Contaminant Exposure Linked to Cellular and Endocrine Biomarkers in Southern California Bottlenose Dolphins

Cetaceans in the Southern California
Bight (SCB) are exposed to
high levels of halogenated organic contaminants (HOCs), which have
previously been linked to impaired reproductive health and immune
responses. We used a combination of molecular tools to examine the
potential physiological impacts of HOC exposure in two bottlenose
dolphin (Tursiops truncatus) ecotypes in the SCB.
We quantified 25 HOCs in the blubber of 22 biopsies collected from
males between 2012 and 2016. We then analyzed genome-wide gene expression
in skin using RNA-sequencing and measured blubber testosterone to
compare HOC exposure with cellular and endocrine biomarkers. We found
high levels of HOCs in both ecotypes with significantly higher total
polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers
(PBDEs), tris­(4-chlorophenyl)­methanol (TCPMOH), and chlordane-related
compounds in the coastal ecotype versus the offshore ecotype. We found
evidence of PBDE bioaccumulation in both ecotypes, however, the pattern
of bioaccumulation or endocrine disruption for other HOCs was different
between the ecotypes, suggesting potential endocrine disruption in
the coastal ecotype. We also observed correlations between HOCs and
gene coexpression networks enriched for xenobiotic metabolism, hormone
metabolism, and immune response that could indicate cellular effects
from HOC exposure. By integrating measurements of HOC load with both
transcriptome profiling and endocrine biomarkers, our approach provides
insight into HOC exposure and potential impacts on wild cetacean health
in southern California.