Size differences among canaries, goldfinches and allies may explain correlated evolution of song and colour.

Sexual signals such as colour ornamentation and birdsong evolve independently of each other in some clades, and in others they evolve positively or negatively correlated. We rarely know why correlated evolution does or does not occur. Here, we show positively correlated evolution between plumage colour and song motor performance among canaries, goldfinches and allies, associated with species differences in body size. When controlling for body size, the pattern of correlated evolution between song performance and colour disappeared. Syllable diversity was not as strongly associated with size, and did not evolve in a correlated manner with colour. We argue that correlated evolution between song and colour was mediated by large size limiting song motor performance, likely due to constraints on the speed of moving heavier bills, and by larger species having less saturated plumage colour, possibly due to life-history traits of larger birds (e.g. longevity, stable pairs) contributing to weaker sexual selection. Results are consistent with the hypothesis that correlated evolution between sexual signals is influenced by how, in a clade, selective pressures and constraints affecting each type of signal happen to be co-distributed across species. Such contingency helps explain the diversity in clade-specific patterns of correlated evolution between sexual signals.

Same Colors for Different Functions: Implications for the Evolution of Carotenoid-Based Ornamentation.

AbstractSexual ornamentation is often assumed to be costly, allowing honest signaling of individual quality, and carotenoid-based colors have been proposed to bear significant costs. If carotenoid-based colors are costly to produce, sexually selected signals should use more concentrated carotenoid pigments and have more saturated color than nonsexual signals, where honesty-guaranteeing costs are not required. We tested this prediction comparing carotenoid-based colors across canaries, goldfinches, and allies because many of these species use yellow plumage as sexual ornamentation but also have yellow rumps that appear to be nonsexual flash marks. Only in the breast, but not the rump, was there an asymmetric codistribution of male and female color saturation, with males similarly or more saturated than females, indicating evolution of breast color by sexual selection. Yellow was not consistently more saturated in the breast than in the rump, and the codistribution of rump and breast color saturation indicated that saturated rumps can persist irrespective of breast color. This challenges the assumption that carotenoid-based colors bear significant costs. The use of carotenoid coloration as sexual signals in this clade may instead be due to social costs, cost-free index mechanisms for signaling quality, and/or socially monogamous species evolving low-cost signals to mostly discriminate against the lowest-quality mates.

High-density lipoprotein receptor SCARB1 is required for carotenoid coloration in birds.

Yellow, orange, and red coloration is a fundamental aspect of avian diversity and serves as an important signal in mate choice and aggressive interactions. This coloration is often produced through the deposition of diet-derived carotenoid pigments, yet the mechanisms of carotenoid uptake and transport are not well-understood. The white recessive breed of the common canary (Serinus canaria), which carries an autosomal recessive mutation that renders its plumage pure white, provides a unique opportunity to investigate mechanisms of carotenoid coloration. We carried out detailed genomic and biochemical analyses comparing the white recessive with yellow and red breeds of canaries. Biochemical analysis revealed that carotenoids are absent or at very low concentrations in feathers and several tissues of white recessive canaries, consistent with a genetic defect in carotenoid uptake. Using a combination of genetic mapping approaches, we show that the white recessive allele is due to a splice donor site mutation in the scavenger receptor B1 (SCARB1; also known as SR-B1) gene. This mutation results in abnormal splicing, with the most abundant transcript lacking exon 4. Through functional assays, we further demonstrate that wild-type SCARB1 promotes cellular uptake of carotenoids but that this function is lost in the predominant mutant isoform in white recessive canaries. Our results indicate that SCARB1 is an essential mediator of the expression of carotenoid-based coloration in birds, and suggest a potential link between visual displays and lipid metabolism.

Song determined by phylogeny and body mass in two differently constrained groups of birds: manakins and cardinals.

The songs of birds are complex signals that may have several functions and vary widely among species. Different ecological, behavioural and morphological factors, as well as phylogeny, have been associated as predictors of the evolution of song structure. However, the importance of differences in development, despite their relevance, has seldom been considered. Here, we analysed the evolution of song in two families of songbirds that differ in song development, manakins (suboscines) and cardinals (oscines), with their phylogeny, morphology, and ecology. Our results show that song characteristics had higher phylogenetic signal in cardinals than in manakins, suggesting higher evolutionary lability in the suboscines. Body mass was the main predictor of song parameters in manakins, and together with habitat type, had a major effect on cardinals' song structure. Precipitation and altitude were also associated with some song characteristics in cardinals. Our results bring unexpected insights into birdsong evolution, in which non-learners (manakins) revealed greater evolutionary lability than song learners (cardinals).

Independent evolution of song diversity and song motor performance in canaries, goldfinches and allies indicates clade-specific trade-offs in birdsong.

The diversity and the motor performance of birdsongs can both be sexually selected. In wood warblers, most species with high motor performance sing a greater proportion of trills, presumably to advertise performance, and thus have lower syllable diversity. We tested if this trade-off between motor performance and syllable diversity extends to canaries, goldfinches and allies, a clade with much longer and more varied songs. We assembled a molecular phylogeny and inferred song motor performance based on the speed of frequency modulation either in trills or in within-song intervals. The two metrics of performance were positively, but only mildly, related across species. While performance evaluated in intervals had high phylogenetic signal, performance evaluated in trills changed independently of phylogeny and was constrained by body size. Species in densely vegetated habitats sang fewer trills, but did not differ in motor performance. Contrary to wood warblers, song motor performance did not predict the proportion of trilled syllables nor within-song syllable diversity, perhaps because large differences in the song duration of canaries, goldfinches and allies prevent trills from severely compromising syllable diversity. Opposed results in wood warblers and in these finches indicate the existence of clade-specific trade-offs in the evolution of birdsong.

Why are human newborns so fat? Relationship between fatness and brain size at birth.

The plumpness of the human newborn has long been recognized as a trait in need of explanation among researchers. Using a linear regression analysis, we find that head circumference is significantly and positively associated with BMI at birth, after gestational age and birthlength were controlled for, in a sample of 1,069 healthy liveborn routinely delivered at the University Hospital of Coimbra (partial correlation r = 0.409, P < 0.0001). This significant association is consistent with the idea that newborn fatness is related to the higher need of lipids in newborn humans as an energetic and plastic substrate during its accelerated brain growth period. As birthweight and birth head size are associated with head size and cognitive abilities in childhood and adult life, it could be postulated that these cognitive abilities could have acted as selective pressure responsible for the newborn fatness increase in our lineage.