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Drift by drift: effective population size is limited by advection.

Wares JP, Pringle JM - BMC Evol. Biol. (2008)

Bottom Line: Genetic estimates of effective population size often generate surprising results, including dramatically low ratios of effective population size to census size.This is particularly true for many marine species, and this effect has been associated with hypotheses of "sweepstakes" reproduction and selective hitchhiking.As advection increases, effective population size becomes decoupled from census size as the persistence of novel genetic lineages is restricted to those that arise in a small upstream portion of the species domain.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Genetics, University of Georgia, Life Science Building, Athens, Georgia 30602, USA. jpwares@uga.edu

ABSTRACT

Background: Genetic estimates of effective population size often generate surprising results, including dramatically low ratios of effective population size to census size. This is particularly true for many marine species, and this effect has been associated with hypotheses of "sweepstakes" reproduction and selective hitchhiking.

Results: Here we show that in advective environments such as oceans and rivers, the mean asymmetric transport of passively dispersed reproductive propagules will act to limit the effective population size in species with a drifting developmental stage. As advection increases, effective population size becomes decoupled from census size as the persistence of novel genetic lineages is restricted to those that arise in a small upstream portion of the species domain.

Conclusion: This result leads to predictions about the maintenance of diversity in advective systems, and complements the "sweepstakes" hypothesis and other hypotheses proposed to explain cases of low allelic diversity in species with high fecundity. We describe the spatial extent of the species domain in which novel allelic diversity will be retained, thus determining how large an appropriately placed marine reserve must be to allow the persistence of endemic allelic diversity.

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In both (A) and (B), the domain is initialized with haploid adults containing 5 different alleles, each geographically isolated to 1/5 of the domain, and each adult colored according to its allelic composition. The model is run for 400 generations. In (A), Ladv = 0 km and Ldiff = 10 km. The allelic composition diffuses isotropically away from initial positions, and no allele is favored over others. In (B), Ladv = 4, so larvae preferentially disperse towards positive x (to the right) and the upstream allele quickly dominates the entire domain. Lreten in (B) is 25 km.
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Figure 1: In both (A) and (B), the domain is initialized with haploid adults containing 5 different alleles, each geographically isolated to 1/5 of the domain, and each adult colored according to its allelic composition. The model is run for 400 generations. In (A), Ladv = 0 km and Ldiff = 10 km. The allelic composition diffuses isotropically away from initial positions, and no allele is favored over others. In (B), Ladv = 4, so larvae preferentially disperse towards positive x (to the right) and the upstream allele quickly dominates the entire domain. Lreten in (B) is 25 km.

Mentions: To illustrate how advection reduces genetic diversity in a population, two domains are initialized with five different alleles each in different parts of the domain in the numerical model (figure 1). In one domain, mean transport of larvae Ladv is zero; in the other it is 4 km/generation to the right. In both, the stochastic component of larval transport Ldiff is 10 km/generation. In the case with no mean larval transport, all genetic diversity is retained. However, when there is mean larval transport, only the upstream allele persists and the other alleles are lost downstream, for only the upstream allele begins in the retentive region that lies within Lreten = 25 km of the upstream edge of the domain.


Drift by drift: effective population size is limited by advection.

Wares JP, Pringle JM - BMC Evol. Biol. (2008)

In both (A) and (B), the domain is initialized with haploid adults containing 5 different alleles, each geographically isolated to 1/5 of the domain, and each adult colored according to its allelic composition. The model is run for 400 generations. In (A), Ladv = 0 km and Ldiff = 10 km. The allelic composition diffuses isotropically away from initial positions, and no allele is favored over others. In (B), Ladv = 4, so larvae preferentially disperse towards positive x (to the right) and the upstream allele quickly dominates the entire domain. Lreten in (B) is 25 km.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2536672&req=5

Figure 1: In both (A) and (B), the domain is initialized with haploid adults containing 5 different alleles, each geographically isolated to 1/5 of the domain, and each adult colored according to its allelic composition. The model is run for 400 generations. In (A), Ladv = 0 km and Ldiff = 10 km. The allelic composition diffuses isotropically away from initial positions, and no allele is favored over others. In (B), Ladv = 4, so larvae preferentially disperse towards positive x (to the right) and the upstream allele quickly dominates the entire domain. Lreten in (B) is 25 km.
Mentions: To illustrate how advection reduces genetic diversity in a population, two domains are initialized with five different alleles each in different parts of the domain in the numerical model (figure 1). In one domain, mean transport of larvae Ladv is zero; in the other it is 4 km/generation to the right. In both, the stochastic component of larval transport Ldiff is 10 km/generation. In the case with no mean larval transport, all genetic diversity is retained. However, when there is mean larval transport, only the upstream allele persists and the other alleles are lost downstream, for only the upstream allele begins in the retentive region that lies within Lreten = 25 km of the upstream edge of the domain.

Bottom Line: Genetic estimates of effective population size often generate surprising results, including dramatically low ratios of effective population size to census size.This is particularly true for many marine species, and this effect has been associated with hypotheses of "sweepstakes" reproduction and selective hitchhiking.As advection increases, effective population size becomes decoupled from census size as the persistence of novel genetic lineages is restricted to those that arise in a small upstream portion of the species domain.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Genetics, University of Georgia, Life Science Building, Athens, Georgia 30602, USA. jpwares@uga.edu

ABSTRACT

Background: Genetic estimates of effective population size often generate surprising results, including dramatically low ratios of effective population size to census size. This is particularly true for many marine species, and this effect has been associated with hypotheses of "sweepstakes" reproduction and selective hitchhiking.

Results: Here we show that in advective environments such as oceans and rivers, the mean asymmetric transport of passively dispersed reproductive propagules will act to limit the effective population size in species with a drifting developmental stage. As advection increases, effective population size becomes decoupled from census size as the persistence of novel genetic lineages is restricted to those that arise in a small upstream portion of the species domain.

Conclusion: This result leads to predictions about the maintenance of diversity in advective systems, and complements the "sweepstakes" hypothesis and other hypotheses proposed to explain cases of low allelic diversity in species with high fecundity. We describe the spatial extent of the species domain in which novel allelic diversity will be retained, thus determining how large an appropriately placed marine reserve must be to allow the persistence of endemic allelic diversity.

Show MeSH