Extensive phenotypic diversification coexists with little genetic divergence and a lack of population structure in the White Wagtail subspecies complex (Motacilla alba)

Geographically clustered phenotypes often demonstrate consistent patterns in molecular markers, particularly mitochondrial DNA (mtDNA) traditionally used in phylogeographic studies. However, distinct evolutionary trajectories among traits and markers can lead to their discordance. First, geographic structure in phenotypic traits and nuclear molecular markers can be co‐aligned but inconsistent with mtDNA (mito‐nuclear discordance). Alternatively, phenotypic variation can have little to do with patterns in neither mtDNA nor nuclear markers. Disentangling between these distinct patterns can provide insight into the role of selection, demography and gene flow in population divergence. Here, we examined a previously reported case of strong inconsistency between geographic structure in mtDNA and plumage traits in a widespread polytypic bird species, the White Wagtail (Motacilla alba). We tested whether this pattern is due to mito‐nuclear discordance or discrepancy between morphological evolution and both nuclear and mtDNA markers. We analysed population differentiation and structure across six out of nine commonly recognized subspecies using 17 microsatellite loci and a combination of microsatellites and plumage indices in a comprehensively sampled region of a contact between two subspecies. We did not find support for the mito‐nuclear discordance hypothesis: nuclear markers indicated a subtle signal of genetic clustering only partially consistent with plumage groups, similar to previous findings that relied on mtDNA. We discuss evolutionary factors that could have shaped the intricate patterns of phenotypic diversification in the White wagtail and the role that repeated selection on plumage ‘hotspots’ and hybridization may have played.     

Fluctuating asymmetry in red junglefowl

Fluctuating asymmetry, the random deviation from perfect bilateral symmetry, has recently attracted considerable attention. Levels of asymmetry have been shown to correlate with measures of individual quality. We measured asymmetry in a variety of ornamental and non-ornamental traits in red junglefowl, Gallus gallus and examined the patterns of asymmetry among different traits within an individual. All ornamental traits had significantly higher levels of fluctuating asymmetry than did non-ornamental traits. However, inter-trait correlations of asymmetry were low for both ornamental and non-ornamental traits. We then correlated measures of asymmetry with several potential indicators of male quality, including comb size, body size, and body condition. We found little evidence that asymmetry in any measured trait reflected male quality. We measured asymmetry in ornamental traits at several stages of development and found no relationship between male condition and changes in asymmetry over time. Our results indicate that it is necessary to employ caution when choosing traits to be measured in studies of fluctuating asymmetry and that a relationship between asymmetry and individual quality cannot be assumed.     

Altitudinal variation in sexual dimorphism: a new pattern and alternative hypotheses

The colder climate and disjunct distribution of nesting andforaging habitats at high elevations increases the necessityof biparental care for successful breeding in birds. If differencesin parental investment between the sexes correlate with intensityof sexual selection, the intensity of sexual selection shouldcovary with ecological factors associated with elevation. Iused sexual dimorphism as an indirect measure of intensity ofsexual selection and examined variation in sexual dimorphismin 126 extant species of cardueline finches. I controlled forphylogeny and potential confounding factors and tested the predictionthat the extent of sexual dimorphism negatively covaries withelevation of breeding. As predicted, interspecific variationin sexual dimorphism was more strongly associated with changesin elevation than with habitat, nest dispersion and placement,and migratory status. Species occupying lower elevations weremore sexually dimorphic in plumage than species at higher elevations.This variation was largely due to increased brightness of maleplumage at lower elevations. I address possible explanationsof this trend, which may include increased opportunities forextrapair fertilizations at lower elevations, an increase inthe cost of secondary sexual trait production (i.e., molt) andmaintenance at high elevations, and elevational variation inpredation pressure     

Do bright colors at nests incur a cost due to predation?

Summary Birds show much interspecific variation in the coloration and brightness of their plumage. I examine the hypothesis that selection due to predation on incubating birds and their nest contents can explain part of this diversity. First, I argue that rather than using absolute rates of nest predation to make predictions about the costs of conspicuous colours, we should measure experimentally whether increases in plumage conspicuousness elevate rates of nest predation. Second, I present experimental data investigating the cost of red and brown colour at ground and tree nests. These data provide the first evidence that bright colours do attract predators to nests and that, in addition, this cost varies according to the nesting site. Natural selection seems to most strongly oppose the evolution of conspicuous colours in ground-nesting birds.     

The association between plumage damage and feather-eating in free-range laying hens

Severe feather-pecking (SFP) persists as a highly prevalent and detrimental behavioural problem in laying hens (Gallus gallus domesticus) worldwide. The present experiment investigated the association between feather-eating and plumage damage, a consequence of SFP, in groups of free-range, ISA Brown laying hens. Single feathers were placed on the floor of the home pens. Feathers were sourced from seven different birds. A total of 50 birds in six pens with extensive plumage damage were compared with birds in six control pens with little plumage damage at 41 to 43 weeks of age (n=12 pens, 600 hens). Birds in pens with extensive plumage damage ingested more feathers (F=8.1, DF=1, 8, P=0.02), and also showed shorter latencies to peck at (χ²=54.5, DF=1, P<0.001), and ingest feathers (χ²=55.6, DF=1, P<0.001). Birds ingested feathers from a bird in the free-range facility, in which the testing took place, more quickly than from a bird housed in a separate cage facility (χ² = 39.0, DF=6, P<0.001). A second experiment investigated the predictive relationship between feather-eating and plumage damage. Feathers were presented to 16 pens of 50 pullets prior to the development of plumage damage, at 15 weeks of age, and then to the same hens after plumage damage had become prominent, at 40 weeks of age. Birds had a higher probability of ingesting feathers (F=142.0, DF=1, 231, P<0.001), pecked feathers more times (F=11.24, DF=1, 239, P<0.001), and also pecked (χ² = 127.3, DF=1, P<0.001) and ingested (χ²=189.3, DF=1, P<0.001) the feathers more quickly at 40 than 15 weeks of age. There was a trend for an interaction, where birds pecked feathers from the rump more times than feathers from the back at 40 weeks of age (F=3.46, DF=1, 237, P=0.06). However, a lack of variability in plumage damage between pens in this experiment precluded investigation of the predictive relationship. The results from the present study confirm the association between feather-eating and plumage damage, and suggest that birds may prefer feathers from particular body areas and from particular hens. Future experiments should focus on elucidating whether feather-eating may act as a predictor of SFP.     

The tempo of trait divergence in geographic isolation: Avian speciation across the Marañon Valley of Peru

Geographic isolation is considered essential to most speciation events, but our understanding of what controls the pace and degree of phenotypic divergence among allopatric populations remains poor. Why do some taxa exhibit phenotypic differentiation across barriers to dispersal, whereas others do not? To test factors controlling phenotypic divergence in allopatry, we employed a comparative phylogeographic approach consisting of replicates of ecologically similar Andean bird species isolated across a major biogeographic barrier, the Marañon Valley of Peru. Our study design leverages variation among codistributed taxa in their degree of plumage, morphometric, and vocal differentiation across the Marañon to examine the tempo of phenotypic evolution. We found that substantial plumage differences between populations required roughly two million years to evolve. In contrast, morphometric trait evolution showed greater idiosyncrasy and stasis. Our results demonstrate that despite a large degree of idiosyncrasy in the relationship between genetic and phenotypic divergence across taxa and environments, comparative studies within regions may reveal predictability in the pace of phenotypic divergence. Our results also suggest that social selection is important for driving differentiation of populations found in similar environments.     

Male-like ornamentation in female hummingbirds results from social harassment rather than sexual selection

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