Relocation to avoid costs: a hypothesis on red carotenoid-based signals based on recent CYP2J19 gene expression data

Sexual and social selections promote the evolution of many conspicuous colorations in animals. These traits would act as individual quality signals when they transmit reliable information. Reliability should be assured by production costs unaffordable for low-quality trait bearers or guaranteed if trait expression is tightly linked to individual quality and cannot be falsified (“index signals”). It has been suggested that colored ornaments produced by red ketocarotenoid pigments could meet the latter. These ketocarotenoids are often obtained by enzymatic transformation of dietary yellow carotenoids. Recently, the first enzyme performing this transformation has been described: CYP2J19. This enzyme, belonging to the cytochrome p450 superfamily, is presumably located in the inner mitochondrial membrane, thus linking color expression with cell respiration efficacy. However, it remains to be clarified if the tissue where this intracellular mechanism acts could influence signal reliability and trait evolution. CYP2J19 expression data are now available for different species and tissues. Here, we review current data in birds and hypothesize that CYP2J19 activity could have evolved in some species by being relocated from the liver tissue to the ornaments (epidermis), a pattern more strongly observed in those birds where the red is expressed in non-feathered bare parts (e.g. bill, legs). One potential explanation is that bare parts, unlike feathers, require a constant carotenoid mobilization to maintain color throughout the year. We propose that tissue relocation allows for avoiding production costs derived from potential CYP2J19 interference on vital liver functions. Implications for signal reliability in ornamental evolution are discussed.

It’s a Matter of Taste: Avian Predators Taste Reject Mimetic Prey in Relation to Signal Reliability

Aposematic organisms defend themselves through various means to increase their unprofitability to predators which they advertise with conspicuous warning signals. Predators learn to avoid aposematic prey through associative learning that leads to lower predation. However, when these visual signals become unreliable (e.g., through automimicry or Batesian mimicry), predators may switch from using visual signals to taste sampling prey to choose among them (‘go-slow’ behaviour). In this experiment, we tested this possibility in a field experiment where we released a total of 9600 mealworm prey of two types: (i) undefended prey (injected with water) and (ii) model-mimics (injected with either quinine sulphate [models] or water [mimics]). Prey were deployed at 12 sites, each with a mimic frequency ratio between 0 to 1, at 0.2 intervals. We found that taste rejection peaked at moderate mimic frequencies (0.4 and 0.6), supporting the idea that taste sampling and rejection of prey is related to signal reliability and predator uncertainty. This is the first time that taste-rejection has been shown to be related to the reliability of prey signals in a mimetic prey system.

The design of RIP belts impacts the reliability and quality of the measured respiratory signals

Purpose Evaluate the effect of respiratory inductance plethysmography (RIP) belt design on the reliability and quality of respiratory signals. A comparison of cannula flow to disposable cut-to-fit, semi-disposable folding and disposable RIP belts was performed in clinical home sleep apnea testing (HSAT) studies. Methods This was a retrospective study using clinical HSAT studies. The signal reliability of cannula, thorax, and abdomen RIP belts was determined by automatically identifying periods during which the signals did not represent respiratory airflow and breathing movements. Results were verified by manual scoring. RIP flow quality was determined by examining the correlation between the RIP flow and cannula flow when both signals were considered reliable. Results Of 767 clinical HSAT studies, mean signal reliability of the cut-to-fit, semi-disposable, and disposable thorax RIP belts was 83.0 ± 26.2%, 76.1 ± 24.4%, and 98.5 ± 9.3%, respectively. The signal reliability of the cannula was 92.5 ± 16.1%, 87.0 ± 23.3%, and 85.5 ± 24.5%, respectively. The automatic assessment of signal reliability for the RIP belts and cannula flow had a sensitivity of 50% and a specificity of 99% compared with manual assessment. The mean correlation of cannula flow to RIP flow from the cut-to-fit, semi-disposable, and disposable RIP belts was 0.79 ± 0.24, 0.52 ± 0.20, and 0.86 ± 0.18, respectively. Conclusion The design of RIP belts affects the reliability and quality of respiratory signals. The disposable RIP belts that had integrated contacts and did not fold on top of themselves performed the best. The cut-to-fit RIP belts were most likely to be unreliable, and the semi-disposable folding belts produced the lowest-quality RIP flow signals compared to the cannula flow signal.