Download Genetic principles for captive breeding

Genetic principles for captive breeding
Zoos now and then
Success stories ex‐
situ conservation?
Seed bank on Svalbard
Success stories ex‐
situ conservation?
First species to reach Vulnerable conservation status (2011)
after being extinct in the wild (1972)
Wild popualation: c. 1000
Captive population: c. 6000
Arabian oryx
Breeding endangered animals
• Maximize the number of founders (unrelated animals).
• The population should as soon as possible reach the largest possible population size.
• The genetic contribution should be equal between the founders.
• Avoid inbreeding (maximize Ne)
• Maximize generation time.
• Do not mix populations of different genetic origin.
• Avoid selection.
Effective population size Ne
The size of an ideal population with the same rate of
inbreeding and/or genetic drift as the actual
population
Ne typically much smaller than N
1 male
99 females
N=100, Ne = 3.96
2 males
2 females
N=4, Ne=4
4 x Nm x Nf
Ne =
Nm + Nf
Ne = 4
Ne =
4N
Vk + 2
Ne decreases with increased variance in offspring
Ne over several generations are calculated by the harmonic mean.
1
1
=
*
Ne
t
(
1
1
1
1
+
+
Ne1 Ne2 Ne3 ... Net
)
1
ΔF =
2Ne
The size of an ideal population with the same rate of
inbreeding and/or genetic drift as the actual
population
Ne typically much smaller than N
Pedigreesandinbreeding
calculations
Inbreeding
Matingofrelatedindividualsresultingin
increasedhomozygosityinprogeny(alleles
IdenticalByDescent‐ IBD).
Inbreedingdepression
Homozygosityofdeleterious
recessiveallelesincreases.
Increasedoccurrenceofhereditary
disordersanddiseases.
Anoveralllossoffitness– survival,
fertility,reproduction,productivity,
performance,etc.
Inbreeding
Matingofrelatedindividualsresultinginincreased
homozygosityinprogeny(AllelesIBD).
Inbreedingcoefficient(F):
• Theprobabilitythattwoallelesatalocusareidenticalby
descent(IBD)
• Proportionoflociintheindividual’sgenomethathave
allelesidenticalbydescent(IBD)
Captivepopulationsarepedigreed
Studbook
Name
Dam
Sire
Bella
Pedigree
Bella
Bailey Molly
Max
Bailey
Molly
Max
Roxie
Bella
Bailey
Charlie
Molly
Max
Ginger
Roxie
Charlie
Roxie
Charlie
Ginger
dead
female
male
P‐generation
(parental)
F1‐generation
unknownsex
F2‐generation
Glossary
Founders: individualsthathaveestablishedthepopulation
(unrelatedindividualsinthepedigree)
Commonancestor:theancestorofbothmotherandfather
oftheindividualofinterest
Calculation
numberofancestorsinthepedigree
F=Σ (1/2)n *(1+Fca)
Theprobabilitythatanallele
ispassedontotheoffspring
Theinbreeding
coefficientofthe
commonancestor
Calculation
Coefficient of kinship (k)
• Degree of relatedness between two individuals. • The inbreeding coefficient of a hypothetic offspring.
Kinship coefficients
The inbreeding coefficient of a
hypothetic offspring
• Self
• Full sib • Parent‐offspring
• Half sib
• Uncle‐nephew
• Cousin
0,5
0,25
0,25
0,125
0,125
0,0625
Mean Kinship
• Mean Kinship of an individual is the average of the kinship coefficient between that individual and all other living individuals in the populaiton (including itself).
• Low MK=few relatives=unique animal.
Mean Kinship
A
B
C
D
Mean kinship of C
Coefficient of kinship: Inbreeding coefficient of hypothetic offspring
Mean Kinship
A
C
B
D
Mean kinship of C
•C-A
•C-B
•C-D
•C-C
0,25
0,25
0,25
0,5
0,5+3(0,25)
=0,3125
4
Coefficient of kinship: Inbreeding coefficient of hypothetic offspring
Which
golden lion
tamarin is
most
valuable?
Which
golden lion
tamarin is
most
valuable?
Thelma
Louise
Rita
Robert
Mean
kinship
Thelma
0.625
0.3125
0.125
0
0,27
Louise
0.3125
0.625
0.125
0
0,27
Rita
0.125
0.125
0.5
0
0,19
Robert
0
0
0
0.625
0,16
Captive populations: Conserve
genetic variation in founder
population.
• Random loss of founder alleles because of limited
number of offspring.
• Genetic variation smaller because of unequal founder
contribution.
Retention
• The probability that a founder allele is still present in the populaiton.
Or…
• The proportion of a founder´s genome that is still present in the population
ri = 1-p(loss)
Calculations