Characterization of the female molting cycle and embryonic development in <i>Hyalella azteca</i> : application for short-term reproductive toxicity assessment

Hyalella azteca is a North and Central American amphipod used worldwide to evaluate the toxicity of sediments and water matrices. Although current evaluation procedures extensively use H. azteca standard life-cycle tests, there are no protocols specifically designed in this species to assess contaminant effects on reproductive processes and embryonic development at the individual level. Based on a methodology available in European gammarids, this study aimed to initiate the development of a chronic test, leveraging an advanced knowledge of the female reproductive cycle in these amphipods. Parameters such as molting advancement, embryonic development in marsupium, and realized fecundity were the fundamental endpoints of the proposed 2-week biotest. First, females were monitored between two egg-laying events at three temperatures (16 °C, 20 °C, 24 °C) to describe the molting process and the embryonic development. Afterwards, we proposed a biotest consisting of exposing couples for one reproductive cycle (10 days at 24 °C) starting with females in AB molting stage (postmolting time < 24 hr). Molting impairment and embryonic development are assessed at a first time of observation (Day 6), followed by a measurement of realized fecundity at Day 13 (3 days postlaying in clean water), that is, embryo number in the maternal pouch for the second reproductive cycle. Four control experiments and one exposure test to cadmium (at 1 and 5 µg L-1) validated the robustness and the sensitivity of the method. As in other amphipods, cadmium inhibited the molting and embryonic development in Hyalella. The proposed Hyalella reprotoxicity test offers a rapid tool for specifically assessing reproductive impairments caused by chemicals and environmental matrices, complementing the standardized life-cycle tests available in this species for population-level toxicity assessment.