genetic diversity and fitness in black-footed ferrets before and during a bottleneck s.m. wisely,...
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Genetic Diversity and Fitness in Black-Footed Ferrets Before and During a Bottleneck
S.M. Wisely, S.W. Buskirk, M.A. Fleming, D.B. Mc Donald, and E.A. Ostrander
Presented by: Melanie Crawford and Julie Bernard
Background Information Black-footed ferret
(Mustela nigripes) is an endangered N. American carnivore
Population decline due to habitat loss and land conversion during 20th century
Underwent bottleneck in mid-1980’s
Background Continued 1985 last wild population (N=40) Epizootics of canine distemper and sylvatic
plague 18 individuals captured for breeding By 1986 no individuals living in the wild
and 7 captive adults
Objectives To compare genetic diversity before versus
during the bottleneck To compare the last wild population to two
historical populations To determine whether fitness changes
accompanied population changes
Objectives continued To compare the
genetic diversity in black-footed ferrets to that of two sibling species, the steppe polecat (Mustela eversmanni) and the European polecat (Mustela putorius)
Mustela eversmanni
Mustela putorius
Prediction and Past Info Population genetic theory predicts and some
empirical data suggests that genetic variability will decline, and individual fitness and adaptability will be lowered.
Previous investigations of genetic diversity in black-footed ferrets found little or no allozyme variation
Conservation biologists usually study populations after they become threatened and small
This study makes use of museum specimens to examine the bottleneck, as well as, historical genetic diversity
More accurate because it compares current diversity with past diversity
Estimated genetic diversity in two sibling taxa with different population histories:- an undisturbed population of the steppe polecat (Mustela eversmanni)- a bottlenecked population of the European polecat (Mustela putorius)
Used to determine if interspecific comparisons of genetic diversity would accurately reflect the bottleneck in black-footed ferrets
Measured litter size in pre- and post-bottleneck black-footed ferrets to measure fitness
The data from this experiment provide a test of a fundamental tenet of conservation biology, that severe bottlenecks lead to fitness losses that increase the likelihood of extinction
Materials and MethodsSamples Tissue from 20 black-footed ferrets collected
between 1891 and 1985-Trego County, KS 1891 (n=4; dried skeletal
muscle)-Mellette County, SD 1972 (n=4; frozen skeletal
muscle)-Meeteetse, WY 1983-1985 (12 individuals; frozen kidney, heart, skeletal muscle)
Samples continued Steppe polecats (5 individuals; frozen skeletal
muscle) -from a single location near Ba Daer Hu, Inner
Mongolia European polecats (6 individuals; skeletal muscle
in ethanol) -from a single contemporary population in west-
central England
DNA Analysis DNA Extracted Amplified 24 Microsatellite loci
Statistical Analysis Deviations from HWE in pre-bottleneck WY of
black-footed ferrets using exact test of HWE Linkage Disequilibrium between pairs of loci in
the WY population using an exact test of P Inbreeding within sub-populations of black-
footed ferrets and genetic structure among subpopulations
Statistical Analysis continued Differences in genetic diversity among five
groups of ferrets: steppe polecat, European polecat, KS, SD, and WY
Used three measures of genetic diversity-the number of alleles per locus averaged across
loci (A)
-the percent polymorphic loci (Po)
-expected heterozygosity (He)
Statistical Analysis continued Estimated genetic diversity at 4 time
periods:
-1891: All individuals from 3 subgroups
-1972: SD and WY (Assumed KS extinct)
-1985: WY pre-bottleneck (12 indiv.)
-1985: WY during bottleneck (7 indiv.)
Fitness Used previously published litter sizes Litter size is a measure of female fecundity
and kit survival Compared reintroduced SD (1997-2000)
and pre-bottleneck WY (1982-1985) # of kits above ground with female; kits
were 75-145 days old
Results DNA Analysis
Amplified DNA from 27 high-quality samples at 24 loci
648 possible genotypes Quality of modern and frozen samples much
greater than that of desiccated samples 16 single-locus genotypes dropped from analysis due
to poor quality replicate amplifications (did not match initial DNA)
Results (con’t) Polymorphism
24 loci polymorphic in black-footed ferrets
21 loci p.m. in at least one species
7 loci p.m. in all three species (3 loci p.m. incl. rarest ferret pops)
Allele length in bp (# of alleles)
24 microsattellite markers for three species of Mustela
Results (Con’t) No deviation from Hardy-Weinberg
Equilibrium was found
No significant linkage disequilibrium found
No significant difference in allele size among species
Results (Con’t) Subpopulations
Subpops found to be genetically distinct Fst (0.57 +/- 0.15)
16 alleles in 10 loci unique to Great Plains Greater population differentiation between
Wyoming and Great plains than between South Dakota and Kansas GP subpops contained many alleles absent in WY,
even though sample size was smaller
Results (Con’t) Current distribution
of populations Small circles- origins
of samples Historically,
distribution wider (inset)
KS and SD more similar than WY
Results (Con’t)
Relief Map of Wyoming; non-populated regions correlate with mountainous regions
Results (Con’t) Significant difference in number of alleles
per locus from all ferret species However, no significant difference in
black-footed ferret species, specifically
Results (Con’t) When did we lose genetic diversity?
Tested in four time periods 1891 1972 1985
Pre-Bottleneck During Bottleneck
***Severe loss in diversity between ’72 and ’85– due to extinction of last Great Plains population***
Results (Con’t) Fitness stayed relatively the same Litter size did not differ before and after
bottleneck Before bottleneck:
115 litters , 4 years = 3.1 kits per litter
After bottleneck: 68 litters , 3 years = 3.2 kits per litter
Discussion and Conclusion Genetic diversity of black-footed ferrets
greatest in undisturbed Kansas grassland Greater He Values More polymorphic loci Higher # alleles/locus
Genetic diversity of SD and WY less due to small, isolated nature of habitat Gen. div. positively correlated to pop size
Discussion & Conclusion (Con’t) Gen. div. great among subpops
Can be only partially explained by genetic drift due to large distance between WY/SD and KS
Greatest differentiation between closest subpops (WY/SD)
Least differentiation between farthest subpops (SD/KS)
Conclusion and Discussion (Con’t) Abolishment of KS population had little
effect on genetic diversity Abolishment of SD population, however,
substantially reduced heterozygosity, number of alleles, and % polymorphism
>>>Core Satellite Model of Population
Conclusion and Discussion (Con’t) Small decrease in gen. div. due to
bottleneck associated with founder event Establishment of the captive population
Litter size did not differ between samples species before, or after the bottleneck
Conclusion and Discussion (Con’t) Bottom line:
Comparison of genetic diversity among subpops of black-footed ferrets (over 110 years) suggests that genetic diversity was greater prior to the extinction of the Great Plains subpops
Bottleneck of WY pop in 1985 induced more loss of genetic diversity
Ultimately, population losses, habitat loss, and land conversion account for the loss in genetic diversity
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