Planarian behavioural endpoints in ecotoxicology: A case study evaluating mercury and salinity effects

Area of Science:

• Ecotoxicology
• Environmental Science
• Zoology

Background:

• Freshwater invertebrates are crucial for ecosystem health.
• Assessing contaminant stress requires sensitive biological indicators.
• Behavioral endpoints offer a sensitive measure of ecotoxicological impact.

Purpose of the Study:

• To evaluate the sensitivity of the freshwater planarian Girardia tigrina to contaminant stress.
• To assess the impact of mercury (Hg) and sodium chloride (NaCl) on planarian mortality, feeding, and locomotion.
• To establish planarians as a model organism for ecotoxicological studies using behavioral endpoints.

Main Methods:

• Girardia tigrina were exposed to varying concentrations of Hg and NaCl.
• Mortality was assessed over 96 hours to determine LC50 values.
• Feeding rates were measured using a devised feeding assay.
• Locomotion was quantified using an automated tracking system.

Main Results:

• The 96-hour LC50 values were determined as 176.8 μg L⁻¹ for Hg and 6.79 g L⁻¹ for NaCl.
• Acute Hg exposure caused tissue disintegration and depigmentation.
• Acute NaCl exposure led to motionlessness and tegument rupture.
• Sub-lethal exposures to both Hg and NaCl resulted in inhibited feeding and impaired locomotion.

Conclusions:

• Freshwater planarians, specifically Girardia tigrina, are highly sensitive to environmental stressors like Hg and NaCl.
• Behavioral endpoints such as feeding rate and locomotion provide sensitive measures for evaluating sub-lethal effects of contaminants.
• Planarians are valuable model organisms for ecotoxicological research, offering insights into the impacts of stressors on freshwater invertebrates.