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Genetic consequences of habitat fragmentation
Transcript of Genetic consequences of habitat fragmentation
The genetic consequences
of habitat fragmentation. Joe Smith
BIOL 521: Conservation Biology
Dr. Scott Creel 1. Habitat loss 2. Patch isolation What is habitat fragmentation? 3. Alteration of habitat How does fragmentation affect populations? Demographic stochasticity Environmental stochasticity Negative genetic effects 1. Reduced genetic diversity 2. Inbreeding depression 3. Mutation load 1. Reduced genetic diversity:
Alleles are eventually either fixed or lost from populations due to combinations of selection, drift, and migration.
Expected heterozygosity declines each generation.
Rate of decline inversely proportional to Ne. 2. Inbreeding depression
Offspring more likely to be homozygous for recessive deleterious alleles when close relatives mate (identity by descent).
Well-demonstrated effects on fitness. 3. Mutation load
Also called genetic load.
Accumulation of deleterious alleles in a population.
Can lead to “mutational meltdown” in small populations. Why does spatial pattern matter? Spatial arrangement of habitat affects:
Size of subpopulations (N)
Number of subpopulations (n)
Migration rate between subpopulations (m) What matters most? Higgins & Lynch (2001) modeled the effect of genetic load on single populations and metapopulations, varying K (or N), n, and m.
Used individual-based model.
Extinction time highly sensitive to K.
K and s interact.
"Global" migration model better than "nearest neighbor" migration model. Theodorou & Couvet (2006) examined the relative effects of the three metapopulation parameters (N, n, and m) on genetic load.Modeled a finite “island model” metapopulation. Performed an elasticity analysis and verified with simulations.
Genetic load increased (and fitness decreases) with greater population subdivision.
For a given total population size, fitness increased with subpopulation size.
Size of subpopulation was the strongest determinant of fitness. What about real populations? Jaquiery et al (2008) used an individual-based model to examine the effects of varying N, n, and Nm.
Increasing the size of subpopulations more effective than increasing the number of subpopulations.
Increasing migration among subpopulations increased fitness.
"Island" migration model better than "stepping stone" migration model. Metapopulation (a population of populations) Hs and Fst accounted for 70% of the variation in offspring viability among subpupulations, or 87-92% after accounting for mating system. Hs and N accounted for 68% of the variation in median time to extinction, or 81-86% after accounting for mating system. Mean pairwise Fst with three nearby populations:
Ainsdale: Fst = 0.0346
Saltfleetby: Fst = 0.3137 Heterozygosity explained 26% of deviance in the sample model. Where do we go from here? More field testing.
Increase resolution of genetic information.
Study functional, adaptive genes.