Physiological and Transcriptomic Variability Indicative of Differences in Key Functions Within a Single Coral Colony

Abstract

Polyps in different locations on individual stony coral colonies experience variation in numerous environmental conditions including flow and light, potentially leading to transcriptional and physiological differences across the colony. Here, we describe high-resolution tissue and skeleton measurements and differential gene expression from multiple locations within a single colony of Stylophora pistillata, aiming to relate these to environmental gradients across the coral colony. We observed broad transcriptional responses in both the host and photosymbiont in response to height above the substrate, cardinal direction, and, most strongly, location along the branch axis. Specifically, several key physiological processes in the host appear more active toward branch tips including several metabolic pathways, toxin production for prey capture or defense, and biomolecular mechanisms of biomineralization. Further, the increase in gene expression related to these processes toward branch tips is conserved between S. pistillata and Acropora spp. The photosymbiont appears to respond transcriptionally to relative light intensity along the branch and due to cardinal direction. These differential responses were observed across the colony despite its genetic homogeneity and likely inter-polyp communication. While not a classical division of labor, each part of the colony appears to have distinct functional roles related to polyps’ differential exposure to environmental conditions.

Morpho-functional traits of the coral Stylophora pistillata enhance light capture for photosynthesis at mesophotic depths

“…2 and 5 ). This principle appears to be valid for light gradients within the colony itself, as recently shown by Drake et al 73 : corallites exposed to more light (i.e., at the tip of the branch) were less spaced and larger than corallites at the base and junction of the branch. The greater space occupied by the coenosteum relative to the corallites, as documented for mesophotic-depth colonies, may reflect the host’s response to minimize light limitation for its photosymbionts.…”

“…In total, fragments from 30 colonies were used for this study ( n = 15 per depth). Conspecific coral colonies were sampled at least five meters apart to avoid sampling clone mates, and fragments were sampled from the center of each colony to avoid within colony variation 73 . The samples were submerged in 5% sodium hypochlorite (NaClO) for 24 hours to dissolve the soft tissue, rinsed with distilled water, and air-dried at room temperature.…”

Advances in coral immunity ‘omics in response to disease outbreaks

“…Additionally, efforts to sample from consistent areas on different coral colonies can be prioritized and well documented (e.g. Drake et al, 2021). Finally, field experiments often have unexplained variance due to sampling times, as the amount of time needed to sample a coral underwater and, for example, preserve it on a moving boat, is generally greater than for a lab experiment.…”

Transcriptomic plasticity and symbiont shuffling underpin Pocillopora acclimatization across heat-stress regimes in the Pacific Ocean

“…The mechanisms underlying these capacities as well as their limits and extent among different coral holobiotypes and the relative roles of each symbiotic partner remain under intense investigation. In addition, holobiont transcriptomic adaptation/acclimation can be difficult to assess in some cases because gene expression can be highly variable between polyps within a single coral colony (Drake et al 2021). Finally, acclimation or adaptation of a coral holobiont at the local (reef) scale is often not representative of capacities at larger (ocean) scales and therefore does not allow for accurate global projections of the survival or decline of a species or of reef ecosystems.…”