Inferring ecological selection from multidimensional community trait distributions along environmental gradients.

Understanding the drivers of community assembly is critical for predicting the future of biodiversity and ecosystem services. Ecological selection ubiquitously shapes communities by selecting for individuals with the most suitable trait combinations. Detecting selection types on key traits across environmental gradients and over time has the potential to reveal the underlying abiotic and biotic drivers of community dynamics. Here, we present a model-based predictive framework to quantify the multidimensional trait distributions of communities (community trait spaces), which we use to identify ecological selection types shaping communities along environmental gradients. We apply the framework to over 3600 boreal forest understory plant communities with results indicating that directional, stabilizing, and divergent selection all modify community trait distributions and that the selection type acting on individual traits may change over time. Our results provide novel and rare empirical evidence for divergent selection within a natural system. Our approach provides a framework for identifying key traits under selection and facilitates the detection of processes underlying community dynamics.

The biotic and abiotic contexts of ecological selection mediate the dominance of distinct dispersal strategies in competitive metacommunities.

While the influence of dispersal on ecological selection is the subject of intense research, we still lack a thorough understanding of how ecological selection operates to favour distinct dispersal strategies in metacommunities. To address this issue, we developed a model framework in which species with distinct quantitative dispersal traits that govern the three stages of dispersal-departure, movement and settlement-compete under different ecological contexts. The model identified three primary dispersal strategies (referred to as nomadic, homebody and habitat-sorting) that consistently dominated metacommunities owing to the interplay of spatiotemporal environmental variation and different types of competitive interactions. We outlined the key characteristics of each strategy and formulated theoretical predictions regarding the abiotic and biotic conditions under which each strategy is more likely to prevail in metacommunities. By presenting our results as relationships between dispersal traits and well-known ecological gradients (e.g. seasonality), we were able to contrast our theoretical findings with previous empirical research. Our model demonstrates how landscape environmental characteristics and competitive interactions at the intra- and interspecific levels can interact to favour distinct multivariate and context-dependent dispersal strategies in metacommunities. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Divergent ecological selection maintains species boundaries despite gene flow in a rare endemic tree, Quercus acerifolia (maple-leaf oak).

Strong gene flow from outcrossing relatives tends to blur species boundaries, while divergent ecological selection can counteract gene flow. To better understand how these two forces affect the maintenance of species boundaries, we focused on a species complex including a rare species, maple-leaf oak (Quercus acerifolia), which is found in only four disjunct ridges in Arkansas. Its limited range and geographic proximity to co-occurring close relatives create the possibility for genetic swamping. In this study, we gathered genome-wide single nucleotide polymorphisms (SNPs) using restriction-site-associated DNA sequencing (RADseq) from 190 samples of Q. acerifolia and three of its close relatives, Q. shumardii, Q. buckleyi, and Q. rubra. We found that Q. shumardii and Q. acerifolia are reciprocally monophyletic with low support, suggesting incomplete lineage sorting, introgression between Q. shumardii and Q. acerifolia, or both. Analyses that model allele distributions demonstrate that admixture contributes strongly to this pattern. Populations of Q. acerifolia experience gene flow from Q. shumardii and Q. rubra, but we found evidence that divergent selection is likely maintaining species boundaries: 1) ex situ collections of Q. acerifolia have a higher proportion of hybrids compared to the mature trees of the wild populations, suggesting ecological selection against hybrids at the seed/seedling stage; 2) ecological traits co-vary with genomic composition; and 3) Q. acerifolia shows genetic differentiation at loci hypothesized to influence tolerance of radiation, drought, and high temperature. Our findings strongly suggest that in maple-leaf oak, selection results in higher divergence at regions of the genome despite gene flow from close relatives.

Evolution of Chromosomal Inversions across an Avian Radiation.

Chromosomal inversions are structural mutations that can play a prominent role in adaptation and speciation. Inversions segregating across species boundaries (trans-species inversions) are often taken as evidence for ancient balancing selection or adaptive introgression, but can also be due to incomplete lineage sorting. Using whole-genome resequencing data from 18 populations of 11 recognized munia species in the genus Lonchura (N = 176 individuals), we identify four large para- and pericentric inversions ranging in size from 4 to 20 Mb. All four inversions cosegregate across multiple species and predate the numerous speciation events associated with the rapid radiation of this clade across the prehistoric Sahul (Australia, New Guinea) and Bismarck Archipelago. Using coalescent theory, we infer that trans-specificity is improbable for neutrally segregating variation despite substantial incomplete lineage sorting characterizing this young radiation. Instead, the maintenance of all three autosomal inversions (chr1, chr5, and chr6) is best explained by selection acting along ecogeographic clines not observed for the collinear parts of the genome. In addition, the sex chromosome inversion largely aligns with species boundaries and shows signatures of repeated positive selection for both alleles. This study provides evidence for trans-species inversion polymorphisms involved in both adaptation and speciation. It further highlights the importance of informing selection inference using a null model of neutral evolution derived from the collinear part of the genome.

Microhabitat partitioning between sympatric intertidal fish species highlights the importance of sediment composition in gravel beach conservation.

Gravel beaches in the Mediterranean ecoregion represent an economically important and unique habitat type. Yet, burgeoning tourism, intensive coastal development and artificial nourishment of beaches may jeopardize their ecological communities. To date, species that reside on gravel beaches and the consequences of beach alterations are poorly understood, which hampers the development of a sustainable coastal tourism industry along the region's shorelines. Using a simple collection method based on dredging buckets through the intertidal section of beaches, we quantified the microhabitat association of two sympatric clingfish species in the genus Gouania at seven natural and an artificial gravel beach based on sediment characteristics. We hypothesized that slender (G. pigra) and stout (G. adriatica) morphotypes would partition interstitial niche space based on sediment size, which may affect the vulnerability of the species to changes in gravel beach composition due to coastal development. We detected substantial differences in gravel composition within and among the sampled beaches which suggests scope for microhabitat partitioning in Gouania. Indeed, we found significant relationships between species identity and the presence/absence and abundance of individuals in hauls based on their positioning on PC1. Our results suggest that modifications of gravel beaches through coastal development, including beach nourishment, intensifying coastal erosion, or artificial beach creation, may have detrimental consequences for the two species if sediment types or sizes are altered. We posit that, given the simplicity and efficacy of our sampling method and the sensitivity of Gouania species to prevailing gravel composition, the genus could serve as an important indicator for gravel beach management in the Mediterranean ecoregion.

Genomic clines across the species boundary between a hybrid pine and its progenitor in the eastern Tibetan Plateau.

Most species have clearly defined distribution ranges and ecological niches. The genetic and ecological causes of species differentiation and the mechanisms that maintain species boundaries between newly evolved taxa and their progenitors are, however, less clearly defined. This study investigated the genetic structure and clines in Pinus densata, a pine of hybrid origin on the southeastern Tibetan Plateau, to gain an understanding of the contemporary dynamics of species barriers. We analyzed genetic diversity in a range-wide collection of P. densata and representative populations of its progenitors, Pinus tabuliformis and Pinus yunnanensis, using exome capture sequencing. We detected four distinct genetic groups within P. densata that reflect its migration history and major gene-flow barriers across the landscape. The demographies of these genetic groups in the Pleistocene were associated with regional glaciation histories. Interestingly, population sizes rebounded rapidly during interglacial periods, suggesting persistence and resilience of the species during the Quaternary ice age. In the contact zone between P. densata and P. yunnanensis, 3.36% of the analyzed loci (57 849) showed exceptional patterns of introgression, suggesting their potential roles in either adaptive introgression or reproductive isolation. These outliers showed strong clines along critical climate gradients and enrichment in a number of biological processes relevant to high-altitude adaptation. This indicates that ecological selection played an important role in generating genomic heterogeneity and a genetic barrier across a zone of species transition. Our study highlights the forces that operate to maintain species boundaries and promote speciation in the Qinghai-Tibetan Plateau and other mountain systems.

Testing drivers of acoustic divergence in cicadas (Cicadidae: Tettigettalna).

Divergence in acoustic signals may have a crucial role in the speciation process of animals that rely on sound for intra-specific recognition and mate attraction. The acoustic adaptation hypothesis (AAH) postulates that signals should diverge according to the physical properties of the signalling environment. To be efficient, signals should maximize transmission and decrease degradation. To test which drivers of divergence exert the most influence in a speciose group of insects, we used a phylogenetic approach to the evolution of acoustic signals in the cicada genus Tettigettalna, investigating the relationship between acoustic traits (and their mode of evolution) and body size, climate and micro-/macro-habitat usage. Different traits showed different evolutionary paths. While acoustic divergence was generally independent of phylogenetic history, some temporal variables' divergence was associated with genetic drift. We found support for ecological adaptation at the temporal but not the spectral level. Temporal patterns are correlated with micro- and macro-habitat usage and temperature stochasticity in ways that run against the AAH predictions, degrading signals more easily. These traits are likely to have evolved as an anti-predator strategy in conspicuous environments and low-density populations. Our results support a role of ecological selection, not excluding a likely role of sexual selection in the evolution of Tettigettalna calling songs, which should be further investigated in an integrative approach.

Geographical variation of the acoustic signals in the spot-legged treefrog (Polypedates megacephalus) of Hainan Island.

Geographical divergence in acoustic signals is often affected by multiple selective pressures. Environmental factors are expected to shape signals by adjusting for greater propagation efficiency. Nevertheless, such habitat-driven hypotheses have not been well-examined with multi-signal and multi-habitat types included simultaneously. In this study, we evaluated call similarity of the spot-legged treefrog (Polypedates megacephalus), characterized by multiple call types, from 11 geographic populations across Hainan Island. We also examined multiple factors (i.e. body mass, temperature, altitude, and vegetation) among different acoustical geographic clusters, and tested whether the variation in acoustic length and frequency among different habitats was in accordance with the prediction derived from the acoustic adaptation hypothesis. We showed that P. megacephalus from Hainan Island included 3 acoustic geographic clusters: the northeastern flatlands, the southwest mountains, and the hills around the mountains. We also showed that environmental factors (i.e. altitude and vegetation) varied across these 3 acoustically distinct areas. Moreover, the duration of the different call types supported the hypothesis that they should have optimal transmission in their own habitats. Thus, our results reveal the roles of ecological selection in the geographical divergence of anuran acoustic signals.

Host association, environment, and geography underlie genomic differentiation in a major forest pest.

Diverse geographic, environmental, and ecological factors affect gene flow and adaptive genomic variation within species. With recent advances in landscape ecological modelling and high-throughput DNA sequencing, it is now possible to effectively quantify and partition their relative contributions. Here, we use landscape genomics to identify determinants of genomic differentiation in the forest tent caterpillar, Malacosoma disstria, a widespread and irruptive pest of numerous deciduous tree species in North America. We collected larvae from multiple populations across Eastern Canada, where the species experiences a diversity of environmental gradients and feeds on a number of different host tree species, including trembling aspen (Populus tremuloides), sugar maple (Acer saccharum), red oak (Quercus rubra), and white birch (Betula papyrifera). Using a combination of reciprocal causal modelling (RCM) and distance-based redundancy analyses (dbRDA), we show that differentiation of thousands of genome-wide single nucleotide polymorphisms (SNPs) among individuals is best explained by a combination of isolation by distance, isolation by environment (spatial variation in summer temperatures and length of the growing season), and differences in host association. Configuration of suitable habitat inferred from ecological niche models was not significantly related to genomic differentiation, suggesting that M. disstria dispersal is agnostic with respect to habitat quality. Although population structure was not discretely related to host association, our modelling framework provides the first molecular evidence of host-associated differentiation in M. disstria, congruent with previous documentation of reduced growth and survival of larvae moved between natal host species. We conclude that ecologically mediated selection is contributing to variation within M. disstria, and that divergent adaptation related to both environmental conditions and host association should be considered in ongoing research and management of this important forest pest.

Noise constrains the evolution of call frequency contours in flowing water frogs: a comparative analysis in two clades.

BACKGROUND: The acoustic adaptation hypothesis (AAH) states that signals should evolve towards an optimal transmission of the intended information from senders to intended receivers given the environmental constraints of the medium that they traverse. To date, most AAH studies have focused on the effect of stratified vegetation on signal propagation. These studies, based on the AAH, predict that acoustic signals should experience less attenuation and degradation where habitats are less acoustically complex. Here, we explored this effect by including an environmental noise dimension to test some AAH predictions in two clades of widespread amphibians (Bufonidae and Ranidae) that actively use acoustic signals for communication. By using data from 106 species in these clades, we focused on the characterization of the differences in dominant frequency (DF) and frequency contour (i.e., frequency modulation [FM] and harmonic performances) of mating calls and compared them between species that inhabit flowing-water or still-water environments. RESULTS: After including temperature, body size, habitat type and phylogenetic relationships, we found that DF differences among species were explained mostly by body size and habitat structure. We also showed that species living in lentic habitats tend to have advertisement calls characterized by well-defined FM and harmonics. Likewise, our results suggest that flowing-water habitats can constrain the evolutionary trajectories of the frequency-contour traits of advertisement calls in these anurans. CONCLUSIONS: Our results may support AAH predictions in frogs that vocalize in noisy habitats because flowing-water environments often produce persistent ambient noise. For instance, these anurans tend to generate vocalizations with less well-defined FM and harmonic traits. These findings may help us understand how noise in the environment can influence natural selection as it shapes acoustic signals in affected species.

Ecological Drivers and Sex-Based Variation in Body Size and Shape in the Queensland Fruit Fly, Bactrocera tryoni (Diptera: Tephritidae).

The Queensland fruit fly (Bactrocera tryoni; Q-fly) is an Australian endemic horticultural pest species, which has caused enormous economic losses. It has the potential to expand its range to currently Q-fly-free areas and poses a serious threat to the Australian horticultural industry. A large number of studies have investigated the correlation between environmental factors and Q-fly development, reproduction, and expansion. However, it is still not clear how Q-fly morphological traits vary with the environment. Our study focused on three morphological traits (body size, wing shape, and fluctuating asymmetry) in Q-fly samples collected from 1955 to 1965. We assessed how these traits vary by sex, and in response to latitude, environmental variables, and geographic distance. First, we found sexual dimorphism in body size and wing shape, but not in fluctuating asymmetry. Females had a larger body size but shorter and wider wings than males, which may be due to reproductive and/or locomotion differences between females and males. Secondly, the body size of Q-flies varied with latitude, which conforms to Bergmann's rule. Finally, we found Q-fly wing shape was more closely related to temperature rather than aridity, and low temperature and high aridity may lead to high asymmetry in Q-fly populations.

Dispersal Reduction: Causes, Genomic Mechanisms, and Evolutionary Consequences.

Recent biological analyses suggest that reductions in dispersal ability have been key drivers of diversification across numerous lineages. We synthesise emerging data to highlight similarities regarding the causes and consequences of dispersal reduction across taxa and ecosystems, as well as the diverse genomic mechanisms underpinning these shifts. Natural selection has acted on standing genetic variation within taxa to drive often rapid - and in some cases parallel - losses of dispersal, and ultimately speciation. Such shifts can thus represent an important nexus between adaptive and neutral diversification processes, with substantial evolutionary consequences. Recognition of the links between these concepts that are emerging from different fields, taxa and ecosystems is transforming our understanding of the fascinating role of dispersal reduction in the formation of biodiversity.

The association between morphological and ecological characters across a global passerine radiation.

Strong relationships between morphological and ecological characters are commonly predicted to reflect the association between form and function, with this hypothesis being well supported in restricted taxonomic and geographical contexts. Conversely, among broader sets of species, ecological variables have been shown to have limited power to explain morphological variation. To understand these apparent discrepancies, for a large and globally distributed passerine radiation, we test whether (a) the character states of four ecological variables (foraging mode, diet, strata and habitat) have different morphological optima, (b) ecological variables explain substantial variance in morphology and (c) ecological character states can be accurately predicted from morphology. We collected 10 linear morphological measurements for 782 species of corvoid passerines, and assessed (a) the fit of models of continuous trait evolution with different morphological optima for each ecological character state, (b) variation in morphological traits among ecological character states using phylogenetically corrected regressions and (c) the accuracy of morphological traits in predicting species-level membership of ecological character states using linear discriminant analysis (LDA). Models of morphological evolution with different ecological optima were well supported across numerous morphological axes, corresponding with significant differences in trait distributions among ecological character states. LDA also showed that membership of the ecological categories can be predicted with relatively high accuracy by morphology. In contrast to these findings, ecological variables explain limited amounts of variation in morphological traits. For a global radiation of passerine birds, we confirm that the generation of morphological variation is generally consistent with ecological selection pressures, but that ecological characters are of limited utility in explaining morphological differences among species. Although selection towards different optima means that membership of ecological character states tend to be well predicted by morphology, the overall morphospace of individual ecological character states tend to be broad, implying that morphology can evolve in multiple ways in response to similar selection pressures. Extensive variation in morphological adaptations among similar ecological strategies is likely to be a widespread phenomenon across the tree of life.

Pleistocene glacial cycles drove lineage diversification and fusion in the Yosemite toad (Anaxyrus canorus).

Species endemic to alpine environments can evolve via steep ecological selection gradients between lowland and upland environments. Additionally, many alpine environments have faced repeated glacial episodes over the past two million years, fracturing these endemics into isolated populations. In this "glacial pulse" model of alpine diversification, cycles of allopatry and ecologically divergent glacial refugia play a role in generating biodiversity, including novel admixed ("fused") lineages. We tested for patterns of glacial pulse lineage diversification in the Yosemite toad (Anaxyrus [Bufo] canorus), an alpine endemic tied to glacially influenced meadow environments. Using double-digest RADseq on populations densely sampled from a portion of the species range, we identified nine distinct lineages with divergence times ranging from 18 to 724 thousand years ago (ka), coinciding with multiple Sierra Nevada glacial events. Three lineages have admixed origins, and demographic models suggest these fused lineages have persisted throughout past glacial cycles. Directionality indices supported the hypothesis that some lineages recolonized Yosemite from east of the ice sheet, whereas other lineages remained in western refugia. Finally, refugial niche reconstructions suggest that low- and high-elevation lineages have convergently adapted to similar climatic niches. Our results suggest glacial cycles and refugia may be important crucibles of adaptive diversity across deep evolutionary time.

Cryptic speciation in the Chinese white pine (Pinus armandii): Implications for the high species diversity of conifers in the Hengduan Mountains, a global biodiversity hotspot.

Conifers are the largest and ecologically and economically most important component group of the gymnosperms. Despite their slow rate of molecular evolution, rapid and recent diversification was unexpectedly prevalent in this ancient group in the Hengduan Mountains, a world's biodiversity hotspot and gymnosperm diversity center in Southwest China. In this study, we investigated the underlying mechanisms and disentangled the interactions of geography and ecology in speciation and evolution in Pinus armandii, an important forest tree species endemic to China, by integrating analyses of population transcriptomics, population genetics and ecological niche modeling. Many lines of evidence suggest that cryptic speciation has occurred in P. armandii. During the process, geologically induced formation of Mount Gongga and other massive peaks might trigger the initial vicariance isolation of the northern and southern subdivisions, and ecologically based selection then reinforced their differentiation and local adaptation. Our ecological niche analysis and earlier reciprocal transplant experiments in P. armandii provided convincing evidences for the critical role of ecology in the process of speciation. These findings suggest that both geography and ecology contributed significantly to the abundance of very recent and rapid species divergences, which promoted the rising of the extremely high conifer diversity in the Hengduan Mountains.

Polymorphism and multiple correlated characters: Do flatfish asymmetry morphs also differ in swimming performance and metabolic rate?

Phenotypic polymorphisms often differ in multiple correlated traits including morphology, behavior, and physiology, all of which can affect performance. How selection acts on these suites of traits can be complex and difficult to discern. Starry flounder (Platichthys stellatus) is a pleuronectid flatfish that exhibits rare polymorphism for the direction of eye migration and resulting whole-body asymmetry. P. stellatus asymmetry morphs differ subtly in several anatomical traits, foraging behavior, and stable isotope signatures, suggesting they may be ecologically segregated, yet performance and metabolic differences are unknown.Here we tested the hypothesis that sinistral and dextral P. stellatus asymmetry morphs diverge in performance and routine metabolic rate (RMR) by comparing prolonged swimming endurance (time to exhaustion at a constant swimming speed), fast-start swimming velocity and acceleration, and rate of oxygen consumption. Based on subtle morphological differences in caudal tail size, we expected sinistral P. stellatus to have superior prolonged swimming endurance relative to dextral fish, but inferior fast-start performance.Sinistral P. stellatus exhibited both significantly greater prolonged swimming performance and fast-start swimming performance. However, sinistral P. stellatus also exhibited greater RMR, suggesting that their general swimming performance could be enhanced by an elevated metabolic rate.Divergence between P. stellatus asymmetry morphs in swimming performance and metabolic rates contributes to growing evidence of ecological segregation between them, as well as our understanding of possible ecological consequences of asymmetry direction in flatfishes. These data provide an example of the complexity of polymorphisms associated with multiple correlated traits in a rare case of asymmetry polymorphism in a marine flatfish species.

Intrinsic incompatibilities evolving as a by-product of divergent ecological selection: Considering them in empirical studies on divergence with gene flow.

The possibility of intrinsic barriers to gene flow is often neglected in empirical research on local adaptation and speciation with gene flow, for example when interpreting patterns observed in genome scans. However, we draw attention to the fact that, even with gene flow, divergent ecological selection may generate intrinsic barriers involving both ecologically selected and other interacting loci. Mechanistically, the link between the two types of barriers may be generated by genes that have multiple functions (i.e., pleiotropy), and/or by gene interaction networks. Because most genes function in complex networks, and their evolution is not independent of other genes, changes evolving in response to ecological selection can generate intrinsic barriers as a by-product. A crucial question is to what extent such by-product barriers contribute to divergence and speciation-that is whether they stably reduce gene flow. We discuss under which conditions by-product barriers may increase isolation. However, we also highlight that, depending on the conditions (e.g., the amount of gene flow and the strength of selection acting on the intrinsic vs. the ecological barrier component), the intrinsic incompatibility may actually destabilize barriers to gene flow. In practice, intrinsic barriers generated as a by-product of divergent ecological selection may generate peaks in genome scans that cannot easily be interpreted. We argue that empirical studies on divergence with gene flow should consider the possibility of both ecological and intrinsic barriers. Future progress will likely come from work combining population genomic studies, experiments quantifying fitness and molecular studies on protein function and interactions.

Long-term acclimation to reciprocal light conditions suggests depth-related selection in the marine foundation species Posidonia oceanica.

Phenotypic differences among populations of the same species reflect selective responses to ecological gradients produced by variations in abiotic and biotic factors. Moreover, they can also originate from genetic differences among populations, due to a reduced gene flow. In this study, we examined the extent of differences in photo-acclimative traits of Posidonia oceanica (L.) Delile clones collected above and below the summer thermocline (i.e., -5 and -25 m) in a continuous population extending along the water depth gradient. During a reciprocal light exposure and subsequent recovery in mesocosms, we assessed degree of phenotypic plasticity and local adaptation of plants collected at different depths, by measuring changes in several traits, such as gene expression of target genes, photo-physiological features, and other fitness-related traits (i.e., plant morphology, growth, and mortality rates). Samples were also genotyped, using microsatellite markers, in order to evaluate the genetic divergence among plants of the two depths. Measures collected during the study have shown a various degree of phenotypic changes among traits and experimental groups, the amount of phenotypic changes observed was also dependent on the type of light environments considered. Overall plants collected at different depths seem to be able to acclimate to reciprocal light conditions in the experimental time frame, through morphological changes and phenotypic buffering, supported by the plastic regulation of a reduced number of genes. Multivariate analyses indicated that plants cluster better on the base of their depth origin rather than the experimental light conditions applied. The two groups were genetically distinct, but the patterns of phenotypic divergence observed during the experiment support the hypothesis that ecological selection can play a role in the adaptive divergence of P. oceanica clones along the depth gradient.

The probability of parallel genetic evolution from standing genetic variation.

Parallel evolution is often assumed to result from repeated adaptation to novel, yet ecologically similar, environments. Here, we develop and analyse a mathematical model that predicts the probability of parallel genetic evolution from standing genetic variation as a function of the strength of phenotypic selection and constraints imposed by genetic architecture. Our results show that the probability of parallel genetic evolution increases with the strength of natural selection and effective population size and is particularly likely to occur for genes with large phenotypic effects. Building on these results, we develop a Bayesian framework for estimating the strength of parallel phenotypic selection from genetic data. Using extensive individual-based simulations, we show that our estimator is robust across a wide range of genetic and evolutionary scenarios and provides a useful tool for rigorously testing the hypothesis that parallel genetic evolution is the result of adaptive evolution. An important result that emerges from our analyses is that existing studies of parallel genetic evolution frequently rely on data that is insufficient for distinguishing between adaptive evolution and neutral evolution driven by random genetic drift. Overcoming this challenge will require sampling more populations and the inclusion of larger numbers of loci.

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.