Biology subjects

Alonso-Alvarez, C.

Publications and source records attributed to Alonso-Alvarez, C..

4 recordsLinked to original sources

bioRxiv2026

Carotenoid-based ornaments predict survival in male but not female birds: a meta-analysis

Many vertebrates exhibit colourful ornaments generated by carotenoid pigments that presumably evolve as signals under sexual selection. To function as sexual signals, carotenoid-based coloured ornaments should accurately reveal an individuals quality, commonly defined as fitness potential, which includes the ability to survive. We performed a meta-analysis for testing the association between the expression level of carotenoid-based ornaments and longevity estimates (annual survival or lifespan) in birds, the taxon with the largest body of evidence. We detected a significant positive correlation in males but not in females. This result contrasts with recent meta-analytic work showing a positive association between carotenoid-based coloured traits and avian fecundity in both sexes. The link to survival was consistent among colourations produced by enzymatically transformed pigments (mostly red ketocarotenoids) and those based on dietary yellow carotenoids. The latter suggests that the association with survival holds across the physiological mechanisms involved in the production of these ornaments. In summary, our study reveals sex-specific selection in the evolution of carotenoid-based ornaments.

evolutionary biology↗

bioRxiv2025

Sexual signal reliability in male zebra finches: Food intake explains the impact of immune activation on carotenoid-based coloration

Theory predicts that traits evolving as animal signals must transmit reliable information about the bearers quality. Two hypotheses are often invoked to explain how carotenoid-based colorations function as reliable individual quality signals. The first hypothesis suggests that carotenoid allocation trade-offs between signaling and survival-related functions maintain signal reliability. Only high-quality individuals could resolve these trade-offs without incurring a fitness loss. Such signals are plastic, and the signaler can strategically manage their expression level to increase fitness returns. The second hypothesis posits that certain carotenoid-based signals are strongly constrained in their expression, not allowing strategic manipulations or cheating. We challenged captive male zebra finches (Taeniopygia guttata) with simulated infections by injecting lipopolysaccharides (LPS) derived from Escherichia coli and assessed organ masses, body temperature, and carotenoid levels in several tissues. Compared to controls, LPS-treated birds reduced the bill redness, a sexual signal. However, this reduction was largely explained by decreased food intake caused by LPS. Bill redness negatively correlated with body temperature and spleen mass but positively correlated with blood, spleen and subcutaneous fat carotenoid levels. Overall, our findings suggest that carotenoid-based bill coloration predominantly reflects the recent physiological condition of individuals and resource allocation trade-offs rather than directly signaling individual quality.

evolutionary biology↗

bioRxiv2022

Wild common crossbills produce redder body feathers when their wings are clipped

The animal signaling theory posits that conspicuous colorations exhibited by many animals have evolved as reliable signals of individual quality. Red carotenoid-based ornaments may depend on enzymatic transformations (oxidation) of dietary yellow carotenoids, which could occur in the inner mitochondrial membrane (IMM). Thus, carotenoid ketolation and cell respiration could share the same biochemical pathways. Accordingly, the level of trait expression (redness) would directly reveal the efficiency of individuals metabolism and hence, the bearer quality in an unfalsifiable way. Different avian studies have described that the flying effort may induce oxidative stress. A redox metabolism modified during the flight could thus influence the carotenoid conversion rate and, ultimately, animal coloration. Here, we aimed to infer the link between red carotenoid-based ornament expression and flight metabolism by increasing flying effort in wild male common crossbills Loxia curvirostra (Linnaeus). In this order, 295 adult males were captured during winter in an Iberian population. Half of the birds were experimentally handicapped through wing feather clipping to increase their flying effort, the other half being used as a control group. The rump feathers were also plucked in all the birds to stimulate plumage regrown of a small surface during a short time-lapse. Thirty-four birds with fully grown rump feathers could be recaptured in the subsequent weeks. Among them, male crossbills with experimentally impaired flying capacity showed redder rump feathers than controls. This result would support the hypothesis that the flying metabolism influences the redox enzymatic reactions required for converting yellow dietary carotenoids to red ketocarotenoids. Summary statementCarotenoid-based colorations may depend on pigment enzymatic transformations linked to mitochondrial function. The flight metabolism could influence this. Here, common crossbills with clipped wings produced redder feathers than controls.

evolutionary biology↗

bioRxiv2020

A mitochondria-targeted antioxidant and a thyroid hormone affect carotenoid ketolase gene expression and bill redness in zebra finches

Conspicuous ornaments in animals can evolve to reveal individual quality when their production/maintenance costs make them reliable as signals or if their expression level is intrinsically linked to quality by some unfalsifiable mechanism (quality indices). The latter has been mostly associated with traits constrained by body size. However, red ketocarotenoid-based coloured ornaments may also have evolved as quality indices because their production could be closely linked to individual metabolism and, particularly, to the cell respiration at the inner mitochondrial membrane (IMM). This mechanism would supposedly not depend on resource (yellow carotenoids) availability, thus discarding allocation trade-offs. A gene coding for a ketolase enzyme (CYP2J19) responsible for converting dietary yellow carotenoids to red ketocarotenoids has recently been described in birds. It is not known, however, if this ketolase is involved in mitochondrial metabolism and if its expression level and activity is resource independent. Here, we manipulated the metabolism of captive male zebra finches by an antioxidant designed to penetrate the IMM (mitoTEMPO) and a thyroid hormone (triiodothyronine; T3) with known hypermetabolic effects. The expression levels of a ketocarotenoid-based ornament (bill redness) and CYP2J19 were measured. MitoTEMPO downregulated CYP2J19 expression, supporting the mitochondrial involvement in ketolase function. T3 also reduced CYP2J19 expression, but at an intermediate dosage, this effect being buffered by mitoTEMPO. Bill redness seemed to show a similar interacting effect. Nevertheless, this faded when CYP2J19 expression level was controlled for as a covariate. We argue that the well-known mitoTEMPO effect in reducing mitochondrial reactive oxygen species (ROS) production (particularly superoxide) could have interfered on redox signalling mechanisms controlling ketolase transcription. High T3 levels, contrarily, can lead to high ROS production but also trigger compensatory mechanisms, which may explain the U-shaped effect with dosage on CYP2J19 expression levels. Bill CYP2J19 expression values were also positively correlated to redness and circulating substrate carotenoid levels. Nonetheless, treatment effects did not change when controlling for blood carotenoid concentration, suggesting that resource-availability dependence was irrelevant. Finally, our findings reveal a role for thyroid hormones in the expression of carotenoid-based ornaments that has virtually been ignored until now.

evolutionary biology↗