Abstract
Marine wildlife populations are adapted to survive in highly dynamic environments. However, identifying the effects of endogenous versus exogenous variables on marine mammal physiology remains a substantial challenge in part because of the logistical constraints that limit the collection of physiological data in free-ranging animals. Measuring genome-wide gene expression is one minimally invasive method that can be used to elucidate how free-ranging cetaceans' physiological responses shift with changing environmental conditions or demographic states, i.e. reproductive status and maturity. We identified transcriptomic differences among bottlenose dolphins (Tursiops truncatus) from the Southern California Bight using RNAseq data from the skin of 75 individuals to examine gene expression associated with sex, pregnancy status, sea surface temperature, geographic location and ecotype. We identified transcriptomic variation between two genetically distinct ecotypes as well as variation related to environmental conditions among groups that exhibit little evidence of genetic divergence. Specifically, we found differential expression of genes associated with structural development, cellular starvation and immune response. Sex and pregnancy status explained a small proportion of the observed variation, in contrast to sea surface temperature, which explained a substantial amount of transcriptomic variation. However, these measured variables did not account for all of the differential expression observed between ecotypes and among geographically distinct groups. Additional research is needed to identify other endogenous or exogenous factors that may be contributing to observed transcriptomic differences among ecotypes.
Highlights
Marine mammals inhabit highly dynamic environments where they are regularly exposed to a variety of conditions and stressors, both natural and human mediated (Becker et al, 2010; Carmichael et al, 2012; Forney et al, 2017), which have been linked to changes in reproductive health (Hansen, 2009; Liptrap, 1993; Rensis and Scaramuzzi, 2003; Tilbrook et al, 2000) and survival
We identified transcriptomic differences among bottlenose dolphins (Tursiops truncatus) from the Southern California Bight using RNAseq data from the skin of 75 individuals to examine gene expression associated with sex, pregnancy status, sea surface temperature, geographic location and ecotype
This study represents the one of first RNAseq analyses of marine mammals and temperature in the Southern California Bight (SCB) and one of the few RNAseq analyses that have been conducted for wild cetaceans in the USA
Summary
Marine mammals inhabit highly dynamic environments where they are regularly exposed to a variety of conditions and stressors, both natural and human mediated (Becker et al, 2010; Carmichael et al, 2012; Forney et al, 2017), which have been linked to changes in reproductive health (Hansen, 2009; Liptrap, 1993; Rensis and Scaramuzzi, 2003; Tilbrook et al, 2000) and survival. Detecting physiological changes in wild marine mammals in situ remains a substantial challenge due to the logistical constraints that limit the ability to collect physiological data from free-ranging animals. Skin tissue collected through biopsies is one sample type that has been used to monitor physiology in situ in many marine mammal populations (Fossi et al, 1992; Mollenhauer et al, 2009; Van Dolah et al, 2015). Marine mammal skin serves as the primary protective barrier from the external environment and maintains internal homeostasis (Elias, 1988; Elias et al, 1987) and is one of the only tissue types widely accessible for genetic and physiological analysis (Kellar et al, 2013, 2006). Much of this work has centred upon on identifying in vitro cellular responses to contaminant exposure (Fossi et al, 2010, 1992; Panti et al, 2011) and has yet to be applied widely to physiological questions in wild populations
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