Site-specific variation in gene expression from Symbiodinium spp. associated with offshore and inshore Porites astreoides in the lower Florida Keys is lost with bleaching and disease stress

Abstract

Scleractinian coral are experiencing unprecedented rates of mortality due to increases in sea surface temperatures in response to global climate change. Some coral species however, survive high temperature events due to a reduced susceptibility to bleaching. We investigated the relationship between bleaching susceptibility and expression of five metabolically related genes of Symbiodinium spp. from the coral Porites astreoides originating from an inshore and offshore reef in the Florida Keys. The acclimatization potential of Symbiodinium spp. to changing temperature regimes was also measured via a two-year reciprocal transplant between the sites. Offshore coral fragments displayed significantly higher expression in Symbiodinium spp. genes PCNA, SCP2, G3PDH, PCP and psaE than their inshore counterparts (p<0.05), a pattern consistent with increased bleaching susceptibility in offshore corals. Additionally, gene expression patterns in Symbiodinium spp. from site of origin were conserved throughout the two-year reciprocal transplant, indicating acclimatization did not occur within this multi-season time frame. Further, laboratory experiments were used to investigate the influence of acute high temperature (32°C for eight hours) and disease (lipopolysaccharide of Serratia marcescens) on the five metabolically related symbiont genes from the same offshore and inshore P. astreoides fragments. Gene expression did not differ between reef fragments, or as a consequence of acute exposure to heat or heat and disease, contrasting to results found in the field. Gene expression reported here indicates functional variation in populations of Symbiodinium spp. associated with P. astreoides in the Florida Keys, and is likely a result of localized adaptation. However, gene expression patterns observed in the lab imply that functional variation in zooxanthellae observed under conditions of chronic moderate stress is lost under the acute extreme conditions studied here.

Proteomic Signatures of Corals from Thermodynamic Reefs

“…This is so even despite few individual proteins differing in concentration between corals from upwelling and non-upwelling reefs. Such upwelling reef vs. non-upwelling coral proteomic differences were maintained even after one week of exposure to a non-native temperature regime (in half the cases); in other words, the concentrations of numerous proteins showed “site fidelity.” Others have documented site fidelity in coral [ 47 ] and Symbiodiniaceae [ 48 , 49 , 50 , 51 , 52 ] gene expression patterns, which can persist even across large spatio-temporal scales [ 53 ]. Since corals herein were only maintained in laboratory aquarium culture for several weeks (including the acclimation period), it would be interesting to see if such site fidelity is eventually lost after longer periods of time in a common garden setting or if these site-associated proteome-scale differences are truly entrained in their biology.…”

Variation in Immune-Related Gene Expression Provides Evidence of Local Adaptation in Porites astreoides (Lamarck, 1816) between Inshore and Offshore Meta-Populations Inhabiting the Lower Florida Reef Tract, USA

“…Supporting our assumptions, Kenkel et al [20,23] observed very little gene flow between inshore and offshore populations of Porites astreoides inhabiting the FRT. Similarly, Hauff-Salas et al [46] observed collection site-specific responses in the zooxanthellae.…”

“…Coral fragments were processed as previously described [46]. Briefly, excess skeletal fragments were removed after first pulverizing fragments into smaller pieces in LN 2 with a dounce-style stainless steel homogenizer, and the remaining tissue sample ground using a ceramic mortar and pestle.…”

“…RNA was isolated according to previously described methods [46] from 110 mg of processed sample powder using a mixture of guanidine thiocyanate and phenol in a monophase solution (TRI Reagent: Sigma-Aldrich, St. Louis, MO, USA). Each RNA extraction was dissolved in 100 µL of RNase and DNase-free water and integrity determined with a Caliper Lab Chip GX (Perkin Elmer: Waltham, MA, USA).…”

“…Reaction components were removed from the cDNA product by the following previously described methods [46]. The resultant cDNA was stored at −20 • C for less than one week prior to qRT-PCR.…”