Size differentiation in Finnish house sparrows follows Bergmann's rule with evidence of local adaptation

Signatures of natural selection in morphological quantitative traits in Argentinean populations of Senegalia gilliesii (Fabaceae)

In order to elucidate the role of evolutionary forces in shaping the variation of quantitative traits in Senegalia gilliesii we evaluate seven phenotypic traits in three Argentinean populations, two of them sharing environmental and vegetation type conditions, and a third one ecologically differentiated from the former. The phenotypic traits were compared with molecular markers. Here, we search for signatures of selection by means of the comparison PST-FST . We assessed if the averages of the seven phenotypic traits were different among populations by means of ANOVA and we performed discriminant analysis of principal components (DAPC) for both morphological and molecular data. The ANOVA showed significant results only for two traits. For all foliar traits and two spine traits, the PST-FST comparison suggested the occurrence of stabilizing selection. The DAPC obtained from AFLP data showed three well defined groups of populations; when the same analysis was conducted with morphological data the scatterplot showed high overlapping among individuals and could not separate the populations. Overall, our findings suggest a prominent role of stabilizing selection in all foliar traits and stipular spine length. These results could be extrapolated to other tropical and subtropical acacias. Further studies are needed to analyse the mechanisms underlying genetic differentiation in natural populations of S. gilliesii, find its relationship with eco-geographical variables.

Strong phenotypic divergence in spite of low genetic structure in the endemic Mangrove Warbler subspecies (Setophaga petechia xanthotera) of Costa Rica

Despite the enormous advances in genetics, links between phenotypes and genotypes have been made for only a few nonmodel organisms. However, such links can be essential to understand mechanisms of ecological speciation. The Costa Rican endemic Mangrove Warbler subspecies provides an excellent subject to study differentiation with gene flow, as it is distributed along a strong precipitation gradient on the Pacific coast with no strong geographic barriers to isolate populations. Mangrove Warbler populations could be subject to divergent selection driven by precipitation, which influences soil salinity levels, which in turn influences forest structure and food resources. We used single nucleotide polymorphisms (SNPs) and morphological traits to examine the balance between neutral genetic and phenotypic divergence to determine whether selection has acted on traits and genes with functions related to specific environmental variables. We present evidence showing: (a) associations between environmental variables and SNPs, identifying candidate genes related to bill morphology (BMP) and osmoregulation, (b) absence of population genetic structure in neutrally evolving markers, (c) divergence in bill size across the precipitation gradient, and (d) strong phenotypic differentiation (P ST) which largely exceeds neutral genetic differentiation (F ST) in bill size. Our results indicate an important role for salinity, forest structure, and resource availability in maintaining phenotypic divergence of Mangrove Warblers through natural selection. Our findings add to the growing body of literature identifying the processes involved in phenotypic differentiation along environmental gradients in the face of gene flow.

A coalescent-based estimator of genetic drift, and acoustic divergence in the Pteronotus parnellii species complex

Determining the processes responsible for phenotypic variation is one of the central tasks of evolutionary biology. While the importance of acoustic traits for foraging and communication in echolocating mammals suggests adaptation, the seldom-tested null hypothesis to explain trait divergence is genetic drift. Here we derive FST values from multi-locus coalescent isolation-with-migration models, and couple them with estimates of quantitative trait divergence, or PST, to test drift as the evolutionary process responsible for phenotypic divergence in island populations of the Pteronotus parnellii species complex. Compared to traditional comparisons of PST to FST, the migration-based estimates of FST are unidirectional instead of bidirectional, simultaneously integrate variation among loci and individuals, and posterior densities of PST and FST can be compared directly. We found the evolution of higher call frequencies is inconsistent with genetic drift for the Hispaniolan population, despite many generations of isolation from its Puerto Rican counterpart. While the Hispaniolan population displays dimorphism in call frequencies, the higher frequency of the females is incompatible with sexual selection. Instead, cultural drift toward higher frequencies among Hispaniolan females might explain the divergence. By integrating Bayesian coalescent and trait analyses, this study demonstrates a powerful approach to testing genetic drift as the default evolutionary mechanism of trait differentiation between populations.

Phenotypic divergence despite low genetic differentiation in house sparrow populations

Studying patterns of phenotypic variation among populations can shed light on the drivers of evolutionary processes. The house sparrow (Passer domesticus) is one of the world's most ubiquitous bird species, as well as a successful invader. We investigated phenotypic variation in house sparrow populations across a climatic gradient and in relation to a possible scenario of an invasion. We measured variation in morphological, coloration, and behavioral traits (exploratory behavior and neophobia) and compared it to the neutral genetic variation. We found that sparrows were larger and darker in northern latitudes, in accordance with Bergmann's and Gloger's biogeographic rules. Morphology and behavior mostly differed between the southernmost populations and the other regions, supporting the possibility of an invasion. Genetic differentiation was low and diversity levels were similar across populations, indicating high gene flow. Nevertheless, the southernmost and northern populations differed genetically to some extent. Furthermore, genetic differentiation (F _ST) was lower in comparison to phenotypic variation (P _ST), indicating that the phenotypic variation is shaped by directional selection or by phenotypic plasticity. This study expands our knowledge on evolutionary mechanisms and biological invasions.

Sympatric divergence and clinal variation in multiple coloration traits of Ficedula flycatchers

Geographic variation in phenotypes plays a key role in fundamental evolutionary processes such as local adaptation, population differentiation and speciation, but the selective forces behind it are rarely known. We found support for the hypothesis that geographic variation in plumage traits of the pied flycatcher Ficedula hypoleuca is explained by character displacement with the collared flycatcher Ficedula albicollis in the contact zone. The plumage traits of the pied flycatcher differed strongly from the more conspicuous collared flycatcher in a sympatric area but increased in conspicuousness with increasing distance to there. Phenotypic differentiation (PST ) was higher than that in neutral genetic markers (FST ), and the effect of geographic distance remained when statistically controlling for neutral genetic differentiation. This suggests that a cline created by character displacement and gene flow explains phenotypic variation across the distribution of this species. The different plumage traits of the pied flycatcher are strongly to moderately correlated, indicating that they evolve non-independently from each other. The flycatchers provide an example of plumage patterns diverging in two species that differ in several aspects of appearance. The divergence in sympatry and convergence in allopatry in these birds provide a possibility to study the evolutionary mechanisms behind the highly divergent avian plumage patterns.