Conservation Genetics (Lec 8)

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Definition of conservation genetics

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interdisciplinary science aiming to apply genetic methods to the conservation of biodiversity

aims to preserve species as dynamic entities capable of coping with environmental change, and to minimize their extinction risks

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Importance of genetic diversity

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fundamental level of biodiversity -> directly relevant to biodiversity conservation

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Evolutionary importance of biodiversity

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genome

potential to serve as starting point for the evolution of new genomes

homogenisation

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genome

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each genome represents cumulative adaptation to a given set of circumstances

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potential

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each genome has potential to serve as starting point for the evolution of new genomes (modification by descent)

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homogenisation

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or loss of genomes results in loss of potentially new evolutionary pathways to counter changing environments

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SGD (standing genetic diversity)

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presence of more than one allele at a locus in a population

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threespine stickleback (gasterosteus aculeatus)

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marine populations have 30-36 bony plates on body

protect against puncture wounds from predators

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Plates are associated with ____ gene

Some aspects of this gene

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Eda

has both low (L) and high (C) alleles evolved 1-2 million years ago

marine populations low frequency of L allele (~1%)

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CC gene =

CL gene =

LL gene =

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CC = lots of plates

CL = half covered in plates

LL = no plates

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SGD (standing genetic diversity)

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marine ancestors recently invaded deglaciated freshwater

have become low plated

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In freshwater

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plates are bad - they cost minerals and energy

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fish with reduced armor

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grow faster, are less prone to predation by insects, breed earlier and are more fecund

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Barrett et al. sampled marine populations and used ...

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heterozygotes to seed 4 freshwater populations

sub-sampled (at random) the F1 offspring over 1 year; F2 over 2 years

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L allele frequency ...

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increased significantly in all 4 populations

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genotypic frequencies changed significantly from ..

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the expected by hardy-weinberg equilibrium

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Evolution occurred within just 2 generations making it...

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rapid evolution

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this rapid evolution shows the importance of...

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SGD in rapid adaptability and evolutionary capability of populations

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Experiment about sticklebacks shows in terms of temperature that...

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freshwater sticklebacks are able to tolerate much lower temperatures than marine sticklebacks

this difference is heritable

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Extinct species

how many global extinction since 1600?

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more than 700 recorded

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Standing genetic diversity is very important for...

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rapid evolution - may help prevent extinctions

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how much of modern extinctions are caused by humans?

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99%

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Importance of demography

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more than 700 recorded global extinctions since 1600

much higher extinction rates on insular systems (islands)

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percentage of extinctions per group on islands

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mammals: 60

birds: 81

reptiles: 95

amphibians: 0

fish: 4

molluscs: 79

invertebrates: 49

flowering plants: 36

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small isolated populations

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human activities -> fragmentation into small, isolated populations -> extinction prone

susceptible to environmental and demographic stochasticity

genetic factors contribute to extinctions as well

even when condition improve, genetic problems associated with small population size can linger

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inbreeding

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mating between individuals carrying alleles identical

increased homozygosity and thus likelihood of exposing deleterious alleles

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deleterious alleles are often...

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hidden in heterozygotic individuals by dominant alleles

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high levels of inbreeding can result in

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inbreeding depression

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Inbreeding depression

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reduction in the fitness and/or survival of populations due to increased inbreeding

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Genetic drift

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stochastic fluctuations in allele frequencies due to random sampling of gametes each generation

offspring receive 1 allele from each parent

by chance, some alleles not passed to offspring, so alleles can 'drift'

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genetic drift in small isolated populations

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genetic variation dominated by genetic drift

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genetic drift in large populations

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genetic variation dominated by natural selection

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Effective populations size (Ne)

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size of an idealized population exhibiting the same genetic properties as the one being studied

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Census population size (Nc)

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actual population size

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Ne vs Nc

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Ne = 4NfNm / Nf+Nm

= % of censused population

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Over average Ne/Nc =

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0.11

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What can Ne be used for?

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to monitor the health of exploited/threatened/endangered species

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Extinction vortex

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small pop -> inbreeding and genetic drift -> loss of genetic variability -> higher mortality and lower reproduction -> reduction in individual fitness and population adaptability

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What can be done for small populations

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encourage habitat restoration

prevent further habitat fragmentation

develop habitat corridors to aid dispersal and gene flow

genetic rehabilitation through translocations

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Translocation example

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Florda panthers

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Florida panthers

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declared endangered in 1967

by 1990s there were 20-25 adults left in Florida peninsula

inbreeding depression so severe that often >1 genetic anomaly per individual

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Translocation: Florida panthers

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extinction imminent

translocation of 8 Texas puma females in 1995

assessed genetic health using 23 molecular markers:

pre vs post-translocation population

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Genetic risks from translocation

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mixing? can avoid inbreeding depression

not mixing? can cause losses in genetic diversity

outbreeding depression

population homogenization

reverse speciation

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outbreeding depression

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reduced fitness from mating of unrelated individuals

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reverse speciation

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hydribization and homogenization of genome

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Critical information for management of endangered species

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population structure

population connectivity

effective population size

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population structure

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number and arrangement of populations within landscape

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population connectivity

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metapopulation structure

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effect population size

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inherent fitness component

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Effective population size is useful for...

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as a metric of vulnerability

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SGD (standing genetic diversity)

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may enable evolution and adaptability