Sex-Biased Gene Flow Among Elk in the Greater Yellowstone Ecosystem

We quantified patterns of population genetic structure to help understand gene flow among elk populations across the Greater Yellowstone Ecosystem. We sequenced 596 base pairs of the mitochondrial control region of 380 elk from eight populations. Analysis revealed high mitochondrial DNA variation within populations, averaging 13.0 haplotypes with high mean gene diversity (0.85). The genetic differentiation among populations for mitochondrial DNA was relatively high (FST = 0.161; P = 0.001) compared to genetic differentiation for nuclear microsatellite data (FST = 0.002; P = 0.332), which suggested relatively low female gene flow among populations. The estimated ratio of male to female gene flow (mm/mf = 46) was among the highest we have seen reported for large mammals. Genetic distance (for mitochondrial DNA pairwise FST) was not significantly correlated with geographic (Euclidean) distance between populations (Mantel’s r = 0.274, P = 0.168). Large mitochondrial DNA genetic distances (e.g., FST . 0.2) between some of the geographically closest populations (,65 km) suggested behavioral factors and/or landscape features might shape female gene flow patterns. Given the strong sex-biased gene flow, future research and conservation efforts should consider the sexes separately when modeling corridors of gene flow or predicting spread of maternally transmitted diseases. The growing availability of genetic data to compare male vs. female gene flow provides many exciting opportunities to explore the magnitude, causes, and implications of sex-biased gene flow likely to occur in many species

Potential for gene-flow from cultivated Irish grasses and cereals

End of project reportThe importance of gene movement from cultivated plants has been highlighted in regard to minimising the movement of seed and/or pollen between GM and non-GM crops (i.e. gene flow). Although ryegrass covers in excess of 90% of Ireland’s agricultural area, very little is known about gene flow from ryegrass populations from an Irish context. The goal of this project was to address this lack of data by measuring the degree of pollen-mediated gene-flow between two Lolium spp. in a field environment. Ryegrass (esp. Lolium perenne) was selected because as the dominant pasture grass it is critical for the livestock industry as well as being a current target for novel improvements. The results from this research indicate that the potential for pollen-mediated gene flow from perennial ryegrass decreases exponentially with increased distance from the pollen source, with hybridisation events recorded out at 192m. In parallel to this research, a separate study was conducted to assess the degree of genetic diversity within feral and wild Lolium spp across Ireland and also within the important crop weed Avena fatua (‘wild oats’); thereby providing an insight into the degree of historic gene flow that has occurred within each species and in regard to the latter, identifying the potential for non-native A. fatua to colonise the Irish agrienvironment

Landscape genetics and gene flow in the banana pathogenic fungus Mycosphaerella fijiensis

Among the different evolutionary forces driving population genetics, gene flow related to dispersal plays a major role in local adaptation processes. However very few studies on plant pathogenic fungi focussed on deciphering gene flow patterns at the scale of a producing area. The causal agent of the black leaf streak disease on Banana crops, Mycosphaerella fijiensis, can be considered as a good biological model to study the adaptive potential of plant fungal pathogens: populations show relative demographic stability and panmixia so that most methods of population genetics can be properly applied. For gene flow analysis, we focussed on small farming production units which are scarcely distributed among large producing areas and rarely subjected to fungicide spraying. Previous population genetic studies of M. fijiensis allowed us to define the spatial scale to be considered and warned us about the effect of some putative barriers for gene flow analysis. Here we aimed at taking into account landscape in our population genetic analysis to i) delineate pathogen populations and determine the nature and importance of the barriers to gene flow and ii) assess M. fijiensis dispersal pattern within a continuous population. Around 850 isolates were sampled in a referenced area in Cameroon and genotyped using 22 microsatellite markers. The effect of landscape features on gene flow was investigated using a population genetics method explicitly taking spatial location of samples into account (Landscape genetics). Two distinct populations were detected across a 50x50 km area, but no landscape feature matches the observed genetic discontinuity. Within the largest of the two pathogen populations, the dispersal pattern of M. fijiensis was examined using the continuous model of isolation by distance. The observed dispersal pattern is further discussed in the light of simulation results predicting dispersal patterns according to some realistic demographic scenarios for this plant pathogenic fungus. (Texte intégral

High levels of gene flow and genetic diversity in Irish populations of Salix caprea L. inferred from chloroplast and nuclear SSR markers

peer-reviewedBackground Salix caprea is a cold-tolerant pioneer species that is ecologically important in Europe and western and central Asia. However, little data is available on its population genetic structure and molecular ecology. We describe the levels of geographic population genetic structure in natural Irish populations of S. caprea and determine the extent of gene flow and sexual reproduction using both chloroplast and nuclear simple sequence repeats (SSRs). Results A total of 183 individuals from 21 semi-natural woodlands were collected and genotyped. Gene diversity across populations was high for the chloroplast SSRs (H T  = 0.21-0.58) and 79 different haplotypes were discovered, among them 48% were unique to a single individual. Genetic differentiation of populations was found to be between moderate and high (mean G ST  = 0.38). For the nuclear SSRs, G ST was low at 0.07 and observed heterozygosity across populations was high (H O  = 0.32-0.51); only 9.8% of the genotypes discovered were present in two or more individuals. For both types of markers, AMOVA showed that most of the variation was within populations. Minor geographic pattern was confirmed by a Bayesian clustering analysis. Gene flow via pollen was found to be approximately 7 times more important than via seeds. Conclusions The data are consistent with outbreeding and indicate that there are no significant barriers for gene flow within Ireland over large geographic distances. Both pollen-mediated and seed-mediated gene flow were found to be high, with some of the populations being more than 200 km apart from each other. These findings could simply be due to human intervention through seed trade or accidental transportation of both seeds and pollen. These results are of value to breeders wishing to exploit natural genetic variation and foresters having to choose planting material.Teagasc Walsh Fellowship Programm

Dispersal and gene flow in free-living marine nematodes

Dispersal and gene flow determine connectivity among populations, and can be studied through population genetics and phylogeography. We here review the results of such a framework for free-living marine nematodes. Although field experiments have illustrated substantial dispersal in nematodes at ecological time scales, analysis of the genetic diversity illustrated the importance of priority effects, founder effects and genetic bottlenecks for population structuring between patches <1 km apart. In contrast, only little genetic structuring was observed within an estuary (<50 km), indicating that these small scale fluctuations in genetic differentiation are stabilized over deeper time scales through extensive gene flow. Interestingly, nematode species with contrasting life histories (extreme colonizers vs persisters) or with different habitat preferences (algae vs sediment) show similar, low genetic structuring. Finally, historical events have shaped the genetic pattern of marine nematodes and show that gene flow is restricted at large geographical scales. We also discuss the presence of substantial cryptic diversity in marine nematodes, and end with highlighting future important steps to further unravel nematode evolution and diversity

Developing know-how for the improvement and sustainable management of teak genetic resources

The project had the following objectives: To trace and quantify genetic diversity of teak within its natural range, DNA markers were used to assay the current distribution of genetic diversity within and between populations, investigate its mating system and establish historical migration patterns. To evaluate the amount of contemporary gene flow through pollen and seed, hypervariable microsatellite DNA markers have been developed for parentage analysis. The molecular work was complemented by field observations of teak flower insect pollinators. To assess the influence of human disturbance, the genetic diversity in teak forests that have been undisturbed, lightly or heavily disturbed have been assessed and compared for both population genetic diversity and contemporary gene flow processes

Wildlife friendly agriculture: which factors do really matter? A genetic study on field vole

The distribution of genetic differentiation and the directions of gene flow were determined mainly by landscape factors: thus the expectation that organic fields act as genetic reservoir was not met. The fact that agricultural area presented more sub-populations than the undisturbed one, together with the importance of connectivity and habitat size in shaping gene flow and genetic differentiation, shows that switching to organic farming might not be enough to ensure the conservation of species in the agricultural environment. These results emphasise the need to include landscape structure in management policies