Phenotypic and transcriptomic responses to salinity stress across genetically and geographically divergent Tigriopus californicus populations

Abstract

Species inhabiting the North American west coast intertidal must tolerate an extremely variable environment, with large fluctuations in both temperature and salinity. Uncovering the mechanisms for this tolerance is key to understanding species' persistence. We tested for differences in salinity tolerance between populations of Tigriopus californicus copepods from locations in northern (Bodega Reserve) and southern (San Diego) California known to differ in temperature, precipitation and humidity. We also tested for differences between populations in their transcriptomic responses to salinity. Although these two populations have ~20% mtDNA sequence divergence and differ strongly in other phenotypic traits, we observed similarities in their phenotypic and transcriptomic responses to low and high salinity stress. Salinity significantly affected respiration rate (increased under low salinity and reduced under high salinity), but we found no significant effect of population on respiration or a population by salinity interaction. Under high salinity, there was no population difference in knock-down response, but northern copepods had a smaller knock-down under low salinity stress, corroborating previous results for T. californicus. Northern and southern populations had a similar transcriptomic response to salinity based on a principle components analysis, although differential gene expression under high salinity stress was three times lower in the northern population compared to the southern population. Transcripts differentially regulated under salinity stress were enriched for "amino acid transport" and "ion transport" annotation categories, supporting previous work demonstrating that the accumulation of free amino acids is important for osmotic regulation in T. californicus.

Novel microRNAs are associated with population divergence in transcriptional response to thermal stress in an intertidal copepod

“…Divergence in the use of cuticle protein genes was particularly striking in that BR downregulated 34 such genes, while SD only 6, with no overlap between them (Figure d; Supporting information Tables and ). In a recent study of salinity stress in T. californicus , DeBiasse, Kawji, and Kelly () detected overrepresentation of genes associated with ion transport and cuticle. Specifically, ion transport genes were downregulated during high‐salinity stress, indicating a likely shared mechanism with response to temperature stress.…”

“…Specifically, ion transport genes were downregulated during high‐salinity stress, indicating a likely shared mechanism with response to temperature stress. Cuticle genes, however, were observed to be significantly upregulated in response to low‐salinity (DeBiasse et al, ). The functional explanations for these differences between populations and across different stressors are not known but could provide a framework for understanding adaptations in this physiologically hardy species.…”

Multi-omic approach provides insights into osmoregulation and osmoconformation of the crab Scylla paramamosain

“…These genes are likely to function in osmoconformation by regulating production of free amino acids. For example, glutamate dehydrogenase is a potential control factor for the synthesis of proline and alanine, and has been found to participate in osmoconformation in decapods 18 and copepods 52 . Aspartate aminotransferase participates in metabolism of alanine, arginine, cysteine and proline 53 .…”

Differential responses to ocean acidification between populations ofBalanophyllia eleganscorals from high and low upwelling environments

“…We first assembled a transcriptome with trinity ‐v2.3.2 (Grabherr et al, ) using all of the reads (both HU and LU combined), but this yielded an assembly with 127,739 contigs. This large number of contigs suggests that high sequence divergence between populations was causing population‐specific alleles to be assembled as separate contigs in the hybrid assembly (Debiasse, Kawji, & Kelly, ; Schoville et al, ). This becomes problematic when comparing differential gene expression between populations because reads preferentially map to contigs from their own population, potentially creating a signal of population‐specific gene expression, even where none exists.…”