less polluted by untreated water than before. To analyze the impact of wastewater reduction in this river basin, we studied the native silverside (Basilichthys microlepidotus), which inhabits both polluted and unpolluted areas of the river basin. Previous studies reported the overexpression of the ornithine decarboxylase (odc) gene, heterozygote deficit, and high frequency of a homozygote odc genotype in silverside populations that inhabit wastewater‐polluted sites, suggesting a phenotypic change and genotypic selection in response to pollution. Here, a population affected and another population unaffected by wastewater were studied before and after implementing the wastewater collector. The physicochemical data of water samples, changes in odc expression and microsatellite variability, and odc genotype frequencies were analyzed. The results showed physicochemical changes in the affected site before and after the operation of the wastewater collector. The microsatellite loci showed no changes in either population. The odc expression in the affected site was higher before the operation of the wastewater collector. Significant changes in the genotype frequencies of the odc gene before and after the wastewater collector operation were detected only at the affected site, wherein the homozygous dominant genotype decreased from >59% to <25%. Our results suggest that public policies aimed at mitigating aquatic pollution can indirectly affect both gene expression and genotype frequencies of important functional genes.
Highlights
Human activities, such as excessive water use, transformation of watercourses, introduction of exotic species, and pollution (Arthington, Dulvy, Gladstone, & Winfield, 2016; Clavero, Blanco-Garrido, & Prenda, 2004; Dynesius & Nilsson, 1994; Mora, Metzger, Rollo, & Myers, 2007; Myers, 1995), negatively impact populations inhabiting freshwater systems, affecting their survival and adaptation to new environmental conditions
No studies have been performed to determine the relationship between pollution reduction and allele or genotype frequency changes in freshwater fish populations, which can be further associated with phenotype and gene expression that contribute to an organism's fitness (Agashe, Martinez-Gomez, Drummond, & Marx, 2013; Goudet & Keller, 2002)
The results showed apparent changes in the odc expression and genotype frequencies of silversides after the operation of the wastewater collector
Summary
Human activities, such as excessive water use, transformation of watercourses, introduction of exotic species, and pollution (Arthington, Dulvy, Gladstone, & Winfield, 2016; Clavero, Blanco-Garrido, & Prenda, 2004; Dynesius & Nilsson, 1994; Mora, Metzger, Rollo, & Myers, 2007; Myers, 1995), negatively impact populations inhabiting freshwater systems, affecting their survival and adaptation to new environmental conditions. It is important to note that these results were based on the samples analyzed before the construction of the wastewater collector (Vega-Retter et al, 2018) This system is a suitable model to determine the effects of pollution reduction on genotype selection. The variability of eight microsatellite loci used as the control loci in the same sites was used to describe possible changes in neutral loci variability over time
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