The Maintenance of Genetic Variation Due to Asymmetric Gene Flow in Dendritic Metapopulations

Morrissey,; Kerckhove, D.G. de

doi:10.2307/27735901

Cited by 9 publications

(12 citation statements)

References 26 publications

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“…2 A-D, hαi RN ¼ 5:72, hαi 2D ¼ 6:72, paired t test, t 5 = 9.23, P = 0.0003). These results confirm theoretical predictions on the role of directional dispersal from both individual-and metacommunity-based models (7,32,33). Specifically, we experimentally observe that the anisotropy induced by directional dispersal has a strong impact on the spatial configuration of the species occupancy, reflected in α-and β-diversity (Figs.…”

Section: Resultssupporting

confidence: 88%

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Dendritic connectivity controls biodiversity patterns in experimental metacommunities

Carrara

Altermatt²,

Rodrı́guez-Iturbe³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

311

377

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Biological communities often occur in spatially structured habitats where connectivity directly affects dispersal and metacommunity processes. Recent theoretical work suggests that dispersal constrained by the connectivity of specific habitat structures, such as dendrites like river networks, can explain observed features of biodiversity, but direct evidence is still lacking. We experimentally show that connectivity per se shapes diversity patterns in microcosm metacommunities at different levels. Local dispersal in isotropic lattice landscapes homogenizes local species richness and leads to pronounced spatial persistence. On the contrary, dispersal along dendritic landscapes leads to higher variability in local diversity and among-community composition. Although headwaters exhibit relatively lower species richness, they are crucial for the maintenance of regional biodiversity. Our results establish that spatially constrained dendritic connectivity is a key factor for community composition and population persistence.A major aim of community ecology is to identify processes that define large-scale biodiversity patterns (1-8). For simplified landscapes, often described geometrically by linear or lattice structures, a variety of local environmental factors have been brought forward as the elements creating and maintaining diversity among habitats (9-12). Many highly diverse landscapes, however, exhibit hierarchical spatial structures that are shaped by geomorphological processes and neither linear nor 2D environmental matrices may be appropriate to describe biodiversity of species living within dendritic ecosystems (13,14). Furthermore, in many environments intrinsic disturbance events contribute to spatiotemporal heterogeneity (14, 15). Riverine ecosystems, among the most diverse habitats on earth (16), represent an outstanding example of such mechanisms (7,(17)(18)(19).Here, we investigate the effects of directional dispersal imposed by the habitat-network structure on the biodiversity of metacommunities (MCs), by conducting a laboratory experiment using aquatic microcosms. Experiments were conducted in 36-well culture plates (Fig. 1), thus imposing by construction a metacommunity structure (20, 21): Each well hosted a local community (LC) within the whole landscape and dispersal occurred by periodic transfer of culture medium among connected LCs (22), following two different geometries (Materials and Methods, Fig. S1, and SI Materials and Methods). We compared spatially heterogeneous MCs following a river network (RN) geometry (Fig. 1D), with spatially homogeneous MCs, in which every LC has a 2D lattice of four nearest neighbors (2D) (Fig. 1E). The coarse-grained RN landscape is derived from a scheme (13) known to reproduce the scaling properties observed in real river systems (Fig. 1A).To single out the effects of connectivity, we deliberately avoided reproducing other geomorphic features of real river networks, such as the bias in downstream dispersal, the growing habitat capacity with accumulated contributing...

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Section: Resultssupporting

confidence: 88%

“…Nevertheless, our causal approach sheds light on the sole effect of directional dispersal on biodiversity. Note that the patterns we found in river network geometry are predicted to be even stronger in the presence of a downstream dispersal, which is typical for many passively transported riparian and aquatic species in river basins (19,33).…”

Section: Resultsmentioning

confidence: 60%

Dendritic connectivity controls biodiversity patterns in experimental metacommunities

Carrara

Altermatt²,

Rodrı́guez-Iturbe³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

311

377

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“…Also, asymmetrical gene flow among demes does not necessarily imply reduced meta-N e . Morrissey and de Kerckhove (2009) showed that under conditions of hierarchical spatial structuring in dendritic systems, such as often seen in freshwater, asymmetrical gene flow can maintain high genetic diversity and thereby lead to high meta-N e . Studies on anadromous salmonid fish (for example, Hindar et al, 2004;Fraser et al, 2007;Kuparinen et al, 2010), however, report that metapopulation effective size can be much reduced compared with the sum of local deme effective sizes.…”

Section: Introductionmentioning

confidence: 99%

Demographic and genetic factors shaping contemporary metapopulation effective size and its empirical estimation in salmonid fish

Palstra

Ruzzante

2011

Heredity

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The preservation of biodiversity requires an understanding of the maintenance of its components, including genetic diversity. Effective population size determines the amount of genetic variance maintained in populations, but its estimation can be complex, especially when populations are interconnected in a metapopulation. Theory predicts that the effective size of a metapopulation (meta-N e ) can be decreased or increased by population subdivision, but little empirical work has evaluated these predictions. Here, we use neutral genetic markers and simulations to estimate the effective size of a putative metapopulation in Atlantic salmon (Salmo salar). For a weakly structured set of rivers, we find that meta-N e is similar to the sum of local deme sizes, whereas higher genetic differentiation among demes dramatically reduces meta-N e estimates. Interdemic demographic processes, such as asymmetrical gene flow, may explain this pattern. However, simulations also suggest that unrecognized population subdivision can also introduce downward bias into empirical estimation, emphasizing the importance of identifying the proper scale of distinct demographic and genetic processes. Under natural patterns of connectivity, evolutionary potential may generally be maintained at higher levels than the local population, with implications for conservation given ongoing species declines and habitat fragmentation.

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“…It will also demonstrate which regions are most important to the genetic diversity of the overall population and how changes in these areas can impact the genetic structure of the species over the rest of its range. Theoretical work argues that novel genetic information introduced into the upstream edge of a population is likely to persist (10)(11)(12)(13). Neutral genotypes that are introduced or arise elsewhere in the range will tend to be lost as deceased adults are replaced by migrants from farther upstream.…”

mentioning

confidence: 99%

Asymmetric dispersal allows an upstream region to control population structure throughout a species’ range

Pringle

Blakeslee

Byers

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

100

126

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In a single well-mixed population, equally abundant neutral alleles are equally likely to persist. However, in spatially complex populations structured by an asymmetric dispersal mechanism, such as a coastal population where larvae are predominantly moved downstream by currents, the eventual frequency of neutral haplotypes will depend on their initial spatial location. In our study of the progression of two spatially separate, genetically distinct introductions of the European green crab (Carcinus maenas) along the coast of eastern North America, we captured this process in action. We documented the shift of the genetic cline in this species over 8 y, and here we detail how the upstream haplotypes are beginning to dominate the system. This quantification of an evolving genetic boundary in a coastal system demonstrates that novel genetic alleles or haplotypes that arise or are introduced into upstream retention zones (regions whose export of larvae is not balanced by import from elsewhere) will increase in frequency in the entire system. This phenomenon should be widespread when there is asymmetrical dispersal, in the oceans or on land, suggesting that the upstream edge of a species' range can influence genetic diversity throughout its distribution. Efforts to protect the upstream edge of an asymmetrically dispersing species' range are vital to conserving genetic diversity in the species.invasive species | marine genetics | phylogeography | physical oceanography N ovel genetic material can appear in a population through mutation, migration, or long-distance dispersal events which may be human-mediated. In a single well-mixed population, the evolution of the frequency of novel neutral alleles will be governed by random genetic drift, not their initial spatial distribution (1). However, spatial structure and complexity can alter this expectation. In a metapopulation linked by migration, alleles introduced into source populations are more likely to persist than those that are introduced into sinks (2-4). Many metapopulations are embedded in complex spatial systems with a preferential direction of migration ("asymmetric dispersal"). In these systems, little is known about the equilibrium frequency of novel alleles or how this frequency depends on the location where these new lineages appear.Asymmetric dispersal is common where propagules are carried long distances by wind or water. In atmospheric, riverine, and oceanic flows, there is usually a predominant flow direction (downstream or downwind) that biases dispersal, and eddies or weather systems that slow or reverse such flow add a stochastic (and potentially upstream) component of migration. For example, many terrestrial plant species have propagules that can be dispersed by the winds (5), and a recent study of the spatial patterns of diversity in moss, liverwort, and lichen flora in the Southern Hemisphere were found to be best explained by the predominantly downwind dispersal (6). Further evidence that asymmetric dispersal can structure a species' genetic patter...

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The Maintenance of Genetic Variation Due to Asymmetric Gene Flow in Dendritic Metapopulations

Cited by 9 publications

References 26 publications

Dendritic connectivity controls biodiversity patterns in experimental metacommunities

Dendritic connectivity controls biodiversity patterns in experimental metacommunities

Demographic and genetic factors shaping contemporary metapopulation effective size and its empirical estimation in salmonid fish

Asymmetric dispersal allows an upstream region to control population structure throughout a species’ range

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