RESUMO
PREMISE OF THE STUDY: The traditional approach used in analyses of population genetic data for historical inference is to average across multiple marker loci, but averaging conflates the different evolutionary signals provided by stable vs. labile markers. METHODS: We used a battery of microsatellites with a wide range of mutation/substitution rates, grouping them into two sets (stable and hypervariable) to provide a more nuanced reconstruction of the population genetics and evolutionary history of the allotriploid peat moss Sphagnum × falcatulum across three disjunct regions. KEY RESULTS: Shannon diversity translation analyses show that the relative apportionment of total within-species allelic diversity (∆WS ) within and among strata ranges widely, both between the two sets and within and among regions. The majority of diversity in the stable set was inherited directly from the ancestors of this genetically complex allopolyploid, but most of the diversity in the hypervariable set has developed post-hybrid-origin. CONCLUSIONS: It is useful to group markers into sets having similar evolutionary lability, with each set being analyzed separately, particularly for allopolyploids. A methodology for determining how to group markers into such sets is presented, which can be applied to the requirements of other studies. Within-individual allelic diversity (ΔWI ) should be addressed in genetic studies on allopolyploids. Allotriploid haplotypes based on a set of nine highly stable microsatellites appear to serve as a clonal-detection set for S. × falcatulum. An additive "allele-metric" diversity approach is introduced, which facilitates a direct comparison of within- and among-stratum diversity components at all levels of diversity.
Assuntos
Marcadores Genéticos , Variação Genética , Ploidias , Sphagnopsida/genética , Alelos , Repetições de MicrossatélitesRESUMO
PREMISE OF THE STUDY: Flowering initiation, duration and magnitude, and degree of flowering synchrony within a population can affect the reproductive fitness of individuals. We examined the flowering phenology within a population of the tropical dry forest Guanacaste tree (Enterolobium cyclocarpum) to gauge the impact of phenological variation among trees on fruit production and progeny vigor. METHODS: We monitored the flowering phenology of 93 trees weekly during 2005, 2006, and 2007, using a scale based on the percentage of the crown with open flowers. We also monitored fruit production for each tree in 2005, 2006, 2007, and 2008. Finally, we evaluated the relationship between phenological variation and progeny performance. KEY RESULTS: Ten measures of flowering phenology and synchrony among flowering trees, based on the number of weeks when anthesis of the crown exceeded 50%, were used to develop four phenological profiles. These profiles were correlated with significant differences in fruit production and progeny vigor. Trees with flowers in >50% of their crown for at least 2 weeks produced more fruits and more vigorous progeny than trees with other profiles. Trees also tended to produce the same phenological profile among years than predicted by chance. CONCLUSIONS: Guanacaste trees vary significantly in the initiation of anthesis, duration and magnitude of flowering, and degree of synchrony among trees. Trees also tend to maintain the same flowering profile among years. Finally, the flowering behavior of E. cyclocarpum leads to significant differences in fruit and seed production, germination, and early progeny growth.
Assuntos
Fabaceae/fisiologia , Flores/fisiologia , Árvores/fisiologia , Frutas/crescimento & desenvolvimento , Germinação , Plântula/crescimento & desenvolvimento , Fatores de TempoRESUMO
Background and Aims: Allopolyploids exhibit both different levels and different patterns of genetic variation than are typical of diploids. However, scant attention has been given to the partitioning of allelic information and diversity in allopolyploids, particularly that among homeologous monoploid components of the hologenome. Sphagnum × falcatulum is a double allopolyploid peat moss that spans a considerable portion of the Holantarctic. With monoploid genomes from three ancestral species, this organism exhibits a complex evolutionary history involving serial inter-subgeneric allopolyploidizations. Methods: Studying populations from three disjunct regions [South Island (New Zealand); Tierra de Fuego archipelago (Chile, Argentina); Tasmania (Australia)], allelic information for five highly stable microsatellite markers that differed among the three (ancestral) monoploid genomes was examined. Using Shannon information and diversity measures, the holoploid information, as well as the information within and among the three component monoploid genomes, was partitioned into separate components for individuals within and among populations and regions, and those information components were then converted into corresponding diversity measures. Key Results: The majority (76 %) of alleles detected across these five markers are most likely to have been captured by hybridization, but the information within each of the three monoploid genomes varied, suggesting a history of recurrent allopolyploidization between ancestral species containing different levels of genetic diversity. Information within individuals, equivalent to the information among monoploid genomes (for this dataset), was relatively stable, and represented 83 % of the grand total information across the Holantarctic, with both inter-regional and inter-population diversification each accounting for about 5 % of the total information. Conclusions: Sphagnum × falcatulum probably inherited the great majority of its genetic diversity at these markers by reticulation, rather than by subsequent evolutionary radiation. However, some post-hybridization genetic diversification has become fixed in at least one regional population. Methodology allowing statistical analysis of any ploidy level is presented.
Assuntos
Evolução Biológica , Hibridização Genética , Sphagnopsida/genética , Triploidia , Alelos , Argentina , Austrália , Chile , Variação Genética , Genoma de Planta , Repetições de Microssatélites , Nova Zelândia , TasmâniaRESUMO
PREMISE OF THE STUDY: Variation in a species is a blend of adaptive, random, and migratory responses. Pitch pine (Pinus rigida), a highly variable eastern conifer, has occupied multiple glacial refugia, whose harsh conditions favored adaptations enhancing subsequent dispersal and recolonization of newly deglaciated sites. We assessed phenotypic diversity in long-term growth trials to elucidate both the adaptations and likely refugia. METHODS: Pitch pine progeny from 31 areas were grown in common gardens in six locations, from eastern Massachusetts to Korea. KEY RESULTS: Survival increased with source latitude, but seedlings from southern latitudes were tallest in the first (postplanting) year, but that advantage dissipated in later years. Progeny from northern latitudes were precocious, highly fecund, had smaller seeds, and more seeds per cone. Seed mass decreased with latitude in both parents and progeny. Serotinous cones were notably common in the New Jersey Pine Plains and Acadia National Park. Various disease agents and frost burn exhibited latitudinal trends that were nonlinear, with a break in the regression slope at about 40°N latitude. Cluster analysis identified both northern and southern groups, largely split between unglaciated and deglaciated terrain, but with Acadia and the Pine Plains as unique outliers. Within the southern group, provenances were organized into contiguous subgroups, but geographic structure was less evident in the northern group. CONCLUSIONS: The present range of pitch pine was colonized by migrants from at least three different refugia, including at least one on the exposed continental shelf during the Last Glacial Maximum.
Assuntos
Aclimatação , Pinus/fisiologia , Dispersão Vegetal , Pinus/crescimento & desenvolvimento , Quebeque , Reprodução , Estados UnidosRESUMO
Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure--without explicitly considering food webs--has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.
Assuntos
Conservação dos Recursos Naturais , Cadeia Alimentar , Rios , Animais , Organismos Aquáticos , Arquitetura de Instituições de Saúde , Estados UnidosRESUMO
SUMMARY: GenAlEx: Genetic Analysis in Excel is a cross-platform package for population genetic analyses that runs within Microsoft Excel. GenAlEx offers analysis of diploid codominant, haploid and binary genetic loci and DNA sequences. Both frequency-based (F-statistics, heterozygosity, HWE, population assignment, relatedness) and distance-based (AMOVA, PCoA, Mantel tests, multivariate spatial autocorrelation) analyses are provided. New features include calculation of new estimators of population structure: G'(ST), G''(ST), Jost's D(est) and F'(ST) through AMOVA, Shannon Information analysis, linkage disequilibrium analysis for biallelic data and novel heterogeneity tests for spatial autocorrelation analysis. Export to more than 30 other data formats is provided. Teaching tutorials and expanded step-by-step output options are included. The comprehensive guide has been fully revised. AVAILABILITY AND IMPLEMENTATION: GenAlEx is written in VBA and provided as a Microsoft Excel Add-in (compatible with Excel 2003, 2007, 2010 on PC; Excel 2004, 2011 on Macintosh). GenAlEx, and supporting documentation and tutorials are freely available at: http://biology.anu.edu.au/GenAlEx. CONTACT: rod.peakall@anu.edu.au.
Assuntos
Genética Populacional/educação , Genética Populacional/métodos , Software , Biologia Computacional/métodos , Frequência do Gene , Marcadores Genéticos , Haplótipos , Desequilíbrio de Ligação , Interface Usuário-ComputadorRESUMO
In theory, conservation genetics predicts that forest fragmentation will reduce gene dispersal, but in practice, genetic and ecological processes are also dependent on other population characteristics. We used Bayesian genetic analyses to characterize parentage and propagule dispersal in Heliconia acuminata L. C. Richard (Heliconiaceae), a common Amazonian understory plant that is pollinated and dispersed by birds. We studied these processes in two continuous forest sites and three 1-ha fragments in Brazil's Biological Dynamics of Forest Fragments Project. These sites showed variation in the density of H. acuminata. Ten microsatellite markers were used to genotype flowering adults and seedling recruits and to quantify realized pollen and seed dispersal distances, immigration of propagules from outside populations, and reproductive dominance among parents. We tested whether gene dispersal is more dependent on fragmentation or density of reproductive plants. Low plant densities were associated with elevated immigration rates and greater propagule dispersal distances. Reproductive dominance among inside-plot parents was higher for low-density than for high-density populations. Elevated local flower and fruit availability is probably leading to spatially more proximal bird foraging and propagule dispersal in areas with high density of reproductive plants. Nevertheless, genetic diversity, inbreeding coefficients and fine-scale spatial genetic structure were similar across populations, despite differences in gene dispersal. This result may indicate that the opposing processes of longer dispersal events in low-density populations vs. higher diversity of contributing parents in high-density populations balance the resulting genetic outcomes and prevent genetic erosion in small populations and fragments.
Assuntos
Variação Genética , Genética Populacional , Heliconiaceae/genética , Teorema de Bayes , Brasil , DNA de Plantas/genética , Fluxo Gênico , Genótipo , Repetições de Microssatélites , Modelos Genéticos , Densidade Demográfica , Dispersão de SementesRESUMO
PREMISE OF THE STUDY: Fire in the New Jersey Pine Plains has selectively maintained a dwarf growth form of pitch pine (Pinus rigida), which is distinct from the surrounding tall forest of the Pine Barrens and has several other inherited adaptations that enable it to survive in an environment dominated by fire. METHODS: Pitch pine progeny from two Pine Plains sites, the West and East Pine Plains, were grown in common garden environments with progeny from two Pine Barrens stands, Batsto and Great Egg Harbor River. The tests were replicated in five locations: in New Jersey, Connecticut, two sites in Massachusetts, and Korea. One of the tests was monitored for up to 36 yr. KEY RESULTS: Progeny of Pine Plains origin were, in general, shorter, more crooked, precocious, bore more cones, had a higher frequency of serotinous cones, and had a higher frequency of stem cones than did Pine Barrens progeny, wherever they were grown. CONCLUSIONS: The Pine Plains is an ecotype that has evolved in response to disturbance. The several characters that distinguish it from the surrounding tall forest of the Pine Barrens are inherited. The dwarf stature and crooked form not only enable the ecotype to persist in an environment of frequent fires but also increase its flammability.
Assuntos
Ecossistema , Incêndios , Pinus , Adaptação Biológica , Evolução Biológica , New Jersey , Reprodução , Plântula/crescimento & desenvolvimentoRESUMO
Seed dispersal shapes ecological and evolutionary dynamics of plant populations. Here, we extend classical diversity measures to study the impact of disperser behavior on seed dispersal. We begin by extending our previous diversity structure approach, which partitioned seed source diversity within and among dispersal sites, into the more general framework of traditional diversity measures. This statistical approach allows an assessment of the extent to which foraging behavior shapes α and γ diversity, as well as the divergence in seed sources among dispersal sites, which we call δ. We also introduce tests to facilitate comparisons of diversity among dispersal sites and seed vectors and to compare overall diversity among sampled systems. We then apply these tools to investigate the diversity blend of parentage resulting from seed dispersal by two avian seed vectors with very different social and foraging behaviors: (1) acorn woodpeckers, transporting Quercus agrifolia acorns, and (2) long-wattled umbrellabirds, transporting Oenocarpus bataua palm nuts. Using these diversity and divergence measures, we test the hypothesis that different foraging behaviors generate distinctive diversity partitions for the two focal tree species. This approach provides a new tool for assessment of the impact of dispersal agents on the seed source structure of plant populations, which can be extended to include the impact of virtually any propagule vector for a range of systems.
Assuntos
Arecaceae/fisiologia , Aves/fisiologia , Ecologia/métodos , Quercus/fisiologia , Dispersão de Sementes , Animais , Arecaceae/genética , Biodiversidade , California , Equador , Genótipo , Técnicas de Genotipagem , Masculino , Repetições de Microssatélites , Modelos Biológicos , Quercus/genética , Aves Canoras/fisiologia , Árvores/genética , Árvores/fisiologiaRESUMO
The spatial pattern of established seedlings yields valuable information about variation in fecundity, dispersal, and spatial structure of distributed recruits, but separating maternal and paternal contributions in monoecious species has been hampered by the "2 parent" problem. It is now possible to determine the maternal parentage of established recruits with genetic assay of maternally derived tissues of the seed or fruit, but the DNA of weathered maternal tissues often yields unreliable genotypes, reducing the practical range of such assay. We develop a mixed assay of seedling and seed (pericarp) tissues and illustrate it with distributed recruits of California valley oak (Quercus lobata Née). Detailed analysis indicates correct maternal assignment rates of canopy patch recruits of 56% (seedling assay only) versus 94% (mixed assay). For open patch recruits, maternal assignment rates were less than 50% (seedling assay only) versus 91% (mixed assay). The strategy of choice is to use seedling genotypes to identify a small set of credible parental candidates and then deploy 3-4 well-chosen pericarp/endocarp loci to reduce that list to a single obvious maternal candidate. The increase in the number of recruits available for subsequent analysis is pronounced, increasing precision and statistical power for subsequent inference.
Assuntos
Linhagem , Quercus/genética , Plântula/genética , Sementes/genética , California , Genética Populacional , Genótipo , Escore LodRESUMO
Landscape characteristics and social behavior can affect the foraging patterns of seed-dependent animals. We examine the movement of acorns from valley oak (Quercus lobata) trees to granaries maintained by acorn woodpeckers (Melanerpes formicivorus) in two California oak savanna-woodlands differing in the distribution of Q. lobata within each site. In 2004, we sampled Q. lobata acorns from 16 granaries at Sedgwick Reserve in Santa Barbara County and 18 granaries at Hastings Reserve in Monterey County. Sedgwick has lower site-wide density of Q. lobata than Hastings as well as different frequencies of other Quercus species common to both sites. We found acorn woodpeckers foraged from fewer Q. lobata seed source trees (K(g) = 4.1 ± 0.5) at Sedgwick than at Hastings (K(g) = 7.6 ± 0.6) and from fewer effective seed sources (N(em)* = 2.00 and 5.78, respectively). The differences between sites are due to a greater number of incidental seed sources used per granary at Hastings than at Sedgwick. We also found very low levels of seed source sharing between adjacent granaries, indicating that territoriality is strong at both sites and that each social group forages on its own subset of trees. We discovered an interesting spatial pattern in the location of granaries. At Sedgwick, acorn woodpeckers situated their granaries within areas of higher-than-average tree density, while at Hastings, they placed them within areas of lower-than-average tree density, with the outcome that granaries at the two sites were located in areas of similar valley oak density. Our results illustrate that landscape characteristics might influence the number of trees visited by acorn woodpeckers and the locations of territories, while woodpecker social behavior, such as territoriality, shapes which trees are visited and whether they are shared with other social groups.
Assuntos
Aves , Comportamento Alimentar , Quercus , Sementes , Territorialidade , Animais , California , Ecossistema , Densidade DemográficaRESUMO
Movement of individual organisms is fundamental to life, quilting our planet in a rich tapestry of phenomena with diverse implications for ecosystems and humans. Movement research is both plentiful and insightful, and recent methodological advances facilitate obtaining a detailed view of individual movement. Yet, we lack a general unifying paradigm, derived from first principles, which can place movement studies within a common context and advance the development of a mature scientific discipline. This introductory article to the Movement Ecology Special Feature proposes a paradigm that integrates conceptual, theoretical, methodological, and empirical frameworks for studying movement of all organisms, from microbes to trees to elephants. We introduce a conceptual framework depicting the interplay among four basic mechanistic components of organismal movement: the internal state (why move?), motion (how to move?), and navigation (when and where to move?) capacities of the individual and the external factors affecting movement. We demonstrate how the proposed framework aids the study of various taxa and movement types; promotes the formulation of hypotheses about movement; and complements existing biomechanical, cognitive, random, and optimality paradigms of movement. The proposed framework integrates eclectic research on movement into a structured paradigm and aims at providing a basis for hypothesis generation and a vehicle facilitating the understanding of the causes, mechanisms, and spatiotemporal patterns of movement and their role in various ecological and evolutionary processes. "Now we must consider in general the common reason for moving with any movement whatever." (Aristotle, De Motu Animalium, 4th century B.C.).
Assuntos
Migração Animal , Ecologia/métodos , Modelos Biológicos , Movimento , Animais , Humanos , Dinâmica PopulacionalRESUMO
Since the days of allozyme analysis, we have been enamored with the idea that if we just had enough polymorphic mendelian loci, we could gauge the inbreeding level of individuals by measuring heterozygosity and simultaneously measure the degree of genetic relatedness between pairs of individuals. Given Mendel's Laws, we have always known that we would need numerous independently segregating loci to achieve any reasonable degree of accuracy. Santure et al. (2010, this issue) use a 771 marker SNP panel to assess heterozygosity levels and to assess pairwise relatedness, and compare both with theoretical expectations obtained from a carefully recorded pedigree of a zebra finch breeding colony, as a function of increasing numbers of SNP markers. They also compare the SNP results with those from a 20-locus microsatellite panel, showing that adding SNPs to a fairly large microsatellite panel improves accuracy, but given an existing panel of 125 SNPs, little is to be gained by adding microsatellites. They show that the accuracy available for estimating individual levels of inbreeding is somewhat limited. They also show that the average pairwise relatedness measures bracket pedigree relationship very nicely, but the variances for individual pairs remain substantial, even with a very large panel.
Assuntos
Tentilhões/genética , Genética Populacional , Endogamia , Polimorfismo de Nucleotídeo Único , Animais , Heterozigoto , Repetições de Microssatélites , Modelos Genéticos , LinhagemRESUMO
We examined spatial genetic structure (SGS) in Enterolobium cyclocarpum (the Guanacaste tree), a dominant tree of Central American dry forests in 4 sites in Guanacaste Province, Costa Rica. In disturbed dry forest sites (e.g., pastures), E. cyclocarpum is primarily dispersed by cattle and horses, whose movements are restricted by pasture boundaries. The study sites varied in tree densities and disturbance. Allozyme analyses of adult trees demonstrated significant levels of SGS in 3 of 4 sites. SGS was primarily due to clusters of young adults located along seasonal streams, rocky areas, and in abandoned pastures. SGS was highest in the first distance class in the least disturbed population, which also had the lowest density of large adults. Low, but significant SGS characterized the site with the highest number of large adults located in individual pastures. The semiurban site, had no clusters of young adults and, probably as a result, failed to exhibit SGS. Our results demonstrate that disturbance can strongly influence SGS patterns and are consistent with a landscape model in which the location of potential recruitment sites, restricted seed disperser movements, and the number and location of maternal individuals dictate the level and pattern of SGS.
Assuntos
Meio Ambiente , Fabaceae/genética , Genética Populacional , Costa Rica , Demografia , Ecossistema , Fabaceae/fisiologia , Fluxo Gênico/fisiologia , Especiação Genética , Variação Genética/fisiologia , ÁrvoresRESUMO
For plant populations, gene movement through pollen and seed dispersal governs the size of local genetic neighbourhoods and shapes the opportunities for natural selection and genetic drift. A critical question is how together these two processes influence the evolutionary dynamics of local populations. To assess the respective contributions of pollen and seed flow, we propose a novel indirect assessment of the separate male and female gametic contributions to total effective parental size (N(e)), based on parental correlations estimated via kinship coefficients, that can be applied to data sets that include unambiguous genotypes for male and female gametic contributions. Using the endemic Californian valley oak (Quercus lobata) as our study species, we apply this method to a set of microsatellite genotypes for two distinct ecological sets of naturally recruiting seedlings with acorns attached. We found that the effective numbers of contributing male parents (N(ep)) exceed effective numbers of female parents (N(em)) for seedlings established beneath adult trees (N(ep) = 8.1 and N(em) = 1.1), as well as for seedlings established away from adult trees (N(ep) = 15.4 and N(em) = 2.7), illustrating that seed dispersal enhances pollen dispersal and increases the effective number of seed sources in open seedling patches. The resulting effective parental size of seedling populations translates into smaller effective numbers of parents for undispersed vs. dispersed seedlings (N(e) = 3.6 and N(e) = 6.7, respectively). This study introduces a novel statistic method and provides important new evidence that, on a short-term temporal scale, seed dispersal shapes the local neighbourhood size of new recruits.
Assuntos
Variação Genética , Genética Populacional , Quercus/genética , DNA de Plantas/genética , Genótipo , Repetições de Microssatélites , Modelos Estatísticos , Pólen/genética , Pólen/fisiologia , Quercus/fisiologia , Reprodução/fisiologia , Plântula/genética , Plântula/fisiologia , Sementes/genética , Sementes/fisiologiaRESUMO
For organisms with limited vagility and/or occupying patchy habitats, we often encounter nonrandom patterns of genetic affinity over relatively small spatial scales, labelled fine-scale genetic structure. Both the extent and decay rate of that pattern can be expected to depend on numerous interesting demographic, ecological, historical, and mating system factors, and it would be useful to be able to compare different situations. There is, however, no heterogeneity test currently available for fine-scale genetic structure that would provide us with any guidance on whether the differences we encounter are statistically credible. Here, we develop a general nonparametric heterogeneity test, elaborating on standard autocorrelation methods for pairs of individuals. We first develop a 'pooled within-population' correlogram, where the distance classes (lags) can be defined as functions of distance. Using that pooled correlogram as our null-hypothesis reference frame, we then develop a heterogeneity test of the autocorrelations among different populations, lag-by-lag. From these single-lag tests, we construct an analogous test of heterogeneity for multilag correlograms. We illustrate with a pair of biological examples, one involving the Australian bush rat, the other involving toadshade trillium. The Australian bush rat has limited vagility, and sometimes occupies patchy habitat. We show that the autocorrelation pattern diverges somewhat between continuous and patchy habitat types. For toadshade trillium, clonal replication in Piedmont populations substantially increases autocorrelation for short lags, but clonal replication is less pronounced in mountain populations. Removal of clonal replicates reduces the autocorrelation for short lags and reverses the sign of the difference between mountain and Piedmont correlograms.
Assuntos
Estruturas Genéticas/genética , Variação Genética , Modelos Genéticos , Algoritmos , Genética Populacional , Trillium/genética , Trillium/crescimento & desenvolvimentoRESUMO
We introduce a novel indirect method of estimating the pollen dispersal curve from mother-offspring genotypic data. Unlike an earlier indirect approach (TwoGener), this method is based on a normalized measure of correlated paternity between female pairs whose expectation does not explicitly depend on the unknown effective male population density (d(e)). We investigate the statistical properties of the new method, by comparison with those of TwoGener, considering the sensitivity to reductions of d(e), relative to census density, resulting from unequal male fecundity and asynchronous flowering. Our main results are: (i) it is possible to obtain reliable estimates of the average distance of pollen dispersal, delta, from indirect methods, even under nonuniform male fecundity and variable flowering phenology; (ii) the new method yields more accurate and more precise delta-estimates than TwoGener under a wide range of sampling and flowering scenarios; and (iii) TwoGener can be used to obtain approximate d(e) estimates, if needed for other purposes. Our results also show that accurately estimating the shape of the tail of the pollen dispersal function by means of indirect methods remains a very difficult challenge.
Assuntos
Pólen/genética , Flores/genética , Genes de Plantas , Genótipo , Modelos Genéticos , Modelos Estatísticos , Reprodução/genéticaRESUMO
The use of diversity metrics has a long history in population ecology, while population genetic work has been dominated by variance-derived metrics instead, a technical gap that has slowed cross-communication between the fields. Interestingly, Rao's Quadratic Entropy (RQE), comparing elements for 'degrees of divergence', was originally developed for population ecology, but has recently been deployed for evolutionary studies. We here translate RQE into a continuous diversity analogue, and then construct a multiply nested diversity partition for alleles, individuals, populations, and species, each component of which exhibits the behavior of proper diversity metrics, and then translate these components into [0,1]-scaled form. We also deploy non-parametric statistical tests of the among-stratum components and novel tests of the homogeneity of within-stratum diversity components at any hierarchical level. We then illustrate this new analysis with eight nSSR loci and a pair of close Australian marsupial (Antechinus) congeners, using both 'different is different' and 'degree of difference' distance metrics. The total diversity in the collection is larger than that within either species, but most of the within-species diversity is resident within single populations. The combined A. agilis collection exhibits more diversity than does the combined A. stuartii collection, possibly attributable to localized differences in either local ecological disturbance regimes or differential levels of population isolation. Beyond exhibiting different allelic compositions, the two congeners are becoming more divergent for the arrays of allele sizes they possess.
Assuntos
Alelos , Biodiversidade , Animais , Marcadores Genéticos , Marsupiais/genética , Repetições de Microssatélites/genéticaRESUMO
Lyme disease is a major vector-borne bacterial disease in the USA. The disease is caused by Borrelia burgdorferi, and transmitted among hosts and humans, primarily by blacklegged ticks (Ixodes scapularis). The ~25 B. burgdorferi genotypes, based on genotypic variation of their outer surface protein C (ospC), can be phenotypically separated as strains that primarily cause human diseases-human invasive strains (HIS)-or those that rarely do. Additionally, the genotypes are non-randomly associated with host species. The goal of this study was to examine the extent to which phenotypic outcomes of B. burgdorferi could be explained by the host communities fed upon by blacklegged ticks. In 2006 and 2009, we determined the host community composition based on abundance estimates of the vertebrate hosts, and collected host-seeking nymphal ticks in 2007 and 2010 to determine the ospC genotypes within infected ticks. We regressed instances of B. burgdorferi phenotypes on site-specific characteristics of host communities by constructing Bayesian hierarchical models that properly handled missing data. The models provided quantitative support for the relevance of host composition on Lyme disease risk pertaining to B. burgdorferi prevalence (i.e. overall nymphal infection prevalence, or NIPAll) and HIS prevalence among the infected ticks (NIPHIS). In each year, NIPAll and NIPHIS was found to be associated with host relative abundances and diversity. For mice and chipmunks, the association with NIPAll was positive, but tended to be negative with NIPHIS in both years. However, the direction of association between shrew relative abundance with NIPAll or NIPHIS differed across the two years. And, diversity (H') had a negative association with NIPAll, but positive association with NIPHIS in both years. Our analyses highlight that the relationships between the relative abundances of three primary hosts and the community diversity with NIPAll, and NIPHIS, are variable in time and space, and that disease risk inference, based on the role of host community, changes when we examine risk overall or at the phenotypic level. Our discussion focuses on the observed relationships between prevalence and host community characteristics and how they substantiate the ecological understanding of phenotypic Lyme disease risk.
Assuntos
Borrelia burgdorferi/isolamento & purificação , Doença de Lyme/epidemiologia , Roedores/parasitologia , Infestações por Carrapato/epidemiologia , Carrapatos/microbiologia , Animais , Humanos , Doença de Lyme/transmissão , Prevalência , Infestações por Carrapato/parasitologia , Carrapatos/classificação , Estados Unidos/epidemiologiaRESUMO
Transgenic crops expressing Bacillus thuringiensis (Bt) toxins have been widely and successfully deployed for the control of target pests, while allowing a substantial reduction in insecticide use. The evolution of resistance (a heritable decrease in susceptibility to Bt toxins) can pose a threat to sustained control of target pests, but a high-dose refuge (HDR) management strategy has been key to delaying countervailing evolution of Bt resistance. The HDR strategy relies on the mating frequency between susceptible and resistant individuals, so either partial dominance of resistant alleles or nonrandom mating in the pest population itself could elevate the pace of resistance evolution. Using classic Wright-Fisher genetic models, we investigated the impact of deviations from standard refuge model assumptions on resistance evolution in the pest populations. We show that when Bt selection is strong, even deviations from random mating and/or strictly recessive resistance that are below the threshold of detection can yield dramatic increases in the pace of resistance evolution. Resistance evolution is hastened whenever the order of magnitude of model violations exceeds the initial frequency of resistant alleles. We also show that the existence of a fitness cost for resistant individuals on the refuge crop cannot easily overcome the effect of violated HDR assumptions. We propose a parametrically explicit framework that enables both comparison of various field situations and model inference. Using this model, we propose novel empiric estimators of the pace of resistance evolution (and time to loss of control), whose simple calculation relies on the observed change in resistance allele frequency.