Rnr 4103 Conservation Genetics: Lect 14 Metapopulations And Fragmentation

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metapopulation

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A population that consists of a number of sub populations in suitable habitat patches where the absence of individuals is determined by extinction and their presence is determined by recolonization from other sub
populations
-balance between extinction & recolonization; linked by gene flow

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long term Ne

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•Long-term Ne: rate at which genetic variation is lost over 10s or 100s of generations within metapopulations
•Long-term Ne is related to the decline of expected heterozygosity if the entire metapopulation were panmictic, HT

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short term Ne

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•Short-term Ne: amount of drift within local populations (allele frequency changes from generation to generation)
•Short-term Ne is related to the decline in HS, the expected average heterozygosity within subpopulations

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Panmixia

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large short-term Ne (high HS) but small long-term Ne (low HT)

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3) If metapopulations are completely isolated, different alleles are fixed by chance in different populations. What does this mean for HT in the global metapopulation?

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HT in the global metapopulatio nwill become frozen and will not decline (as long as subpops do not go extinct)
•HSlost = 1/2NS= 1/50 = 2% per generation
•But, different alleles will be fixed by chance in different subpopulations

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If there is panmixia among all populations, how is HT in the global metapopulation affected?

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•Eventually, all subpopulations will go to fixation for the same allele and HT= 0

•HTlost = 1/2NT= 1/300 = 0.3% per generation

•So, HT in the global metapopulationwill decline at the same rate as the local subpopulation

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Complete isolation and metapopulations

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small short-term Ne (low HS) and large long-term Ne (high HT)

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panmixia and metapopulations

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large short-term Ne (high HS) but small long-term Ne (low HT)

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How is genetic variation affected if there is a high rate of extinction and recolonization In a metapopulation?

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•reduce Ne, increase drift, and deplete genetic variation
•Often associated with population bottlenecks
•Ne will be lower than Nc, if all extant populations are from a single ancestral population

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When should short-term genetic goals be applied and how do they relate to local pops versus the entire species

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Short-term goals address inbreeding in local pops & rely on gene flow from neighbouring pops to maintain genetic variation

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When should long-term genetic goals be applied and how do they relate to local pops versus the entire species

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Long-term goals address the balance between loss of variation through drift and introduction of new variation through mutation in the global pop (sp or subsp) –no neighbouring pops available to provide novel variation

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Describe four things that affect gene flow.

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1) Mobility
2) Barriers to
3) Mode of reproduction dispersal
4) Interspecific interactions

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3) Mode of reproduction dispersal

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•Outcrossingor a mix of outcrossing& selfing/cloning = higher levels of gene flow
•Selfing/cloning = low levels of gene flow
•Plants: outcrossingsppare usually wind-or animal-pollinated so can travel great distances
•Self-fertilizing plants lack mechanisms for pollen dispersal
•Seeds usually travel short distances -pollen is the m

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1) Mobility

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e.g. mean max. dispersal distance in 77 sppof birds was 148 km, in 40 mammal sppit was 75 km -good gene flow in these bird spp

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2) Barriers to

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•Water bodies, mountain ranges for terrestrial spp, dry land for aquatic spp
•Few barriers in the ocean (currents, salinity), planktoniclarvae could be potentially carried everywhere: dispersal sometimes related to whether larvae are long-lived or short-lived

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4) Interspecificinteractions

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•Plant-herbivore e.g. fruit and frugivores
•Predator-prey e.g. voles and sawfly cocoons
•Parasites & hosts : parasite often at mercy of host dispersal, but parasites can influence dispersal in hosts e.g. magpies & cuckoos (Martinez et al. 1999)