Food limitation in Chironomus tepperi: Effects on survival, sex ratios and development across two generations

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Abstract

Species from the Dipteran family Chironomidae are widely used in laboratory and field studies to identify toxicity in freshwater environments. However, toxicity assessments can be influenced by food availability, which can alter endpoints in assays including viability, sex ratios and development time. The aim of this study was to determine if food limitation affected the endpoints used in toxicity tests with the Australian model organism, Chironomus tepperi, including responses in offspring. First instar larvae were subjected to food treatments with larval density controlled and offspring were either raised under the same food conditions as their parents or under standard conditions. In lower food density treatments adults in the F0 generation experienced delayed emergence and females produced fewer egg masses. F0 diet affected the performance of F1 to continued exposure and there was evidence that the quality of the offspring was compromised. Although sex ratios were not skewed, males and females responded differently to food limitation, especially in the F1 generation where female development was more delayed. These results demonstrate that endpoints used in toxicity evaluation in C. tepperi also respond to food availability, highlighting the need to control for food in both laboratory and field toxicity studies. Multiple generations should ideally be exposed to stressors under laboratory conditions to elucidate likely long term effects in the field.

Highlights

► The sublethal effects of food limitation in Chironomus tepperi were examined. ► Effects were investigated across two generations. ► Food limitation does not affect sex ratios in either generation. ► Food limitation delayed larval development to adulthood. ► Developmental delays were more pronounced in the second generation and the sexes responded differently.

Section snippets

Additional information

The effects of food limitation were investigated over two generations in the Australian Chironomidae species, Chironomus tepperi, which is used in laboratory toxicity testing and field biomonitoring. Food rations were selected to avoid mortality so sublethal effects could be investigated. In the F0 generation a reduced food ration had no effect on adult sex ratios but caused significant delays in the development of larvae. Both sexes experienced delays in development, although their responses

Experimental design

The experimental protocol was adapted from the guidelines recommended by OECD, 2004a, OECD, 2004b. Chironomus tepperi were obtained from three different laboratory cultures originating from the University of Melbourne, Latrobe University and CSIRO Land and Water, South Australia. Inbreeding depression is a problem with laboratory experiments, so to increase the genetic variability of the laboratory population and mask potential inbreeding depression the cultures were crossed. First instar

Survival

Survival to adulthood (successful adult emergence) was not significantly affected by food treatment in the F0 generation (F4.9=1.17, P=0.39), although survival was lower and more variable in the 0.10 food treatment (Fig. 1a). The offspring of these adults were affected by food treatment. In the case of F1 raised in standard feeding conditions, the food treatment of parents had a significant effect on survival (F3.8=10.87, P=0.003), with animals of the 0.50 ration parents having higher survival

Discussion

Chironomus tepperi were affected by food limitation, and endpoints commonly used in Chironomus toxicity tests were significantly impacted. Parental diet affected the response of F1 under continued food limitation and also the quality of F1 reared under standard conditions. Food limitation affected the development of both sexes, although effects were especially pronounced for female fecundity. These results have implications for laboratory and field studies where multiple generations may be

Conclusion

Food limitation affected several endpoints that are frequently used in ecotoxicological studies with Chironomus species. Although mortality and sex ratios were unaffected, development rate was delayed under food limitation. Both sexes were affected, although the magnitude of delays and reduced fecundity in food limited females suggest higher nutritional developmental requirements in female C. tepperi. These results also suggest that females may be more sensitive to other stressors and highlight

Acknowledgments

We would like to thank Jon Martin from the University of Melbourne, Anupama Kumar from CSIRO and Latrobe University for the provision of the stock cultures of Chironomus tepperi. Jon Martin is also thanked for providing breeding and culture tanks for C. tepperi. Sara Long provided advice on conducting the laboratory tests, and two anonymous reviewers provided their helpful comments on the manuscript. Funding for this research was provided by Melbourne Water Corporation, the Victorian Department

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