# Interactive Effects of Copper Contamination and Salinization Across Multiple Genotypes of Daphnia magna

## TL;DR

The study shows how different genotypes of Daphnia magna from the US and France respond to copper and salinity stress, highlighting the importance of genetic diversity in ecosystem resilience.

## Contribution

The study reveals genotype-specific responses to combined copper and salinity stress, suggesting cross-tolerance mechanisms in some populations.

## Key findings

- Copper exposure increased mortality across all genotypes, with US genotypes being more sensitive.
- US genotypes showed improved survival under combined copper and salinity stress, indicating possible cross-tolerance.
- Genotype-specific variation was observed both within and between populations under stress conditions.

## Abstract

Understanding how organisms respond to multiple environmental stressors is essential for predicting ecosystem impacts in the face of increasing anthropogenic pressures. However, few studies have explicitly examined how genotypes of the same species respond to combined stressors, with the specific objective of disentangling variation both within and across geographic locations. In this study, we examined the individual and combined effects of copper contamination and elevated salinity on multiple genotypes of
Daphnia magna
from US and French populations. Our findings revealed that copper exposure consistently increased mortality across all genotypes, with US genotypes displaying greater sensitivity than French counterparts. Salinity stress primarily reduced fecundity, and again, US genotypes exhibited lower resilience. Under combined copper and salinity stress, however, US genotypes showed survival benefits, suggesting potential cross‐tolerance mechanisms between these stressors. Moreover, there was substantial variation in the response to both stressors within both locations. This genotype‐specific variation underscores the necessity of considering genetic factors and genotype‐specific sensitivity/tolerance in ecosystem management and conservation strategies, particularly under multiple‐stressor scenarios. Further exploration of the genetic pathways and adaptation potential driving these responses will enhance our ability to support biodiversity and ecosystem resilience amid global environmental change.

This study examined how
Daphnia magna
genotypes from US and French populations respond to copper and salinity stress, alone and in combination. US genotypes were generally more sensitive but showed improved survival under combined stress, indicating possible cross‐tolerance mechanisms. The strong genotype‐specific variation observed—both within and between populations—underscores the importance of incorporating genetic diversity into multiple‐stressor research and ecosystem management.