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P eda ion on Mul iple T ophic Le els Shapes he E olu ion o Pa hogen Vi ulence
F iman, Ville-Pe i; Linds ed , Ca i a; Laakso, Jouni; Mappes, Johanna
F iman, V.-P., Linds ed , C., Hil unen, T., Laakso, J. & Mappes, J. (2009). P eda ion on
mul iple ophic le els shapes he e olu ion o pa hogen i ulence. PLoS ONE, 4 (8),
e6761.
2009
P eda ion on Mul iple T ophic Le els Shapes he
E olu ion o Pa hogen Vi ulence
Ville-Pe i F iman
1,2
*, Ca i a Linds ed
1
, Teppo Hil unen
1
, Jouni Laakso
1,2
, Johanna Mappes
1
1Depa men o Biological and En i onmen al Science, Cen e o Excellence in E olu iona y Resea ch, Uni e si y o Jy a
¨skyla
¨, Jy a
¨skyla
¨, Finland, 2Depa men o
Biological and En i onmen al Science, Uni e si y o Helsinki, Helsinki, Finland
Abs ac
The pa hogen i ulence is adi ionally hough o co-e ol e as a esul o ecip ocal selec ion wi h i s hos o ganism. In
na u al communi ies, pa hogens and hos s a e ypically embedded wi hin a web o in e ac ions wi h o he species, which
could a ec indi ec ly he pa hogen i ulence and hos immuni y h ough ade-o s. He e we show ha selec ion by
p eda ion can a ec bo h pa hogen i ulence and hos immune de ence. Exposing oppo unis ic bac e ial pa hogen
Se a ia ma cescens o p eda ion by p o ozoan Te ahymena he mophila dec eased i s i ulence when measu ed as hos
mo h Pa asemia plan aginis su i al. This was p obably because he bac e ial an i-p eda o y ai s we e aded o wi h
bac e ial i ulence ac o s, such as mo ili y o esou ce use e iciency. Howe e , he hos su i al depended also on i s
alloca ion o wa ning signal ha is used agains a ian p eda ion. When in ec ed wi h mos i ulen ances al bac e ial s ain,
hos la ae wi h a small wa ning signal su i ed be e han hose wi h an e ec i e la ge signal. This sugges s ha la al
immune de ence could be aded o wi h e ec i e de ence agains bi d p eda o s. Howe e , he signal size had no e ec
on la al su i al when less i ulen con ol o e ol ed s ains we e used o in ec ion sugges ing ha an i-p eda o y
de ence agains a ian p eda o s, migh be less cons ained when he in ading pa hogen is a he low in i ulence. Ou
esul s demons a e ha p eda ion can be impo an indi ec d i e o he e olu ion o bo h pa hogen i ulence and hos
immuni y in communi ies wi h mul iple species in e ac ions. Thus, he pa hogen i ulence should be iewed as a esul o
bo h pas e olu iona y his o y, and cu en ecological in e ac ions.
Ci a ion: F iman V-P, Linds ed C, Hil unen T, Laakso J, Mappes J (2009) P eda ion on Mul iple T ophic Le els Shapes he E olu ion o Pa hogen Vi ulence. PLoS
ONE 4(8): e6761. doi:10.1371/jou nal.pone.0006761
Edi o : Niyaz Ahmed, Uni e si y o Hyde abad, India
Recei ed June 4, 2009; Accep ed July 13, 2009; Published Augus 25, 2009
Copy igh : ß2009 F iman e al. This is an open-access a icle dis ibu ed unde he e ms o he C ea i e Commons A ibu ion License, which pe mi s
un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal au ho and sou ce a e c edi ed.
Funding: The s udy was unded by he Academy o Finland (Cen e o Excellence in E olu ion Resea ch and P ojec No. 1106993). The unde s had no ole in
s udy design, da a collec ion and analysis, decision o publish, o p epa a ion o he manusc ip .
Compe ing In e es s: The au ho s ha e decla ed ha no compe ing in e es s exis .
* E-mail: [email p o ec ed]
In oduc ion
The pa hogen i ulence has been adi ionally hough o co-
e ol e in ecip ocal selec ion wi h i s hos o ganism [1]. Howe e ,
in na u e pa hogens and hei hos s a e ypically embedded wi hin
a web o in e ac ions wi h o he species, which could a ec
indi ec ly he e olu ion o pa hogen i ulence and hos immuni y
[2-4]. Fo example, p eda ion could inc ease o dec ease he
p e alence o in ec ious diseases depending on how i a ec s he
equency o in ec ed indi iduals o high-quali y hos s in he
popula ion [2,4]. Mo eo e , ecen indings sugges ha p eda ion
could a ec also di ec ly he pa hogen i ulence (abili y o ha m
hos ) and hos immuni y h ough ade-o s o posi i e gene ic
co ela ions wi h ai s connec ed o an i-p eda o y de ence [5-7].
The e o e, mul i- ophic-le el p eda ion could be impo an
selec i e o ce a ec ing he e olu ion o diseases in na u al
communi ies [2]. Ye , expe imen al s udies whe e he e olu iona y
consequences o p eda ion on bo h pa hogen i ulence and hos
immuni y had been es ed simul aneously a e a e.
P o ozoan p eda ion could inc ease he pa hogen i ulence
because bac e ial de ensi e adap a ions migh also ha e a signi ican
ole in bac e ial pe sis ence and i ulence [6,8]. Fo example,
p o ozoa could be impo an o he en ichmen o po en ially mo e
pa hogenic, bio ilm- o ming Vib io chole ae s ains, which is he
p incipal cause o chole a epidemics [9]. In addi ion, he su i al
and success ul eplica ion o bac e ia inside he p o ozoan cells ha e
p obably ga e ise o se e al acul a i e and obliga e in acellula
pa hogens, such as Lis e ia,Ricke sia,Mycobac e ium,Legionella and
Chlamydia [10] because he amoebae and mac ophages sha e
analogous phagocy ic mechanisms, e.g. p ey ecogni ion by cell
su ace ecep o s [11], p ey killing by oxygen adicals [12] and
simila diges i e enzymes [13].
Al e na i ely, p o ozoan p eda ion could also lead o a dec ease in
bac e ial i ulence i inc eased alloca ion o an i-p eda o y ai s is
aded o wi h i ulence ac o s o he pa hogen. Su p isingly, his
hypo hesis has no been es ed empi ically ye , e en hough p e ious
esea ch sugges s ha alloca ion o ai s connec ed o bo h de ence
and i ulence can be cos ly [14,15]. Fo example, p eda ion by
p o ozoan Te ahymena he mophila has been shown o cause a apid
e olu iona y inc ease in he an i-p eda o de ence o an oppo unis ic
bac e ium pa hogen Se a ia ma cescens [15]. Howe e , p eda ion also
dec eased S. ma cescens’ abili y o use esou ces e icien ly and
dec eased he syn hesis o he ed pigmen p odigiosin [15], which
has been linked o he exp ession o se e al i ulence ac o s in his
pa hogen [16] (Fig. 1). The e o e, p o ozoan p eda ion could lead o
an e olu iona y inc ease o dec ease in bac e ial i ulence depending
on which bac e ial de ensi e ai s a e selec ed o , and how hese
ai s a e co ela ed wi h bac e ial i ulence ac o s.
Simila ly, p eda ion could a ec di ec ly he s eng h o he hos
immune sys em because he esou ces a e o en limi ed and an i-
PLoS ONE | www.plosone.o g 1 Augus 2009 | Volume 4 | Issue 8 | e6761
p eda o y de ence and immuni y incu cos s [5,17-20]. In addi ion,
an i-p eda o y de ences can be aded o wi h ai s a ec ing hos
immuni y [5,21,22]. Fo example, Rigby and Jokela [5] ound ha
high in es men in de ence agains p eda o s inc eased eshwa e
snail’s (Lymnaea s agnalis) suscep ibili y o pa hogens. Thus, inc easing
alloca ion o de ence agains p eda ion could ha e indi ec cos s o
educed hos immunocompe ence [5]. In e es ingly, his kind ade-
o s has been shown o play impo an ole in de e mining he
s uc u e o na u al communi ies [7].
To s udy how selec ion by p eda ion a ec s bac e ial i ulence
and hos immune de ence, h ee di e en s ains o he ubiqui ous
bac e ium S. ma cescens wi h di e en e olu iona y his o ies we e
used o in ec Pa asemia plan aginis A c iid hos mo h la ae om wo
selec ion lines ha di e ed in an i-p eda o y de ence agains a ian
p eda o s. The bac e ial s ains included an ances o S. ma cescens
s ain (ATCC s ain #13880) and wo ances o -de i ed s ains
which had been le o e ol e in he absence (con ol s ain) o in
he p esence (e ol ed s ain) o p o ozoan p eda o , Te ahymena
he mophila, o 14 weeks [15]. All h ee bac e ial s ains consis ed o
a mix u e o andomly isola ed clones (see me hods). Few po en ial
i ulence ac o s o e e y bac e ial s ain we e also measu ed
(mo ili y and di e si y). The hos selec ion lines we e a i icially
selec ed o ha e a small (mo e melanic) o a la ge (less melanic)
o ange pa ch exp essed on an o he wise black body [23]. This
wa ning signal is used o indica e unp o i abili y o bi d p eda o s
and ac s hus as an i-p eda o y de ence [24,25] (Fig. 1). The
bac e ia in he genus Se a ia a e common pa hogens o many
insec s including he Lepidop e a [26] and he e o e hese s udy
species can also po en ially encoun e in he wild. In he in ec ion
expe imen , h ee hos g oups wi hin bo h selec ion lines we e
in ec ed wi h one o he ee bac e ial s ains. In addi ion, s e ilized
wa e was injec ed in o he ou h g oups o la ae o con ol he
physical damage caused by he injec ion i sel . La al su i al was
moni o ed o 72 h om in ec ion h ee imes pe day by sco ing
he la ae as dead o ali e.
On he basis o p e ious expe imen , we hypo hesied ha
p o ozoan p eda ion would lead o dec eased pa hogen i ulence
due o ade-o wi h an i-p eda o y and o he li e-his o y ai s
(e.g. esou ce use abili y, [15]). Simila ly, hos alloca ion o a la ge
wa ning signal, i.e s ong de ence agains a ian p eda o s could
lead o dec eased immune de ence h ough educ ion in he
amoun o la al cu icula melanin (Fig. 1). This is because he
black, melanin-based pigmen is known o co ela e wi h highe
phenoloxidase enzyme ac i i y, which is an impo an pa o he
humo al immune esponse cascade in insec s [27,28].
Resul s
When he la al su i al was analysed o e he hos signal lines,
ances o and con ol S. ma cescens s ains dec eased he la al
su i al compa ed o la ae in ec ed wi h he S. ma cescens s ain
e ol ed in he p esence o p eda o s (ances o s. e ol ed, Chi-
Squa e = 7.32, P,0.007, con ol s. e ol ed, Chi-Squa e = 3.87,
P,0.049 and con ol s. ances o , Chi-Squa e = 1.17, P= 0.279,
Fig. 2a).
The la al su i al did no di e be ween signal lines (Chi-
Squa e = 0.23, P= 0.627). Howe e , he bac e ial s ains had
di e en e ec s on la al su i al when analysed wi hin he la ge
and small signal lines sepa a ely (signal line se as a s a i ied ac o
in he analysis). Wi hin he small wa ning signal line, all he
bac e ial s ains had simila e ec s on la al su i al (all P.0.05,
Fig. 2b). In con as , wi hin he la ge signal line, he la al su i al
was highe wi h con ol and e ol ed s ains, compa ed o he
ances o s ain (con ol s. ances o : Chi-Squa e = 6.47, P= 0.011,
e ol ed s. ances o : Chi-Squa e = 11.47, P= 0.001, Fig. 2c).
The la al su i al was analysed also wi hin di e en bac e ial
ea men s (bac e ial ea men se as s a i ied ac o in he
su i al analysis). When he mos i ulen ances o s ain was used
o in ec ion, he la ae wi h a small wa ning signal had highe
su i al compa ed o la ae wi h a la ge wa ning signal
Figu e 1. The e ec o p eda ion on he e olu ion o hos -pa hogen in e ac ion h ough ade-o s.
doi:10.1371/jou nal.pone.0006761.g001
E olu ion o Vi ulence
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(Chi-Squa e = 4.85, P= 0.028, Fig. 2b and c). Howe e , signal line
had no e ec on la al su i al when con ol (Chi-Squa e = 0.54,
P= 0.459, Fig. 2b and c) o e ol ed s ain was used o in ec ion
(Chi-squa e = 1.033, P= 0.309, and also wi h Cox- eg ession
analysis me hod, Wald s a is ics = 4.76, P= 0.092, Fig. 2b and c).
Damage caused by he injec ion alone was negligible as none o
he la ae died when injec ed wi h s e ilized wa e (Fig. 2a). In
addi ion, alloca ion o a la ge wa ning signal did no dec ease he
encapsula ion esponse o he la ae (small s. la ge signal line,
F
1, 172
= 0.02, P= 0.882).
The mo ili y o con ol and e ol ed bac e ial s ains was
conside ably lowe compa ed o ances o s ain ( - es o
di e ence in bo h cases P,0.001, Fig. 3a). Ye , he mo ili y o
e ol ed bac e ial s ain was lowes ( - es o di e ence be ween
con ol and e ol ed s ain, P= 0.014, Fig. 3a). The equency o
ed pigmen exp essing bac e ial clones was highes wi h he
ances o , in e media e wi h he con ol, and lowes wi h he
e ol ed bac e ial s ain (main e ec o bac e ial s ain,
F
1, 8
= 62.69, P,0.001, in all pai wise compa isons P= 0.002 o
smalle , Fig. 3b). Con e sely, he equency o non-pigmen ed
bac e ial clones was highes wi h he e ol ed, in e media e wi h
he con ol, and lowes wi h he ances o bac e ial s ain (main
e ec o bac e ial s ain, F
1, 8
= 62.69, P,0.001, in all pai wise
compa isons P= 0.005 o smalle , Fig. 3b). The di e si y was
lowes wi h he ances o s ain bu did no di e be ween con ol
and e ol ed s ains (main e ec o bac e ial s ain, F
1, 8
= 50.83,
P,0.001, ances o s. con ol o e ol ed s ain P,0.001, con ol
s. e ol ed s ain, P= 0.11, Fig. 3b).
Discussion
We ound ha inc eased alloca ion o de ence agains p o ozoan
p eda ion dec eased he S. ma cescens’ i ulence (Fig. 2a). The
bac e ial s ains’ e ec on hos su i al depended also on he hos
alloca ion o wa ning signal used o de ence agains a ian
p eda ion: all he bac e ial s ains had simila e ec s on la al
su i al wi hin he small wa ning signal (Fig. 2b), while he la al
su i al was highe wi h con ol and e ol ed s ains compa ed o
he ances o s ain wi hin he la ge signal line (Fig. 2c). This
sugges s ha a pa hogen’s abili y o cause in ec ions does no only
depend on i s own pas e olu iona y his o y, bu is also a ec ed by
he gene ic backg ound o i s hos .
Figu e 2. The su i al o hos la ae in ec ed wi h bac e ial s ains di e ing in hei e olu iona y his o ies. Panel a: su i al (%) o P.
plan aginis mo h la ae when in ec ed wi h ances o (black iangles), con ol (g ey iangles), and e ol ed (whi e iangles) s ains o he bac e ia S.
ma cescens. The s aigh line (black ci cles) deno es he su i al o con ol la ae injec ed wi h s e ilized wa e . Su i al (%) o P. plan aginis mo h
la ae wi hin he small, panel b, and la ge, panel c, wa ning signal lines.
doi:10.1371/jou nal.pone.0006761.g002
Figu e 3. The mean mo ili y (panel a) and di e si y (panel b) o di e en bac e ial s ains. In panel a, ances o e sus con ol s ain
(P= 0.001), ances o e sus e ol ed s ain (P,0.001) and con ol e sus e ol ed s ain (P= 0.014), N = 3 o e e y s ain. In panel b, he mean colony
equencies (ba s) and di e si y (line) o di e en bac e ial s ains de e mined on he basis o he syn hesis o ed pigmen , p odigiosin.
doi:10.1371/jou nal.pone.0006761.g003
E olu ion o Vi ulence
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When he e ec s o bac e ial s ains we e compa ed be ween he
signal lines, and when he mos i ulen ances al s ain was used o
in ec ion, he la ae wi h small wa ning signal had highe su i al
compa ed o la ae wi h la ge wa ning signal (Fig. 2a and b). This
sugges s ha alloca ion o e ec i e de ence agains bi d p eda o s
(i.e. la ge wa ning signal size) can ade o wi h immune de ence
agains pa hogenic bac e ia. Howe e , he signal size had no e ec
on la al su i al when less i ulen con ol o e ol ed s ains we e
used o in ec ion (Fig. 2b and c). Thus, alloca ion o e ec i e
wa ning signal, i.e. mo e e ec i e an i-p eda o y de ence agains
isual p eda o s, migh be less cons ained when he in ading
pa hogen is a he low in i ulence (Fig. 2c).
P o ozoan-d i en e olu iona y dec ease in S. ma cescens’ i u-
lence could be explained by dec eased mo ili y o esou ce use
abili y [15]. Dec eased mo ili y has been shown o be connec ed o
he dec eased i ulence o Campylobac e jejunum in pigle s [29] and
ha o Db1140 S. ma cescens s ain in C. elegans [30]. Mo ili y could
o example a ec he bac e ial abili y o each a ou able habi a s
wi hin he hos [14]. We obse ed ha p o ozoan p eda ion
dec eased he mo ili y o S. ma cescens mos ela i e o he ances o
s ain (Fig. 3a). A dec ease in bac e ial mo ili y, caused p obably
by down- egula ion o lagellum syn hesis o o he ac o s ela ed
o bac e ial mo ili y [31,32], could ha e educed he p eda o
encoun e a e leading o mo e de ensi e bu less i ulen bac e ia
[33,34]. Since he mo ili y o he con ol s ain was lowe ela i e
o he ances o , bu highe ela i e o he e ol ed s ain,
demons a es ha selec ion by labo a o y condi ions could no
alone selec o dec eased i ulence in S. ma cescens (Fig. 3a).
Replica ion o he in ec ion expe imen wi h ano he hos , g ea e
wax mo h (Galle ia mellonella), ga e consis en esul s adding mo e
suppo o iew ha me e labo a o y condi ions can dec ease he
S. ma cescens i ulence bu he exposu e o p o ozoan p eda ion
dec eases he S. ma cescens i ulence mos (F iman & Mikon an a,
unpublished, Figu e S1).
Ano he explana ion o he dec eased i ulence in addi ion o
mo ili y could lie in he p eda o -induced dec ease in p ey
esou ce use abili y [15]; he less i ulen S. ma cescens could
simply be ine icien in ob aining esou ces wi hin he hos , leading
o poo e ep oduc ion, and hus a less ha m ul in ec ion. This
hypo hesis is suppo ed by he ac ha he equency o whi e S.
ma cescens clones ha we e poo a using esou ces [15] was highes
wi h he e ol ed s ain (Fig. 3b).
In addi ion, in ec ion wi h mix u e o clones ins ead o a single
clone can a ec he bac e ial i ulence indi ec ly h ough
compe i i e o co-ope a i e in e ac ions be ween di e en bac e-
ial clones [35,36]. Fo example, i bac e ia a e mainly compe ing
o esou ces wi hin hei hos , pa hogen di e si y is expec ed o
inc ease i ulence h ough e icien esou ce use and as hos
exploi a ion [37]. Howe e , i bac e ia co-ope a e, i.e. use
exoenzymes o ex ac nu ien s, high ela edness (low di e si y)
is expec ed o lead highes esou ce use and hus also highes
i ulence [38]. Ou da a suppo s he o me hypo hesis because
highes i ulence was a ained wi h leas di e se mix u e o clones,
i.e. wi h he ances o s ain (Fig. 3b). In he case o S. ma cescens,
p oduc ion o i on sca enging side opho es could be one possible
o m o co-ope a ion a ec ing also o i s i ulence [39]. Howe e ,
o assess hese po en ial explana ions in mo e de ail, in ec ion
expe imen s based on indi idual clones a e needed o cha ac e ise
he gene ic co ela ions be ween he ai s connec ed o de ence
agains p eda ion and i ulence in S. ma cescens.
We ound ha a small wa ning signal, i.e. mo e melanic
colou a ion o la ae, was posi i ely linked wi h de ence agains
he mos i ulen ances o S. ma cescens s ain (Fig. 2b–c). Howe e ,
he possible cos s o p oducing melanin could ha e coun e balanced
he immunological bene i s o mo e melanic la ae when in ec ed
wi h less pa hogenic bac e ia [24]. P e ious s udies ha e also shown
ha he la ae wi h la ge wa ning signal a e as e a g owing
[40,24] and mos likely explana ion o his is ha hey simply
consume mo e ood. This could also help hem o boos hei
immune sys em because many plan s con ain oxins, which can be
used o example o igh agains pa asi es [41]. The e o e, i is
possible ha la ae wi h la ge wa ning singal we e able o
compensa e hei immune sys em by seques e ing plan oxins
mo e e icien ly a e and du ing he in ec ion ( ood plan , Ta axacum
o icinale, was a ailable h oughou he in ec ion expe imen ).
In gene al, P. plan aginis la ae seemed o alloca e mo e on
de ence agains pa asi oids han pa hogens. The amoun o
cu icula melanin did no a ec he s eng h o he la al
encapsula ion esponse, which is gene ally used o desc ibe he
immunocompe ence o insec s agains na u al pa asi oids
[27,42,43]. Thus, e ec i e de ence agains mac opa asi es could
ha e been impo an o P. plan aginis in i s pas e olu iona y
his o y because alloca ion o an e ec i e wa ning signal dec eased
only i s esis ance agains bac e ial pa hogens. Howe e , mo e
de ailed immunological measu es a e needed o ully unde s and
he linkage be ween insec cu icula melanin and immune de ence
agains pa asi es and bac e ial pa hogens.
Based on p eda o s’ lea ning e iciency, selec ion is assumed o lead
o uni o mi y and conspicuousness in signal exp ession he eby
dec easing he a ia ion in signal size [25,44]. Howe e , a ia ion in
wa ning signal exp ession is common, which sugges s ha he s eng h
and di ec ion o selec ion on signal size could a y spa ially and
empo ally [24]. We p opose ha he obse ed a ia ion in wa ning
signal pa e n o P. plan aginis la ae [24] could be pa ly explained
wi h con as ing selec ion by a ian p eda o s and bac e ial pa hogens
om di e en ophic le els. Thus, la ge wa ning signal size could be
a ou ed when bi ds a e he main cause o la al mo ali y [25] and
he pa hogens a e a he ha mless. Con e sely, when he isk o
bac e ial in ec ion is high (e.g. du ing he win e hibe na ion pe iod),
la ae wi h small wa ning signal, and be e immune de ence could
ha e ad an age. Mos impo an ly, ou expe imen shows ha he
pa hogen success is no only dependen on i s own e olu iona y his o y
bu is also hugely a ec ed by he hos geno ype.
The e is cu en ly conside able knowledge abou he gene ic
p ope ies and mechanisms ha a e essen ial o many pa hogenic
bac e ia o be able o colonise and in ec hei hos s [42,45-47]. A
he same ime, ela i ely li le is known abou he selec i e agen s
and en i onmen al condi ions ha igge ha mless bac e ia o
quickly e ol e in o disease-causing pa hogens [1]. He e we show
ha p o ozoan p eda ion can dec ease he i ulence o oppo u-
nis ic bac e ial pa hogen S. ma cescens. Mo eo e , he hos immune
de ences can e ol e indi ec ly in esponse o o he species
in e ac ions, such as p eda ion, which can u he a ec he
success o pa hogens. These esul s demons a e ha i ulence is a
unc ion o bo h pas e olu iona y his o ies and p esen ecological
in e ac ions o hos s and pa hogens. Thus, in o de o unde s and
he eme gence and dynamics o diseases i could be necessa y o
unde s and how e olu ion a ec s he pa hogen’s abili y o cause
diseases and he hos ’s abili y o esis in ec ions in communi ies
wi h mul iple species in e ac ions. This could be achie ed by
b inging he p inciples o communi y ecology, e olu iona y heo y
and hos -pa hogen epidemiology oge he .
Ma e ials and Me hods
Bac e ial s ains and in ec ion o la ae
The bac e ial clones o e ol ed and con ol s ains we e
o iginally isola ed om wo ea men s used in he p e ious
E olu ion o Vi ulence
PLoS ONE | www.plosone.o g 4 Augus 2009 | Volume 4 | Issue 8 | e6761

expe imen [15] whe e bac e ia we e cul u ed in he absence o
p esence o p o ozoa Te ahymena he mophila (ATCC s ain
#30008) o 14 weeks (app oxima ely 2500 bac e ial gene a ions).
In bo h o hese ea men s, bac e ia we e o iginally he same as
he ances o S. ma cescens s ain ecei ed om he Ame ican Type
Cul u e collec ion (ATCC s ain #13880), which was chosen as
he hi d bac e ial s ain. All bac e ial s ains comp ised a mix u e
o 48 andomly isola ed clones ( ou mic ocosm eplica es we e
used pe bac e ial s ain and 12 clones we e isola ed andomly pe
eplica e). Wi h ances al s ain, all clones we e isola ed om one
aga pla e. The ubiqui ous bac e ia S. ma cescens can be ound in
bo h aqua ic and soil ecosys ems, and ha e an ex emely b oad
hos ange including plan s, nema odes, insec s and mammals
[26,45-47]. Bac e ial s ains we e i s cul i a ed a 25uConNB
aga pla es (con aining 2.5 g o yeas ex ac , 10 g o nu ien b o h
and 15 g o aga in one li e o dH
2
O). A e 48h o g ow h,
bac e ial colonies we e inocula ed in phospha e bu e [15] and
dilu ed o op ical densi ies con aining he same numbe o
bac e ial cells (colony o ming uni s, main e ec o bac e ial
s ain, F
1, 8
= 0.129, P= 0.881). The ea e , he s ains we e
di ided o aliquo s, mixed wi h glyce ol and s o ed a -80uC o
la e use. Be o e in ec ion, aliquo s o all s ains we e hawed o
1 h a 25uC. Fi e ml o well-mixed bac e ial solu ion (app oxi-
ma ely 1.66*10
6
bac e ial cells), o s e ilized wa e o he con ols,
we e injec ed be ween he second and hi d segmen s o la ae
wi h a 10 ml Hamil on sy inge. A o al o 232 la ae we e injec ed
du ing he expe imen : 55 con ol la ae injec ed wi h wa e , 60
la ae wi h he ances o S. ma cescens s ain, 60 la ae wi h e ol ed
S. ma cescens s ain, and 57 la ae wi h con ol S. ma cescens s ain.
In ec ion ook place o e 6 consecu i e days unde cons an
labo a o y condi ions. La al su i al was no a ec ed by he
in ec ion day, F
5, 231
= 0.4, P= 0.847. Be o e in ec ion, all la ae
we e weighed (only la ae be ween 90 and 160 mg we e used) and
assigned o ou g oups (pe signal line) wi h app oxima ely he
same mean weigh o exclude possible condi ion dependen e ec s
(la al weigh be ween he bac e ial ea men s had no e ec on
su i al, F
3, 230
= 0.96, P= 0.412, mean weigh 6S.E. o la ae
in ec ed wi h wa e : 114.3662.37 mg, he ances o s ain:
116.662.27 mg, he e ol ed s ain: 111.5662.21 mg, o wi h
he con ol S. ma cescens s ain: 113.1261.91 mg.). Each bac e ial
ea men g oup consis ed o , on a e age, 58 la ae; 29 wi h a
small and 29 wi h a la ge signal (see below). In ec ion expe imen
was also eplica ed wi h wax mo h la ae (Galle ia mellonella) o
each bac e ial s ain (N = 12) as explained abo e wi h he
excep ion ha he amoun o in ec ed bac e ial cells was
conside ably lowe (app oxima ely 10-30 bac e ial cells). The
injec ion me hod has been c i icized because i bypasses he en y
o mic obes h ough na u al ou es o in ec ion, e.g. o ally [45].
Howe e , bac e ia also access hemocoel di ec ly h ough b each-
ing he cu icle [47] and bo h in ec ion me hods (injec ion o o al
inges ion) ha e been used wi h S. ma cescens o in ec a wide ange
o insec hos s [46,47].
T ai measu emen s o he bac e ial s ains
Bac e ial mo ili y assays we e done by s abbing ace amoun
(2 ml) o each bac e ial s ain on he cen e o semi- luid NB aga
pla es con aining 0.7% o aga wi h s e ile plas ic loops (VWR).
The mo ili y o s ains was de e mined as he a ea (mm
2
) bac e ia
we e able o colonise on he aga pla es in 24h (N = 3 o e e y
s ain). The equencies o ed (p odigiosin pigmen exp essing)
and whi e (non-pigmen ed) bac e ial clones we e coun ed om 3
eplica e pla es o each bac e ial s ain. The bac e ial di e si y
was es ima ed as Shannon di e si y index on he basis o ed and
whi e colony equencies.
Hos selec ion lines di e ing in an i-p eda o y de ence
Selec ion lines on he ex emes o wa ning signal size in P.
plan aginis we e es ablished in 2004. The la ae we e ea ed unde
con olled labo a o y condi ions: empe a u e, ea ing densi y and
ood esou ce (dandelion, Ta axacum sp.) we e kep cons an . Fi y-
one amilies we e used o ob ain selec ion lines o di e gen
pheno ypes ( o la ge and small o ange signals) by applying a
unca ed amily selec ion p o ocol [23]. In o he wo ds,
indi iduals wi h la ge (p opo ion o o ange o e 46% o la ae,
i.e..5 o ange segmen s) and small (p opo ion o o ange less han
31% o la ae, i.e.,5 o ange segmen s) signals we e selec ed and
hen c ossed wi hin he selec ion lines o se e al gene a ions. A e
he 7
h
gene a ion o selec ion, he size o he wa ning signal
(p opo ion o he o ange signal in ela ion o he whole body) was
on a e age 3060.1% wi hin small, and 5260.1% wi hin la ge,
selec ion lines (one-way Ano a, F
1, 230
= 209, P,0.001). Nei he
la al weigh no leng h di e ed be ween selec ion lines con i m-
ing ha signal sizes we e no a esul o di e ences in body size
(one-way ANOVA o weigh and leng h: F
1, 230
= 195, P= 0.659
and F
1, 230
= 0.45, P= 0.502, espec i ely).
Encapsula ion assessmen
Encapsula ion eac ion is a gene al esponse o o eign
in usions in insec s [27,43]. The encapsula ion esponse o all
la ae was measu ed be o e he bac e ial injec ion. La ae we e
anaes he ized wi h CO
2
, a e which a small nylon implan was
inse ed inside he la ae be ween he second and he hi d
segmen s. The immune sys em o he la ae was allowed o eac
o 5 hou s. Subsequen ly, he implan was emo ed, d ied and
pho og aphed unde a mic oscope wi h 106magni ica ion wi h a
Panasonic w -CL702 ideo eco de . The mean g ey alue o he
implan was measu ed wi h ImageP o Plus 4.0 (Media Cybe ne -
ics) on 1 mm o he implan , measu ed om he end implan ed
inside he la a. The g ey alue o he backg ound was sub ac ed
om he g ey alue o he implan o co ec o any a ia ion in
ligh ing du ing pho og aphy. Highe g ey alues (da ke implan )
indica ed a s onge encapsula ion esponse.
S a is ical analysis
Cox- eg ession model was buil o es i he weigh o he la ae
be o e injec ion was a signi ican co a ia e in he model. Due o
high insigni icance (P= 0.638 and coe icien 1.005), he la al
weigh was omi ed om he inal analysis and Kaplan-Meie
su i al analysis and Log- ank s a is ics we e used in analysis. The
main e ec s o bac e ial ea men and signal line we e analysed
i s a e he e ec o bac e ial ea men wi hin he signal line and
he e ec o signal line wi hin he bac e ial ea men s we e
analysed using s a i ica ion. The Righ censo ing me hod was
used o include he la ae ha did no die wi hin 72 hou s in he
analysis. The encapsula ion abili y o la ae was analysed wi h a
one-way ANOVA, and when mul iple g oups we e compa ed, a
wo-way ANOVA was used.
Suppo ing In o ma ion
Figu e S1 The su i al o al e na i e hos , Wax mo h la ae
(Galle ia mellonella), when in ec ed wi h ances o (black iangles),
con ol (g ey iangles), and e ol ed (whi e iangles) s ains o he
bac e ia S. ma cescens. The s aigh line (black ci cles) deno es he
su i al o con ol la ae injec ed wi h s e ilized wa e (ances o s.
con ol o e ol ed s ain, P = 0.032 and p,0.001 espec i ely;
con ol s. e ol ed s ain, P = 0.05, N = 12 o all g oups).
Found a : doi:10.1371/jou nal.pone.0006761.s001 (1.16 MB TIF)
E olu ion o Vi ulence
PLoS ONE | www.plosone.o g 5 Augus 2009 | Volume 4 | Issue 8 | e6761
Acknowledgmen s
We hank E. Ihalainen, H. Rowland, B. Hol , and membe s o Jou nal
Club o Ecology and En i onmen al sec ion o he Uni e si y o Jy a¨skyla¨
o hei help ul commen s on he manusc ip , T. Pehkonen and H.
Hu unen o assis ance in he labo a o y, and K. Viipale o concep ual
help.
Au ho Con ibu ions
Concei ed and designed he expe imen s: VPF CL TH JL JM. Pe o med
he expe imen s: VPF CL TH. Analyzed he da a: VPF. Con ibu ed
eagen s/ma e ials/analysis ools: JL JM. W o e he pape : VPF CL TH JL
JM.
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