507
breaks, responsive genes for DNA damage, and apoptosis when exposed to weathered DWH surrogate oil WAF concentrations ranging from 300 μg/L to 3000 μg/L
∑50PAH. These exposure levels were chosen to simulate PAH concentrations
found in field-collected sediments (284 to >8000 μg/L ∑50PAH) not long after the
DWH spill (Pilcher et al. 2014).
29.3.8 Reproduction
Reproduction in fish is controlled by an organized endocrine system, the
hypothalamic- pituitary-gonadal axis (HPG axis), which consists of the hypothalamus, pituitary gland, and gonadal glands. In oviparous females, the HPG axis is
referred to as the HPG-liver axis given that many egg yolk and chorionic (e.g., vitellogenin and choriogenin) proteins are synthesized in the liver, necessary for oocyte
growth and development.
There is evidence that oil exposure can impact reproductive fitness of fish through
endocrine disruption and cytotoxic effects on germ cells (Iwanowicz and Blazer
2009; Zhang et al. 2016; Lee et al. 2017). However, there have been relatively few
studies investigating the impacts on reproduction from the 2010 DWH oil spill.
Microarray and RNA-seq analysis of gene expression in field-collected Gulf killifish showed a decrease of vitellogenin, choriogenin, and zona pellucida (glycoprotein layer surrounding egg) genes in the liver (Whitehead et al. 2012; Garcia et al.
2012) coinciding with upregulation of the CYP/AhR pathway genes. Though these
studies illustrate alterations of genes involved in egg development, what remains
unclear are the long-term consequences oil exposure may have on egg development
and fecundity. In a full life-cycle (larvae through reproduction) study using sheepshead minnows exposed to oil-contaminated sediments for 19 weeks, Raimondo
et al. (2016) were able to demonstrate a decrease in the first-generation fecundity of
fish exposed to 358 and 751 mg/kg∑50PAH contaminated sediments. While these
studies may shed light on possible mechanisms of impairment, additional studies
are warranted to determine the sublethal effects of the DWH oil spill on reproductive fitness and the ramifications those effects have on wild populations.
29.3.9 Transcriptomic Effects Not Yet “Anchored”
by Phenotypic Observations
The use of global transcriptome profiling techniques has great utility for understanding subtle, sublethal effects of contaminant exposure on exposed species
(Schirmer et al. 2010). The recent development and adoption of RNA-seq as a high
throughput sequencing approach has allowed researchers to rapidly and accurately
quantify the state of the transcriptome in non-model fish species following exposure
29 Digging Deeper than LC/EC50: Nontraditional Endpoints and Non-model Species…
breaks, responsive genes for DNA damage, and apoptosis when exposed to weathered DWH surrogate oil WAF concentrations ranging from 300 μg/L to 3000 μg/L
∑50PAH. These exposure levels were chosen to simulate PAH concentrations
found in field-collected sediments (284 to >8000 μg/L ∑50PAH) not long after the
DWH spill (Pilcher et al. 2014).
29.3.8 Reproduction
Reproduction in fish is controlled by an organized endocrine system, the
hypothalamic- pituitary-gonadal axis (HPG axis), which consists of the hypothalamus, pituitary gland, and gonadal glands. In oviparous females, the HPG axis is
referred to as the HPG-liver axis given that many egg yolk and chorionic (e.g., vitellogenin and choriogenin) proteins are synthesized in the liver, necessary for oocyte
growth and development.
There is evidence that oil exposure can impact reproductive fitness of fish through
endocrine disruption and cytotoxic effects on germ cells (Iwanowicz and Blazer
2009; Zhang et al. 2016; Lee et al. 2017). However, there have been relatively few
studies investigating the impacts on reproduction from the 2010 DWH oil spill.
Microarray and RNA-seq analysis of gene expression in field-collected Gulf killifish showed a decrease of vitellogenin, choriogenin, and zona pellucida (glycoprotein layer surrounding egg) genes in the liver (Whitehead et al. 2012; Garcia et al.
2012) coinciding with upregulation of the CYP/AhR pathway genes. Though these
studies illustrate alterations of genes involved in egg development, what remains
unclear are the long-term consequences oil exposure may have on egg development
and fecundity. In a full life-cycle (larvae through reproduction) study using sheepshead minnows exposed to oil-contaminated sediments for 19 weeks, Raimondo
et al. (2016) were able to demonstrate a decrease in the first-generation fecundity of
fish exposed to 358 and 751 mg/kg∑50PAH contaminated sediments. While these
studies may shed light on possible mechanisms of impairment, additional studies
are warranted to determine the sublethal effects of the DWH oil spill on reproductive fitness and the ramifications those effects have on wild populations.
29.3.9 Transcriptomic Effects Not Yet “Anchored”
by Phenotypic Observations
The use of global transcriptome profiling techniques has great utility for understanding subtle, sublethal effects of contaminant exposure on exposed species
(Schirmer et al. 2010). The recent development and adoption of RNA-seq as a high
throughput sequencing approach has allowed researchers to rapidly and accurately
quantify the state of the transcriptome in non-model fish species following exposure
29 Digging Deeper than LC/EC50: Nontraditional Endpoints and Non-model Species…