Effects of parental co-exposure to heat wave and copper on zebrafish (Danio rerio) offspring thermal tolerance

Abstract

Climate change driven intensification of heat waves and increased occurrence of toxins in the aquatic environments pose a challenge for ectotherms, such as fish. Changes in the environment not only can shape the individual plasticity within a generation, but this phenotypic adjustment can be transferred to the next generation through transgenerational plasticity. Toxicity of metals and temperature have synergistic effects, however, very little is known about their combined transgenerational effects in fish. Previous studies have shown that heat exposed parents can produce offspring with enhanced thermal tolerance. Therefore, this study aimed to investigate whether parental exposure to (1) laboratory induced heat wave (33 °C), (2) copper (50 µg/l), and (3) combination of both could elicit effects also to subsequent generation and cause change in the phenotype of the offspring. To achieve this, fish offspring from each parental exposure group were reared in control and parental exposure conditions and development was monitored for 5 days. Furthermore, thermal tolerances as well as heat shock protein 70 (HSP70) and hypoxia inducible factor-1α (HIF-1α) protein levels were measured. Results showed that parental heat wave exposure caused negative effects on offspring morphology and co-exposure magnified them. Parental heat wave exposure resulted in high phenotypic variation in offspring thermal tolerance compared to control offspring. This effect was not seen in offspring from co-exposed parents. This suggests that heat wave exposure has higher adaptive transgenerational potential when not combined with toxin exposure. In conclusion, results from this study highlight the importance of considering combined effects of stressors faced by parental generation on the transgenerational effects seen in offspring.