Wendt, S. | bioRxiv Science

bioRxiv2018

Relative value perception in an insect: positive and negative incentive contrasts in ants

Humans tend to value things not on their absolute values, but relative to reference points such as former experience or expectations. People rate the quality of a new salary relative to their previous salary and the salaries of their peers, instead of appreciating its absolute value. Here, we demonstrate a similar effect in an insect: ants, which had previously experienced a low quality food source, showed higher acceptance of medium quality food (e.g. 0.1M then 0.5M; positive contrast) than if they had received the medium food all along (e.g. 0.5M then 0.5M; control), and vice versa for high expectations. Further experiments demonstrate that these contrast effects arise from cognitive rather than mere sensory or pre-cognitive perceptual causes. Pheromone deposition also correlates with perceived reward value, and ants showed successive contrasts in their pheromone deposition. Relative value perception can therefore be expected to have strong effects not only on individual behaviour, but also on collective decision-making. Contrast effects were also social: the quality of food received from other ants affected the perceived value of food found later. Value judgement is a key element in decision making, and thus relative value perception will strongly influence how animals interact with their environment.

animal behavior and cognition↗

bioRxiv2016

Standard Issue: Copy number heterogeneity of JC virus standards discovered through next-generation sequencing

Quantitative PCR is a diagnostic mainstay of clinical virology, and accurate quantitation of viral load among labs requires the use of international standards. However, the use of multiple passages of viral isolates to obtain sufficient material for international standards may result in genomic changes that complicate their use as quantitative standards. We performed next-generation sequencing to gain single-nucleotide resolution and relative copy number of JC virus (JCV) clinical standards. Strikingly, the WHO international standard and ExactTM v1/v2 prototype standards for JCV showed 8-fold and 4-fold variation in genomic coverage between different loci in the viral genome, respectively, due to large deletions in the large T-antigen region. No such variation was seen for a clinical sample with high copy-number of JCV nor a plasmid control. Intriguingly, several of the JCV standards sequenced in this study with large T-antigen deletions were cultured in cell lines immortalized using SV40 T-antigen, suggesting the possibility of trans-complementation in cell culture. Using a cut-off of 2% variant allele fraction for junctional reads to define the presence of a strain, 11 different strains were present in the WHO standard. In summary, targeting of different regions of the same international standard could result in up to an 8-fold difference in quantitation. We recommend the use of next-generation sequencing to validate standards in clinical virology.

microbiology↗