Nutritional condition drives spatial variation in physiology of Antarctic lipid-storing copepods

Abstract

Lipid-rich copepods form an essential link between primary producers and higher trophic levels in high-latitude oceans. These zooplankton can take advantage of ephemeral phytoplankton blooms to fuel development and reproduction. However, we have limited understanding of how the physiological condition of these animals varies in relation to environmental factors such as food availability. Due to high advection, it is likely that physiological plasticity, rather than local adaptation, is primarily responsible for physiological differences within a region. We use transcriptomics and other physiological metrics to understand how two species of copepods (Calanoides acutusandCalanus propinquus) vary across environmental gradients along the West Antarctic Peninsula. For the primarily herbivorousC. acutus, physiological separation between sampling locations appears to be driven by feeding status, and gene expression differences indicate differential expression of genes regulating lipid metabolism, reproduction, aerobic metabolism, and protein translation. For the more omnivorousC. propinquus,physiology and gene expression did not segregate as clearly by location, showed minimal signs of food deprivation at any location, and had a weaker relationship with chlorophyll compared toC. acutus. By comparing these results with concurrent starvation experiments, we find thatspatial variation in gene expression reflects short-term differences in food availability (particularly forC. acutus,), and we identify genes whose expression indicates recent feeding status. Further examination of the relationships between food availability, copepod physiology, and population dynamics will ultimately improve our capacity to predict how copepod populations will respond to rapidly changing environmental conditions in the West Antarctic Peninsula ecosystem.

Comparative analysis of the molecular starvation response of Southern Ocean copepods

“…However, due to logistical constraints, we could not always remove some small algal cells (<3 microns) from the starved treatments. Nonetheless, changes in physiological condition, gene expression, and the correlation of our experimental response with field chlorophyll measurements reported in Berger et al (2023) indicate that our starvation treatment captured a bona fide response to food deprivation.…”

“…Clade-level analyses also found evidence for low dN/dS in CSGs across the copepod phylogeny. Starvation-response genes had less variable expression than other genes in our paired field study (Berger et al, 2023) while having similar dispersion across species, strongly suggesting the action of stabilizing selection on expression level (Price et al, 2022). While purifying selection on sequence and stabilizing selection on expression need not go hand in hand, we found that genes under strong coding constraint tend to have less expression variability among individuals (Fig.…”

“…Adult female copepods were sampled during the PAL-LTER survey cruise in austral summer 2019 aboard the ARSV Laurence M. Gould (detailed in Berger et al, 2023). To assess spatial variation in copepod physiology, we performed RNA-seq on C. acutus collected from 6 field sites and C. propinquus from 4 sites.…”

“…To address how metabolic gene expression varies across environmental conditions and experimental feeding manipulations, we sequenced and assembled transcriptomes for C. acutus and C. propinquus . In an accompanying paper, we report patterns of gene expression and other physiological metrics spanning the PAL-LTER study region (Berger et al, 2023). Here, we report ship-based starvation experiments conducted during the same research cruise.…”

Exploring circadian rhythms, food intake, and their interactions in marine invertebrates

“…To address how metabolic gene expression varies across environmental conditions and experimental feeding manipulations, we sequenced and assembled transcriptomes for C. acutus and C. propinquus. In an accompanying paper, we report patterns of gene expression and other physiological metrics spanning the PAL-LTER study region (Berger et al, 2023b).…”