Mutations in different pigmentation genes are associated with parallel melanism in island flycatchers.

The independent evolution of similar traits across multiple taxa provides some of the most compelling evidence of natural selection. Little is known, however, about the genetic basis of these convergent or parallel traits: are they mediated by identical or different mutations in the same genes, or unique mutations in different genes? Using a combination of candidate gene and reduced representation genomic sequencing approaches, we explore the genetic basis of and the evolutionary processes that mediate similar plumage colour shared by isolated populations of the Monarcha castaneiventris flycatcher of the Solomon Islands. A genome-wide association study (GWAS) that explicitly controlled for population structure revealed that mutations in known pigmentation genes are the best predictors of parallel plumage colour. That is, entirely black or melanic birds from one small island share an amino acid substitution in the melanocortin-1 receptor (MC1R), whereas similarly melanic birds from another small island over 100 km away share an amino acid substitution in a predicted binding site of agouti signalling protein (ASIP). A third larger island, which separates the two melanic populations, is inhabited by birds with chestnut bellies that lack the melanic MC1R and ASIP allelic variants. Formal FST outlier tests corroborated the results of the GWAS and suggested that strong, directional selection drives the near fixation of the MC1R and ASIP variants across islands. Our results, therefore, suggest that selection acting on different mutations with large phenotypic effects can drive the evolution of parallel melanism, despite the relatively small population size on islands.

The genetic and developmental basis of an exaggerated craniofacial trait in East African cichlids.

The evolution of an exaggerated trait can lead to a novel morphology that allows organisms to exploit new niches. The molecular bases of such phenotypes can reveal insights into the evolution of unique traits. Here, we investigate a rare morphological innovation in modern haplochromine cichlids, a flap of fibrous tissue that causes a pronounced projection of the snout, which is limited to a single genus (Labeotropheus) of Lake Malawi cichlids. We compare flap size in our focal species L. fuelleborni (LF) to homologous landmarks in other closely related cichlid species that show a range of ecological overlap with LF, and demonstrate that variation in flap size is discontinuous among Malawi cichlid species. We demonstrate further that flap development in LF begins at early juvenile stages, and scales allometrically with body size. We then used an F2 hybrid mapping population, derived via crossing LF to a close ecological competitor that lacks this trait, Tropheops "red cheek" (TRC), to identify quantitative trait loci (QTL) that underlie flap development. In all, we identified four loci associated with variation in flap size, and for each the LF allele contributed to a larger flap. We next cross-referenced our QTL map with population genomic data, comparing natural populations of LF and TRC, to identify divergent polymorphisms within each QTL interval. Candidate genes for flap development are discussed. Together, these data indicate a relatively simple and tractable genetic basis for this morphological innovation, which is consistent with its apparently sudden and saltatory evolutionary history. J. Exp. Zool. (Mol. Dev. Evol.) 324B: 662-670, 2015. © 2015 Wiley Periodicals, Inc.

Kin selection may contribute to lek evolution and trait introgression across an avian hybrid zone.

Understanding the mechanism(s) that favour cooperation among individuals competing for the same resources provides direct insights into the evolution of grouping behaviour. In a hybrid zone between golden-/yellow-collared (Manacus vitellinus) and white-collared (Manacus candei) manakins, males form aggregations composed of white and yellow males solely to attract females ('mixed leks'). Previous work shows that yellow males in these mixed leks experience a clear mating advantage over white males, resulting in the preferential introgression of yellow plumage allele(s) into the white species. However, the yellow male mating advantage only occurs in mixed leks with high frequencies of yellow males, and only a few of these males probably mate. Hence, it remains unclear why unsuccessful males join leks. Here, we used microsatellite markers to estimate pairwise relatedness among males within and between leks to test whether indirect genetic benefits of helping kin ('kin selection') can promote grouping. We found that yellow males are significantly more related to each other within than between leks, while relatedness among white males did not differ within and between leks. This suggests that yellow males may indirectly enhance their own reproductive success by preferentially lekking with relatives because yellow plumage is under positive frequency-dependent selection (positive FDS). Our results are consistent with the hypothesis that kin selection may promote grouping and facilitate positive FDS for yellow males, mediating the movement of yellow plumage across this hybrid zone.