Pathways to elaboration of sexual dimorphism in bird plumage patterns

Population and risk assessment of sympatric pheasant species in Palas Valley, Pakistan

Abstract Pheasants are declining everywhere in the world and therefore updated information about their population and habitats are important for conservation and management. The present study was conducted in the Palas Valley, District Kohistan, Pakistan in late spring (May and June) 2020 and early spring (March and April) 2021 to assess the population and anthropogenic stress. The major focus was on three sympatric pheasant species, including Western Horned Tragopan (Tragopan melanocephalus), Himalayan Monal (Lophophorus impejanus), and Koklass Pheasant (Pucrasia macrolopha). We used the “Call Count Method” for the population assessment in the field, and a questionnaire survey was conducted to document the risk assessment of local residents of the valley. The population assessments revealed that the Koklass Pheasant is more adapted to increasing anthropogenic activities and its population appeared more or less similar as 22 years ago. In the past 22 years, Western Tragopan and Himalayan Monal have lost about 40–50% of their populations. Human interference in the form of illegal hunting, deforestation, and overgrazing was found to be common in the valley. The study concludes that the Palas Valley habitat is ideal for pheasant species; however, human interference in the form of urbanization, habitat fragmentation, illegal hunting, and deforestation is occurring at a rapid pace, causing havoc in the pheasant population.

Ecology and behavior predict an evolutionary trade-off between song complexity and elaborate plumages in antwrens (Aves, Thamnophilidae)

The environment can impose constraints on signal transmission properties such that signals should evolve in predictable directions (Sensory Drive Hypothesis). However, behavioral and ecological factors can limit investment in more than one sensory modality leading to a trade-off in use of different signals (Transfer Hypothesis). In birds, there is mixed evidence for both sensory drive and transfer hypothesis. Few studies have tested sensory drive while also evaluating the transfer hypothesis, limiting understanding of the relative roles of these processes in signal evolution. Here, we assessed both hypotheses using acoustic and visual signals in male and female antwrens (Thamnophilidae), a species-rich group that inhabits diverse environments and exhibits behaviors, such as mixed-species flocking, that could limit investment in different signal modalities. We uncovered significant effects of habitat (sensory drive) and mixed-species flocking behavior on both sensory modalities, and we revealed evolutionary trade-offs between song and plumage complexity, consistent with the transfer hypothesis. We also showed sex- and trait-specific responses in visual signals that suggest both natural and social selection play an important role in the evolution of sexual dimorphism. Altogether, these results support the idea that environmental (sensory drive) and behavioral pressures (social selection) shape signal evolution in antwrens.

Layered patterns in nature, medicine, and materials: quantifying anisotropic structures and cyclicity

Various natural patterns-such as terrestrial sand dune ripples, lamellae in vertebrate bones, growth increments in fish scales and corals, aortas and lamellar corpuscles in humans and animals-comprise layers of different thicknesses and lengths. Microstructures in manmade materials-such as alloys, perlite steels, polymers, ceramics, and ripples induced by laser on the surface of graphen-also exhibit layered structures. These layered patterns form a record of internal and external factors regulating pattern formation in their various systems, making it potentially possible to recognize and identify in their incremental sequences trends, periodicities, and events in the formation history of these systems. The morphology of layered systems plays a vital role in developing new materials and in biomimetic research. The structures and sizes of these two-dimensional (2D) patterns are characteristically anisotropic: That is, the number of layers and their absolute thicknesses vary significantly in different directions. The present work develops a method to quantify the morphological characteristics of 2D layered patterns that accounts for anisotropy in the object of study. To reach this goal, we use Boolean functions and an N-partite graph to formalize layer structure and thickness across a 2D plane and to construct charts of (1) "layer thickness vs. layer number" and (2) "layer area vs. layer number." We present a parameter disorder of layer structure (DStr) to describe the deviation of a study object's anisotropic structure from an isotropic analog and illustrate that charts and DStr could be used as local and global morphological characteristics describing various layered systems such as images of, for example, geological, atmospheric, medical, materials, forensic, plants, and animals. Suggested future experiments could lead to new insights into layered pattern formation.

Evolution of Sexual Dimorphism in Tube Blennies (Teleostei: Chaenopsidae)

The study of sexual differences provides insights into selective factors operating on males and females, especially for clades exhibiting varied levels of dimorphism. Sexual differences in morphology and coloration (melanophores) were compiled for 66 of the 89 species of tube blennies (Blenniiformes, Chaenopsidae) from the systematic literature and examination of preserved specimens. Chaenopsids include essentially monomorphic species and those in which males and females differ in as many as 17 morphological and 14 coloration features. While the sexes of most species differ in coloration (at least at the time of breeding), they are morphologically similar in Acanthemblemaria, Hemiemblemaria, and Lucayablennius. While other genera exhibit an intermediate level of dimorphism, species of Coralliozetus, Cirriemblemaria, and Emblemaria are dramatically dimorphic. Character maps on a phylogenetic hypothesis indicate that this extreme level of dimorphism evolved independently in these genera. A complex history of evolution is implied by examination of jaw length with both increases and decreases in one or both sexes leading to either dimorphism or monomorphism. Several features related to shelter defense are monomorphic in species where both sexes inhabit shelters, but dimorphic where only males occupy shelters. Other dimorphic features increase the conspicuousness of male courtship and aggressive displays.

Production of plumage ornaments among males and females of two closely related tropical passerine bird species

The evolution of elaborate secondary sexual traits (i.e., ornaments) is well‐studied in males but less so in females. Similarity in the appearance of ornaments between males and females supports the view that female ornaments arise as a neutral byproduct of selection on male traits due to genetic correlation between sexes, but recent research suggests an adaptive function of female ornaments in at least some contexts. Information on the degree to which production of ornaments differs between the sexes can shed light on these alternative perspectives. We therefore characterized the structural underpinnings of melanin‐based plumage production in males and females of two closely related passerine bird species (genus Malurus). Importantly, both ornamented and unornamented phenotypes in each sex are present between these two species, providing an opportunity to test the null expectation of equivalent modes of production in male and female ornamented phenotypes. In Malurus alboscapulatus, ornamented females are qualitatively similar to males, but we describe a distinctive ornamented female phenotype that differs from that of males in lacking a blue sheen and in lower feather barbule density. In M. melanocephalus, unornamented males and females are also similar in appearance, and we describe a similarity between unornamented phenotypes of males and females in both color and underlying feather barbule structure and pigment composition. Unornamented male M. melanocephalus can flexibly transition to the ornamented phenotype in weeks, and we found extreme differences in color and feather structure between these two alternative male phenotypes. These results contradict the idea that female ornaments have evolved in this system following a simple switch to male‐like plumage by demonstrating greater complexity in the production of the ornamented phenotype in males than in females.

A global analysis of bird plumage patterns reveals no association between habitat and camouflage

Evidence suggests that animal patterns (motifs) function in camouflage. Irregular mottled patterns can facilitate concealment when stationary in cluttered habitats, whereas regular patterns typically prevent capture during movement in open habitats. Bird plumage patterns have predominantly converged on just four types-mottled (irregular), scales, bars and spots (regular)-and habitat could be driving convergent evolution in avian patterning. Based on sensory ecology, we therefore predict that irregular patterns would be associated with visually noisy closed habitats and that regular patterns would be associated with open habitats. Regular patterns have also been shown to function in communication for sexually competing males to stand-out and attract females, so we predict that male breeding plumage patterns evolved in both open and closed habitats. Here, taking phylogenetic relatedness into account, we investigate ecological selection for bird plumage patterns across the class Aves. We surveyed plumage patterns in 80% of all avian species worldwide. Of these, 2,756 bird species have regular and irregular plumage patterns as well as habitat information. In this subset, we tested whether adult breeding/non-breeding plumages in each sex, and juvenile plumages, were associated with the habitat types found within the species' geographical distributions. We found no evidence for an association between habitat and plumage patterns across the world's birds and little phylogenetic signal. We also found that species with regular and irregular plumage patterns were distributed randomly across the world's eco-regions without being affected by habitat type. These results indicate that at the global spatial and taxonomic scale, habitat does not predict convergent evolution in bird plumage patterns, contrary to the camouflage hypothesis.

Evolutionary pathways to convergence in plumage patterns

Background

Avian plumage is ideal for investigating phenotypic convergence because of repeated evolution of the same within-feather patterns. In birds, there are three major types of regular patterns within feathers: scales, bars and spots. Existing models of within-feather pattern development suggest that scales have the simplest developmental mechanism, bars require more stringent regulation than scales, and spots have the strictest developmental parameters. We hypothesized that increasing stringency in the mechanism of pattern formation predicts the evolutionary trajectory of patterns, and hence scales should evolve first, followed by bars and finally spots. Here, using Bayesian phylogenetic modeling we reconstructed pattern evolution in the most spectacularly patterned avian clades – aquatic waterfowl (Anseriformes) and terrestrial gamebirds (Galliformes).

Results

Our analyses suggest that the ancestral state of plumage is an absence of patterns, but with some variability. Independent analyses of seven feather patches reveal that spots evolve after bars and scales. However, both scales and bars evolve frequently from an absence of patterns, contradicting our predictions. Over the whole body, many constraints are conserved from the level of patches, for example the largest number of steps from the ancestral state was required for spots to evolve.

Conclusions

Overall there was remarkable similarity in the inferred evolutionary trajectories of plumage pattern evolution in Galliformes and Anseriformes, suggesting that developmental constraint is similar in these two orders, despite large ecological differences. These evolutionary transitions are largely congruent with a reaction–diffusion based model of pattern formation, but the evolution of bars from an unpatterned ancestor is more common than expected. Our study highlights the promise of testing models of development using comparative methods.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0741-x) contains supplementary material, which is available to authorized users.

The evolution of pattern camouflage strategies in waterfowl and game birds

Visual patterns are common in animals. A broad survey of the literature has revealed that different patterns have distinct functions. Irregular patterns (e.g., stipples) typically function in static camouflage, whereas regular patterns (e.g., stripes) have a dual function in both motion camouflage and communication. Moreover, irregular and regular patterns located on different body regions ("bimodal" patterning) can provide an effective compromise between camouflage and communication and/or enhanced concealment via both static and motion camouflage. Here, we compared the frequency of these three pattern types and traced their evolutionary history using Bayesian comparative modeling in aquatic waterfowl (Anseriformes: 118 spp.), which typically escape predators by flight, and terrestrial game birds (Galliformes: 170 spp.), which mainly use a "sit and hide" strategy to avoid predation. Given these life histories, we predicted that selection would favor regular patterning in Anseriformes and irregular or bimodal patterning in Galliformes and that pattern function complexity should increase over the course of evolution. Regular patterns were predominant in Anseriformes whereas regular and bimodal patterns were most frequent in Galliformes, suggesting that patterns with multiple functions are broadly favored by selection over patterns with a single function in static camouflage. We found that the first patterns to evolve were either regular or bimodal in Anseriformes and either irregular or regular in Galliformes. In both orders, irregular patterns could evolve into regular patterns but not the reverse. Our hypothesis of increasing complexity in pattern camouflage function was supported in Galliformes but not in Anseriformes. These results reveal a trajectory of pattern evolution linked to increasing function complexity in Galliformes although not in Anseriformes, suggesting that both ecology and function complexity can have a profound influence on pattern evolution.