Heterosis analysis of heat and cold tolerance in hybrid offspring of sea urchin Mesocentrotus nudus: Implications for breeding

This study investigated the heterosis of heat and cold tolerance in hybrid offspring derived from Dalian, Liaoning, China (DL) and Weihai, Shandong, China (WH) populations of the sea urchin Mesocentrotus nudus. Through chronic heating and cooling experiments, we compared four experimental groups: reciprocal hybrids (WH ♀ × DL ♂ [WD], DL ♀ × WH ♂ [DW]) and parental controls (WH ♀ × WH ♂ [WW], DL ♀ × DL ♂ [DD]). Survival time, upper thermal tolerance (UTT), and cooling-degree days (CDD) were analyzed with heterosis calculations. Under chronic heating stress, the WD hybrid exhibited: 1. Significantly prolonged survival time compared to WW and DW groups (Log-rank test, P < 0.05). 2. Enhanced UTT with 5.0% mid-parent heterosis (MPH) and 5.9%/4.2% single-parent heterosis (SPH) over WW/DL respectively. The heat tolerance of the four populations ranked as: WD > DD ≥ WW ≥ DW. During chronic cold exposure, WD demonstrated: 1. Superior survival duration and CDD relative to all groups (P < 0.05). 2. 11.5% MPH with 12.9%/10.0% SPH over WW/DL. The cold tolerance of the four populations ranked as: WD > DW ≥ DD ≥ WW. Notably, DW hybrids displayed negative heat heterosis (-2.3% MPH) but marginal cold heterosis (3.8% MPH). These findings identify WD hybrids as promising germplasm for breeding temperature-resilient sea urchin strains, with specific heterosis patterns suggesting maternal effects in thermal adaptation.