Managed Breeding for Conservation:Sustainability of Ex Situ Populations

Kevin Zippel - CBSG/WAZA

Amphibian Program Officer

Materials produced by:

R. Andrew Odum, CuratorDepartment of HerpetologyToledo Zoological Society

Why do we maintain records?

Records are kept…

• To manage a collection• To manage multiple collections in

coordination (population management)

• To learn about the animals in our charges (Do Science)

Records are kept…

To communicate

Records are kept as part of our responsibilities

for the animals in our charges

Data for Collection Management

• Identifiers• Sex• Parentage • Where are they• Who are they with• What they did while they were here• Husbandry• Medical

Data for population management

• Genetic – parentage

• Demographic – Sex

– Location

– Immigration

– Emigration

– Births

– Deaths

• Genetic Data

• Demographic Data

Records for Population Management

Genetic data is most

important!No!

Demographic data is most important!

You guys sound like a bunch of

treefrogs! They are both

important!

Minimal Data Set

• How Obtained (demographic)

• Arrival Data (demographic)

• Sex (demographic)

• Birth Date (demographic)

• Parents (genetic)

Minimal Data Set

• Death date (demographic)

• Departure data (demographic)

• Specimen Identification (acc. #, pit tag, photograph, etc.)

Why do we cooperatively manage populations?

• For preservation of genetic diversity (GD) for the future (The Ark)

• For future reintroduction

• To efficiently utilize captive resources

Preserve Gene Diversity

Maintain a specific amount of Gene Diversity (GD) for a specific amount of

time

e.g. 90% for 100 years

THE ARK

SPARKS

PM-2000

Managed vs. Unmanaged

Arabian oryx• N = 13 in 1965• 10 founders • N = 416 in 1995• Stable• 92% gene diversity• Ne/N = 0.30• Mean Inbreeding=0.07

Markhor• N = 35 in 1965• 11 founders• N = 81 in 1995• Unstable• 86% gene diversity• Ne/N = 0.07• Mean Inbreeding=0.19

All populations fluctuate:stable populations fluctuate little.

100 @ 10% 100 @ 50%x 0.90 = 90 x 0.50 = 50

x 1.10 = 99 x 1.50 = 75

x 0.90 = 89 x 0.50 = 38

x 1.10 = 98 x 1.50 = 56

x 0.90 = 88 x 0.50 = 28

x 1.10 = 97 x 1.50 = 42

Good years don’t cancel bad years

0 2 4 6 8 10 12 14 16 18 20

Year

0

10

20

30

40

50

60

70

80

90

100

Po

pu

lati

on

Siz

e10% Annual Fluctuation

0

10

20

30

40

50

60

70

80

90

100

Projection of dolphin population: Initial N = 100; K = 200

Projection of dolphin population: Initial N = 10; K = 20

Carrying Capacity (N)Founders

Expansion Phase

Maintenance Phase

N

Tim

e

• Nt = Nt‑1 + (B – D) + (I – E)

Factors that effect N from one census to the next

Tomorrow Today

Loss of Gene Diversity by Drift

The problem with small populations

AB CD

AD BD

AD

DB

Unrelated Animals

Allele C is lost

Loss of gene diversity due to drift

1000500

250

100

5010

Generation

% G

ene

Div

ersi

ty

N0

20

40

60

80

100

0 20 40 60 80 100

Inbreeding

• Mating between relatives

• Reduces gene diversity (GD)

• Greatly increases probability of expressing deleterious alleles

• Reversible

I love my cousin

Inbreeding

1 2

3 4

5 6

Unrelated Animals

Non-inbred offspring

Inbred offspring

Inbreeding Depression

Inbreeding Depression Expressed by XX

Following deleterious allele X through a pedigree

AB CX

AX BX

XB XX

A

B

XX

XXX

B

Unrelated Animals

Non-inbred offspring

Inbred offspring

X is a rare deleterious allele

Inbreeding reduces fitnessLook What I Made Now!

Inbred vs. Non-Inbred Crested Wood Partridges at MN Zoo

• 8% reduction in egg volume

• 10% reduction in egg weight

• 20% reduction in hatch rate

• 51% reduction in 30 day survival

• Inbred birds have 41% more medical notes than do their non-inbred counterparts!

Inbreeding is Reversible

If an inbred animal is bred with an unrelated animal, the resulting

offspring are not inbred

Outbreeding

OutbreedingUnrelated Animals

Non-inbred offspring

Inbred #5 & #6

Unrelated Female

Non-Inbred Offspring

1 2

3 4

5 6 7

8

8 is not inbred, but GD is lost

The Bad vs. The Good

• Small populations• Few breeders• Isolationist, possessive

management• Little or no genetic

management• Poor records

• Larger populations• More breeders• Cooperative

management• Careful genetic

management• Good records

Population Management Goals

• Maintain 90% gene diversity for 100 years

• Defined target population size– Founders vs. offspring

• Stable numbers– Stable age distribution

• Avoid inbreeding, drift

• Maximize Ne/N

How is managed breeding achieved?

• data collected

• compiled at institution - ARKS IV

• compiled internationally - ISIS (future = ZIMS)

• polished by studbook keeper - SPARKS

• management recommendations - PM2000

• population modeling - VORTEX

Data to collect

• Provenance

• Genetic – Parentage

• Demographic – Gender– Birth/capture date– Immigration– Emigration– Births/Breeding behavior/Development– Deaths

Studbooks

• 300 Population Management Plans (PMPs)– Designated Population Manager keeps studbook

and makes management recommendations

• 90 Species Survival Plans (SSPs)– Species Coordinator & Management Group

• elected committee, outside advisors

– Established genetic goals for 50-100 years– Participation required of AZA member zoos– Field Conservation integral to program

1. Quantify InbreedingThe Inbreeding Coefficient (F)

F = probability that homologous alleles at a random locus are

“identical by descent”

How to Make Breeding Recommendations?

Inbreeding CoefficientF=0

F= 0

F = 0.25

AB CX

AX BX

XB XX

Inbreeding Coefficients of a Simple Pedigree

2. Select breeding pairs using the principle of inbreeding coefficient to

determine relatedness

Kinship

How to Make Breeding Recommendations?

How related are we?Kinship

Kinship Coefficients of a Simple Pedigree

1 2

3 4

5 6

H H

F=0

F= 0

F = 0.25

F = 0.375

k= 0 between #1 and #2

k= 0.25 between #3 and #4

k= 0.375 between #5 and #6

Hypothetical cross of #5 & #6

3. Calculate Mean Kinship:

the average of all the kinships of an animal to the rest of the population

How to Make Breeding Recommendations?

MK of PedigreeALL ANIMALS LIVING

MK=0.225

MK=0.3375

MK=0.3875

1 2

3 4

5 6 7

8

#7 is the most important animal

MK=0.4125

MK=0.05

MK=0.2275

Mean Kinship

• Determines Best Pairings

• Determines Animals to Surplus

Incomplete data

• May remove animals from analysis process

• May create errors in analysis

• May prevent analysis

Incorrect data

• May create significant errors in analysis

• Usually hurts captive population

The Future: Applying Our Knowledge

• Cooperation among institutions• Larger populations, backup• More breeders• Careful genetic management• Population planning• Group management• Good records

Population Management is Balanced on Good Records

Husbandry

Demography Genetics

GOOD RECORDS