Abstract
The area and timing of the Deepwater Horizon oil spill highlight the need to study oil and hypoxia exposure in early life stage fishes. Though critical to health, little research has targeted the effect of oil and hypoxia exposure on developing immune systems. To this end, we exposed sheepshead minnows (Cyprinodon variegatus) at three early life stages: embryonic; post-hatch; and post-larval, to a high energy water accommodated fraction (HEWAF) of oil, hypoxia, or both for 48 hours. We performed RNAseq to understand how exposures alter expression of immune transcripts and pathways. Under control conditions, the embryonic to post-hatch comparison (first transition) had a greater number of significantly regulated immune pathways than the second transition (post-hatch to post-larval). The addition of oil had little effect in the first transition, however, hypoxia elicited changes in cellular and humoral immune responses. In the second transition, oil exposure significantly altered many immune pathways (43), and while hypoxia altered few pathways, it did induce a unique signature of generally suppressing immune pathways. These data suggest that timing of exposure to oil and/or hypoxia matters, and underscores the need to further investigate the impacts of multiple stressors on immune system development in early life stage fishes.
Highlights
Our data suggest that in the first life stage transition, exposure to oil, hypoxia, or both has only a marginal effect on the regulation of immune pathways in sheepshead minnows. This may be partially due to the fact that the immune system is still undergoing development and during this transition fish are being fully exposed to their environment for the first time, which is likely to contain bacteria, viruses, parasites, and other foreign antigens that induce immune responses and swamp out any potential stressor-induced effects
In the second transition, exposure to oil under both normoxic and hypoxic conditions caused significant alteration of many immune pathways (40 in normoxic oil, 22 in hypoxic oil, 18 present in both). These data indicate that early life stage fish display differential susceptibility to contaminant-induced effects on immune pathways; that small age www.nature.com/scientificreports differences can have dramatic effects on immune-related transcriptomic responses to stressors; and that larval fish in the transition from post-hatch to post-larval may have increased susceptibility to contaminant-induced immune effects
In the normoxic control exposure scenarios, this may indicate that immune-related pathways are developing and being activated, as the fish transition from embryo to yolk-sac larvae, and from yolk-sac larvae to free feeding larvae
Summary
The goal of this research was to understand how both stressors alone and in combination impact the immune system of developing C. variegatus by using RNA sequencing (RNAseq) to assess the expression of immune-related genes and pathways in three early life stages
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