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Abstract: 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. [ABSTRACT FROM AUTHOR]

Abstract: Historical associations of genes and proteins are thought to delineate pathways available to subsequent evolution; however, the effects of past functional involvements on contemporary evolution are rarely quantified. Here, we examined the extent to which the structure of a carotenoid enzymatic network persists in avian evolution. Specifically, we tested whether the evolution of carotenoid networks was most concordant with phylogenetically structured expansion from core reactions of common ancestors or with subsampling of biochemical pathway modules from an ancestral network. We compared structural and historical associations in 467 carotenoid networks of extant and ancestral species and uncovered the overwhelming effect of pre‐existing metabolic network structure on carotenoid diversification over the last 50 million years of avian evolution. Over evolutionary time, birds repeatedly subsampled and recombined conserved biochemical modules, which likely maintained the overall structure of the carotenoid metabolic network during avian evolution. These findings explain the recurrent convergence of evolutionary distant species in carotenoid metabolism and weak phylogenetic signal in avian carotenoid evolution. Remarkable retention of an ancient metabolic structure throughout extensive and prolonged ecological diversification in avian carotenoid metabolism illustrates a fundamental requirement of organismal evolution – historical continuity of a deterministic network that links past and present functional associations of its components. [ABSTRACT FROM AUTHOR]

Abstract: Evolution of adaptive phenotypic flexibility requires a system that can dynamically restore and update a functional phenotype in response to environmental change. The architecture of such a system evolves under the conflicting demands of versatility and robustness, and resolution of these demands should be particularly evident in organisms that require external inputs for reiterative trait production within a generation, such as in metabolic networks that underlie yearly acquisition of diet‐dependent coloration in birds. Here, we show that a key structural feature of carotenoid networks–redundancy of biochemical pathways–enables these networks to translate variable environmental inputs into consistent phenotypic outcomes. We closely followed life‐long changes in structure and utilization of metabolic networks in a large cohort of free‐living birds and found that greater individual experience with dietary change between molts leads to wider occupancy of the metabolic network and progressive accumulation of redundant pathways in a functionally active network. This generated a regime of emergent buffering whereby greater dietary experience was mechanistically linked to greater robustness of resulting traits and an increasing ability to retain and implement previous adaptive solutions. Thus, experience‐related buffering links evolvability and robustness in carotenoid‐metabolizing networks and we argue that this mechanistic principle facilitates the evolution of phenotypic flexibility. [ABSTRACT FROM AUTHOR]

The network of the interactions among genes, proteins, and metabolites delineates a range of potential phenotypic diversifications in a lineage, and realized phenotypic changes are the result of differences in the dynamics of the expression of the elements and interactions in this deterministic network. Regulatory mechanisms, such as hormones, mediate the relationship between the structural and dynamic properties of networks by determining how and when the elements are expressed and form a functional unit or state. Changes in regulatory mechanisms lead to variable expression of functional states of a network within and among generations. Functional properties of network elements, and the magnitude and direction of evolutionary change they determine, depend on their location within a network. Here, we examine the relationship between network structure and the dynamic mechanisms that regulate flux through a metabolic network. We review the mechanisms that control metabolic flux in enzymatic reactions and examine structural properties of the network locations that are targets of flux control. We aim to establish a predictive framework to test the contributions of structural and dynamic properties of deterministic networks to evolutionary diversifications. [ABSTRACT FROM AUTHOR]

The complexity of organismal organization channels and accommodates novel genomic and developmental modifications. Here, I extend this perspective to suggest that emergent processes that dominate homeostasis—co-option, re-use, and recombination of accumulated elements—can create configurations and dependencies among these elements that strongly reduce the number of evolutionary steps needed for the evolution of precise novel adaptations. Evolutionary retention and environmental matching of such configurations are further facilitated when they include elements of homeostasis that are responsive to particular environmental cues. I apply this perspective to the study of evolution of sex-biased egg-laying in birds, a phenomenon that combines precision, complexity, context-dependency, and reversibility. I show that homeostatic hitchhiking can overcome the main difficulty in the evolution of this adaptation—the perceived necessity of de novo co-evolution of oogenesis, sex-determination, and order of ovulation in each environmental context—something that would require unrealistic expectations of evolutionary rates and population sizes and is not a desirable outcome for a process that needs to retain substantial environmental sensitivity. First, I explain the rationale behind the homeostatic-hitchhiking hypothesis and outline its predictions specifically for studies of sex-bias in order of egg-laying. Second, I show that a combination of self-regulatory and emergent processes and ubiquitous re-use of conserved growth factors make oogenesis particularly amendable to homeostatic hitchhiking. Third, I review empirical evidence for this mechanism in the rapid evolution of adaptive sex-biased order of egg-laying that accompanied colonization of North America by the house finch (Carpodacus mexicanus). [ABSTRACT FROM AUTHOR]

Divergent selection on traits involved in both local adaptation and the production of mating signals can strongly facilitate population differentiation. Because of its links to foraging morphologies and cultural inheritance song of birds can contribute particularly strongly to maintenance of local adaptations. In two adjacent habitats—native Sonoran desert and urban areas—house finches ( Carpodacus mexicanus) forage on seeds that are highly distinct in size and shell hardness and require different bite forces and bill morphologies. Here, we first document strong and habitat-specific natural selection on bill traits linked to bite force and find adaptive modifications of bite force and bill morphology and associated divergence in courtship song between the two habitats. Second, we investigate the developmental basis of this divergence and find that early ontogenetic tissue transformation in bill, but not skeletal traits, is accelerated in the urban population and that the mandibular primordia of the large-beaked urban finches express bone morphogenetic proteins (BMP) earlier and at higher level than those of the desert finches. Further, we show that despite being geographically adjacent, urban and desert populations are nevertheless genetically distinct corroborating findings of early developmental divergence between them. Taken together, these results suggest that divergent selection on function and development of traits involved in production of mating signals, in combination with localized learning of such signals, can be very effective at maintaining local adaptations, even at small spatial scales and in highly mobile animals. [ABSTRACT FROM AUTHOR]

Diversity in organismal forms among taxa is thought to reflect distinct selection pressures across environments. The central assumption underlying this expectation is that taxa experiencing similar selection have similar response to that selection. However, because selection acts on trait function, taxa similarity in selection response depends crucially on the relationship between function and morphology. Further, when a trait consists of multiple parts, changes in function in response to selection can result from modification of different parts, and adaptation to the same environment might result in functional but not morphological similarity. Here, we address the extent to which functional and morphological diversity in masticatory apparatus of soricid shrews reflects a shared ecological characteristic of their diet type. We examine the factors limiting morphological variation across shrew species by assessing the relative contribution of trait function (biomechanics of the jaw), ecology, and phylogeny to species similarity in mandibular traits. We found that species that shared diet type were functionally but not morphologically similar. The presence of multiple semi-independently varying traits enabled functional equivalence of composite foraging morphologies and resulted in variable response to selection exerted by similar diet. We show that functional equivalence of multiple morphologies enabled persistence of differences in habitat use (e.g., habitat moisture and coverage) among species that specialize on the same diet. We discuss the importance of developmental and functional integration among traits for evolutionary diversification of morphological structures that generate equivalent functions. [ABSTRACT FROM AUTHOR]

Evolutionary diversifications are commonly attributed to the continued modifications of a conserved genetic toolkit of developmental pathways, such that complexity and convergence in organismal forms are assumed to be due to similarity in genetic mechanisms or environmental conditions. This approach, however, confounds the causes of organismal development with the causes of organismal differences and, as such, has only limited utility for addressing the cause of evolutionary change. Molecular mechanisms that are closely involved in both developmental response to environmental signals and major evolutionary innovations and diversifications are uniquely suited to bridge this gap by connecting explicitly the causes of within-generation variation with the causes of divergence of taxa. Developmental pathways of bone formation and a common role for bone morphogenetic proteins (BMPs) in both epigenetic bone remodeling and the evolution of major adaptive diversifications provide stich opportunity. We show that variation in timing of ossification can result in similar phenotypic patterns through epigenetically induced changes in gene expression and propose that both genetic accommodation of environmentally induced developmental pathways and flexibility in development across environments evolve through heterochronic shifts in bone maturation relative to exposure to unpredictable environments. We suggest that such heterochronic shifts in ossification can not only buffer development under fluctuating environments while maintaining epigenetic sensitivity critical for normal skeletal formation, but also enable epigenetically induced gene expression to generate specialized morphological adaptations. We review studies of environmental sensitivity of BMP pathways and their regulation of formation, remodeling, and repair of cartilage and bone to examine the hypothesis that BMP-mediated skeletal adaptations are facilitated by evolved reactivity of BMPs to external signals. Surprisingly, no empirical study to date has identified the molecular mechanism behind developmental plasticity in skeletal traits. We outline a conceptual framework for future studies that focus on mediation of phenotypic plasticity in skeletal development by the patterns of BMP expression. [ABSTRACT FROM AUTHOR]

A tremendous diversity of avian color displays has stimulated numerous studies of natural and sexual selection. Yet, the developmental mechanisms that produce such diversification, and thus the proximate targets of selection pressures, are rarely addressed and poorly understood. In particular, because feathers are colored during growth, the dynamics of feather growth play a deterministic role in the variation in ornamentation. No study to date, however, has addressed the contribution of feather growth to the expression of carotenoid-based ornamentation. Here, we examine the developmental basis of variation in ornamental feather shapes in male house finches (Carpodacus mexicanus)--a species in which carotenoid displays are under strong natural and sexual selection. First, we use geometric morphometrics to partition the observed shape variation in fully grown feathers among populations, ages, degrees of elaboration, ornamental body parts, and individuals. Second, we use a biologically informed mathematical model of feather growth to predict variation in shape of ornamental feathers due to simulated growth rate, angle of helical growth of feather barbs, initial number of barb ridges, rate of addition of new barbs, barb diameter, and ramus-expansion angle. We find close concordance between among-individual variation in feather shape and hue of entire ornament, and show that this concordance can be attributed to a shared mechanism--growth rate of feather barbs. Predicted differences in feather shape due to rate of addition of barbs and helical angle of feather growth explained observed variation in ornamental area both among individuals and between populations, whereas differences in helical angle of growth and the number of barbs in the feather follicle explained differences in feather shape between ornamental parts and among males of different ages. The findings of a close association of feather growth dynamics and overall ornamentation identify the proximate targets of selection for elaboration of sexual displays. Moreover, the close association of feather growth and pigmentation not only can reinforce condition-dependence in color displays, but can also enable phenotypic and genetic accommodation of novel pigments into plumage displays providing a mechanism for the observed concordance of within-population developmental processes and between-population diversification of color displays. [ABSTRACT FROM AUTHOR]

In species that produce broods of multiple offspring, parents need to partition resources among simultaneously growing neonates that often differ in growth requirements. In birds, multiple ovarian follicles develop inside the female at the same time, resulting in a trade-off of resources among them and potentially limiting maternal ability for sex-specific allocation. We compared resource acquisition among oocytes in relation to their future sex and ovulation order in two populations of house finches with contrasting sex-biased maternal strategies. In a native Arizona population, where mothers do not bias offspring sex in relation to ovulation order, the male and female oocytes did not show sex-specific trade-offs of resources during growth and there was no evidence for spatial or temporal segregation of male and female oocytes in the ovary. In contrast, in a recently established Montana population where mothers strongly bias offspring sex in relation to ovulation order, we found evidence for both intra-sexual trade-offs among male and female oocytes and sex-specific clustering of oocytes in the ovary. We discuss the importance of sex-specific resource competition among offspring for the evolution of sex-ratio adjustment and sex-specific maternal resource allocation. [ABSTRACT FROM AUTHOR]

Presents a study which examined the evolution of sexual size dimorphism in the house finch. Materials and methods; Results; Discussion.

Examines the relationship between song and plumage elaborations in cardueline finches. Relation of both song complexity and carotenoid-based plumage traits to overall individual condition; Different signaling strategies in variable environments; Effects of potential covariates on song attributes of cardueline finches.

Presents a study that examined the divergence in sexual dimorphism of adults between established Montana and Alabama populations of the house finch Carpodacus mexicanus. Attributes to population differences in growth of males and females; Comparisons of the ontogeny of males and females in diverged populations that differ in sexual dimorphism of adults.

Examines the ontogeny of sexual size dimorphism in an isolated population of the house finch Carpodacus mexicanus. Identification of sex; Growth patterns in males and females; Sexual dimorphism for bill traits in relation to age.

Presents information on a study which examined the evolution of sexual size dimorphism in a passerine bird called the house finch. Discussion on sexual dimorphism; Methodology; Results and discussion.

Presents information on a study which analyzed the evolution of sexual morphological variance-covariance matrices for seven house finch population. Methodology of the study; Results and discussion on the study.

Presents a study which determined the role of current net selection in shaping and maintaining contemporary sexual dimorphism in an established population of the house finch, Carpodacus mexicanus in Montana. Methodology; Results; Discussion.

Asymmetry in bilateral traits is often used to assess an individual's quality and stress resistance, but stress-induced variation in developmental stability is largely undocumented for free-living populations. Over many years, grizzly bears (Ursus arctos horribilis) extensively foraged around garbage dumps in Yellowstone National Park. Abrupt closure of these dumps 26 years ago was a severely stressful event and was followed by excessive mortality and a many-fold increase in grizzly home-range size. I examine how this stress affected developmental stability by comparing dentition of bears born before and after the dump closure. I predicted that (1) asymmetry in dentition should be greater in bears born after dump closure compared to before closure, and asymmetry in sexually selected canines should change more than nonsexually selected premolars following dump closure and (2) the relationship between tooth asymmetry and tooth size should change in the populations following the stressful events as compared with populations before stressful events. I found that developmental stability of canines, which are under directional sexual selection in males, was more responsive to stress compared to that of male premolars or female dentition (both under stabilizing selection), and, because of the increased cost of canine production, fewer animals were able to achieve both large size and symmetrical development of these teeth, and thus the slope of the relationship between fluctuating asymmetry and canine size increased. I conclude that stress appears to act as an honesty-reinforcement mechanism in sexual selection for symmetrical dentition. [ABSTRACT FROM AUTHOR]

The colder climate and disjunct distribution of nesting and foraging habitats at high elevations increases the necessity of biparental care for successful breeding in birds. If differences in parental investment between the sexes correlate with intensity of sexual selection, the intensity of sexual selection should covary with ecological factors associated with elevation. I used sexual dimorphism as an indirect measure of intensity of sexual selection and examined variation in sexual dimorphism in 126 extant species of cardueline finches. I controlled for phylogeny and potential confounding factors and tested the prediction that the extent of sexual dimorphism negatively covaries with elevation of breeding. As predicted, interspecific variation in sexual dimorphism was more strongly associated with changes in elevation than with habitat, nest dispersion and placement, and migratory status. Species occupying lower elevations were more sexually dimorphic in plumage than species at higher elevations. This variation was largely due to increased brightness of male plumage at lower elevations. I address possible explanations of this trend, which may include increased opportunities for extrapair fertilizations at lower elevations, an increase in the cost of secondary sexual trait production (i.e., molt) and maintenance at high elevations, and elevational variation in predation pressure [ABSTRACT FROM AUTHOR]

Focuses on sexual dichromatism in birds with emphasis on the importance of nest predation and nest location for females as opposed to males. Cause of sexual dichromatism in birds; Significance of more concealed nest sites.

Studies nest site fidelity of female Wild Turkeys. Background on the study; Site fidelity, age, and nest predation; Reproductive performance and site fidelity; Spring dispersal; Previous nesting habitat.