Project description:As apex predators, cetaceans are recognized as sentinels for the health of marine ecosystems. The ability to identify the impacts of anthropogenic contamination on the health of a species requires long term monitoring to establish baseline health parameters. This makes health measurements that can be sampled from free ranging animals highly desirable. In the current study, we investigate the utility of skin gene expression profiling to monitor the physiological, health, and contaminant exposure status in bottlenose dolphins. Remote integument biopsies were obtained from bottlenose dolphins at three locations in the northern Gulf of Mexico prior to oil exposure (May 2010) and during summer and winter of the two years (2010-2011) following their exposure to oil from the Deepwater Horizon oil spill. A bottlenose dolphin-specific oligonucleotide microarray was used to characterize the skin transcriptomes of 94 individuals from three genetically distinguishable populations in Barataria Bay, Louisiana, Chandeleur Sound, Louisiana, and Mississippi Sound, Mississippi. Location did not significantly affect the transcriptome patterns of the dolphins included in the study. In contrast, season had a profound effect on gene expression, with nearly one-third of all genes on the array differing significantly in expression between winter and the warmer seasons (p<0.01, fold-change >1.5). Gene ontology enrichment analysis revealed that processes related to cell proliferation, motility and differentiation dominated the seasonal differences in expression, which likely reflects the differences in ambient temperature to which the skin is exposed, and possibly changes in blood flow. More subtle differences were seen between spring and summer transcriptomes (1.5% differentially expressed), with two presumed oil-exposed animals presenting gene expression profiles more similar to the summer (exposed) animals than the other spring animals. Xenobiotic pathway components also showed some seasonal trends, which may reflect crosstalk between xenobiotic pathways and those regulating corticoids, hormones, and cytokines. Seasonal effects have not previously been considered in studies assessing gene expression in cetaceans, but clearly must be taken into account when applying transcriptomic analyses to investigate their exposure or health status.

Project description:Common bottlenose dolphins serve as sentinels for the health of their coastal environments as they are susceptible to health impacts from anthropogenic inputs through both direct exposure and food web magnification. Remote biopsy samples have been widely used to reveal contaminant burdens in free-ranging bottlenose dolphins, but do not address the health consequences of this exposure. To gain insight into whether remote biopsies can also identify health impacts associated with contaminant burdens, we employed RNA sequencing (RNA-seq) to interrogate the transcriptomes of remote skin biopsies from 116 bottlenose dolphins from the northern Gulf of Mexico and southeastern U.S. Atlantic coasts. Gene expression was analyzed using principal component analysis, differential expression testing, and gene co-expression networks, and the results correlated to season, location, and contaminant burden. Season had a significant impact, with over 30% of genes differentially expressed between spring/summer and winter months. Geographic location exhibited lesser effects on the transcriptome, with 15% of genes differentially expressed between the northern Gulf of Mexico and the southeastern U.S. Atlantic locations. Despite a large overlap between the seasonal and geographical gene sets, the pathways altered in the observed gene expression profiles were somewhat distinct. Co-regulated gene modules and differential expression analysis both identified epidermal development and cellular architecture pathways to be expressed at lower levels in animals from the northern Gulf of Mexico. Although contaminant burdens measured were not significantly different between regions, some correlation with contaminant loads in individuals was observed among co-expressed gene modules, but these did not include classical detoxification pathways. Instead, this study identified other, possibly downstream pathways, including those involved in cellular architecture, immune response, and oxidative stress, that may prove to be contaminant responsive markers in bottlenose dolphin skin.

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Tursiops truncatus

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