Single Source Population Research Articles

Deep 610-MHz Giant Metrewave Radio Telescope observations of theSpitzerextragalactic First Look Survey field - III. The radio properties of infrared-faint radio sources

Infrared-faint radio sources (IFRSs) are a class of source which are bright at radio frequencies, but do not appear in deep infrared images. We report the detection of 14 IFRSs within the Spitzer extragalactic First Look Survey field, eight of which are detected near to the limiting magnitude of a deep R-band image of the region, at R ∼ 24.5. Sensitive Spitzer Space Telescope images are stacked in order to place upper limits on their mid-infrared flux densities, and using recent 610-MHz and 1.4-GHz observations we find that they have spectral indices which vary between a = 0.05 and 1.38, where we define a such that S ν = S 0 ν -α , and should not be thought of as a single source population. We place constraints on the luminosity and linear size of these sources, and through comparison with well-studied local objects in the Revised Revised Third Cambridge catalogue demonstrate that they can be modelled as being compact (<20 kpc) Fanaroff-Riley type II (FR II) radio galaxies located at high redshift (z ∼ 4).

Invasion of Europe by the western corn rootworm, Diabrotica virgifera virgifera: multiple transatlantic introductions with various reductions of genetic diversity

The early stages of invasion involve demographic bottlenecks that may result in lower genetic variation in introduced populations as compared to source population/s. Low genetic variability may decrease the adaptive potential of such populations in their new environments. Previous population genetic studies of invasive species have reported varying levels of losses of genetic variability in comparisons of source and invasive populations. However, intraspecific comparisons are required to assess more thoroughly the repeatability of genetic consequences of colonization events. Descriptions of invasive species for which multiple introductions from a single source population have been demonstrated may be particularly informative. The western corn rootworm (WCR), Diabrotica virgifera virgifera, native to North America and invasive in Europe, offers us an opportunity to analyse multiple introduction events within a single species. We investigated within- and between-population variation at eight microsatellite markers in WCR in North America and Europe to investigate the routes by which WCR was introduced into Europe, and to assess the effect of introduction events on genetic variation. We detected five independent introduction events from the northern USA into Europe. The diversity loss following these introductions differed considerably between events, suggesting substantial variation in introduction, foundation and/or establishment conditions. Genetic variability at evolutionarily neutral loci does not seem to underlie the invasive success of WCR in Europe. We also showed that the introduction of WCR into Europe resulted in the redistribution of genetic variance from the intra- to the interpopulational level contrary to most examples of multiple introductions.

Large scale unicoloniality: the population and colony structure of the invasive Argentine ant (Linepithema humile) in New Zealand

The Argentine ant is native to South America and has spread widely across the globe. In this study, we use genetic analyses and behavioural assays to examine the colony structure of Argentine ants in New Zealand. Diet modification studies were also carried out in order to help identify what factors influence these behavioural assays. There was no aggression observed between any pairings tested across the North Island of New Zealand, though we found that diet manipulations in the laboratory could lead to low levels of aggression between previously amiable Argentine ant nests. The New Zealand population of Argentine ants was characterized by low levels of genetic variation in six microsatellite loci from their nuclear genome. Additionally, the population also lacked significant genetic structuring with no patterns of regional differentiation or isolation by distance. An analysis of molecular variation(AMOVA) found that themajority of genetic variation was present at a nest level (93% of total genetic variance), with little genetic differentiation observed within or between regions (3 – 4% of total genetic variance). No correlation between aggression and genetic relatedness was observed. This evidence suggests that Argentine ants in New Zealand effectively form a unicolonial population, which is likely the result of colonization from a single source population. As far as we know, this is the first country to have an entirely unicolonial population of Argentine ants.

Rapid evolutionary responses in a translocated population of intertidal snail (Bembicium vittatum) utilise variation from different source populations

The artificial movement of individuals between populations (translocation) can be an effective way to increase genetic diversity within populations, but few studies have undertaken long term genetic monitoring to determine if variation introduced by translocation is maintained over many generations or whether it can be used to adapt to local conditions. Here, we report on the changes in morphological and molecular variation over a 12-year period in a population of an intertidal littorine snail (Bembicium vittatum) that was created by mixing individuals from three geographically disjunct populations. These source populations differ genetically in shell shape and in allele frequency at several allozyme loci. We found that the translocated population had higher allozyme diversity than any of the source populations and that this pattern was maintained over multiple generations. Variation in shell shape also increased, but this declined over time as shells became taller. Some allozyme loci also showed significant changes in frequency over time. These changes were not consistently towards the genetic makeup of a single source population, and in the case of shell shape, were towards a phenotype that was most suited to the local environment. Our results suggest that genetic variation introduced into a population by translocation can be rapidly incorporated and used to adapt to local conditions without domination by a single source population’s genome. However, more studies are needed before generalisations on the benefits of mixing individuals from disjunct populations can be made.

Mitochondrial DNA and Peopling of South America

The initial peopling of South America is largely unresolved, in part because of the unique distribution of genetic diversity in native South Americans. On average, genetic diversity estimated within Andean populations is higher than that estimated within Amazonian populations. Yet there is less genetic differentiation estimated among Andean populations than estimated among Amazonian populations. One hypothesis is that this pattern is a product of independent migrations of genetically differentiated people into South America. A competing hypothesis is that there was a single migration followed by regional isolation. In this study we address these hypotheses using mtDNA hypervariable region 1 sequences representing 21 South American groups and include new data sets for four native Peruvian communities from Tupe, Yungay, and Puno. An analysis of variance that compared the combined data from western South America to the combined data from eastern South America determined that these two regional data sets are not significantly different. As a result, a migration from a single source population into South America serves as the simplest explanation of the data.

Chloroplast and microsatellite DNA diversities reveal the introduction history of Brazilian peppertree (Schinus terebinthifolius) in Florida

Brazilian peppertree (Schinus terebinthifolius) is a woody perennial that has invaded much of Florida. This native of northeastern Argentina, Paraguay, and Brazil was brought as an ornamental to both the west and east coasts of Florida at the end of the 19th century. It was recorded as an invader of natural areas in the 1950s, and has since extended its range to cover over 280 000 ha. Our goals were to understand the history of this invasion, as one step toward understanding why this exotic was so successful, and ultimately to improve development of biological control agents. We sampled plants from the native and exotic ranges, particularly Florida, and genotyped these individuals at nuclear and chloroplast loci. Nuclear microsatellite and cpDNA loci reveal strong genetic population structure consistent with limited dispersal in the introduced and native ranges. Bayesian clustering of microsatellite data separates the east and west coast plants in Florida into distinct populations. The two chloroplast haplotypes found in Florida are also concordant with this separation: one predominates on the east coast, the other on the west coast. Analysis of samples collected in South America shows that haplotypes as distinct as the two in Florida are unlikely to have come from a single source population. We conclude that the genetic evidence supports two introductions of Brazilian peppertree into Florida and extensive hybridization between them. The west coast genotype likely came from coastal Brazil at about 27 degrees south, whereas the east coast genotype probably originated from another, as yet unidentified site. As a result of hybridization, the Florida population does not exhibit low genetic variation compared to populations in the native range, possibly increasing its ability to adapt to novel environments. Hybridization also has important consequences for the selection of biocontrol agents since it will not be possible to identify closely co-adapted natural enemies in the native range, necessitating more extensive host testing.

Variable Costs of Mating, Longevity, and Starvation Resistance inMusca domestica(Diptera: Muscidae)

Studies on conflict and cooperation in insect mating behavior usually assay the relative costs and benefits of mating in unreplicated experimental designs. We assayed multiple populations for such potential costs and benefits in Musca domestica L. under different nutritional environments. We used four populations, each derived from the same field site, ranging from six to 46 generations in the laboratory. Under benign environmental conditions (i.e., ad libitum food and water), mated females lived up to 13% longer than virgins, but this difference was not significant. Under extreme nutritional stress (i.e., no food or water), mated females lived significantly longer, but in only one of the populations tested. Under more moderate stress (i.e., water alone), mated females of one population died significantly earlier. Thus, aspects of both cooperation and conflict were found, but the effects were not repeatable across populations or nutritional environments. Overall, older females were more susceptible to stress. Moreover, the populations were significantly different in longevity (1.5-fold difference) and starvation resistance (2.2-fold difference). The youngest population lived longer, was more resistant to nutritional stress, and was the only line to exhibit significant costs of mating. Thus, the reduced selection pressures of the laboratory could have allowed the erosion of ejaculate toxicity, longevity, and starvation resistance. However, the simplest explanation is that replicate samples from a single geographic source population show appreciable among-line variation in fitness parameters and the consequences of mating. In conclusion, sexual selection studies on the costs and benefits of mating should consider environmental conditions, evolutionary history, and, perhaps most importantly repeatability.

Islands on the plains: metapopulation dynamics and female biased dispersal in hyraxes (Hyracoidea) in the Serengeti National Park.

Two species of hyrax, Heterohyrax brucei and Procavia johnstoni, inhabit rock outcrops, or kopjes, in the Serengeti National Park, Tanzania. Such distinct 'island' habitats provide an excellent model to investigate natural metapopulation dynamics with distinct small populations with extinction and colonization events, as well as migration between populations. Allele frequencies, genetic variability and genetic distances between populations were calculated based on DNA microsatellite markers. The genetic diversity in both species of hyrax, especially P. johnstoni, was surprisingly low: allelic diversity ranged from 2 to 7 alleles per locus. This may have been induced by colonization by a small number of individuals from single source populations. F-statistics, assignment tests and calculations of pairwise relatedness all indicated female-biased dispersal in H. brucei but not P. johnstoni. Values of FIS in P. johnstoni showed an excess of homozygotes indicative of high rates of inbreeding; evidence for inbreeding could not be detected in H. brucei. Although female dispersal patterns in H. brucei seem to prevent inbreeding and consequently reduce risk of local extinction, this seems not to be the case in P. johnstoni.

SYSTEMATICS AND PHYLOGEOGRAPHY OF THE INVASIVE RED ALGA, POLYSIPHONIA HARVEYI

Polysiphonia harveyi Bailey was first described from Connecticut in 1848 and morphologically similar species, such as P. japonica and P. strictissima, have subsequently been described many times from different localities such as Japan and New Zealand, placing the taxonomy and nomenclature of this morphologically variable species in confusion. Polysiphonia harveyi is regarded as an alien in the British Isles and the north‐eastern North Atlantic and is reported to be spreading rapidly. The first confirmed collection of P. harveyi from the British Isles was in 1908; the source of the British introduction remains unknown. In conjunction with breeding data, rbcL sequences for samples of P. harveyi, P. strictissima, P. japonica and P. akkeshiensis collected from New Zealand, Atlantic and Pacific North America, Japan and Europe, reveal that P. harveyi, P. japonica and P. akkeshiensis constitute a single biological species. The correct name for this is P. harveyi, whilst P. strictissima from New Zealand is a sibling species, distinct from P. harveyi. The center of genetic diversity of P. harveyi is in Japan. The original source of the introduced P. harveyi in the British Isles, Europe and Nova Scotia appears to be Hokkaido, Japan. Separate introductions from a single source population into New Zealand and Pacific and Atlantic North America from Honshu, Japan, apparently have occurred.

Freezer anthropology: new uses for old blood.

Archived blood fractions (plasma, settled red cells, white cells) have proved to be a rich and valuable source of DNA for human genetic studies. Large numbers of such samples were collected between 1960 and the present for protein and blood group studies, many of which are languishing in freezers or have already been discarded. More are discarded each year because the usefulness of these samples is not widely understood. Data from DNA derived from 10-35-year-old blood samples have been used to address the peopling of the New World and of the Pacific. Mitochondrial DNA haplotypes from studies using this source DNA support a single wave of migration into the New World (or a single source population for the New World), and that Mongolia was the likely source of the founding population. Data from Melanesia have shown that Polynesians are recent immigrants into the Pacific and did not arise from Melanesia.

Colonization dynamics and relative abundance of three plant species (Antennaria dioica, Hieradum pilosella and Hypochoeris maculata) in dry semi‐natural grasslands

The objective of this study was to examine how population recruitment depends on seed size, and if relative abundance depends on colonization, in three plant species inhabiting dry semi‐natural grasslands All three species, Antennaria dioica, Hieracium pitosella and Hvpochoeris maculata belong to the same family, Asteraceae, and possess similarly structured wind‐dispersed fruits, achenes with pappus They occupy the same range of habitats, but are not equally abundant The seed size hierarchy is Hypochoeris Hieracium Antennaria Results from experiments suggest that recruitment is promoted by small disturbances, but limited also by seed availability Seed size differences explain interactions during recruitment, Hypochoeris“wins” over the other two species, and Hteracium wins over Antennaria Seed arrival order did not alter this hierarchy A model of relative abundance of the species was developed, based on observed differences in recruitment and seed output from local populations The model was able to predict observed relative abundance patterns at a large spatial scale, especially at marginal sites along road verges (Hieracium Hypochoeris Aniermaria), but not at smaller scales, where Antennaria was more frequent than Hypochoeris The results support a metapopulation approach to abundance patterns in landscapes, and, more specifically, they support the hypothesis that species abundance reflects colonizing ability An additional implication is that single source populations may be of great importance for species persistence in landscapes, a conclusion which has bearing on development of conservation and management plans for endangered habitats

THE DISTRIBUTION AMONG POPULATIONS IN PHENOTYPIC VARIANCE WITH INBREEDING.

The effects of inbreeding on the phenotypic variance within populations were measured in a set of 30 bottlenecked lines derived from a single source population of Drosophila melanogaster. Inbred lines had significant variance among lines in the amount of phenotypic variance within lines, for thorax length, and sternopleural bristle scores. When significance levels were corrected on an experimentwide basis, no line had significant increases in phenotypic variance for sternopleural bristle counts, although two lines had significant increases in thorax length variance. These results demonstrate that inbred lines cannot be treated as necessarily more uniform than outbred lines and that results on changes in variance due to inbreeding should be treated with caution unless there has been sufficient replication. These results also demonstrate the validity of an important assumption of models of evolution by variance-mediated mechanisms, such as the variance-induced peak-shift model.

Dynamic Relationship Between Hydraulics and Sedimentation in the Altamaha Estuary

ABSTRACT Flood and ebb tidal cycles in the Altamaha Estuary produce differing bedforms, sedimentary structures, thicknesses of sedimentary units, and grain size distributions. Differences are the result of changes in bed shear, flow regime, and mechanisms of sediment transport. The salt wedge developed on flood cycles produces a stratified estuary with highest flow velocity below the highest rate of salinity change. This relation results in upper flow regime as predicted by the densimetric Froude relation; trochoidal in phase waves to 2 m in height are formed. Surface waves and internal waves are seen in the salinity stratification. Ebb flow modifies the sand. wave surface, and sediment transport is by ripples and dunes in the lower flow regime. Large-scale planar cross-bedding is produced by flood flow, small-scale ripple and dune structures are developed by ebb flow. The estuary is an effective mechanism for size segregation. Suspension populations are removed by both flood and ebb flow. There is a net inland transport of suspended sediment with deposition on tidal flats and marshes. A single log-normal source population is fractionated into several differing populations by bedload transport, suspension and recycling during successive tidal cycles. Characteristic log-probability size distributions are developed in different environments.

Dynamic Relationship between Estuary Hydraulics and Sedimentation: ABSTRACT

Flood- and ebb-tide cycles produce differing bedforms, sedimentary structures, thicknesses of sedimentary units, and most important, grain-size distributions. Differences are the result of changes in bed shear, flow regime, and mechanisms of sediment transport. The salt wedge developed in flood-tide flow produces a stratified highest rate of salinity change. This relation results in upper flow regime as predicted by the densimatic Froude relation; trochoidal sand waves to 2 m in height are formed. Surface waves and internal waves are seen in the salinity stratification. Ebb flow modifies the sand wave surface, and sediment transport is by ripples and dunes in the lower flow regime. Large-scale planar crossbedding is produced by flood flow; small-scale ripple and dune structures are developed by ebb flow. The estuary is an effective mechanism for size segregation. Suspension populations are removed by both flood and ebb flows. There is a net inland transport of suspended sediment with deposition on tidal flats and marshes. A single log-normal source population is fractionated into several differing populations by bedload transport, suspension, and recycling during successive tidal cycles. Characteristic log-probability size distributions are developed in different environments. End_of_Article - Last_Page 659------------