Abstract
In western South America (WSA) two subspecies of bottlenose dolphin are recognized: Tursiops truncatus gephyreus, predominantly found in estuaries and river mouths, and Tursiops truncatus truncatus, occurring along the continental shelf. Despite a partial spatial overlap, both subspecies are considered to occupy different habitats and ecological niches. In the present study, chemical analyzes as well as biochemical and molecular biomarkers were used to investigate the influence of niche partitioning over metabolic pathways associated with the detoxification of persistent organic pollutants (POPs), antioxidant metabolism, immune activity and lipid metabolism in Tursiops truncatus subspecies living in parapatry. Overall, the profile and levels of bioaccumulated PCBs, pesticides and PBDEs were similar between groups, with a greater variety of pesticides, such as γ-HCHs, heptachlor, oxychlordane and o,p'DDT, detected in T. truncatus gephyreus. Multivariate analysis of variance (MANOVA) and non-metric multidimensional scaling (NMDS) results indicated that glutathione reductase (GR) and superoxide dismutase (SOD) enzymatic activities were higher in coastal dolphins, as were the mRNA levels of metallothionein 2A (MT2A), interleukin-1α (IL-1α), ceramide synthase 3 (CERS3) and fatty acid elongase (ELOVL4). In parallel, mRNA levels of fatty acid synthase complex 1 (FASN 1) were higher in oceanic dolphins. These findings suggest that, due to their occurrence in coastal habitats, T. truncatus gephyreus is more exposed to environmental pollutants and pathogenic microorganisms. Likewise, niche partitioning may influence lipid biosynthesis, possibly due to differences on feeding habits, reflecting in an enhanced long chain ceramides biosynthesis in T. truncatus gephyreus. Collectively, these data reinforce the need to address habitat specificities in conservation efforts, since distinct groups can be facing different anthropogenic pressures in WSA.
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