Temperature stress effects on fatty acid, specific proteins, and HSP70 expression in Scylla serrata mud crab sex phenotypes

Mud crab Scylla serrata is a commercially important crustacean and an interesting species to study because aside from its male and female sex phenotypes, this species is known to have a sexually-immature adult-sized mud crabs. The biology and market value of Scylla serrata are largely dependent on its sex phenotypes. The increase in the environmental temperature, which is expected to impact habitat temperature, continues to be a threat to the mud crab industry. There have been few studies which show sex-specific effects of temperature stress on some ectotherms, which is why in this study, the differential physiological effects of heat stress in terms of specific proteins, fatty acid profile and HSP70 expression were observed among Scylla serrata sex phenotypes. Adult-sized mud crabs were subjected to heat stress. Temperature for the control group was set at 26±2ºC, while temperature for the experimental group was increased up to 32 ºC at a rate of 2°C/day and was kept for 72 hours. Gill tissue were used for protein and HSP70 expression analysis, while muscle tissue were used for fatty acid analysis. Fatty acid distribution, protein profile, and HSP70 expression and were determined using GCMS, SDS-PAGE, and qRT-PCR, respectively. The general fatty acid composition of S. serrata did not change in response to temperature-stress and sex phenotype. Protein expression of S. serrata also did not display differences among sex phenotype. However, protein expression between control and experimental group was found to be significantly different, with lesser protein expression observed in the experimental group. Protein intensity and HSP70 expression have an approximately moderate correlation. HSP70 expression increased in the experimental group, where less protein expression was observed; and HSP70 expression is consistently low in the control group, where high protein expression was observed. Control and experimental groups are reacting as expected, and this is seen when compared within the same sex phenotype. Overall, the data indicate that the differences in fatty acid, proteins and HSP70 expression of S. serrata is not due to sex phenotype. However, high variation within groups suggest that other possible factors (e.g. genetic variation, site adaptation) obscure the differences observed in the study. Findings in this study will provide information for studies focused on filtering of SNP markers for the sexually-immature adult-sized mud crabs

Comparative transcriptome profiling of heat stress response of the mangrove crab Scylla serrata across sites of varying climate profiles

Background: The fishery and aquaculture of the widely distributed mangrove crab Scylla serrata is a steadily growing, high-value, global industry. Climate change poses a risk to this industry as temperature elevations are expected to threaten the mangrove crab habitat and the supply of mangrove crab juveniles from the wild. It is therefore important to understand the genomic and molecular basis of how mangrove crab populations from sites with different climate profiles respond to heat stress. Towards this, we performed RNA-seq on the gill tissue of S. serrata individuals sampled from 3 sites (Cagayan, Bicol, and Bataan) in the Philippines, under normal and heat-stressed conditions. To compare the transcriptome expression profiles, we designed a 2-factor generalized linear model containing interaction terms, which allowed us to simultaneously analyze within-site response to heat-stress and across-site differences in the response. Results: We present the first ever transcriptome assembly of S. serrata obtained from a data set containing 66 Gbases of cleaned RNA-seq reads. With lowly-expressed and short contigs excluded, the assembly contains roughly 17,000 genes with an N50 length of 2,366 bp. Our assembly contains many almost full-length transcripts – 5229 shrimp and 3049 fruit fly proteins have alignments that cover >80% of their sequence lengths to a contig. Differential expression analysis found population-specific differences in heat-stress response. Within-site analysis of heat-stress response showed 177, 755, and 221 differentially expressed (DE) genes in the Cagayan, Bataan, and Bicol group, respectively. Across-site analysis showed that between Cagayan and Bataan, there were 389 genes associated with 48 signaling and stress-response pathways, for which there was an effect of site in the response to heat; and between Cagayan and Bicol, there were 101 such genes affecting 8 pathways. Conclusion: In light of previous work on climate profiling and on population genetics of marine species in the Philippines, our findings suggest that the variation in thermal response among populations might be derived from acclimatory plasticity due to pre-exposure to extreme temperature variations or from population structure shaped by connectivity which leads to adaptive genetic differences among populations.This work was funded by the Department of Science and Technology Philippine Council for Agriculture and Aquatic Resources Research and Development (DOST-PCARRD) Mangrove Crab Program to De La Salle University-Manila through MCAL. AMSS was partially funded by University Research Coordination Office, De La Salle University-Manila. The funders had no role in study design, data collection, and analysis, decision to publish, or preparation of the manuscript