Beringia as a high-latitude engine of avian speciation.

Beringia is a biogeographically dynamic region that extends from northeastern Asia into northwestern North America. This region has affected avian divergence and speciation in three important ways: (i) by serving as a route for intercontinental colonisation between Asia and the Americas; (ii) by cyclically splitting (and often reuniting) populations, subspecies, and species between these continents; and (iii) by providing isolated refugia through glacial cycles. The effects of these processes can be seen in taxonomic splits of shallow to increasing depths and in the presence of regional endemics. We review the taxa involved in the latter two processes (splitting-reuniting and isolation), with a focus on three research topics: avian diversity, time estimates of the generation of that diversity, and the regions within Beringia that might have been especially important. We find that these processes have generated substantial amounts of avian diversity, including 49 pairs of avian subspecies or species whose breeding distributions largely replace one another across the divide between the Old World and the New World in Beringia, and 103 avian species and subspecies endemic to this region. Among endemics, about one in three is recognised as a full biological species. Endemic taxa in the orders Charadriiformes (shorebirds, alcids, gulls, and terns) and Passeriformes (perching birds) are particularly well represented, although they show very different levels of diversity through evolutionary time. Endemic Beringian Charadriiformes have a 1.31:1 ratio of species to subspecies. In Passeriformes, endemic taxa have a 0.09:1 species-to-subspecies ratio, suggesting that passerine (and thus terrestrial) endemism might be more prone to long-term extinction in this region, although such 'losses' could occur through their being reconnected with wider continental populations during favourable climatic cycles (e.g. subspecies reintegration with other populations). Genetic evidence suggests that most Beringian avian taxa originated over the past 3 million years, confirming the importance of Quaternary processes. There seems to be no obvious clustering in their formation through time, although there might be temporal gaps with lower rates of diversity generation. For at least 62 species, taxonomically undifferentiated populations occupy this region, providing ample potential for future evolutionary diversification.

From genetics to biotechnology: Synthetic biology as a flexible course-embedded research experience.

The need for changing how science is taught and the expansion of undergraduate research experiences is essential to foster critical thinking in the Natural Sciences. Most faculty research programs only involve a small number of upper-level undergraduate students each semester. The course-based undergraduate research experience (CURE) model enables more students to take ownership over an independent project and experience authentic research. Further, by creating projects that fit into a curriculum's learning goals and student-oriented outcomes, departments help strengthen critical thinking skills in the classroom. Here, we report on the incorporation of a synthetic biology CURE into a mid-level cellular biology course and two advanced level genetics/molecular biology courses. Synthetic biology involves systematic engineering of novel organisms, such as bacteria and plants, to work as functional devices to solve problems in medicine, agriculture, and manufacturing. The value of synthetic biology and its ultimate utility as a teaching tool relies on reusable, standard genetic parts that can be interchanged using common genetic engineering principles. This Synthetic biology CURE effectively achieves five essential goals: (1) a sense of project ownership; (2) self-efficacy: mastery of a manageable number of techniques; (3) increased tolerance for obstacles through challenging research; (4) increased communication skills; and (5) a sense of belonging in a larger scientific community. Based upon our student assessment data, we demonstrate that this course-based synthetic biology laboratory engages students directly in an authentic research experience and models important elements of collaboration, discovery, iteration, and critical thinking.

Phylogeny and biogeography of Poecilia (Cyprinodontiformes: Poeciliinae) across Central and South America based on mitochondrial and nuclear DNA markers.

Poeciliids are a diverse group of small Neotropical fishes, and despite considerable research attention as models in ecology and evolutionary biology, our understanding of their biogeographic and phylogenetic relationships is still limited. We investigated the phylogenetic relationships of South and Central American Poecilia, by examining 2395 base pairs of mitochondrial DNA (ATPase 8/6, COI) and nuclear DNA (S7) for 18 species across six subgenera. Fifty-eight novel sequences were acquired from newly collected specimens and 20 sequences were obtained from previously published material. Analyses of concatenated and partitioned mitochondrial DNA and nuclear DNA sets resulted in a well-supported phylogeny that resolved several monophyletic groups corresponding to previously hypothesized subgenera and species complexes. A divergence-dating analysis supported the hypothesis of the genus Poecilia dispersing into Central America in the early Pliocene (ancestors of Psychropoecilia+Allopoecilia+Mollienesia: 7.3-2.0Mya) from predominantly South America. Subsequently, one lineage (subgenus Allopoecilia: 5.1-1.3Mya) expanded deeper into South America from Lower-Central America, and one lineage expanded from Nuclear-Central America into South America (subgenus Mollienesia: 0.71-0.14Mya). The subgenus Mollienesia diverged into three monophyletic groups that can be identified by nuptial male dorsal fin morphology and inner jaw dentition. A subclade of the unicuspid short-fins (subgenus Mollienesia) was the lineage that expanded into South America during the middle Pleistocene. Species in this subclade are now distributed across northern South America, where they are partially sympatric with Allopoecilia. However the P. (A.) caucana complex was not monophyletic, with P. (A.) wandae clustering in the Mollienesia subclade that expanded into South America. It is apparent that characters (body size, scale count, pigmentation, and gonopodium morphology) used to define the P. (A.) caucana complex are homoplastic and suggestive of rapid convergence in northern South America. Our improved taxon sampling and divergence-time calibration allowed for insights into the timing and direction of dispersals, and provides an improved understanding of the biogeographic history of an enigmatic group of fishes. Furthermore, we provided strong evidence for the monophyly of the subgenus Mollienesia and further substantiated its species complexes; therefore, we advise a taxonomic re-evaluation for the P. (A.) caucana complex to maintain monophyly of both Mollienesia and Allopoecilia.

Development and characterization of microsatellite loci for common raven (Corvus corax) and cross species amplification in other Corvidae.

BACKGROUND: A priority for conservation is the identification of endemic populations. We developed microsatellite markers for common raven (Corvus corax), a bird species with a Holarctic distribution, to identify and assess endemic populations in Alaska. RESULTS: From a total of 50 microsatellite loci, we isolated and characterized 15 loci. Eight of these loci were polymorphic and readily scoreable. Eighteen to 20 common ravens from Fairbanks, Alaska were genotyped showing the following variability: 3-8 alleles per locus, 0.25-0.80 observed heterozygosity (Ho), and 0.30-0.80 expected heterozygosity (He). All loci were in Hardy-Weinberg equilibrium and linkage equilibrium and many loci amplified and were polymorphic in related taxa. CONCLUSIONS: These loci will be used to identify endemic populations of common raven and assess their genetic diversity and connectivity.

Development and characterization of microsatellite loci for the endangered scrub lupine, Lupinus aridorum (Fabaceae).

PREMISE OF THE STUDY: Microsatellite primers were developed in scrub lupine (Lupinus aridorum, Fabaceae), an endemic species to Florida that is listed as endangered in the United States, to assess connectivity among populations, identify hybrids, and examine genetic diversity. METHODS AND RESULTS: We isolated and characterized 12 microsatellite loci polymorphic in scrub lupine or in closely related species (i.e., sky-blue lupine [L. diffusus] and Gulf Coast lupine [L. westianus]). Loci showed low to moderate polymorphism, ranging from two to 14 alleles per locus and 0.01 to 0.86 observed heterozygosity. CONCLUSIONS: These loci are the first developed for Florida species of lupine and will be used to determine differentiation among species and to aid in conservation of the endangered scrub lupine.

How migratory thrushes conquered northern North America: a comparative phylogeography approach.

Five species of migratory thrushes (Turdidae) occupy a transcontinental distribution across northern North America. They have largely overlapping breeding ranges, relatively similar ecological niches, and mutualistic relationships with northern woodland communities as insectivores and seed-dispersing frugivores. As an assemblage of ecologically similar species, and given other vertebrate studies, we predicted a shared pattern of genetic divergence among these species between their eastern and western populations, and also that the timing of the coalescent events might be similar and coincident with historical glacial events. To determine how these five lineages effectively established transcontinental distributions, we used mitochondrial cytochrome b sequences to assess genetic structure and lineage coalescence from populations on each side of the continent. Two general patterns occur. Hermit and Swainson's thrushes (Catharus guttatus and C. ustulatus) have relatively deep divergences between eastern and western phylogroups, probably reflecting shared historic vicariance. The Veery (C. fuscescens), Gray-cheeked Thrush (C. minimus), and American Robin (Turdus migratorius) have relatively shallow divergences between eastern and western populations. However, coalescent and approximate Bayesian computational analyses indicated that among all species as many as five transcontinental divergence events occurred. Divergence within both Hermit and Swainson's thrushes resembled the divergence between Gray-cheeked Thrushes and Veeries and probably occurred during a similar time period. Despite these species' ecological similarities, the assemblage exhibits heterogeneity at the species level in how they came to occupy transcontinental northern North America but two general continental patterns at an among-species organizational level, likely related to lineage age.

A parapatric propensity for breeding precludes the completion of speciation in common teal (Anas crecca, sensu lato).

Speciation is a process in which genetic drift and selection cause divergence over time. However, there is no rule dictating the time required for speciation, and even low levels of gene flow hinder divergence, so that taxa may be poised at the threshold of speciation for long periods of evolutionary time. We sequenced mitochondrial DNA (mtDNA) and eight nuclear introns (nuDNA) to estimate genomic levels of differentiation and gene flow between the Eurasian common teal (Anas crecca crecca) and the North American green-winged teal (Anas crecca carolinensis). These ducks come into contact in Beringia (north-eastern Asia and north-western North America) and have probably done so, perhaps cyclically, since the Pliocene-Pleistocene transition, ~2.6 Ma, when they apparently began diverging. They have diagnosable differences in male plumage and are 6.9% divergent in the mtDNA control region, with only 1 of 58 crecca and 2 of 86 carolinensis having haplotypes grouping with the other. Two nuclear loci were likewise strongly structured between these teal (Φ(st) ≥ 0.35), but six loci were undifferentiated or only weakly structured (Φ(st) = 0.0-0.06). Gene flow between crecca and carolinensis was ~1 individual per generation in both directions in mtDNA, but was asymmetrical in nuDNA, with ~1 and ~20 individuals per generation immigrating into crecca and carolinensis, respectively. This study illustrates that species delimitation using a single marker oversimplifies the complexity of the speciation process, and it suggests that even with divergent selection, moderate levels of gene flow may stall the speciation process short of completion.

Avoidance behavior by prairie grouse: implications for development of wind energy.

New wind-energy facilities and their associated power transmission lines and roads are being constructed at a rapid pace in the Great Plains of North America. Nevertheless, little is known about the possible negative effects these anthropogenic features might have on prairie birds, one of the most threatened groups in North America. We examined radiotelemetry tracking locations of Lesser Prairie-Chickens (Tympanuchus pallidicinctus) and Greater Prairie-Chickens (T. cupido) in two locations in Oklahoma to determine whether these birds avoided or changed movement behavior near power lines and paved highways. We tracked 463 Lesser Prairie-Chickens (15,071 tracking locations) and 216 Greater Prairie-Chickens (5,750 locations) for 7 and 3 years, respectively. Individuals of both species avoided power lines by at least 100 m and Lesser Prairie-Chickens avoided one of the two highways by 100 m. Prairie-chickens crossed power lines less often than expected if birds moved randomly (p < 0.05) but did not appear to perceive highways as a movement barrier (p > 0.05). In addition, home ranges of Lesser Prairie-Chickens overlapped the power line less often than would be expected by chance placement of home ranges; this result was supported by kernel-density estimation of home ranges. It is likely that new power lines (and other tall structures such as wind turbines) will lead to avoidance of previously suitable habitat and will serve as barriers to movement. These two factors will likely increase fragmentation in an already fragmented landscape if wind energy development continues in prairie habitats.

Movements of birds and avian influenza from Asia into Alaska.

Asian-origin avian influenza (AI) viruses are spread in part by migratory birds. In Alaska, diverse avian hosts from Asia and the Americas overlap in a region of intercontinental avifaunal mixing. This region is hypothesized to be a zone of Asia-to-America virus transfer because birds there can mingle in waters contaminated by wild-bird-origin AI viruses. Our 7 years of AI virus surveillance among waterfowl and shorebirds in this region (1998-2004; 8,254 samples) showed remarkably low infection rates (0.06%). Our findings suggest an Arctic effect on viral ecology, caused perhaps by low ecosystem productivity and low host densities relative to available water. Combined with a synthesis of avian diversity and abundance, intercontinental host movements, and genetic analyses, our results suggest that the risk and probably the frequency of intercontinental virus transfer in this region are relatively low.

Northwestern song sparrow populations show genetic effects of sequential colonization.

Two genetic consequences are often considered evidence of a founder effect: substantial loss in genetic diversity and rapid divergence between source and founder populations. Single-step founder events have been studied for these effects, but with mixed results, causing continued controversy over the role of founder events in divergence. Experiments of serial bottlenecks have shown losses of diversity, increased divergence, and rapid behavioural changes possibly leading to reproductive isolation between source and final populations. The few studies conducted on natural, sequentially founded systems show some evidence of these effects. We examined a natural vertebrate system of sequential colonization among northwestern song sparrows (Melospiza melodia). This system has an effectively linear distribution, it was probably colonized within the last 10,000 years, there are morphological and behavioural differences among populations, and the westernmost populations occur in atypical habitats for the species. Eight microsatellite loci from eight populations in Alaska and British Columbia (n = 205) showed stepwise loss of genetic diversity, genetic evidence for strong population bottlenecks, and increased population divergence. The endpoint population on Attu Island has extremely low diversity (H(E) = 0.18). Our study shows that sequential bottlenecks or founder events can have powerful genetic effects in reducing diversity, possibly leading to rapid evolutionary divergence.