The transcriptome-wide effects of exposure to a pyrethroid pesticide on the Critically Endangered delta smelt Hypomesus transpacificus

Abstract

Research into the effects of contaminants on fishes is often conducted on wellstudied model test species, whose responses may be different than those of endangered species. We developed an oligonucleotide microarray consisting of 12 595 genes to examine the effects of the pesticide permethrin on an endangered fish in California, USA, the delta smelt Hypomesus transpacificus. The microarray was used in combination with quantitative PCR (qPCR) assessments. We exposed larval delta smelt to permethrin for 96 h at concentrations of 0.69, 1.37, 2.56, 4.84, 12.88 and 24.94 µg l −1 , and compared the responses to a control group. The 96 h 50% lethal concentration (LC 50 ) was 4.07 µg l −1 , which is lower than those reported for model test species and similar to other endangered species. With increasing exposure concentration, we detected the differential expression of 3342 microarray features with elevated expression of genes involved in protein degradation and apoptosis, and decreased expression of immune function genes. Functional analysis indicated that genes involved in protein degradation, immune function, an unfolded protein response, meta bolism and cell signaling cascades were affected by exposure to permethrin. Many of the gene responses in the 0.69 µg l −1 treatment group differed in their directional change in expression from those at higher exposure concentrations, suggesting a potential mechanistic threshold of sub-lethal toxicity at concentrations below the lowest observed effect concentration (LOEC) of 2.56 µg l −1 . These results are consistent with non-monotonic response patterns to contaminants, and demonstrate the effects on a sensitive fish species of a widely used pyrethroid pesticide at concentrations below those that affect model test species.

Effects of high temperatures on threatened estuarine fishes during periods of extreme drought

“…Therefore, all trimmed reads were first aligned to the 454 isotig set from the previous transcriptome assembly (generated using Newbler software; Roche, Pleasanton, CA, USA; details in Jeffries et al, 2015) with Burrows-Wheeler Aligner (BWA) short read aligner v.0.6.2 (Li and Durbin, 2010). The reads that did not align were normalized and assembled using Trinity to generate 67,556 contigs.…”

“…This can be preferable to extrapolating responses of surrogate species to those of immediate conservation concern, as many stress responses can be species-specific (e.g. Jeffries et al, 2015). Understanding how high water temperatures affect threatened and endangered estuarine fishes is a crucial research focus with major ramifications for global species conservation.…”

Is Extinction Inevitable for Delta Smelt and Longfin Smelt? An Opinion and Recommendations for Recovery

“…Contaminants have been considered one of the important stressors for Delta Smelt (IEP-MAST 2015); however, the lack of a direct empirical measure of impact on fish abundance has made this factor difficult to assess. Importantly, laboratory studies using Delta Smelt have demonstrated that ambient Delta waters result in a variety of measurable impacts to Delta Smelt gene regulation, physiology, growth and fitness (Connon et al 2009(Connon et al , 2012Hasenbein et al 2014;Hammock et al 2015;Jeffries et al 2015), making this a critical topic to include in future study and manage decision-making.…”

Contaminant Effects on California Bay–Delta Species and Human Health

“…Although identification of chemical classes responsible for these effects is limited, because of the complexities resulting from mixtures of multiple chemicals, several studies (see Table 1) have highlighted pyrethroid pesticides as responsible for toxicity, endocrine disruption, and neurological impairments in both fish and their prey (Brander et al 2013(Brander et al , 2016bHasenbein et al 2015c;Jeffries et al 2015b;Weston et al 2015a). …”

“…Pyrethroids have been documented to cause general stress responses and effects on the immune, nervous, muscular and osmoregulatory systems (Jeffries et al 2015b). Decreased growth, abnormal development, and altered behavior have been detected from exposure to pyrethroids at levels detected in the Delta Jeffries et al 2015b). However, pyrethroids are not the only contaminant thought to be negatively affecting Delta Smelt.…”