Divergent thermal challenges elicit convergent stress signatures in aposymbioticAstrangia poculata

Abstract

7Corals are threatened worldwide due to rapidly warming oceans associated with anthropogenic 8 climate change. A growing body of work has explored how corals respond to heat stress, however, 9responses of corals across the full range of their thermal breadth are rarely explored even though 10 winter colds are also known to induce coral stress. Here, we leverage the temperate stony coral, 11Astrangia poculata, which naturally exhibits a facultative symbiosis with Symbiodiniaceae, to 12 explicitly examine how thermal challenges influence coral hosts in isolation from their symbionts. 13Aposymbiotic A. poculata were collected from Woods Hole, MA, the northern range limit for this 14 species. Corals were thermally challenged in two independent common garden experiments (Heat 15 challenge: 31˚C, 10 days; Cold challenge: 6˚C, 16 days) to determine the effects of divergent 16thermal stressors. Behavioural responses to food stimuli were monitored throughout the thermal 17 challenges and genome-wide gene expression profiling (TagSeq) was used to characterize 18 molecular underpinnings of the coral's response to stress in its aposymbiotic state. Behaviourally, 19both thermal challenges induced polyp retraction and colonies failed to respond to food stimuli. 20Surprisingly, seven times as many genes were differentially expressed under cold challenge heat 21 challenge. Despite a greater magnitude of response under cold challenge, significant similarities 22 in gene expression were detected across the two thermal challenge experiments, with many of the 23 most responsive genes having been previously implicated in coral heat stress response. Given that 24 our data were generated from aposymbiotic colonies, we hypothesize that these genes previously 25linked to heat stress are more likely indicative of a generalized stress response. Overall this work 26 highlights the unique insights facultatively symbiotic corals offer for deciphering the stress 27 response of the coral host in the absence of bleaching. 28 29 30

An algal symbiont (Breviolum psygmophilum) responds more strongly to chronic high temperatures than its facultatively symbiotic coral host (Astrangia poculata)

“…When contrasting the heat stress response separately in symbiotic and aposymbiotic ramets of A. poculata, we found fewer differentially expressed genes between symbiotic control and symbiotic heat-stressed ramets (n=13) than we found between aposymbiotic control and heat-stressed ramets (n=76, Figure 5A). The overall low levels of differential expression align with recent work on aposymbiotic colonies of A. poculata, which demonstrated that seven times as many genes were differentially expressed under cold stress compared to heat stress in shortterm experiments (Wuitchik et al, 2020). In response to chronic heat stress, aposymbiotic colonies in the present study mounted a significant inflammatory response.…”

Applying model approaches in non-model systems: A review and case study on coral cell culture

“…Traits such as the potential to exist in multiple symbiotic states (symbiotically and aposymbiotically) living sympatrically (e.g. Astrangia poculata, aposymbiotic Astrangia do not harbor symbionts whereas their symbiotic counterparts harbor Breviolum psygmophilum, [38,39] will allow the study of facultative symbiosis ranging from cellular, to organismal, to ecological approaches [38,40,41]. Although scleractinian corals are considered non-model systems, they manifest PLOS ONE many qualities of model systems.…”