Tag Archives: gene flow

Hydrochoric gene flow in invasive riparian Impatiens

Hydrochoric gene flow in invasive riparian Impatiens

Hydrochoric gene flow in invasive riparian Impatiens

Riparian systems are prone to invasion by alien plant species, which may be facilitated by hydrochory, the transport of seeds by water. Love et al. study gene flow associated with hydrochoric dispersal of the invasive riparian plant Impatiens glandulifera (Himalayan balsam) in two contrasting river systems and find a significant increase in levels of genetic diversity downstream, consistent with the accumulation of propagules from upstream source populations. There is strong evidence for organisation of this diversity between different tributaries, reflecting the dendritic organisation of the river systems studied. The results indicate that hydrochory, rather than anthropogenic dispersal, is primarily responsible for the spread of I. glandulifera in these river systems.

 

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Measuring the flow of transgenes from GM crops into wild plants

Gene flow under contrasting levels of human disturbance

Gene flow under contrasting levels of human disturbance

Rapid development of biotechnology offers new opportunities to ensure our future food supply. Novel traits can be introduced into crops by transgene technology more efficiently than by conventional crop breeding. Since the first commercialization of a genetically modified (GM) crop in 1996, the global area of GM crops has grown steadily and reached 170·3 million hectares in 2012. Increasing numbers of GM crops with different traits are being produced and released into the environment. The introduction of new transgenes into crops has raised concerns about possible negative effects on the environment. Transgenes could move from crops into wild relatives via gene flow. Depending on the nature of the transgene and its product, such transgene flow may lead to unwanted ecological and evolutionary consequences in wild populations

The process of transgene flow from crops into wild relatives involves several steps: first, the formation of crop–wild hybrids with a transgene through hybridization between crops and wild populations; second, the establishment of the transgene in local wild populations through backcrossing with wild plants; third, the spread of the transgene across the whole metapopulation of the wild species via pollen and seed dispersal. The majority of previous studies have focused only on evaluating the first two steps of transgene introgression. A recent paper in Annals of Botany examines the role of metapopulation dynamics in transgene spread.

Wild populations close to crop fields are usually strongly affected by human disturbance. Habitat loss and fragmentation due to human disturbance may alter the level of gene flow among patches and the rate of patch turnover. If gene dispersal becomes limited under strong human disturbance, the distribution pattern of genetic diversity may change dramatically in the metapopulation. In this case, a newly emerged gene, such as a transgene in a local wild population, may not be able to spread through the metapopulation. Conversely, human-mediated dispersal may enhance connectivity among populations in areas where anthropogenic disturbance is high, which would lead to increased spread of an escaped transgene. However, it is difficult to study the effects of human disturbance and associated habitat changes on gene flow, because finding intact wild populations as controls is hard and the effects of other factors may interfere with those of human disturbance.

The authors compared historical and contemporary patterns of gene flow in a wild carrot metapopulation, testing the null hypothesis that human disturbance did not change gene flow in the metapopulation and that contemporary gene flow was similar to historical gene flow in wild carrots and aiming to answer the following questions:

  1. What is the rate of gene flow in the wild carrot metapopulation?
  2. Is contemporary gene flow equal to historical gene flow in the wild carrot metapopulation?
  3. How does the rate of gene flow affect the chance of transgene introgression into the wild carrot metapopulation?

They found that the contemporary gene flow was five times higher than the historical estimate, and the correlation between them was very low. Moreover, the contemporary gene flow in roadsides was twice that in a nature reserve, and the correlation between contemporary and historical estimates was much higher in the nature reserve. Mowing of roadsides may contribute to the increase in contemporary gene flow.

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Direct and reverse pollen-mediated gene flow between GM rice and red rice weed

13042-TR3The potential risks of genetically modified crops must be identified before their commercialization. In this context, several studies have reported the transfer of transgenes from transgenic rice to red rice weed. However, gene flow also occurs in the opposite direction, resulting in transgenic seeds that have incorporated the traits of wild red rice. In a new study in AoB PLANTS, Serrat et al. found that this reverse flow was higher than direct gene flow, but that transgenic seeds carrying wild genes remained in the spike and were thus mostly removed at harvesting. Nevertheless, this phenomenon must be considered in fields used for elite seed production and in developing countries where there is a risk of increasing GM red rice weed infestation.

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Species coherence in a cytogenetically diverse sedge

Species coherence in a cytogenetically diverse sedge

Species coherence in a cytogenetically diverse sedge

The sedge genus Carex, the most diversified angiosperm genus of the northern temperate zone, is known for its holocentric chromosomes and karyotype variability. Escudero et al. provide the first comprehensive study of population-level patterns of molecular and cytogenetic differentiation in the genus. They demonstrate dispersal and genetic connectivity among populations of the North American Carex scoparia that differ in chromosome numbers, demonstrating that cytogenetically variable sedge species can still cohere genetically. This finding is important to our understanding of what constitutes a species in one of the world’s largest angiosperm genera.

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Pollen-mediated gene flow along an altitudinal gradient

Pollen-mediated gene flow along an altitudinal gradient

Pollen-mediated gene flow along an altitudinal gradient

Genetic connectivity is crucial in rapidly changing environments as it allows exchange and dispersal of adaptive genes among plant populations. Matter et al. study patterns of historic gene flow, flowering phenology and contemporary pollen flow in two common herbs, Ranunculus bulbosus and Trifolium montanum, along an altitudinal gradient of 1200–1800 m a.s.l. among alpine meadows in Switzerland, a habitat type thought to be particularly sensitive to climate change. They determine that pollen-flow along the gradient is extensive, explaining the very low genetic differentiation along the mountain slope. Congruent with this finding, they find that despite the delay in flowering caused by altitude, the overlap in flowering periods is large enough to allow for extensive pollen dispersal between populations.

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Biogeography of Prunus africana in Afromontane forests

Biogeography of <i>Prunus africana</i> in Afromontane forests

Biogeography of Prunus africana in Afromontane forests

Afromontane forest ecosystems share a high similarity of plant and animal biodiversity, although they occur mainly on isolated mountain massifs throughout the African continent. Kadu et al. use Prunus africana, one of the character trees of the ecosystem, as a model for understanding the biogeography of this vegetation zone and find strong genetic divergence amongst the five main Afromontane regions, which are most likely associated with Pleistocene changes in climatic conditions. Contrasting estimates of recent and historical gene flow indicate a shift of the main barrier to gene flow from the Lake Victoria basin to the Eastern Rift Valley, highlighting the dynamic environmental and evolutionary history of the region.

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Gene flow in mountain environments

Gene flow in mountain environments

Gene flow in mountain environments

Responses of high-mountain plant species to global change are highly influenced by the genetic background of the species, including genetic diversity or gene flow between populations. García-Fernández et al. study the genetic patterns of Silene ciliata (Caryophyllaceae), a high-mountain cushion plant that shows local adaptation to altitude, by examining populations along two altitudinal gradients on separate mountains in central Spain. They find that genetic diversity is similar in all populations, and although substantial gene flow is found both along altitudinal gradients and horizontally within each elevation belt, greater values are obtained along altitudinal gradients.

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Inbreeding and outbreeding depression in Grevillea

Inbreeding and outbreeding depression in <i>Grevillea</i>

Inbreeding and outbreeding depression in <i>Grevillea</i>

For many Australian plants little is known about either their population genetics or the effects on mating systems of variation in pollen transfer distances. Forrest et al. manipulate pollination of Grevillea mucronulata to allow assessment of the reproductive success of crosses made within and among populations at varying distances and find evidence of both inbreeding and outbreeding depression. Pollen from populations at intermediate distances consistently produces superior outcomes for most aspects of fitness. Natural matings may currently be suboptimal and involve largely near-pollen transfer.

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Reproductive isolation and mycorrhizae in Orchis

Reproductive isolation and mycorrhizae in <i>Orchis</i>

Reproductive isolation and mycorrhizae in <i>Orchis</i>

Mycorrhizal fungi are needed for germination and seedling establishment in orchids, so associations may be involved in determining hybridization between species. Jacquemyn et al.  show that in three species of the genus Orchis (O. anthropophora, O. militaris and O. purpurea) seeds originating from hybrid crosses readily germinate in the field, and protocorms show overlap in mycorrhizal associations with their respective parents. Thus associations appear to contribute little to reproductive isolation in these species.

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Gene dispersal in wild carrot populations

Wild carrot

How far can a gene disperse? Historical and contemporary gene dispersal can be estimated from spatial genetic structure and paternity analysis, and Rong et al. (pp. 285–296) find that an estimate of gene flow in Daucus carota ssp. carota based on contemporary pollen dispersal is much larger than an estimate of historical flow. The results have implications for the ease with which transgene flow might occur from cultivated GM carrots to wild carrot populations.

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