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1.
Previous studies on the geographical distributions of both shell polymorphisms and mitochondrial haplotypes in Cepaea land snails have suggested varying contributions of natural selection, random genetic drift and population history to the origin and persistence of variation. We combine previous studies of polymorphism within two species of Cepaea , with new molecular data from two mitochondrial genes. The distributions of mitochondrial variants suggest that elements of population history may have been influential in creating patterns of diversity. However, some patterns of amino acid substitution that are found in a protein coding gene are also consistent with the action of diversifying selection. This suggests the possibility that in addition to stochastic processes such as repeated founder events, local extinctions and random genetic drift within a structured population, adaptive molecular change may have affected mitochondrial diversity.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87 , 167–184.  相似文献   

2.
Based on population genetic theory and empirical studies of small populations, we expect that species with very small ranges (narrow endemics) will exhibit reduced genetic diversity, increasing their susceptibility to the negative effects of genetic homogeneity. Although this pattern of reduced diversity applies to most narrow endemics, conservation biologists have yet to identify a general pattern for the degree of spatial population genetic structure expected in species with very small ranges. In part, this is because the degree of population structure within narrow endemics will be highly variable depending on the equilibrium between the homogenizing effects of dispersal and the diversifying effects of drift and local selection in small populations, thus precluding general predictions about the relative importance of small range, small population sizes, and habitat patchiness for maintaining genetic diversity in narrowly-distributed species. We document a striking example of high population structure in the tiny geographic range of a stream-dwelling catfish, Trichogenes longipinnis , endemic to the Atlantic Forest of Brazil. The maintenance of this diversity results from a combination of asymmetrical and limited dispersal, and drift in small populations. Our results highlight the need to understand population structure, and not only overall genetic diversity, of narrowly-distributed species for their conservation planning.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 259–274.  相似文献   

3.
The pollination biology of Syzygium sayeri was documented using the special capabilities of the Australian Canopy Crane. Syzygium sayeri is a xenogamous species with poor self-compatibility, moderate levels of natural out-crossing, and the producer of copious amounts nectar throughout the day and night. Of a diverse fauna associated with, and visiting the flowers of S. sayeri , larger vertebrates (blossom bats and honeyeaters) account for approximately half its natural pollination rate, while the balance of pollination is attributable to a host of invertebrate visitors (wasps, flies, thrips, butterflies). Day and night pollinators contributed approximately equally to the successful pollination of S. sayeri ; although the number of individuals visiting flowers was greater during the day, further experimentation might reveal night visitors to be more effective pollinators. The co-occurrence of vertebrates and invertebrates, as well as day and night visitors, suggests that S. sayeri has a generalist pollination system, whereby the absence of a discrete set of faunae could be compensated for by the presence of other pollinators. What is not clear is the contribution of different pollinators to the population success (i.e. gene flow) of this species. Further study is needed to determine the contribution of each pollinator group to the flow of genetic material in populations of S. sayeri . © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 69–84.  相似文献   

4.
Meiotic drive is an evolutionary force in which natural selection is uncoupled from organismal fitness. Recently, it has been proposed that meiotic drive and genetic drift represent major forces in the evolution of the mammalian karyotype. Meiotic drive involves two types of genetic elements, Responders and Distorters , the latter being required to induce transmission ratio distortion at the former. We have previously described the Om meiotic drive system in mouse chromosome 11. To investigate the natural history of this drive system we have characterized the alleles present at the distorter in wild-derived inbred strains. Our analysis of transmission of maternal alleles in both classical and wild-derived inbred strains indicated that driving alleles are found at high frequency in natural populations and that the existence of driving alleles predates the split between the Mus spicilegus and M. musculus lineages.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 487–492.  相似文献   

5.
The population genetic structure of marine species lacking free-swimming larvae is expected to be strongly affected by random genetic drift among populations, resulting in genetic isolation by geographical distance. At the same time, ecological separation over microhabitats followed by direct selection on those parts of the genome that affect adaptation might also be strong. Here, we address the question of how the relative importance of stochastic vs. selective structuring forces varies at different geographical scales. We use microsatellite DNA and allozyme data from samples of the marine rocky shore snail Littorina saxatilis over distance scales ranging from metres to 1000 km, and we show that genetic drift is the most important structuring evolutionary force at distances > 1 km. On smaller geographical scales (< 1 km), divergent selection between contrasting habitats affects population genetic structure by impeding gene flow over microhabitat borders (microsatellite structure), or by directly favouring specific alleles of selected loci (allozyme structure). The results suggest that evolutionary drivers of population genetic structure cannot a priori be assumed to be equally important at different geographical scales. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 31–40.  相似文献   

6.
Within populations, the stochastic effect of genetic drift and deterministic effect of natural selection are potentially weakened or altered by gene flow among populations. The influence of gene flow on Lake Erie populations of the common garter snake has been of particular interest because of a discontinuous colour pattern polymorphism (striped vs. melanistic) that is a target of natural selection. We reassessed the relative contributions of gene flow and genetic drift using genetic data and population size estimates. We compared all combinations of two marker systems and two analytical approaches to the estimation of gene flow rates: allozymes (data previously published), microsatellite DNA (new data), the island model ( F ST-based approach), and a coalescence-based approach. For the coalescence approach, mutation rates and sampling effects were also investigated. While the two markers produced similar results, gene flow based on F ST was considerably higher (Nm > 4) than that from the coalescence-based method (Nm < 1). Estimates of gene flow are likely to be inflated by lack of migration-drift equilibrium and changing population size. Potentially low rates of gene flow (Nm < 1), small population size at some sites, and positive correlations of number of microsatellite DNA alleles and island size and between M , mean ratio of number of alleles to range in allele size, and island size suggest that in addition to selection, random genetic drift may influence colour pattern frequencies. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79, 389–399.  相似文献   

7.
Pollination success and pollen dispersal in natural populations depend on the spatial‐temporal variation of flower abundance. For plants that lack rewards for pollinators, pollination success is predicted to be negatively related to flower density and flowering synchrony. We investigated the relationships between pollination success and flower abundance and flowering synchrony, and estimated pollinia dispersal distance in a rewardless species, Changnienia amoena (Orchidaceae). The results obtained in the present study revealed that male pollination success was negatively influenced by population size but was positively affected by population density, whereas female pollination success was independent of both population size and density. Phenotypic analysis suggested that highly synchronous flowering was advantageous through total pollination success, which is in contrast to previous studies. These results indicate that pollination facilitation rather than competition for pollinator visits occurs in this rewardless plant. The median distance of pollinia dispersal was 11.5 m (mean distance = 17.5 m), which is comparable to that of other rewardless plants but longer than for rewarding plants. However, pollen transfer occured mainly within populations; pollen import was a rare event. Restricted gene flow by pollinia and seeds probably explains the previous population genetic reporting a high degree of genetic differentiation between populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 477–488.  相似文献   

8.
Patterns of variation at nine enzyme loci were examined in 528 plants representing diploid and tetraploid populations of Parnassia palustris s. l. in Europe to assess genetic variation patterns and migration history. Half of the plants showed a unique multilocus phenotype and 75% of all phenotypes occurred only in Scandinavia. Diploid populations showed similar levels of genetic diversity as other widespread outbreeding species with animal-mediated pollination and F -statistics indicated excessive heterozygosity and low rates of gene flow among them. In spite of dramatic population histories caused by the ice ages, diploid populations have maintained the same genetic diversity in Scandinavia as in central and southern Europe. Northern populations have apparently been established through the gradual advance of genetically variable populations and patterns of variation at individual loci indicate different migration routes, from the south-south-west and the east-north-east, respectively. The data strongly support a repeated autoploid origin of the tetraploid cytotype which has been much more successful than the diploid progenitors in colonizing new land since the last ice age. High genetic diversity in Scandinavia has apparently been obtained by a combination of immigration of plants from different source areas and recurrent formation of autotetraploids from diploid progenitors.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 347−372.  相似文献   

9.
The relationship between diversity of large trees and altitude was investigated in a Tanzanian tropical rain forest. In total, 231 samples of 20 trees of ≥ 20 cm d.b.h. from the East and West Usambara mountains, covering an elevation range from 280 m to 2180 m a.s.l., were analysed. An ordination demonstrated a constant turnover of species, genera, family and orders with elevation. There were no obvious zones or discontinuities. There was no decline in plot richness with respect to altitude for species, genera or orders. Family richness was shown to increase with altitude. A measure of genetic diversity, the avalanche index, was calculated for each plot to investigate the effect of incorporating phylogenetic relatedness of individuals into the diversity measure. Distances between taxa were extracted from a recent molecular phylogeny of the angiosperms. Incorporation of phylogenetic diversity at family level enhanced the positive correlation between plot diversity and altitude.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 217–228.  相似文献   

10.
All extant populations of Hebe speciosa (Plantaginaceae), a threatened endemic New Zealand shrub, were investigated using the amplified fragment length polymorphism technique (AFLP). Genetic diversity indices varied significantly among geographical regions and were positively correlated with population size. Among-population genetic differentiation was high (mean pairwise ΦST = 0.47), implying complex historical relationships between disjunct populations and negligible contemporary gene flow. Southern populations exhibited extremely low genetic diversity relative to those found in Northland, suggesting that these populations may be more recent in origin. Patterns of genetic relationship among some populations indicate pre-European Māori dispersal and cultivation. The three northernmost populations were found to contain the majority of the species' remaining genetic diversity and thus, should be a focus for future conservation management. Some southern sites may also be culturally significant as evidence of Māori trade and cultivation of Hebe speciosa .  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 229–239.  相似文献   

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