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 physiological 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 appear more active toward branch tips, including toxin production for prey capture or defense, several metabolic pathways, and 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.…”