Heat stress induces gonadal transcriptomic reprogramming and histopathological alterations in the mud crab Scylla paramamosain

Rising seawater temperature poses a severe threat to crustaceans and marine ecosystem stability by perturbing reproductive physiology, whereas the underlying molecular mechanisms remain largely elusive. To address this knowledge gap, the present study conducted transcriptomic and histopathological analyses on gonadal tissues (ovary and testis) of Scylla paramamosain sampled at 0, 6, 24, and 72 h following exposure to heat stress (HS, 35 °C). Differential expression analysis revealed progressive transcriptomic reprogramming in both gonads, with the number of DEGs increasing over time. HS profoundly modulated the expression of key genes involved in sex determination and differentiation, as well as molting, including Fru, MIH1/2, CHT1/2/3, ECD, RXR2 and EcR1/2. Sex-specific reproductive impairments were further characterized in response to HS. In females, HS modulated the expression of genes associated with ovarian development, including those in the CHH, ecdysone, Wnt/β-catenin, and MAPK pathways. Meanwhile, HS suppressed the expression of germline maintenance (nanos, Vasa, Piwi1/3) and upregulated the expression of vitellogenesis-associated (Vtg, VtgR) genes. In males, HS altered the expression of endocrine regulators (IR, IR2), germ cell marker genes (Piwi3, Vasa, nanos), spermatogenic progression genes (Dmrt11E, SOX21, KIFC1). Furthermore, HS modulated the expression of genes associated with gonadal antioxidant defense and apoptosis pathways, with an increased number of DEGs in these pathways. Consistent with transcriptomic alterations, histopathological examinations confirmed progressive morphological deterioration in both gonadal tissues. Collectively, these findings demonstrate that HS alters gonadal gene expression and structure in S. paramamosain, with implications for gonadal function, aquaculture sustainability, and marine ecological conservation of crustaceans.