This study compared the effects occurring at molecular and population levels in Daphnia magna exposed to copper concentrations in the range of 15-120 microg/l. The qualitative and quantitative modifications arising in random amplified polymorphic DNA (RAPD) profiles as a measure of DNA effects were compared with a number of key ecological fitness parameters, namely, the age-specific survival, age-specific fecundity, net reproductive rate, and intrinsic rate of population increase. Results suggested that growth, reproduction, and most of the fitness parameters as well as genomic template stability (a qualitative measure reflecting changes in RAPD profiles) were significantly affected at copper concentrations of 90 and 120 microg/l. Among the fitness parameters, the age-specific fecundity and net reproductive rate were the most sensitive parameters of toxicity. Changes in RAPD patterns generally occurred at copper concentrations of 90 and 120 microg/l, but with one primer, changes significantly arose at all copper concentrations. Overall, molecular and population parameters compared well and represented a sensitive means to measure toxicity induced by copper in Daphnia magna. In conclusion, the measurement of parameters at both molecular and population levels is valuable for investigating the specific effects of agents interacting with DNA. Ultimately, this methodology may allow the ecotoxicological examination of the link between molecular alterations and measurable adverse effects at higher levels of biological organization.

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The input of anthropogenic contaminants to the aquatic environment is a major concern for scientists, regulators and the public. This is especially relevant in areas such as the Tamar valley in SW England, which has a legacy of contamination from industrial activity in the nineteenth and twentieth centuries. Following on from previous laboratory validation studies, this study aimed to assess the relationship between genotoxic and cytotoxic responses and heavy metal concentrations in two bivalve species sampled from locations along the Tamar estuary. Adult cockles, Cerastoderma edule, and blue mussels, Mytilus edulis, were sampled from five locations in the Tamar and one reference location on the south Devon coast. Bivalve haemocytes were processed for comet and neutral red retention (NRR) assays to determine potential genotoxic and cytotoxic effects, respectively. Sediment and soft tissue samples were analysed for metal content by inductively coupled plasma mass spectrometry. Sediment concentrations were consistent with the physico-chemical nature of the Tamar estuary. A significant correlation (P = 0.05) was found between total metal concentration in sediment and C. edule soft tissues, but no such correlation was found for M. edulis samples. DNA damage was elevated at the site with highest Cr concentrations for M. edulis and at the site with highest Ni and Pb concentrations for C. edule. Analysis of NRR revealed a slight increase in retention time at one site, in contrast to comet data. We conclude that the comet assay is a reliable indicator of genotoxic damage in the field for both M. edulis and C. edule and discuss reasons for the apparent discrepancy with NRR.

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Highlights d Retrograde viruses express mRNA at levels detectable in single-cell sequencing d Different transgenes can be multiplexed in a single sequencing run d VECTORseq identifies both cortical and subcortical projection neurons d VECTORseq defines new superior colliculus and zona incerta projection populations