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