Abstract
For natural populations to adapt to anthropogenic threats, heritable variation must persist in tolerance traits. Silver nanoparticles, the most widely used engineered nanoparticles, are expected to increase in concentrations in freshwaters. Little is known about how these particles affect wild populations, and whether genetic variation persists in tolerance to permit rapid evolutionary responses. We sampled wild adult whitefish and crossed them in vitro full factorially. In total, 2896 singly raised embryos of 48 families were exposed to two concentrations (0.5 μg/L; 100 μg/L) of differently sized silver nanoparticles or ions (silver nitrate). These doses were not lethal; yet higher concentrations prompted embryos to hatch earlier and at a smaller size. The induced hatching did not vary with nanoparticle size and was stronger in the silver nitrate group. Additive genetic variation for hatching time was significant across all treatments, with no apparent environmental dependencies. No genetic variation was found for hatching plasticity. We found some treatment‐dependent heritable variation for larval length and yolk volume, and one instance of additive genetic variation for the reaction norm on length at hatching. Our assessment suggests that the effects of silver exposure on additive genetic variation vary according to trait and silver source. While the long‐term fitness consequences of low‐level silver exposure on whitefish embryos must be further investigated to determine whether it is, in fact, detrimental, our results suggest that the evolutionary potential for adaptation to these types of pollutants may be low.
Highlights
Technological innovations can pose significant threats to natural populations if their products or by-products are released into the environment
Due to variable fertilization success among females, the design was condensed at 136.5 degree days (DD) postfertilization, and embryos were redistributed to 24-well plates, again such that a set of two plates contained one replicate set
In the context of our experimental conditions, we found that treatment of whitefish embryos with both AgNP and silver nitrate did not increase embryonic mortality
Summary
Technological innovations can pose significant threats to natural populations if their products or by-products are released into the environment. One of the foremost challenges that aquatic organisms have faced is exposure to various toxicants through the effluents of sewage treatment plants (Fabrega et al 2011; Brazzola et al 2014). AgNP in particular are anticipated to increase in concentrations in natural waters in the coming decade (Handy et al 2008; Scown et al 2010b). It is notoriously challenging to quantify concentrations in the wild (Mueller and Nowack 2008; Gottschalk et al 2009), as nanoparticles are prone to undergoing dynamic transformations once in the environment (Scown et al 2010b; Schultz et al 2015). Monitoring of silver residues in sewage influents and effluents was largely suspended in the 1990s (Muth-Ko€hne et al 2013), making it difficult to quantify potential discharge
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