Development Of Genetic Structure Research Articles

Development of genetic structure in a heterogeneous landscape over a short time frame: the reintroduced Asiatic wild ass

Understanding the dynamics of genetic structures which arise during a population’s range expansion can be applied to the conservation of recovering species and species that are shifting their range. Theoretical models, supported by several empirical findings, have indicated that fine-scaled genetic structure can arise at the wave front of a spatially expanding population. We explored the development of population genetic structure in the reintroduced Asiatic wild ass (Equus hemionus) in Israel, four generations after the onset of reintroduction, during which the population experienced demographic growth and range expansion over a complex landscape. Blood samples of the ‘founding-population’ and fecal samples of the ‘wild-population’, collected throughout the range of distribution were analyzed using mtDNA markers. Fecal samples were delimitated to ‘subpopulations’ according to their geographical locations. The “East” subpopulation, at the wave front of the wild population’s distribution, was found to be significantly different than the rest of the population (AMOVA, ΦST = 0.13, P = 0.04). These findings were supported by an FST-test, Spatial-AMOVA and a Barrier analysis. The “East” region is characterized by high quality habitat patches and low landscape connectivity to the rest of the area, which possibly led to its relative isolation. The “East” subpopulation was probably initiated following a founder-effect of dispersers from the release area, which remained in the ‘new area’, due to its high habitat quality. This genetic structure, though it might diminish over time due to gene flow and additional range expansion, has the potential of facilitating adaptive evolution and thereby affecting the population’s long term persistence.

Complex migration and the development of genetic structure in subdivided populations: an example from Caribbean coral reef ecosystems

A matrix‐based projection model is used in conjunction with the results of a coupled bio‐physical dispersal model to examine the spread of alleles through subdivided populations over time, and the associated development of genetic structural patterns. Applying this approach, it becomes possible to quantitatively evaluate the contribution of spatially explicit migration towards patterns of genetic structure observed in the field. To provide a concrete example, the model was used to examine genetic dispersal between coral reef patches of the Caribbean. Using generic life‐history parameters, the model shows the formation of a strong genetic break between eastern and western patches, as well as the development of a gradient along the length of the Bahamian archipelago, corresponding with evidence previously collected for coral and fish species. The data also suggest that Jamaica and the Cayman Islands are important stepping stones between the reefs of the northern Caribbean (Hispaniola and the Bahamas) and the Mesoamerican Barrier Reef. The model provides an effective means of evaluating regional‐scale genetic connectivity through time and identifying natural clusters of genetic exchange.

Gene flow among native bush rat,Rattus fuscipes(Rodentia: Muridae), populations in the fragmented subtropical forests of south‐east Queensland

Abstract Many natural populations in areas of continuous habitat exhibit some form of local genetic structure. Anthropogenic habitat fragmentation can also strongly influence the dynamics of gene flow between populations. We used eight microsatellite markers to investigate the population genetic structure of an abundant forest species, the Australian bush rat (Rattus fuscipes), in the subtropical forests of south‐east Queensland. Five sites were sampled, allowing pairwise comparisons within continuous habitat and across clearings. Weak, but significant population differentiation and a significant pattern of isolation by distance was detected over the small scale (<10 km) of this study. Fine‐scale analysis at a single site (<1 km) showed a significant correlation between individual female genetic distance and geographical distance, but no similar pattern among male individuals. There was no evidence of increased population differentiation across clearings relative to comparisons within continuous forest. This was attributed to dispersal within corridors of remnant and revegetated habitat between the forested areas. We concluded that an inherently restricted dispersal ability, female philopatry and natural habitat heterogeneity play an important part in the development of genetic structure among populations ofR. fuscipes. It is important to understand the relationship between landscape features and the pattern of gene flow among continuous populations, as this allows us to predict the impact of fragmentation on natural populations.

Genetic Structure of a Mimosoid Tree Deprived of Its Seed Disperser, the Spider Monkey

To assess the genetic consequences for a Neotropical tree of the loss of its main seed disperser, we compared the genetic structure of Inga ingoides in a site where the spider monkey (Ateles paniscus) was abundant and a site where it had been eliminated by subsistence hunting. Gene flow should be reduced in the site where the spider monkey is absent, and there should be a corresponding subpopulation differentiation of seedlings within the spatial range of the movements of these primates in the absence of between-site differences in allelic frequencies. At the microhabitat ( family) scale, seedlings growing under parent plants should be genetically more related in the absence of the spider monkey than in its presence. Subpopulation differentiation was smaller where the spider monkey was present ( four loci, FST = 0.011) than where it was absent ( four loci, FST = 0.053) for the first year of study, but not for the second year (three loci, FST = 0.005 vs. 0.003). The number of alleles in common among seedlings growing under parent plants was smaller in the presence of the spider monkey than in its absence, showing family genetic structure in the first generation for both years of study ( Mann-Whitney, z = -2.17, p = 0.03 and z = -2.72, p = 0.006 for 1996 and 1997, respectively). This family genetic structure in the first generation should accelerate the development of population genetic structure. Development of genetic structure might result in demographic changes, one of which would be a fitness reduction if the species were self-incompatible, as suggested for Inga by available evidence. Large birds and mammals are the main targets of subsistence hunting in the Neotropics. Extinction of seed-dispersing frugivores may result in pronounced changes in the demographic and genetic structure of tree species in Neotropical forests.