Microplastics reduce population viability without shifting clonal structure in Daphnia pulex.

Area of Science:

• Environmental Science
• Ecotoxicology
• Aquatic Ecology

Background:

• Microplastics (MPs) are pervasive aquatic pollutants with unknown impacts on zooplankton intraspecific competition and genotype sorting.
• Understanding MP effects on keystone species like Daphnia pulex is crucial for assessing freshwater ecosystem health.

Purpose of the Study:

• To investigate the long-term effects of microplastic exposure on the clonal composition and demographic structure of Daphnia pulex populations.
• To determine if microplastics induce genotype sorting or alter competitive hierarchies in zooplankton under controlled conditions.

Main Methods:

• A 30-day experiment exposed mixed-habitat Daphnia pulex populations (three genotype pairs) to environmentally relevant concentrations of polystyrene microplastics (1 µm and 25 µm).
• Populations were maintained under moderate food limitation and density-dependent conditions.
• Demographic parameters (population density, adult/juvenile abundance, reproduction) and clonal composition were monitored.

Main Results:

• Microplastic exposure significantly reduced total population density in two of three clone pairs, primarily due to decreased adult abundance.
• Juvenile density was also reduced in a pair-dependent manner, though reproductive metrics like clutch size remained unaffected.
• Despite demographic impacts, clonal proportions and competitive hierarchies remained stable, indicating limited short-term evolutionary sorting.

Conclusions:

• Short-term microplastic exposure impairs zooplankton demographic performance but does not readily drive rapid evolutionary changes in genotype frequencies.
• Gradual population performance erosion, including increased adult losses and reduced juvenile numbers, was observed.
• Further chronic or multigenerational studies are needed to ascertain the potential for microplastics to induce evolutionary change in zooplankton.