DNA methylation and seasonal environmental effects on growth and reproduction in the mysid mesopodopsis slabberi

The high sensitivity to environmental variation makes mysid species effective bioindicators for assessing climate change impacts. Seasonal changes in temperature and salinity can affect their growth, body size, reproduction, and development time. Mysids are ecologically significant and serve as model organisms in environmental and ecotoxicological studies due to their advantageous biological traits. Emerging evidence also suggests that epigenetic mechanisms may mediate their responses to environmental stressors. This study examined seasonal and environmental influences on the morphology, reproduction, and epigenetic responses of Mesopodopsis slabberi. Seasonal analysis revealed significant differences in female body length, brood size, and newborn length, with larger females and offspring observed during winter, although brood size was smaller. Correlation analysis indicated a trade-off between offspring size and number, with larger females producing fewer but larger offspring. Morphological measurements showed strong positive correlations between body length and appendage dimensions. Experiments under different temperature and salinity conditions revealed that temperature significantly affected body length in the 3 mm size class, while salinity significantly influenced the 4 mm size class under specific conditions. Regarding epigenetics, this study reports the first quantification of DNA methylation in M. slabberi , revealing global levels ranging from 0.05-1.13% of the genome. Although no statistically significant effects of sex, temperature, or salinity on methylation were observed, variations across treatments suggest potential for environmentally mediated epigenetic responses. Understanding these dynamics is crucial, as climate-induced shifts in temperature and salinity may strongly affect the life cycles, morphological and epigenetic responses of estuarine mysids, potentially leading to cascading ecological impacts. • Larger females produce fewer but larger offspring, particularly during winter; • Body length varied with temperature and salinity, notably at 26 °C; • DNA methylation peaks at 1.13% at 20 °C and salinity 30; • No sex-specific differences in DNA methylation were detected.