Transcript Genetic distance, outbreeding

Florida panther:
declined due to habitat loss, poaching, road kills
evidence of inbreeding:
low fertility, sperm abnormalities, cowlicks, kinked tails,
cardiac defects, undescended testicles, high disease rate
Florida panther:
Genetic studies indicated low variability:
Florida
Western US
Other felids
P
4.9
9.9
8-21
H
1.8
4.3
3-8
DNA H
10.4
29.7
45.9
Found to have hybridized with S. American subspecies; introgressed animals with higher P
Florida panther:
Outbred with sub-species from Texas - added 8 females in 1995
F1 hybrid kittens do not have cowlinks or kinked tails
Texas genes are now 15-29% of total
Variation:
Variation is present
• within individuals
• among individuals within populations
• among populations
metapopulations
- networks of populations that have some degree of gene flow
among geographically separate populations
- regular extinction and recolonization events
Populations that are spatially isolated will
tend to diverge genetically
• each population is representative of the species, but may
not contain all of the species’ variation
• many populations may disappear before the species is
endangered
Metapopulations
endangered Glanville fritillary butterfly (Finland) – occupies meadows
1600 meadows, of which 320-524 were occupied in 1993-96
approx 200 extinctions and 114 colonizations per year
Alan Barnes
Populations that are spatially isolated will
tend to diverge genetically
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how many subpopulations can we afford to lose?
which ones do we choose to save? how many?
how many do we have habitat for?
how different is different enough to warrant
isolation/preservation?
Populations that are spatially isolated will
tend to diverge genetically
•
•
•
•
how many subpopulations can we afford to lose?
which ones do we choose to save? how many?
how many do we have habitat for?
how different is different enough to warrant
isolation/preservation?
how well can we describe differences among populations?
Measurement of genetic differentiation among
populations: genetic distance (D)
• Quantitative measure of genetic divergence between two
sequences, individuals, or taxa
• Relative estimate of the time that has passed since two
populations existed as a single, panmictic population
Three most commonly used distance measures
• Nei’s genetic distance (Nei, 1972)
• Cavalli-Sforza chord measure (Cavalli-Sforza and
Edwards, 1967)
• Reynolds, Weir, and Cockerham’s genetic distance (1983)
• Nei’s assumes that differences arise due to mutation and
genetic drift, C-S and RWC assume genetic drift only
Genetic distance
Nei’s genetic distance surveyed over wide variety of taxa:
geographic populations
0.024 + 0.003
subspecies
0.171 + 0.004
species
0.626 + 0.028
genera
1.340 + 0.064
Avise and Smith 1977, Davis 1983
Dendrogram of genetic distances:
(clustered using UPGMA, Unweighted Pair-Group Method with Arithmetic Mean:
each new unit has a distance to the cluster = average of the distance from unit to each
species in the cluster)
Genetic distance (D)
Lampsilis cardium
(pocketbook mussel)
Lampsilis ovata
(pocketbook mussel)
Lampsilis cardium
(pocketbook mussel)
WV L. ovata
IL
L. cardium
WV L. cardium
VT L. “ovata”
MO L. cardium
WV L. fasciola
0.00
0.01
0.02
0.03
0.04
Nei’s genetic distance
Lampsilis ovata
(pocketbook mussel)
0.9
Tuatara – New Zealand
• Habitat loss (mosquito control)
• Spraying for mosquitoes added pesticides to food web
• Reserve established; highway constructed through it
(to connect Kennedy Space Center w. Disney World)
• Marsh drained
• Last 7 males cross-bred with related sub-species –
unsuccessful
• Last sparrow died in 1987
dusky seaside
sparrow
Genetic distance (D)
Genetic distance (D)
Issues with genetic diversity among populations
outbreeding depression/hybridization
• local adaptation
example: ibex extirpated from Czechoslovakia (Capra ibex ibex)
- transplanted from Austria successfully (Capra ibex ibex)
- then added bezoars (C. i. aegagrus) and Nubian ibex (C. i. nubiana)
- fertile hybrids rutted in early fall instead of winter (as natives did)
- kids of hybrids born in February, coldest
month of year, entire population
went extinct
David Hall
Issues with genetic diversity among populations
outbreeding depression/hybridization
• local adaptation
• co-adapted gene complexes
Reproductive success
inbreeding
depression
inbreeding
outbreeding
depression
random mating
inter-breeding
Loss of fitness due to Inbreeding:
accumulation of homozygous recessives
loss of superior heterozygotes
Outbreeding:
reduced fitness of F1 generation
- disruption of local adaptation
- epistatic interactions
reduced fitness of F2 generation
- breakup of co-adapted gene complexes
More empirical studies on inbreeding than outbreeding….
Populations that are spatially isolated will
tend to diverge genetically
p = .5
q = .5
p = .7
q = .3
p = .55
q = .45
p = .5
q = .5
p = .8
q = .2
Genetic diversity among populations
• Increases due to isolation, followed by
– genetic drift
– inbreeding
– selection
– local adaptation
• Decreases due to gene flow (migration)
as migrants move between populations, they homogenize
allele frequencies among populations
Genetic diversity among populations
• Increases due to isolation, followed by
– genetic drift
– inbreeding
– selection
– local adaptation
• Decreases due to gene flow (migration)
as migrants move between populations, they homogenize
allele frequencies among populations
• larger populations diverge slowly through drift
– few migrants needed to counteract
• small populations diverge rapidly through drift
– more migrants needed to counteract
Changes in genetic diversity among populations
m = proportion of population that migrates
Nm = number of migrants randomly exchanged per generation
Ne = 1,000, m = 0.01, Nm = 10
Ne = 100, m = 0.01, Nm = 1
approx 1 migrant/generation will maintain same alleles among
populations (= qualitative similarity)
but 10 migrants per generation may still permit significant
differences in allelic frequencies ( = quantitative dissimilarity)
Changes in genetic diversity among populations
m = proportion of population that migrates
Nm = number of migrants randomly exchanged per generation
Ne = 1,000, m = 0.01, Nm = 10
Ne = 100, m = 0.01, Nm = 1
“in the absence of natural selection, the amount of genetic
divergence among demes is a function of the absolute
number of migrants exchanged (Nm), not the proportion
of exchange (m)” (Allendorf 1983)
Isolation by distance
p = 0.55
q = 0.45
p = 0.65
q = 0.35
p=0.5
p = 0.5
q=0.5
q = 0.5
p = 0.4
q = 0.6
p = 0.75
q = 0.25
Isolation by distance
Isolation by distance
Mussel ‘lures’ with glochidia
Genetic distance between populations
Elliptio dilatata