Combined effects of spinetoram and Microcystis aeruginosa on Daphnia pulex offspring: Maternal effects and multigenerational implications

Abstract

The increasing occurrence of harmful algal blooms (HABs) in freshwater ecosystems detrimentally affect global water environments. Zooplankton's role in controlling HABs is hindered by contaminant exposure, necessitating research into combined stressors' ecological impacts. The response of Daphnia, a freshwater keystone species, to environmental stressors can be influenced by its maternal effects. Here, we investigated the combined effects of the world-widely used insecticide spinetoram and non-toxic HABs species Microcystis aeruginosa on the life-history traits of D. pulex offspring produced from different maternal food conditions. Four maternal groups were established, with each group receiving a specific blend of C. vulgaris (Ch) and M. aeruginosa (Ma) in varying proportions: A (100% Ch), B (90% Ch + 10% Ma), C (80% Ch + 20% Ma), and D (70% Ch + 30% Ma). The offspring from the third brood were gathered, and a 21-day experiment was carried out, involving various feeding groups (AA, AD, BA, BB, CA, CC, DA, and DD). Results demonstrated that grazing on M. aeruginosa by D. pulex induced maternal effects on their offspring, with the continuous exposure group showing an enhanced tolerance to M. aeruginosa. This study also unveiled that spinetoram could interfere with the molting of D. pulex, leading to developmental retardation. The Recovery Group exhibited an intriguing phenomenon: under the influence of both concentrations of the pesticide spinetoram (0.18, 0.35 μg L−1), D. pulex produced more offspring. This might be due to a combined strategy of allocating more energy towards reproduction in response to low-quality food and a potential hormetic effect from low concentrations of spinetoram. Assessing the interplay of combined stressors across multiple generations, encompassing harmful algal blooms (HABs) and environmental pollutants, is essential for predicting population responses to evolving environmental conditions. This understanding is vital for the protection and management of aquatic environments and ecosystems.