共查询到7条相似文献,搜索用时 0 毫秒
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Hybrids between transgenic crops and wild relatives have been documented successfully in a wide range of cultivated species, having implications on conservation and biosafety management. Nonetheless, the magnitude and frequency of hybridization in the wild is still an open question, in particular when considering several populations at the landscape level. The Beta vulgaris complex provides an excellent biological model to tackle this issue. Weed beets contaminating sugar beet fields are expected to act as a relay between wild populations and crops and from crops-to-crops. In one major European sugar beet production area, nine wild populations and 12 weed populations were genetically characterized using cytoplasmic markers specific to the cultivated lines and nuclear microsatellite loci. A tremendous overall genetic differentiation between neighbouring wild and weed populations was depicted. However, genetic admixture analyses at the individual level revealed clear evidence for gene flow between wild and weed populations. In particular, one wild population displayed a high magnitude of nuclear genetic admixture, reinforced by direct seed flow as evidenced by cytoplasmic markers. Altogether, weed beets were shown to act as relay for gene flow between crops to wild populations and crops to crops by pollen and seeds at a landscape level. 相似文献
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The patterns of hybridization and asymmetrical gene flow among species are important for understanding the processes that maintain distinct species. We examined the potential for asymmetrical gene flow in sympatric populations of Eucalyptus aggregata and Eucalyptus rubida, both long-lived trees of southern Australia. A total of 421 adults from three hybrid zones were genotyped with six microsatellite markers. We used genealogical assignments, admixture analysis and analyses of spatial genetic structure and spatial distribution of individuals, to assess patterns of interspecific gene flow within populations. A high number of admixed individuals were detected (13.9–40% of individuals), with hybrid populations consisting of F1 and F2 hybrids and backcrosses in both parental directions. Across the three sites, admixture proportions were skewed towards the E. aggregata genetic cluster (x=0.56–0.65), indicating that backcrossing towards E. aggregata is more frequent. Estimates of long-term migration rates also indicate asymmetric gene flow, with higher migration rates from E. aggregata to hybrids compared with E. rubida. Taken together, these results indicate a greater genetic input from E. aggregata into the hybrid populations. This asymmetry probably reflects differences in style lengths (E. rubida: ∼7 mm, E. aggregata: ∼4 mm), which can prevent pollen tubes of smaller-flowered species from fertilizing larger-flowered species. However, analyses of fine-scale genetic structure suggest that localized seed dispersal (<40 m) and greater clustering between hybrid and E. aggregata individuals may also contribute to directional gene flow. Our study highlights that floral traits and the spatial distributions of individuals can be useful predictors of the directionality of interspecific gene flow in plant populations. 相似文献
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We propose a method of analysing genetic data to obtain separate estimates of the size (N(p)) and migration rate (m(p)) for the sampled populations, without precise prior knowledge of mutation rates at each locus ( micro(L)). The effects of migration and mutation can be distinguished because high migration has the effect of reducing genetic differentiation across all loci, whereas a high mutation rate will only affect the locus in question. The method also takes account of any differences between the spectra of immigrant alleles and of new mutant alleles. If the genetic data come from a range of population sizes, and the loci have a range of mutation rates, it is possible to estimate the relative sizes of the different N(p) values, and likewise the m(p) and the micro(L). Microsatellite loci may also be particularly appropriate because loci with a high mutation rate can reach mutation-drift-migration equilibrium more quickly, and because the spectra of mutants arriving in a population can be particularly distinct from the immigrants. We demonstrate this principle using a microsatellite data set from Mauritian skinks. The method identifies low gene flow between a putative new species and populations of its sister species, whereas the differentiation of two other populations is attributed to small population size. These distinct interpretations were not readily apparent from conventional measures of genetic differentiation and gene diversity. When the method is evaluated using simulated data sets, it correctly distinguishes low gene flow from small population size. Loci that are not at mutation-migration-drift equilibrium can distort the parameter estimates slightly. We discuss strategies for detecting and overcoming this effect. 相似文献
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