Theory predicts that parallel evolution should be common when the number of beneficial mutations is limited by selective constraints on protein structure. However, confirmation is scarce in natural ...populations. Here we studied the major haemoglobin genes of eight Andean duck lineages and compared them to 115 other waterfowl species, including the bar-headed goose (Anser indicus) and Abyssinian blue-winged goose (Cyanochen cyanopterus), two additional species living at high altitude. One to five amino acid replacements were significantly overrepresented or derived in each highland population, and parallel substitutions were more common than in simulated sequences evolved under a neutral model. Two substitutions evolved in parallel in the αA subunit of two (Ala-α8) and five (Thr-α77) taxa, and five identical βA subunit substitutions were observed in two (Ser-β4, Glu-β94, Met-β133) or three (Ser-β13, Ser-β116) taxa. Substitutions at adjacent sites within the same functional protein region were also observed. Five such replacements were in exterior, solvent-accessible positions on the A helix and AB corner of the αA subunit. Five others were in close proximity to inositolpentaphosphate binding sites, and two pairs of independent replacements occurred at two different α¹β¹ intersubunit contacts. More than half of the substitutions in highland lineages resulted in the acquisition of serine or threonine (18 gains vs. 2 losses), both of which possess a hydroxyl group that can hydrogen bond to a variety of polar substrates. The patterns of parallel evolution observed in these waterfowl suggest that adaptation to high-altitude hypoxia has resulted from selection on unique but overlapping sets of one to five amino acid substitutions in each lineage.
Biodiversity research has been the mainstay of natural history museums, but the traditional uses of biological collections in taxonomy, systematics, and evolutionary biology account for only part of ...these collections' value. Biological collections today are meeting diverse needs. New uses for specimens—as “biological filter paper,” for example—have little relationship to the taxon-oriented research on which collections are based, yet they often have tremendous import for helping us understand changes in populations, species, and the environment. As the major issues in exploration and systematics are resolved and society's interest in biodiversity wavers, museums need to embrace important new uses for natural history collections and, with new partners, begin laying new foundations for a postbiodiversity future. Proactively opening a domain focused on exploration and basic biodiversity to an increase in applied research can enable museums to grow to meet present and future challenges and to bring their true strengths, their collections, to bear on broader issues for both science and society.
Although migration is a common behaviour, the effects of this annual two-way event on the speciation processes are poorly understood, even though birds, which are commonly migratory played a critical ...role in the development of speciation theory. Here I propose that new developments in the theory of sympatric speciation--a process whereby new species can arise through population differentiation without spatial isolation--may help to explain the bursts of speciation observed in some seasonal migrant lineages.
The taxonomic challenge posed by cryptic species (two or more distinct species classified as a single species) has been recognized for nearly 300 years, but the advent of relatively inexpensive and ...rapid DNA sequencing has given biologists a new tool for detecting and differentiating morphologically similar species. Here, we synthesize the literature on cryptic and sibling species and discuss trends in their discovery. However, a lack of systematic studies leaves many questions open, such as whether cryptic species are more common in particular habitats, latitudes or taxonomic groups. The discovery of cryptic species is likely to be non-random with regard to taxon and biome and, hence, could have profound implications for evolutionary theory, biogeography and conservation planning.
Historic events and contemporary processes work in concert to create and maintain geographically partitioned variation and are instrumental in the generation of biodiversity. We sought to gain a ...better understanding of how contemporary processes such as movement and isolation influence the genetic structure of widely distributed vagile species such as birds. Song sparrows (Melospiza melodia) in western North America provide a natural system for examining the genetics of populations that have different patterns of geographic isolation and migratory behavior. We examined the population genetics of 576 song sparrows from 23 populations using seven microsatellite loci to assess genetic differentiation among populations and to estimate the effects of drift and immigration (gene flow) on each population. Sedentary, isolated populations were characterized by low levels of immigration and high levels of genetic drift, whereas those populations less isolated displayed signals of high gene flow and little differentiation from other populations. Contemporary dispersal rates from migratory populations, estimated by assignment test, were higher and occurred over larger distances than dispersal from sedentary populations but were also probably too low to counter the effects of drift in most populations. We suggest that geographic isolation and limited gene flow facilitated by migratory behavior are responsible for maintaining observed levels of differentiation among Pacific coastal song sparrow populations.
Genetic variation is often lower within island populations, however islands may also harbor divergent genetic variation. The likelihood that insular populations are genetically diverse or divergent ...should be influenced by island size and isolation. We tested this assumption by comparing patterns of genetic variation across all major island song sparrow populations along the Pacific North American coast. Allelic richness was moderately lowered even on islands which are close to large, potential sources. The most significant differences in allelic richness occurred on very small or highly remote islands. Gene diversity was significantly lower only on remote or very small islands. We found that island populations contribute to regional genetic variation through both the amount of genetic variation and the uniqueness of that variation. The partitioning of this contribution was associated with the size and isolation of the island populations.
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•Ultraconserved element (UCE) data resolve the phylogeny of migratory Catharus thrushes.•A fully migratory clade of Catharus thrushes has undergone speciation with gene flow.•Historic ...gene flow throughout Catharus has produced reticulate gene phylogenies.•Heteropatric speciation has played an important role in the genus.
New World thrushes in the genus Catharus are small, insectivorous or omnivorous birds that have been used to explore several important questions in avian evolution, including the evolution of seasonal migration and plumage variation. Within Catharus, members of a clade of obligate long-distance migrants (C. fuscescens, C. minimus, and C. bicknelli) have also been used in the development of heteropatric speciation theory, a divergence process in which migratory lineages (which might occur in allopatry or sympatry during portions of their annual cycle) diverge despite low levels of gene flow. However, research on Catharus relationships has thus far been restricted to the use of small genetic datasets, which provide limited resolution of both phylogenetic and demographic histories. We used a large, multi-locus dataset from loci containing ultraconserved elements (UCEs) to study the demographic histories of the migratory C. fuscescens-minimus-bicknelli clade and to resolve the phylogeny of the migratory species of Catharus. Our dataset included more than 2000 loci and over 1700 variable genotyped sites, and analyses supported our prediction of divergence with gene flow in the fully migratory clade, with significant gene flow among all three species. Our phylogeny of the genus differs from past work in its placement of C. ustulatus, and further analyses suggest historic gene flow throughout the genus, producing genetically reticulate (or network) phylogenies. This raises questions about trait origins and suggests that seasonal migration and the resulting migratory condition of heteropatry is likely to promote hybridization not only during pairwise divergence and speciation, but also among non-sisters.
Specimen collection: An essential tool Rocha, L. A.; Aleixo, A.; Allen, G. ...
Science (American Association for the Advancement of Science),
05/2014, Letnik:
344, Številka:
6186
Journal Article
PDF
