Mechanisms of Diapause in Major Crustacean Taxa: Environmental Cues, Gene Regulation, and Adaptive Strategies

Diapause serves as an adaptive dormancy strategy in freshwater, hypersaline, and marine crustaceans, allowing them to survive harsh conditions like temperature extremes, salinity fluctuations, hypoxia, and food scarcity. This review focuses on diapause across major crustacean taxa, with particular emphasis on branchiopods and copepods. However, detailed mechanistic evidence is more prevalent in well-studied species like Artemia, Daphnia, and calanoid copepods, leading to an uneven distribution of evidence across these taxa. Thus, the molecular and physiological mechanisms discussed in this review should not be assumed to be universally conserved across Crustacea, and taxon-specific differences and current knowledge gaps are highlighted where appropriate. The review consolidates the current understanding of crustacean diapause, focusing on environmental cues, gene-regulatory networks, hormonal and epigenetic control, metabolic suppression, and stress resilience. In the best-studied taxa, diapause has been associated with changes in the expression and/or activity of antioxidant defenses, small RNAs, energy-storage pathways, heat shock proteins, and FoxO-associated signaling components; however, the evidence for these mechanisms varies among taxa, and their conservation across Crustacea, remains uncertain. The functions of these responses include developmental arrest, energy conservation, cellular protection, and maintaining viability during dormancy. Their significance varies among different groups of organisms and remains incompletely understood in many cases. Diapause also contributes to the persistence of populations by forming dormant propagule banks, coordinating seasonal processes, linking trophic levels, and increasing resilience to environmental changes. The ecological effects of diapause depend on the life stage and habitat. Recent progress in transcriptomics, epigenomics, long-read sequencing, single-cell methodologies, and multi-omics integration present new opportunities for comparing regulatory responses across species. Molecular data primarily focuses on Artemia, Daphnia, and a limited number of copepod species, posing challenges in generalizing to less represented lineages. Previous syntheses have concentrated on individual taxa, physiological dormancy, or specific molecular mechanisms. This review aims to fill this gap by integrating environmental regulation, taxonomic and life-stage contexts, molecular and physiological mechanisms, and ecological and evolutionary implications systematically. This comparative approach distinguishes between shared regulatory features across species and lineage-specific characteristics, while considering variations in the strength of supporting evidence. Future research should prioritize functional validation, broader taxonomic inclusivity, comparative multi-species analyses, multifactorial experiments, and long-term ecological investigations to enhance understanding of crustacean diapause evolution and refine predictions amidst climate-induced environmental shifts.