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Demographic characterization, inbreeding and
maintenance of genetic diversity in the endangered
Catalonian donkey breed
Pilar Folch, Jordi Jordana
To cite this version:
Note
Demographic
characterization, inbreeding
and
maintenance of
genetic diversity
in
the
endangered
Catalonian
donkey
breed
Pilar
Folch Jordi Jordana*
Unitat de Genètica i Millora
Animal, Departament
dePatologia
i ProducciôAnimals,
Facultat de
Veterinària,
Universitat Autonoma deBarcelona,
08193-Bellaterra, Barcelona, Spain
(Received
20 November1997; accepted
1 March1998)
Abstract - This
study
characterizes thedemographic
andgenealogical
structure of alimited-size
population
indanger
of extinction: the Cataloniandonkey
breed. The purposeof this paper is to establish the most suitable
breeding
criteria andguidelines
to achieve the’Programme
of Conservation and Maintenance of Animal Genetic Resources’ inthis
population.
The two mainobjectives proposed
are:1)
to maintain the maximumgenetic diversity,
with2)
the minimumpossible consanguinity
increase pergeneration.
A
population
size of 109 animals of both sexes, 44 males and 65females,
wasanalysed.
The
pedigree
information was used to calculate thefollowing
items:generation
length
(L),
variances offamily
size(o,2) k ,
effectivepopulation
size(N
e
),
inbreeding
coefficient(F)
andprobability
of geneorigin.
The results obtained andbreeding
criteria to be followed arediscussed. The correct
mating
policy
between a stallion and ajenny
would be that whichwould maximize the so-called
genetic
conservation index and minimize theinbreeding
coefficient of thehypothetical offspring
of thecouple. ©
Inra/Elsevier,
Parisdonkey / endangered breed / pedigree analysis / demographic structure
/
genetic diversity maintenance*
Correspondence
andreprints
E-mail:jordana@guara.uab.es
Résumé - Caractérisation démographique, consanguinité et entretien de la
varia-bilité génétique de la race asine Catalane. Le
présent
travail caractérise la structuredémographique
etgénéalogique
d’unepopulation
en voie d’extinction : la race asine Catalane. La finalité de ce travail a été d’établir les critères et normes dereproduction
lesplus appropriés
pourdévelopper
le « programme de conservation et entretien des ressourcesgénétiques
animales» pour cettepopulation.
Les deuxprincipaux
objectifs proposés
sont :
1)
l’entretien d’unequantité
maximale de diversitégénétique,
avec2)
le minimumprovient
desgénéalogies
a été utilisée pour calculer lesparamètres
suivants : intervallesentres
générations
(L),
variance pour la taille de la famille(a!),
taille effective de lapopulation
(Ne),
coefficient deconsanguinité
(F)
etprobabilité
del’origine
desgènes.
Les résultatsobtenus,
ainsi que les normesreproductives
serontanalysés,
considérantqu’un
accouplement optimal
entre un étalon et une ânesse sera celuiqui
maximise le dénomméIndice de Conservation
Génétique
et celuiqui
minimise laconsanguinité
d’un descendanthypothétique
ducouple
enquestion.
©
Inra/Elsevier,
Parisâne
/
race en voie d’extinction/
analyse de généalogies/
structure démographique/
entretien de la variabilité génétique1. INTRODUCTION
The Catalonian
donkey
is a local tamedonkey
breed located in severalPyrenean
and
pre-Pyrenean
regions
of the Catalonian area of northeastSpain.
Thispopula-tion is in
danger
of extinction. The last census carried outonly slightly
surpassed
100
animals,
a third of which were males(10!.
Following
theguidelines proposed by
theFAO,
investigations
were first carriedout on
morphological
traits(4!,
onhaematological
and clinical biochemicalparam-eters
[7, 11]
and ongenetic
loci[5, 6!,
to characterize this breed.A small and
homogeneous population,
hasimportant
problems
derived frominbreeding.
Therefore,
the twopriorities
accounted for in the Cataloniandonkey
breed Conservation
Programme
are:1)
keeping
the maximumgenetic
diversity,
2)
obtaining
the lowestpossible
inbreeding
rate pergeneration.
The purpose of thispaper is to characterize
demography
and toanalyse
thepedigree
structure of thispopulation
indanger
ofextinction,
to set up thebreeding
criteria to fit to theseobjectives.
2. MATERIALS AND METHODS
The data file information
corresponds
to theperiod
1979-1996. The breedpopulation analysed
consisted of 109individuals,
distributed between 39 foals of both sexes(<
3 yearsold;
18 males and 21females)
and 70 adults: 26 males(aged
3-14)
and 44 females(aged 3-18).
Thepedigree
information was used tocompute:
generation
length
(L),
variances offamily
size(o, 2),
effectivepopulation
size(N
e
),
inbreeding
coefficient andprobability
of geneorigin.
The
N
e
computation
was obtained from the formulaproposed by
[9]
where
N
m
and N
f
are,respectively,
adults males and females withoffspring
and L as the average of thegeneration
intervals calculated for the fourpathways.
Letmale
parent
andcov(
f
,,,,ff)
from each femaleparent.
The variances infamily
size areexpressed
as:<7!;
u£!; afm ! !ff
-The
inbreeding
coefficient(F)
was calculated for every animal in thefile,
using
acomputer
programme based onQuaas-Henderson’s
algorithm
[8, 16).
The evolution of the average coefficient ofinbreeding
was observed over year of birth and summarizedby
the linearregression
over years.The
probability
of geneorigin
was calculated from thegenetic
contributions ofthe founders of the current
population
[2,
3, 13,
15].
A founder is defined as anancestor with unknown
parents
in the file.This effective number of founders
( f
e
)
isequivalent
to the so-called Genetic Conservation Index(GCI)
proposed by
Alderson[1],
which shows the relativecapacity
of an individual to retain the ancestralgenetic
variability
where each founder k can be characterized
by
theexpected
contribution q! to the genepool
considered;
f
e
can be calculated for an individual or a group of individuals(by
definition,
the sumof q
kS
isequal
toone).
If the founder contributions arebalan-ced,
the effective number of founders isequal
tof. Otherwise, f
is lower[2, 3!.
3. RESULTS AND DISCUSSION
3.1.
Demographic
parameters
When
using
the formulaproposed by
Hill!9!,
anN
e
value of 59.97 was obtained.If our
objective
is totry
to maximize this,
N
e
i.e. to minimize theinbreeding
increaseper
generation
(OF),
then we can seeaccording
toequation
(1),
that a series offactors exists that would allow us to increase this
N
e
.
3.1.1. Generation interval
The average
generation
interval betweenparents
andoffspring
was 6.74 f 1.66 years, the maternal interval(7.32 t 2.95)
being
larger
than thepaternal
one(6.16 ! 1.55),
eventhough
the differences between both were notstatistically
sig-nificant. The maternal interval was more variable than the
paternal
one because their variation coefficients(CV)
were,respectively,
40.3%
and 25.1%.
Thegen-eration interval
according
to the four gene transmissionpathways
were thefol-lowing:
L
ss
= 6.15 !1.90; L
sd
= 6.17 !2.45; L
dd
= 7.42 !4.75; L
ds
= 7.213.51,
with s = sires and d = dams.
The average age of the
parents
at birth of their firstoffspring
was 4.23 t 1.57years among stallions and 5.37 :I: 3.89 years among
jennies.
The averagereproduc-tive life was 2.85 t 3.42 and 2.77 t 3.37 years,
respectively.
Despite this,
there wasno
significant
differences between sex, which would indicate that the annualThe
generation
lengths
are determinedby
age at firstmating
andby
reproductive
life. These
parameters
and the totaloffspring
thatparents
leave to the nextgeneration
aredirectly
affectedby
thebreeding policy.
On the otherhand,
the effectivepopulation
size would increase if thesegeneration
intervals would rise(9!.
Generation intervals which have been described in horse breeds
by
otherauthors,
since there are not any references in thedonkey
species,
show a L value muchgreater
than ours. Forexample,
both Moureaux et al.(15!,
analysing
French race andriding
horses and Klemetsdal(12!,
analysing
Norwegian
trotters,
obtained an average L of 10-12 years.According
to Moureaux et al. in theirstudy,
the reason for their intervalsbeing higher
than ours, is due to the fact that the animalsanalysed
wereto be
exploited
forsport.
This means that thesporting
careerpreceded
thebreeding
life,
whereas thedonkeys analysed
here areonly
used forbreeding.
It couldpossibly
be the reasonwhy
nosignificant
differences have been found between thegeneration
lengths
of males and females in our breed.3.1.2.
Family
size variancesProgeny
size was 4.0 t 4.82 per stallion and 2.28 ! 1.34 perjenny.
Thefamily
size distribution for males is more unbalanced than in females because there are a few stallions with more than ten
offspring, approximately
three times as many as the average number ofoffspring
per male. Incontrast,
fewjennies
had more than fourfoals,
andthen,
females show agreater
breeding
homogeneity
than males. Thefamily
size variances calculatedalong
the fourpathways
forgametes
confirm theprevious
remarks:an&dquo;&dquo;
=7.66;
0
,2 m
=
5.83;
or fm 2
=0.90;
0
,2
= 0.90
offspring.
3.1.3.Male/female
proportion
(sex ratio)
When
analysing
thispopulation
census and itsbreeding
structure, twotypes
ofproblems
can be observed. The adult femalepercentage
(62.85 %)
nearly
doubles the maleproportion
(37.14 %),
44 females versus 26 males. On the otherhand,
the number of adult males and females which arebreeding
is less than half the number of adult individuals which couldpotentially
be used asreproducers
(N
f
= 21 andN
m
=12).
In
short,
we would recommendincreasing
theN
e
population,
totry
toequalize
the sex ratio
(n
m
m
N
f
)
and to use the maximum number of adult animals which are nowpresent
in ourpopulation.
To
conclude,
anddirecting
these results to the ConservationProgramme,
the mainobjective
would be to maximize the effectivepopulation
size(N
e
)
toguarantee
that increments of
consanguinity
pergeneration
would be minimal:1)
equalize
the sex ratio(Nm ! N
f
)
avoiding
thefamily
size fluctuations and thatideally,
each male would contribute with a maleoffspring
and each female with a femaleoffspring
to3.2.
Inbreeding
andpedigree completeness
The annual average
inbreeding
(!F),
calculatedby
linearregression
over years, was 0.38%
(figure 1).
The accumulatedconsanguinity
average(F)
was 5.9%.
Theexpected
theoreticalinbreeding
increase was calculated from OF =1/2N
e
whichgave a result of 0.83
%
in the studiedpopulation.
The
pedigree completeness degree
[14]
was measured for each animal in thestudy by calculating
theproportion
of ancestors known in eachpreceding
generation
(figure 2).
Thepedigree thoroughness
was found to be veryincomplete
up to the fifthgeneration
of ancestors because theproportion
of known ancestors was less than 20%.
That iswhy
this situation should be taken into account whenanalysing
the
inbreeding
coefficients.3.3.
Probability
of geneorigin
The effective number of founders
( f
e
),
according
to the formula(2),
was 51.31ancestors,
the total number of founders( f
t
)
was 85.However,
we considered that the total number of founders was veryhigh basically
due to the poorquality
ofpedigree
information.According
to Boichard et al.[3],
these individuals do notrepresent
thegenetic
variability
which exists in the currentpopulation.
In the firstplace,
because these animals havepossibly
been considered as foundersand,
as aresult, genetically independent,
theirrelationship
isvirtually
zero, butperhaps
thisis not true. In the second
place,
because the contributions of thepresent
population
are very unbalancedowing
to the fact that some founders have contributed very little or even not at all.Analysing
therelationship
f
e/
f
t
a result of 60.36%
wasobtained,
thatis,
forstudy
there is another for whom information has been lost. Thisrelationship
has been described in French horsepopulations
[15].
It was noticed thatthey
haveranged
from 2.78%
to 14.03%,
where somepopulations,
such as the TrotteurF!anCais,
wereparticularly
very unbalanced(only
1%
of founders accounted forhalf the current gene
pool).
Probably
these imbalances are due to the fact that the selectionintensity
in thesepopulations
is veryhigh
and thatthey
useonly
the best stallions formatings.
To maintain and to conserve a small
population,
a correctmating
system
isvery
important.
On thewhole,
an idealbreeding policy
would be that which would calculate the effective number of founders and theinbreeding
coefficient of thehypothetical
offspring
of eachpossible
populating
couple.
In this way, thosecouples
which would maximize this effective founder number and minimize theoffspring
inbreeding
coefficient would be chosen.4. CONCLUSION
We must ensure the
equal
contribution of the maximum number of animalspossible
(from
bothsexes),
with as much time aspossible, leaving
offspring
for thenext
generation.
A minimum number ofinbreeding
matings
should be allowed. A maximum number of founder animals(ideally
all ofthem)
would then beACKNOWLEDGEMENTS
The authors wish to thank the
Departament
d’Agricultura,
Ramaderia i Pesca of the Generalitat deCatalunya,
which financed thisstudy;
likewise the AFRAC association for theirhelpful
contribution and forproviding
the data used in theanalysis. Also,
the authors aregrateful
to E. Bedmar forproviding
a computer program forinbreeding
andprobability gene-origin
calculations as well as hiscomputation
assistancethroughout
thispaper.
Also,
we would like to thank Chuck Simmons for theEnglish
revision.REFERENCES
[1]
AldersonG.L.H.,
A system to maximize the maintenance ofgenetic variability
insmall
populations,
in: AldersonL.,
Bod6 I.(Eds.),
Genetic Conservation of DomesticLivestock,
CABInternational, Wallingford, 1992,
pp. 18-29.[2]
BoichardD., Maignel L.,
VerrierE., Analyse généalogique
des races bovines laitieresfranqaises,
Inra Prod. Anim. 9(1996)
323-335.[3]
Boichard D.,Maignel
L., Verrier E., The value ofusing probabilities
of geneorigin
to measure
genetic variability
in apopulation,
Genet. Sel. Evol. 29(1997)
5-23.[4]
FolchP.,
JordanaJ., Characterization,
reference ranges and the influence ofgender
on
morphological
parameters of theendangered
Cataloniandonkey breed,
J.Equine
Vet.Sci. 17
(1997)
102-111.[5]
FolchP.,
JordanaJ.,
Estado actual de resultados delPrograma
de Conservacion Genetica en la raza asnalCatalana,
ITEASuppl.
18(1997)
348-350.[6]
FolchP.,
JordanaJ.,
SdnchezA.,
Genetic variation of theendangered
Cataloniandonkey breed,
Anim. Genet. 27(S2) (1996)
34.[7]
FolchP.,
JordanaJ.,
CuencaC.,
Reference ranges and the influence of age and sex onhaematological
values of theendangered
Cataloniandonkey breed,
Vet. J. 154(1997)
163-168.
[8]
HendersonC.,
Asimple
method forcomputing
the inverse of a numeratorrelation-ship
matrix used in theprediction
ofbreeding
values, Biometrics 32(1976)
69-83.[9]
HillW.G.,
Effective size ofpopulations
withoverlapping generations,
Theor.Popul.
Biol. 3(1972)
278-289.[10]
JordanaJ.,
FolchP.,
Theendangered
Cataloniandonkey
breed: the main ancestorof the American ass or
Mammoth,
J.Equine
Vet. Sci. 16(1996)
436-441.(11J
JordanaJ.,
FolchP.,
CuencaC.,
Clinical biochemical parameters of theendangered
Catalonian
donkey
breed: normal values and the influence of sex, age and managementpractices effect,
Res. Vet. Sci.(1998) (in press).
[12]
KlemetsdalG., Demographic
parameters andinbreeding
in theNorwegian Trotter,
Acta
Agric.
Scand. A-An. 43(1993)
1-8.[13]
Lacy R.C., Analysis
of founderrepresentation
inpedigrees:
founderequivalents
and founder genome
equivalents,
Zoo Biol. 8(1989)
111-123.[14]
MacCluerJ.W., Boyce A.J., Dyke B., Weitkamp L.R.,
Pfenning D.W.,
ParsonsC.J., Inbreeding
andpedigree
structure in Standardbredhorses,
J. Hered.74,
(1983)
394-399.
[15]
MoureauxS.,
VerrierE.,
RicardA.,
MériauxJ.C.,
Geneticvariability
within Frenchrace and
riding
horse breeds fromgenealogical
data and blood markerpolymorphism,
Genet. Sel. Evol. 28,