Food Restriction and Thermal Stress as Independent Inducers of Sexual Reproduction and Ephippia Production in Daphnia magna

Daphnia magna exhibits reproductive plasticity, alternating between parthenogenesis and sexual reproduction with ephippia (resting eggs) formation under stressful conditions. This study evaluated food restriction or thermal stress as independent inducing factors of ephippia in two consecutive 60-day trials (one per treatment) under controlled conditions. In Trial I, neonates were fed Arthrospira platensis at 20 (control), 10 (moderate), or 0.5 (severe) mg L−1 day−1. In Trial II, neonates were maintained at 10, 15, 20, 25, and 30 °C with optimal feeding. Control food levels and temperatures of 20 °C promoted exclusive parthenogenesis, yielding up to 13,170 ± 515 neonates on treatment fed with 20 mg L−1 of A. platensis day−1. Conversely, severe restriction (0.5 mg L−1 day−1) suppressed asexual reproduction by 99.3% and maximized ephippia production (726 ± 10) over 60 days. Thermal extremes (10 and 30 °C) also induced ephippia formation, peaking at 30 °C (85 ± 7). Ephippia quality was stress-dependent: moderate restriction (10 mg L−1 day−1) yielded the highest proportion of twin-egg ephippia (82.3%) and hatching success (82%), whereas severe food restriction or high temperature (30 °C) increased quantity but reduced the viability of ephippia. These findings suggest independent thresholds for inducing sexual reproduction in D. magna. The study provides a standardized protocol for ephippia production with applications in aquaculture, ecotoxicology, and conservation purposes.