The distribution of the P-M system in Drosophila melanogaster strains from the People's Republic of China

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The distribution of the P-M system in Drosophila

melanogaster strains from the People’s Republic of

China

D Anxolabéhère, K Hu, D Nouaud, Georges Périquet

To cite this version:

Original

article

The

distribution of the

P-M

_system

in

_{Drosophila melanogaster}

strains

from the

_{People’s Republic}

of China

D

Anxolabéhère

K Hu

2

D Nouaud

G

_Périquet

₃

1

Université Pierre et Marie

_Curie,

mécanismes moléculaires de la _spéciation,

.j, Place _Jussieu, 75005 Paris;

2

University

of Hainan, Biology Center,

570001, Hainandao, People’s Repubdic

of China;

3

Faculté

des _Sciences, institut de _{biocénotique expérimentale} des _{agrosystèmes,} Parc _Grandmont, 37200 _Tours, France

(Received

20 June _1989;

_accepted

22

_February

₁₉₉₀₎

Summary - An extensive survey of the D

melanogaster

populations collected _during the _period 1982-1987 in the _{People’s Republic} of China was carried out with _respect

to the P - M _system of

_{hybrid dysgenesis. Geographical}

differentiation was found between the continental area where _only the M’ type occurs, and the coastal areas, where the

populations were characterized as weak P or Q types. All _populations studied carried P sequences and had a

_{high frequency}

of the KP element

_(a

_particular P element

deletion-derivative).

The

_geographical

differentiation of eastern Asian _{populations appears} to be a mirror

_image

of that of western Eurasian _populations with the

_highest

_frequencies of P elements _existing in the coastal areas. The causes of this

_geographical

differentiation are discussed.

Drosophila melanogaster / geographical distribution _/ mobile elements

Résumé - Distribution des caractéristiques du système P - M de dysgénésie des

hybrides dans des souches de _{Drosophila melanogaster} collectées en _République

populaire de Chine. Nous _présentons une _analyse des _{caractéristiques}

_génétiques

et

moléculaires du _système P - M de

_dysgénésie

des

_hybrides

de 39

_populations

de D

melanogaster

collectées en _{République populaire} de Chine au cours de la _période 1982-1987. Il existe une

_{différenciation}

_{géographique marquée} entre la

_région

continentale, où les _populations sont de type

A!,

et les _régions côtières dans _lesquelles les _populations

sont _{principalement} de _{type P-faible} ou _Q. Toutes les _populations étudiées _présentent des

séquences P et une _fréquence élevée d’éléments KP

_(une

_sous-famille

d’éléments P dérivée de l’élément P _{autonome par} une délétion interne

spécifique).

Vis-à-vis du

système

_P-M, la

_{différenciation géographique}

des _populations orientales de l’Eurasie se

_présente

comme une _image en miroir de celle des _{populations occidentales,} avec les _plus hautes

_fréquences

d’éléments P sur les _régions côtières. Les causes de cette _{différenciation}

_{géographique}

sont

discutées.

INTRODUCTION

In the P—M

_system

of

_Drosophila

_{melanogaster,}

the

_syndrome

of

_{hybrid dysgenesis}

(inducing

gonadal sterility, high

mutation

_level,

_etc...)

is known to be related to the

activity

of the P element

_family

_{of transposons}

_(Engels,

_1989).

P element structures can be classified into 2 broad _types: autonomous

_(complete)

elements of 2.9

_kb,

and

non-autonomous elements that

_usually

have substained internal deletions of

_varying

sizes.

Strains of

_Drosophila

may be characterized on the basis of 2

_properties

related

to the

_phenotypic

effects of their P elements. Strains are

specific

in their

ability

to mobilize P elements that are in an

_unregulated

state. This

_ability

is referred

to as &dquo;P

_{activity potential&dquo;.}

Strains may also vary in their property to

_regulate

or _suppress the

_activity

of the autonomous P elements _present in their genomes. This _property is referred to as &dquo;P

_{susceptibility&dquo;.}

It covers the

_joint

action of all

mechanisms

_affecting

P element

_regulation,

_including

that of _cytotype

_(Engels,

1979).

Based on these

_properties,

_{strains may} be classified into 4 broad _types,

_according

to their

_phenotypic

characteristics in

_diagnostic

test crosses and the number of P elements

_they

_{possess. P} strains have low to

_high

levels of P

_{activity potential.}

In

_{addition, they}

also have low levels of P

_{susceptibility. Q}

strains have

_extremely

low levels of both P

_{activity potential}

and P

_{susceptibility}

_(<5

%

of induced

gonadal

sterility) (Kidwell, 1979).

Individuals of the P _type or of the

_Q

_type the

have 25-60

_copies

of _{P sequences}

_(complete

_and/or

_deleted)

per

haploid

genome

(Bingham

et

_al,

_1982).

M and M’ strains

_rarely

have _any

_significant

level of P

activity

potential.

M strains are devoid of _{any P} elements and have

_extremely

_high

P element

_{susceptibility.}

M’ strains carry P sequences, from a few _{up to} 50

copies

per

haploid

genome.

Most,

if not all of these sequences are defective

(Bingham

et

_al,

_1982;

Black et

_al,

_1987;

Izaabel et

_al,

_1987).

M’ _{strains vary} for P element

susceptibility

from

_extremely

_high

to

_moderately

low

_{(Anxolab6hbre}

et

_al,

_1985).

A

subtype

of M’

strains,

harbouring

several

_copies

of a

specific

deletion derivative

element

_(the

KP

_element)

has also been described

_(Black

et

_al,

_1987).

These KP elements may

interact,

perhaps by

inhibition of the _transposase of active

elements,

to _repress the level of induced

_hybrid

_dysgenesis.

Genetic and molecular data from.

_long

established

_laboratory

strains

_provide

strong

evidence in favor of a recent invasion of the genome of D

melanogaster by

P

_transposable

elements

_(Kidwell,

_1983;

Kidwell et

_{al, 1983;}

Anxolab6hbre et

_al,

1988).

Surveys

of natural

_populations

have shown

_{pronounced geographical}

differences

(Anxolabéhère

et

_al,

_{1982, 1984;}

_Kidwell,

_1983;

_Boussy,

_1987;

_Boussy

and

Kidwell,

1987).

P strains

predominate

in the Americas and Central

_Africa,

whereas M’

strains

_predominate

in

_Europe,

North Africa and Asia. In

_Eurasia,

a

_gradient

has been shown to occur from western

_Europe,

where most strains are

Q,

to

the mid-Asian area where M’ strains

_predominate

_{(Anxolab6hbre}

et

_al,

_1985).

These

_large

differences in P &mdash; M characteristics between inter and intra continental

areas are consistent with the

_hypothesis

of a worldwide P element invasion of the D

_{yrcelanogaster}

_genome and

_suggest

that the Americas were invaded before

_Europe,

populations

of D

_melanogaster

may offer us the

_opportunity

to

_study

the

_dynamics

of a

transposable

element

through

the _genome of a

species

recently

invaded

by

it.

In this _paper we

_report

a

_genetic

and molecular

analysis

of more than 40

strains collected from natural

_populations

in China

during

the 1982-1987

_period.

The

_geographical

differentiation of the eastern Asian

_populations

_appears to be a mirror

_image

of that of western Eurasian

_populations,

with the lowest

_frequencies

of

P elements found in the

_populations

from the central

_part

of China and the

_highest

frequencies

of P elements in

_populations

from the east coastal

_part.

MATERIALS AND METHODS

Strains studied

Forty-one

wild strains collected in diverse areas of China

(fig 1)

were

investigated

in this

_study.

Each strain was derived from a

_large

number

(> 30)

of individuals

collected in 1982-1983

_{(21 strains)}

and in 1984-1987

_{(20 strains).}

They

were

_kept

under standard

_laboratory

conditions

_by

mass culture. Two series of

genetic

tests were

_performed,

one in 1984 and the other in 1988. The molecular

analysis

was

Classification of strains

Two reference strains were used to determine the P - M status of wild strains:

Harwich,

a _strong P reference

_strain,

and Canton-S an M reference strain

_(Kidwell

et

al,

1977).

The

_diagnostic

tests used were the standard tests

_measuring

_gonadal

sterility

(GD sterility)

potential

(Kidwell,

1983):

cross

A,

Canton-S females x males

of tested

_strain,

and cross

A

*

,

females of tested strain x males of Harwich strain. For each _cross, 15-30

pairs

of flies were crossed in

_half-pint

bottles and

_immediately

allowed to

_develop

at 29°C.

_{Approximately}

2 d after the onset of

eclosion, F

i

progeny were collected and allowed to mature for 2 d at room _temperature. At

least 50 females were then taken at random for dissection. The

_frequency

of GD

sterility

was calculated

by dividing

the number of

dysgenic

_gonads

by

the total

of

_gonads

scored. The rate of GD

_sterility

in cross A

_provided

a measure of the

P-activity

potential

of the strain under test; in cross A* it

_provided

a measure of

P

_{susceptibility.}

Molecular

_analysis

Three methods of molecular

_analysis

were used in order to characterize the strains

for their

_qualitative

and

_quantitative

P elements

_composition:

₁₎

the

_{squashed-blot}

method

_(Tchen

et

al,

1985)

to detect the presence of P element sequences in

single

flies,

2)

in situ

_{hybridization}

to estimate the P _{element copy} number per

haploid

genome,

3)

the Southern blot method to characterize the

_complete

or defective P elements.

The presence of P element sequences was detected

_{by using}

the

_squash

blot

technique

on 10 individual females _per

_strain,

crushed on a

_nylon

filter membrane

treated and

_hybridized

with P element restriction

_{fragments following}

the

_procedure

of Anxolabéhère et al

_(1985).

The

_probe

consisted of the 2 restriction

_fragments

(P

i

and

_P

₂

_,

_{fig 2)}

from the

_p

₇

_r25.1

_plasmid

_(O’Hare

and

_Rubin,

₁₉₈₃₎

eluted from

agarose

gel by

the squeeze freeze

technique

(Tautz

and

_Renz,

₁₉₈₃₎

and

_{purified by}

Gene Clean

_{(BIO 101).}

P

I

contains the 0.84 kb Hind III restriction

_fragment,

of the

complete

P element. Because this

_fragment

is located at the left-hand

_end,

most

of the P

_elements,

_including

the defective _ones, are

_expected

to possess at least

some of the

_P

_I

_sequence.

_P

₂

contains the internal 1.5 kb Hind

_III/Sal

I restriction

fragment

of the P element. Because of its

_location,

many defective P elements are

expected

to lack all or _part of the

_P

₂

_sequence.

P element _copy number was measured

_by

in situ

_{hybridization}

to

_polytene

chromosomes of a tritium dCTP-labelled

_probe:

the

_pir25.1

_plasmid

(O’Hare

and

Rubin,

1983)

containing

the

_full-length

P element

_{plus genomic}

DNA from the 17C

_region.

In order to determine the copy number per

haploid

chromosome

complement,

females of the tested strain were crossed with Gruta strain males

(the

Gruta strain is devoid of P

_elements)

and the

_{squash procedure}

was

_performed

on

3 to 5

F

l

larvae. The 17C label was used as a

hybridization positive

control

_and,

of course, was not counted.

The structure of the P sequences present in some

_specific

strains was

_analyzed

by

Southern

blots in order to test for _{the presence} of

_complete

P elements and

particular

deleted P elements. DNA was extracted from 100 flies _{per strain}

_using

about _{5 pg} of DNA was

performed according

to the manufacturers

_{instructions,}

and Southern blots were

_performed

_using

standard

_techniques

_(Maniatis

et

_al,

1982).

Filters were washed at

_high

_stringency

_(0.1

x

_{SSC, 0.5%}

_SDS;

_65°C).

Uncut

p

7

r25.7

BWC

_(&dquo;both

_wing

_{clipped&dquo;)}

was used as a

_{probe. p}

₇

_r25.7

BWC

_plasmid

contains a P element that lacks 39

_bp

from its 5’ end and 23

_bp

from its 3’ end. All the

_genomic

_sequences that flank the

_complete

element in the

_{original pa25.7}

plasmid,

as well as some of the

_pBR

322 sequences, were removed in the process of

making

px25.7BWC.

RESULTS

P-M status of Chinese

_populations

The rates of GD

_sterility

in tests for P

_{susceptibility}

_(cross

_A

_*

_),

P

_potential

activity

(cross

A)

and intrastrain GD

_sterility

are

_presented

in table I. The 39 localities studied were

_grouped

into 2 areas

_using

the 115th East meridian to

define western and eastern

_populations.

The

_populations

were classified

_according

to their

_geographical

_position

and their level of P

_{susceptibility using}

the criterion

of 50% of GD

sterility

in the females from the A*

_diagnostic

test

_{(table II).}

The observed differences are

_{statistically}

significant

(x

2

=

_22.6,1

df,

P <

_0.001)

_showing

that western

_populations

have

_higher

P

_{susceptibility}

than eastern ones. Since low or no

_significant

P

_activity

_potential

was detected in _any of the

_populations

sampled,

western

_populations

_may be classified as

_{being mainly}

of the M

_type

and eastern ones of weak P or

Q

_type. Intrastrain GD

_sterility

is low for all

strains, suggesting

that there _{is very} little

_hybrid

_dysgenesis

in Chinese

_populations.

GD

_sterility

was detected in some A crosses

(the

_populations

_5,

8 and

_10);

as no intrastrain GD

_sterility

occurs in these

_populations,

this GD

_sterility

_might

correspond

to a very low P

potential activity.

The results of the

squash

blot tests are shown in

_fig

2. All the flies tested _gave

hybridizing

DNA sequences in all 39 strains. Six levels of

_signal

_intensity

were

established,

from 5 to nul. 5 was

_equivalent

to the

_signal

_intensity

of the

_positive

control strain

_Harwich;

0 was

_equivalent

to

_complete

absence of

_{hybridization,}

as seen in the

_negative

control strain Gruta. In all the Chinese

_strains,

_except for 3 the

intensity

level was weaker with the

_P

₂

_probe

than with the

_P

_l

_probe,

a difference not

shown with the Harwich control

_{(table I).}

This

_suggests

the presence of numerous P element deletion-derivatives in these

_populations.

Furthermore,

differences appear between western and eastern

_populations

ac-cording

to the

_{signal they give}

_{(fig 3).}

Strains

_showing

a weak

_homology

with

_P,

and

_especially

with

P

2

probes

are

_mainly

from the most inland areas. This result

could be due either to some differences of

_homology

between the

_probes

used and P _sequences in these

_populations,

or the presence of a different number of P

copies

per genome.

In order to test this

_geographical

_{differentiation,}

a

sample

of 5 strains taken in the inland and 5 in the costal areas was

_{analyzed by}

in situ

_{hybridization}

(table

III).

The P _copy number per

haploid

genome is

high

in Chinese

populations

and as

_expected,

data from the

_squash

blot method were confirmed: P copy number is

_clearly

the

_highest

in

_populations

from coastal areas.

Southern blot

_analysis

populations.

Avail cuts a full-sized P element at 4 sites to

_generate

3 internal

fragments

of

_0.48,

0.54 and 1.84 kb in

_lenght.

The KP element

_(a

_particular

P

element

_{deletion-derivative,}

Black et

_al,

₁₉₈₇₎

is cut at 3 sites

_generating

internal

fragments

of 0.48 and 0.63 kb

_length

_{(fig 2).}

_Fig

4 shows AvaII

_digests

of

_genomic

DNA from several

_populations

collected from the western continental area

_through

to the east coast

_{(fig 4a)}

and others collected from North to South among the coastal

_populations

_{(fig 4b),}

_hybridized

to the

_prr25.7BWC

_probe.

The 1.8 and 0.54 kb

_{fragments, representing}

full-sized P

_elements,

are

irregularly

detected with various

_signal

intensities. The

_signal

_intensity

_{given by}

the 0.63 kb band

_representing

the KP element _{is very}

_strong

and is _present in all the

_populations

tested. The 0.48 kb band can be

_generated

_by

the full sized P

_element,

the KP element and other elements not deleted in the 22-500

_{region. However,}

the weakness of the

_signal

intensity

of the 0.54 kb

_band,

which

_corresponds

to the full-sized P

_element,

and

the relative lack of bands

at

_positions

other than

_1.8,

0.63 and 0.54 kb indicate that the 0.48 kb band is

_mainly

due to the KP element. From these

_results,

the KP

element seems to be

_present

at a

_{high frequency}

in these

_populations.

Genomic

_digests

of DNA from

_populations

collected in the central

_part

of the

coast

_{(21, 33, 34, 36}

and

₃₉₎

seem to indicate more P _sequences, and

especially

the

putative

complete

P

_element,

than other Chinese

_populations.

These results are in

DISCUSSION

Our

_analysis

indicates that the current Chinese

_populations

of D

_melanogaster

contain in their _genome numerous P element _sequences and that

_they

are

M’,

Q

or

weak P _types in the P &mdash; M _system of

_hybrid

_dysgenesis.

The

_high

P

_{susceptibility}

levels of the strains collected in the western

_part

of China contrast with the

ability

of the strains from the coastal area _{to suppress} P

activity.

The presence

of the _{M’ type}

_populations

in inland China and the

Q

type

along

the eastern coast is in accordance with

_previous

_surveys of the P &mdash; M

_properties

in natural

populations performed

during

the

_{eighties, showing}

the occurrence of M’ types in

Eurasian

_populations

_{(Anxolabéhère}

et

_al,

_1985;

_Ronsseray

et

_{al, 1989;}

_Périquet

et

al,

1989),

M’ and

_Q

_type in Korean

_populations

_{(Paik, 1988)}

and the

_predominance

of the

_Q

_type in

_{Japanese populations}

_(Todo

et

_al,

1984;

Yamamoto et

_al,

1984).

Molecular

_{investigations}

of the Chinese

_populations

in which

_genomic

DNA

was extracted and

_probed

with the full-sized P element revealed that

_complete

P elements are

_irregularly

_present, and are found most

_frequently

in coastal

populations.

Conversely,

all of these

_populations

contain numerous KP

elements,

but no

_geographical

differentiation has been detected. The _presence of KP elements in Chinese

_populations

confirms the fact that this

_specific

defective P element

is

_widespread

in natural

_{populations, especially}

in Eurasia

_(Black

et

_al,

_1987;

Ronsseray

et

_al,

_1989;

_P6riquet

et

_al,

₁₉₈₉₎

and in Australia

_(Boussy,

_{1987; Boussy}

et

_al,

_1988).

In a

_previous

_{study, Périquet}

et al

₍₁₉₈₉₎

showed that the

_frequency

of P elements

gradually

decreases from France to central Asia. Strains collected in 1981-1983

on the west side of a border zone between the USSR and the

People’s

Republic

of China

_(PRC)

carried a small number of P

_copies

per genome: Tashkent

13.8,

Chimkent 8.8 and Alma-Ata 7.7. A clear difference was found in the _present

study:

the P _copy number _{per genome in strains} from the Chinese side of this border zone was

_{significantly higher:}

_Urumqi

23.1 and

_Dunhuang

23.4. This difference

_probably

reflects the absence of

_migration

between these 2 areas due to a

_geographical

barrier: the very

high

mountains of the Tien Shan. Our

_squashed

blot and in situ

_analyses

clearly

show that the

_geographical

differentiation of Chinese

_populations

is a mirror

image

of that of western Eurasian

_{populations. Taking}

all the data into _account, there is a clear division in the distribution of characters in the P &mdash; M _system in

Eurasia, ranging

from France to China. The _{P copy}

number,

and the

_frequency

of weak P or

Q

strains is

_higher

in western

_Europe

and eastern

_China,

with M’

strains,

which show the lowest _{P copy}

_{number, being}

_present in the central area.

Molecular

_analysis

of P

_homologous

elements in numerous

_species

of the

Drosophilidae family

(Anxolab6hbre

and

_Periquet,

₁₉₈₇₎

_{have revealed the presence}

of P elements in

_{Drosophila melanogaster,}

but not in its

various

_sibling

_species.

The

findings

of P

_homologues

in more

distantly

related

_species

(Daniels

and

Strasbaugh,

1986)

and,

more

_recently,

of

_transposable

elements in the D willastorti

_species,

ho-mosequential

to the P element of

_{Drosophila melanogaster}

_(Daniels

et

_al,

₁₉₉₀₎

are in favor of the

_hypothesis

of an invasion of

Drosophila melanogaster by

P elements

(Kidwell, 1979).

This invasion could be recent and may have taken

place

during

this _century, before 1950

_{(Kidwell, 1983).}

Or _{it may} be more

_ancient,

but must

and D

simulans,

approximately

one million years ago

(Engels, 1989)

However,

P

elements have

_homogeneous

sequences, a side from internal deletions

(O’Hare

and

Rubin,

1983),

and _surveys of

_laboratory

strains

_sampled

on different continents

since 1920

_suggest

that P elements

spread

in North and South

America, prior

to

becoming

common in other _parts of the world

(Kidwell,

_1983;

Anxolabdh6re et

_al,

1988).

On the other

_hand,

_{biogeographic}

and

_genetic

data _suggests that

_Drosophila

melanogaster

colonized the American continent

_only

a few centuries ago,

going

from

tropical

Africa to

_tropical

America

_(David

and

_Capy,

_1988).

Combined,

these data

_suggest

that P elements have

_recently

been introduced into the

_Drosophila

_melanogaster

_genome. This

_probably

took

_place

in the Americas and _may have involved a

_{neotropical species}

such as D willistoni.

_Then,

these

elements

_spread

into the

_global

_{species, mainly}

_by

their power of

transposition

and

_presumably

aided

_by

increased human

_activity

_during

the XXth _century.

On the basis of the _present results we propose that the P element was introduced into Chinese

_populations

of D

_melanogaster

_by

_migration

from more eastern

populations.

The

_geographical

differentiation of the Eurasian

_populations

could be due to 2 waves of P element

_migration,

one from the west and the other from the

east,

both

_coming

from American

populations.

The molecular

_analysis

_suggests

that the 2

_migrations

have

_{currently stopped}

around the USSR-PRC frontier

_(between

Alma-Ata and

_Urumqi),

a

_high

mountainous area.

When did P elements occur for the first time in Chinese D

melanogaster

populations?

Because of the absence of

_{long-established laboratory}

strains from this

country, a

_{retrospective}

_temporal

_survey is not

_possible.

As the current

_geographical

distribution of P elements in this area _{argues in} favor of an invasion from the

east,

probably

from Korean and

_Japanese

_populations,

we can

_postulate

that the P elements were not introduced into Chinese

_populations

before the end of the 1960s. Mukai et al

₍₁₉₈₅₎

and Choo and Lee

₍₁₉₈₆₎

have

_analyzed

the

_temporal

variations of the detrimental loads _pers chromosomes in a

_{Japanese population}

and in a Korean

_{population respectively.}

Their results _suggest that some mutator

factors such as the P elements may have invaded these

populations

at the end of the 1960s. More direct evidence for the

_timing

of the P element invasion of

Japanese

populations

is

_provided

_by

Yamamoto et al

_(1984):

_laboratory

strains from

Japanese

natural

_populations

were

_mainly

of the M

_type

until 1970. We

_suggest

that the invasion of Chinese

populations by

P elements took

place after,

or at

approximately

the same

_time,

as the invasion of Korean and

_{Japanese populations.}

All

_{presently existing}

natural

_populations

of D

_melanogaster

have

_probably

been invaded

_by

P elements. Clear

_quantitative

and

_qualitative

differences in P element distribution between

_{geographical regions}

can be

_observed,

as a result of

genetic

drift,

founder

_{effects, migration,}

natural selection and the

_development

of a

mechanism

_regulating

P element

_{transposition.}

Since the P &mdash; M

_{hybrid dysgenesis}

system is a manifestation of the recent introduction of P elements in

_Drosophila

melanogaster populations,

it seems

unlikely

that any _pattern seen in nature is stable. We will

_only

be able to understand the evolution of current distributions when we

have a

_{working knowledge}

of the

_dynamics

of P element invasion.

_Although

this

evolution remains to be tested in nature over

_time,

the

_possible

mechanisms of

its

_dynamics

may be evoked. In Eurasian

populations,

such a mechanism

might

may be due to a

regulatory

role in

hybrid dysgenesis,

or to a

_special

_capacity

for

replicative transposition.

Recent studies

_(Jackson

et

_al,

_1988;

_Périquet

et

_al,

_1989,

Ronsseray

el

_al,

_1989;)

_provide

some evidence that

_{internally-deleted}

P

_elements,

in

_particular

the KP

_element,

interact with autonomous P elements and slow down

or _stop their

_spread

in

_{experimental populations.}

If a similar process takes

place

in natural

_populations,

the

_{high frequency}

of KP elements in Chinese

_populations

might

&dquo;immunize&dquo; it

_against

new invasions

by

autonomous P

_elements;

under these

circumstances their _present status in the P &mdash; M _system should evolve _very

_slowly.

ACKNOWLEDGMENTS

Supported

by

the CNRS URA

_{10, Dynamique}

du

_genome

et

_evolution;

URA 1298

Biologie

des

_{populations d’insectes,}

PIREN

_(invasion)

and the MEN.

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