Keywords: a. stress responses; b. population variation
Drosophila melanogaster is an effective model of metal toxicity, but we currently have only a limited understanding of any sex or genetic background effects. Similarly, while essential metals are relatively well studied, many non-essential metals remain understudied despite their chemical similarities to essential metals and their relevance as environmental contaminants. Further, essential and non-essential metals are not independent. The two groups interact with multiple interconnected metal pathways in a complex web with many proteins and mechanisms yet to be elucidated. In the current study, we are quantifying the influence of sex and genetic background on the response to essential and non-essential metal toxicity in D. melanogaster. We are using copper (Cu) and nickel (Ni) as our essential and non-essential metals, both delivered through the fly food. The two are chemically similar metals and can bind to many of the same biological ligands. Our study also includes different homozygous fly lines from the Drosophila Genetic Reference Panel (DGRP) to examine background effects. To date, we have conducted multiple four-day exposure Lethal Concentration 50 (LC50) assays using a range of CuSO4 and NiSO4 concentrations. There are significant effects of sex and genetic background for both metals. Background effects were particularly substantial, and interestingly, the same lines were sensitive or resistant to both metals. We also found similar sex effects and combined sex and line effects for the two metals. Currently, we are quantifying the amount the concentration of metals in the fly samples, not just the fly food using two different methods, one with the non-specific metal chelator 4-(2-pyridylazo)resorcinol (PAR) and the second with Inductively Couple Plasma Mass Spectrometry (ICP-MS). Future work will investigate the genetic and biochemical influences that cause the differences in response to metal toxicity and the effects of simultaneous exposure to both metals. Our results to date clearly demonstrate that sex and genetic background are major influences in the response to essential and non-essential metal toxicity. Understanding the biology of this system, and likely any other biological system, requires experiments with multiple genetic backgrounds and both sexes.