Responses to lowered salinity in the Pacific spiny dogfish, Squalus suckleyi, a marginally euryhaline shark

• Author / Creator

  Cole, Dylan M

• Euryhalinity is the ability to survive in multiple environmental salinities. Full euryhalinity is rare within the elasmobranchs (rays, skates, and sharks), however, marginal euryhalinity is comparatively more common. The physiology underlying these adaptations is relatively understudied in cartilaginous fishes compared to bony fishes. I investigated changes in both gill morphology and the kidney transcriptome in Pacific spiny dogfish (Squalus suckleyi), a marginally euryhaline shark, following an ecologically relevant 65% seawater exposure. Furthermore, I explored the evolutionary basis of salinity tolerance using the current literature on phylogenetic relationships in selachimorphs (sharks). Dogfish were exposed to 65% seawater for up to 48hrs and sampled throughout. After 24hrs, gills were excised for light microscopy, revealing a significant increase in the interlamellar cell mass and the appearance of both lamellar clubbing and epithelial lifting, suggesting reduced surface area and increased cellular damage, respectively. Total plasma osmolality was measured during the time course and exhibited a significant reduction. This was primarily attributed to the loss of plasma urea, as both Na+ and Cl- showed minimal change. I employed RNA-seq to quantify changes in kidney mRNA expression after 0, 12, and 48hrs in 65% seawater. The role of the kidney in low salinity exposure has been previously studied using physiological methods, however, there is a substantial lack of molecular level studies. This technique revealed 1013 unique and differentially expressed transcripts, of which ~60% were functionally annotated. Generally, transcripts that were upregulated or downregulated after 12hrs remained so after 48hrs. Differentially expressed transcripts were involved in numerous cellular functions including protein chaperones, metabolic processes, cell signalling, and responses to stimuli and stress. Importantly, multiple heat shock protein transcripts were upregulated after 12hrs and numerous transcripts encoding protein trafficking were downregulated. Overall, I showed that the transcriptomic response of the kidney to 65% seawater was highly integrative and relied on the regulation of a multitude of processes. Lastly, low salinity tolerance within elasmobranchs has arisen in multiple species and I postulate that the phylogenetic distance between these species has no bearing on the limits of salinity tolerance observed in the literature.

• Subjects / Keywords

  • Euryhalinity
  • Salinity
  • Physiology
  • Dogfish
  • RNA-seq
  • Sharks

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3513VB92

• License

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