Transcriptome profiles link environmental variation and physiological response of Mytilus californianus between Pacific tides

Abstract

Summary The marine intertidal zone is characterized by large variation in temperature, pH, dissolved oxygen and the supply of nutrients and food on seasonal and daily time scales. These oceanic fluctuations drive of ecological processes such as recruitment, competition and consumer-prey interactions largely via physiological mehcanisms. Thus, to understand coastal ecosystem dynamics and responses to climate change, it is crucial to understand these mechanisms. Here we utilize transcriptome analysis of the physiological response of the mussel Mytilus californianus at different spatial scales to gain insight into these mechanisms. We used mussels inhabiting different vertical locations within Strawberry Hill on Cape Perpetua, OR and Boiler Bay on Cape Foulweather, OR to study inter- and intra-site variation of gene expression. The results highlight two distinct gene expression signatures related to the cycling of metabolic activity and perturbations to cellular homeostasis. Intermediate spatial scales show a strong influence of oceanographic differences in food and stress environments between sites separated by ~65 km. Together, these new insights into environmental control of gene expression may allow understanding of important physiological drivers within and across populations.

Latitudinal differences in Mytilus californianus thermal physiology

“…Although we sampled mussels within a relatively small portion of the mid-intertidal at each site (within a few meters), in situ mussel temperatures may be much more variable and could explain observed differences in field-acclimatized populations. However, Place et al (2012) showed that within-site transcriptomes in Mytilus californianus were more similar to each other than between site (> 65 km) transcriptomes, even at a low, mid-, and high tidal heights (Place et al 2012). Nevertheless, this result could be confounded by the circadian rhythmicity found in patterns of gene expression in M. californianus (Gracey et al 2008, Connor & Gracey 2011), since mussels were not sampled at multiple time points.…”

The role of stochastic thermal environments in modulating the thermal physiology of an intertidal limpet, Lottia digitalis

“…Intertidal animals tailor their cellular stress response mechanisms to be quickly initiated following the onset of high tide such that recovery is complete before the start of the next low tide period (Hofmann and Somero, 1996;Tomanek and Somero, 2000;Schill et al, 2002;Clark et al, 2008;Zhang et al, 2014). Transcriptomics of Mytilus californianus have also shown upregulated gene expression of recovery mechanisms, including antioxidants, to return to cellular homeostasis during the high tide period before the next low tide period (Gracey et al, 2008;Place et al, 2012). It may have been that the periods of immersion during high tide were sufficient to mitigate any acquired stress during the daytime low tide periods of the acclimation treatments by available antioxidants.…”

The environmentally tuned transcriptomes ofMytilusmussels

“…Comparisons of M. californianus sampled at locations ranging from Baja Mexico up to British Columbia suggested that thermal variation between locations was the most plausible explanation for the observed differences in gene expression (Place et al, 2008). When studies also took into account within-site variation (higher versus lower on the shore), they revealed that mussels sampled at the same location tended to show expression signatures that were more similar to one another, than to mussels sampled at the same tidal height but at different locations (Place et al, 2012). This finding indicates that there exists a complex interaction between microhabitat differences and broader scale oceanographic process, for example, food availability, and that many environmental variables need to be accounted for when comparing expression data collected from different geographical locations.…”

“…Calibrating and normalizing between-site data so that rhythmic changes in transcript abundance do not degrade the statistical power of the study is a formidable task and has yet to be properly addressed. For example, a biogeographical study reported that both citrate synthase and G2/M mitotic-specific cyclin B were differentially expressed between locations (Place et al, 2012), whereas another study reported that these same genes exhibited extensive hourly variation within a site (Gracey et al, 2008). Caution needs to be exercised when interpreting these patterns because temporal expression changes are likely to confound efforts to identify genes that are intended to serve as molecular markers for site-to-site environmental differences.…”