Symbiont codominance is associated with reduced coral stress
We were next interested in how symbiont codominance is reflected in the host functional profile. In addition to analyzing the effect of codominance on its own, we were also interested in how symbionts’ codominance modifies the host response to heat stress (i.e., codominance:heat interaction). To better interpret the coral host functional profiles, we used eukaryotic orthologous group (KOG) analysis to identify broader functional categories of modulated genes and to formally compare these results to the known profile of Acroporasp. response to various kinds of high-intensity stress (generalized stress response, “GSR”;Dixon et al.,2020). This analysis revealed that host gene expression response to symbiont codominance had no significant correlation with the GSR (Fig 4B), indicating that harboring codominant symbionts does not stress the host. Instead, supporting the GO analysis results, the “translation, ribosomal structure, and biogenesis” category was up-regulated (Fig. 4A), suggesting stimulation of cellular growth (Giordiano et al., 2015;Elser et al., 2003;Bosdriez et al., 2015;López-Maury et al., 2008). As expected, gene expression of the heated corals strongly correlated with the GSR (r = 0.66, p = 0.00058, Fig. 4C), implying that the corals were stressed by the treatment. However, delta-ranks for the heat:codominance interaction term were negatively correlated with the GSR (r=-0.79, p=5.9e-06, fig. 4D), which means that hosting codominant symbionts mitigated the heat stress response.