Isolation by distance

Isolation by distance (IBD) is a term used to refer to the accrual of local genetic variation under geographically limited dispersal.

In a more realistic model, where short-distance dispersal is taken into account,[6] a population is compiled of continuously distributed individuals over a region of space.

Populations in remote locations may become differentiated simply by isolation by distance, restricting the probability of individuals mating with one another.

This ecological isolation by distance, according to Wright, can create genetic differentiation among subpopulations, leading to evolutionary change.

This genetic isolation by distance theory involves concepts of gametic kinship chains, identity by descent, and migration probabilities.

[8] A recent scientific article (Spurgin et al., 2014) tried to differentiate between these processes by utilizing island populations of Anthus berthelotii (Berthelot's pipit) native to three Atlantic archipelagos.

Microsatellite markers and approximate Bayesian computation revealed that the northward colonization of the species produced genetic bottlenecks.

Significant morphological divergence was present that is highly consistent with trends of bottleneck and genetic structure history, not with geographic distance or environmental variation.

One such study where genetic structure among human individuals is investigated is by Relethford and Brennan, (1982) where pedigree and marriage data from Sanday, Orkney Islands in Scotland were used to evaluate temporal patterns in isolation by distance.

Average inbreeding coefficient of all potential spouses (chosen within the known demographic and genealogical limits of the population's structure) of each married male was calculated to determine random kinship values.

[9] The genetic structure, dynamics, and evolution of populations and species are also important from an ecological point of view when considering the probability of colonization and extinction.

When localized, populations that are geographically closer are expected to exchange more migrants and should tend to share neutral genetic markers.

Direct measures of dispersal were determined by quantifying the number of viable floating dormant eggs and larvae that circulated intro overflow traps during flooding events.

FST ratios for all populations increased with geographical distance in all three rock pool sites, indicating a small-scale isolation-by-distance pattern.

Research shows that a distance of 50 meters is an important constraint on the effective dispersal and gene flow for fairy shrimp.

The patterns of isolation by distance as shown among human genetic data representing 346 microsatellite loci taken from 1484 individuals in 78 human populations. The horizontal axis of both charts is geographic distance as measured along likely routes of human migration. The upper graph illustrates that as populations are further from East Africa (represented by the city of Addis Ababa), they have declining genetic diversity as measured in average number of microsatellite repeats at each of the loci. The bottom chart measures the genetic distance between all pairs of populations according to the Fst statistic. Populations separated by greater distance are more dissimilar than those that are geographically close.