Spatial autocorrelation of ovine protein polymorphisms in Europe

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Spatial autocorrelation of ovine protein polymorphisms

in Europe

Jg Ordás, Ja Carriedo

To cite this version:

Note

Spatial

autocorrelation of ovine

_protein

polymorphisms

in

_Europe

JG

_Ordás,

JA

Carriedo

Departamento

de Producciôn Animal

_I,

Facultad de

Yeterinaria,

Universidad de

_{Leén, 24071 Leén, Spain}

(Received

3 June

1996; accepted

8 October

₁₉₉₆₎

Summary - The allelic

_frequencies

of

_{haemoglobin, protein X, arylesterase, transferrin,}

carbonic

_anhydrase

and albumin in 71

_European

ovine

_populations

were studied

_using

spatial

autocorrelation

_{analysis. Haemoglobin}

and transferrin show

_significant

clinal patterns. The observed clines may be a result of

migrations

and

genetic

drift

occurring

since the first domestication of ovines.

sheep

/

protein polymorphism

/

spatial autocorrelation

_/

gene flow

Résumé - Autocorrélation spatiale de polymorphismes protéiques ovins en _Europe.

Les

_fréquences

des

gènes

de

_{l’hémoglobine, la protéine X, l’arylestérase,}

la

_{transfer-Hne,}

l’anhydrasé carbonique

et l’albumine dans 71

_populations

ovines

_européennes

ont été

soumises à une

_analyse

d’autocorrélation

_{spatiale. L’hémoglobine}

et la

_transferrine

mon-trent des structurations

_{spatiales significatives.}

Les clinés observés peuvent être le résultat de migrations et de dérive

_génétique

intervenues

_depuis

la

première

domestication des

ovins.

mouton

_/

_{polymorphisme protéique}

_/

autocorrélation spatiale

/

flux génique

INTRODUCTION

Spatial

autocorrelation

_techniques

can be used to

_study

the

_pattern

of allelic

frequencies

among

populations

in a

_given

area

(Sokal

and

Oden,

1978; Oden,

1984).

This

type

of

technique

has been used in studies of allelic

_frequencies

in different

animal

_species

and humans

_(eg,

Sokal et

_al,

1980; Easteal, 1985;

Barbujani,

1987;

Barbujani

et

_al,

_1994).

Similar studies have not been undertaken on

_species

of

domestic animals.

The aim of this

_study

is to

_analyze

the distribution

patterns

of allelic

_frequencies

of some

protein

polymorphisms

in

European

ovine

populations,

by

spatial

auto-correlation. The

_description

of these

patterns

could contribute to

_improving

our

MATERIALS AND METHODS

We screened 124 _papers

_published

between 1958 and 1994 in 58

_journals.

Those

polymorphisms

for which information is not available from a minimum of 30

populations

were

rejected.

The

analysis

was thus restricted to six loci:

_haemoglobin

beta

_(HBB),

_protein

X

_(X),

_arylesterase

_(ES),

transferrin

_(TF),

carbonic

_anhydrase

(CA)

and albumin

_(ALB)

and 71

_European

ovine

_populations

_{(fig 1).}

All the

bibliographical

sources used

_employ

international allelic nomenclature. A

_complete

list of the data

_analysed

and of the

_respective

_{bibliographical}

sources is available

from the authors on

_request.

The numbers of

_populations

and individuals considered were,

respectively,

69 and

38 840 for

_HBB,

30 and 8 966 for

_X,

37 and 16 442 for

_ES,

53 and 42 162 for

TF,

31 and 13 088 for

_CA,

and 35 and 12 105 for ALB. The

_populations

were

_assigned

to the

_geographical

location indicated

_by

the

_respective

authors. If there were data on two or more flocks in the same

_location,

mean values of allelic

_frequencies

were

calculated. Each local

population

was identified

by

its latitude and

longitude.

Analysis

was carried out

_using

the SAAP

_spatial

autocorrelation _programme

(Wartenberg,

1989)

with ten variable classes of distance. The limits of these classes

were

_{434, 732, 977, 1 167, 1349, 1546, 1 754, 2 032,}

2 417 and 3 082 km. The autocorrelation

coefficient, Gearys’s

c, was

computed

for each class and allele. The

set of autocorrelation coefficients calculated for one allele

(correlogram)

allows an

At diallelic

loci,

that is all

_except

_TF,

the

_correlograms

of the two alleles are

identical. At the TF multiallelic locus the

_correlograms

of alleles

_A,

_B,

C and D

were taken into account. Rare variants of

_CA,

ALB and TF were

_rejected.

RESULTS

Figure

2 shows the

_correlograms

observed for the six

_protein

_{polymorphisms.}

Two

groups of

correlograms

can be differentiated: on the one

_hand,

those for HBB and

TFD are

statistically significant

(P x

0.007 and

P <

_0.001,

respectively);

on the

other

_hand,

those for

_{X, ES,}

CA and ALB and three

_remaining

TF alleles are not

significant.

HBB shows

_significant

_positive

autocorrelations in the short distance classes and

significant

negative

autocorrelations at

_great

distance. In other

words, European

ovine

_populations

show similar HBB allelic

_frequencies

at distances of less than 977

_km,

but

_markedly

different ones at distances

_greater

than 2 032 km. The HBB autocorrelation coefficients vary in almost monotonic fashion from short to

_long

distances. This variation

_pattern

is defined as a cline

(Sokal

and

_Oden,

1978).

HBB

A allelic

_{frequencies gradually}

decrease between 68° and 38°

latitude,

that

_is,

from the north to the south of

_Europe.

The TF D allele is that of

_{highest frequency}

at the transferrin locus. This allele also shows

_significant

positive

autocorrelation in the first distance classes and

_significant

_negative

autocorrelation in the last classes. The c values for this

allele

_generally

increase with distance. Thus the

_geographical

variation

_pattern

for TF D is also clinal. The flocks with the lowest values for TF D are

_generally

to

be found in

_higher

_{European latitudes,}

whilst those with

_high

values of this allele

are more

_frequent

at the low latitudes. The

_gradual

increase from countries in the north to those in the south of

_Europe

for TF

_D,

as well as HBB

_B,

is corroborated

by

linear correlation

_analysis

_(Ordds

and

_{Carriedo, manuscript}

in

_{preparation).}

DISCUSSION

The

_sample

includes _many different breeds each with a certain

_degree

of

inter-breeding

with

_others,

and each with characteristic allele

_frequencies

and

_geographic

distributions.

However,

the

_sample

is not dominated

_by

one or a few breeds.

Con-sequently,

the clines may not be the result of

sheep

breed structure.

It is

_possible

that HBB A could have some

_disadvantage

in warm

_regions

_(Agar

et

_al,

_1972).

TF D could also suffer from some

_disadvantage

in cold

_regions.

On

the other

_hand,

associations between

_production

or

_reproduction

traits and HBB

or TF

_genotypes

have been

established,

but the results obtained are

_quite

different

in ovine breeds

_(eg,

Altaif and

_Dargie,

_1978;

Morris et

_al,

_1988).

Differences in

selection pressures, of the order of mutations

rates,

could be

_enough

to maintain clines

_{(Cavalli-Sforza}

and

_Bodmer,

_1981).

_However,

it must be

_pointed

out that there is no conclusive

_proof

that HBB and TF ovine

_{polymorphisms}

have different

adaptive

values. Because of this the clines found for these loci may not be

stable,

but rather a

_transitory

result of

_migrations

and

_genetic

drift.

Sheep

domestication occurred

_during

the Neolithic

_period

in south-east Asia.

valley

and an exterior one

_along

the Mediterranean coast

_{(Ryder 1984).}

Domestic

sheep

would have reached

_Europe

and the Iberian

_peninsula

in the 7th and 5th

clines could have

_originated

in isolated founder

_populations

with different

_genetic

constitutions,

which

_emerged

in

_{subsequent periods.}

Since the initial

_spread

of

_sheep

into

_Europe

until the

_present

_day

_migrations

would have occurred to a

_greater

or

lesser extent between

_{adjacent populations, giving}

rise to the establishment of clinal

patterns.

This _process is

_{fully compatible}

with that the

_theory

_predicts

on the

_origin

of clinal

_spatial

_patterns

_(Endler

_1977;

Slatkin

_1987,

_1989).

In this _way,

_migration

and

genetic

drift would be the main forces

responsible

for HBB and TF D

_spatial

gene distribution.

In

_conclusion,

it seems more

_parsimonious

to

_regard

the clines observed at the HBB and TF loci as due to

_history

_(ie,

the

_demographic

_processes of

expansion

from

the near east of

_presumably

Neolithic animal

_breeding

_populations)

rather than to

geography

(ie,

adaptation

to

_changing

_{environment).}

A similar conclusion has been

proposed

in

_European

cattle

_(Medjugorac

et

_al,

_1994).

The

generally

accepted

view

whereby

human groups

dispersed

from the near east in the

_Neolithic,

_spreading

their _genes and

_technologies

at the same time

_(Sokal

et

al, 1991; Renfrew, 1992;

Barbujani

and

Pilastro,

1993)

is in full

_agreement

with this

_{interpretation.}

ACKNOWLEDGMENTS

We thank G

_Barbujani

_(Universita

di

_Padova,

_Italy),

for many

suggestions

and critical

reading

of a

_previous

version of the

_manuscript.

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