F equency and Densi y-Dependen Selec ion on Li e-
His o y S a egies – A Field Expe imen
Tapio Mappes
1
*, Minna Koi ula
2
, Esa Koskela
1
, Tuula A. Oksanen
1
, Tiina Sa olainen
1
, Ba y Sine o
3
1Depa men o Biological and En i onmen al Science, Uni e si y o Jy a
¨skyla
¨, Jy a
¨skyla
¨, Finland, 2MTT Bio echnology and Food Resea ch, Jokioinen, Finland,
3Depa men o Ecology and E olu iona y Biology, Uni e si y o Cali o nia San a C uz, San a C uz, Cali o nia, Uni ed S a es o Ame ica
Abs ac
Nega i e equency-dependence, which a o s a e geno ypes, p omo es he main enance o gene ic a iabili y and is o
in e es as a po en ial explana ion o gene ic di e en ia ion. Densi y-dependen selec ion may also p omo e cyclic changes
in equencies o geno ypes. He e we show e idence o bo h densi y-dependen and nega i e equency-dependen
selec ion on opposi e li e-his o y ac ics (low o high ep oduc i e e o , RE) in he bank ole (Myodes gla eolus). Densi y-
dependen selec ion was e iden among he emales wi h low RE, which we e especially a o ed in low densi ies. Ins ead,
bo h nega i e equency-dependen and densi y-dependen selec ion we e shown in emales wi h high RE, which we e
mos success ul when hey we e a e in high densi ies. Fu he mo e, selec ion a he indi idual le el a ec ed he
equencies o ac ics a he popula ion le el, so ha he equency o he a e high RE ac ic inc eased signi ican ly a high
densi ies. We hypo hesize ha hese wo selec ion mechanisms (densi y- and nega i e equency-dependen selec ion) may
p omo e gene ic a iabili y in cyclic mammal popula ions. Ne e heless, i emains o be de e mined whe he he o igin o
gene ic a iance in li e-his o y ai s is causally ela ed o densi y a ia ion (e.g. popula ion cycles).
Ci a ion: Mappes T, Koi ula M, Koskela E, Oksanen TA, Sa olainen T, e al (2008) F equency and Densi y-Dependen Selec ion on Li e-His o y S a egies – A Field
Expe imen . PLoS ONE 3(2): e1687. doi:10.1371/jou nal.pone.0001687
Edi o : Tom T egenza, Uni e si y o Exe e , Uni ed Kingdom
Recei ed Oc obe 11, 2007; Accep ed Janua y 17, 2008; Published Feb ua y 27, 2008
Copy igh : ß2008 Mappes 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: Financial suppo ed by he Academy o Finland (g an no. 206091, 118603, 109165 o T.M; 100143, 78777, 103148, 115961 o E.K.) and Cen e o
Excellence o E olu iona y Resea ch o he Academy o Finland.
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
A undamen al p oblem in e olu iona y biology is o ind
mechanisms main aining addi i e gene ic a ia ion in na u al
popula ions [1,2]. Acco ding o e olu iona y heo y, selec ion
should educe gene ic a ia ion especially in he ai s ha a e
closely associa ed wi h i ness [1]. Howe e , many species s ill
exhibi la ge gene ic a ia ion in i ness- ela ed li e-his o y ai s
[3–6]. A leas i e selec ion mechanisms a e hypo hesized o
main ain gene ic a ia ion in na u e: mu a ion-selec ion balance,
he e osis, an agonis ic pleio opy, nega i e equency-dependen
selec ion (ad an age o a e geno ype) and en i onmen al
he e ogenei y [2,7]. Many heo e ical analyses ha e ocused on
he la e wo selec ion mechanisms (e.g. ecen ly [8]), and hese
models p edic s ha , o example, nega i e equency-dependen
selec ion can be mo e common in na u al popula ions as
p e iously ecognized. S ill, all empi ical s udies exclusi ely consis
o polymo phic popula ions, whe e gene ic colou mo phs a e
e iden (e.g in plan s, ish and ep iles) [9–11]. In polymo phic
sys ems i has been mo e ob ious o es whe he he i ness o
indi iduals depends on hei neighbou s’ geno ype. Among he
o ganisms wi hou isible polymo phism, bu which s ill ha e la ge
gene ic a ia ion in impo an i ness ai s (e.g. in li e-his o y
ai s), nega i e equency-dependen selec ion (ad an age o a e
geno ype) has no ye ecei ed wide a en ion.
He e we aimed o es empi ically wo selec ion mechanisms:
nega i e equency-dependen selec ion and en i onmen al he -
e ogenei y (densi y-dependen selec ion), which a e p edic ed o
main ain gene ic a ia ion in na u al popula ions [12–18].
Selec ion was s udied in he bank ole (Myodes gla eolus), a small
mammal wi h high pheno ypic and gene ic a ia ion in li e-his o y
ai s, such as ep oduc i e e o , o sp ing size and numbe [19].
Signi ican empo al a ia ion o densi y-dependen selec ion is
p omo ed by la ge seasonal [20] and 3–4 yea cyclic densi y
a ia ion in his species [21]. Fu he mo e, compe i ion be ween
e i o ial bank ole emales is a majo mechanism de e mining
hei b eeding success which, especially a high densi ies, leads o
la ge a ia ion in ela i e i ness o indi iduals [22–24]. Toge he
hese selec i e en i onmen s could acili a e he o igin and
exis ence o opposi e li e-his o y ac ics whose success would
depend bo h on he cu en en i onmen and he equency o
opposi e ac ic in he popula ion. This idea is suppo ed by s udies
wi h side-blo ched liza ds (U a s ansbu iana) and common liza ds
(Lace a i ipa a), whe e nega i e equency-dependen selec ion and
densi y a ia ion ha e been shown o con ibu e o gene ic cycles
d i en by al e na i e li e-his o y s a egies [25–27].
He e we ocused on one cen al li e-his o y ai , ep oduc i e
e o (RE) o emales, and expe imen ally s udied whe he
opposi e ac ics (high s. low RE) would be a o ed by di e en
selec ion p essu es. Bo h he equencies ( a e s. common) and
densi ies (low s. high) o he RE ac ics we e manipula ed in la ge
enclosed popula ions, whe e hei ela i e su i al and b eeding
success we e moni o ed o e he b eeding season. Ou aim was o
expe imen ally es whe he condi ions occu ing in cyclic small
mammal popula ions could acili a e he o igin o opposi e li e-
his o y ac ics which would hen p omo e la ge gene ic a ia ion
obse ed in se e al ai s.
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Resul s
When s udying ju enile ec ui men o he adul popula ion, we
ound ha bo h he numbe o o sp ing weaned and p opo ion o
su i ing o sp ing we e ela ed o he le el o ep oduc i e e o and
he equency and densi y o al e na i e RE ac ics in adul emales
(Th ee-way in e ac ions: F
1,64
=7.16, P= 0.009; F
1,64
=7.82,
P= 0.007, espec i ely). This indica es ha he success o RE ac ics
di e ed acco ding o he equencies and densi ies, and so in u he
analyses RE ac ics we e analyzed sepa a ely (Table 1 and 2).
In pa icula , emales wi h low RE we e a o ed a low densi y
bu RE equency had no signi ican e ec on hei b eeding
success (Fig. 1A, S1, Table 1, ). Females wi h high RE we e mos
success ul when hey we e a e in he popula ion and a high
densi y (Fig. 1B, S1, Table 1). Analyses o selec ion g adien s
suppo hese esul s as hey indica e di ec ional densi y-dependen
selec ion owa ds highe ep oduc i e e o only among a e
ac ics (Fig. 2). So, nega i e equency-dependen selec ion on
highe ep oduc i e e o wo ks e ec i ely in high densi y
popula ions. Toge he , hese indings sugges ha low RE emales
a e success ul only in low popula ion densi ies.
Acco ding o li e-his o y heo y, he success o al e na i e RE
ac ics can also be shaped by he ade-o be ween RE and
ep oduc i e cos s. Indeed, signi ican equency-dependen su i al
cos s we e associa ed wi h high RE ac ics, especially when hey we e
common in he popula ion (Table 2). O no e, he main esul s o he
densi y- and equency-dependen e ec s on b eeding success
(Fig. 1A,B, S1, Table 1) we e no biased by su i al cos s, as he
su i al o emales was no ye a ec ed by RE ac ic o manipula ions
o equencies and densi ies du ing hei i s b eeding (Linea logi
model, G,0.090, P.0.663 o all main e ec s and in e ac ions).
Such su i al cos s we e mani es ed in la e b eeding episodes.
The su i al o mo he s and hei o sp ing we e moni o ed
un il he end o he b eeding season o es ima e he changes in
equencies o RE ac ics a he popula ion le el. F equency o
high RE ac ics inc eased signi ican ly when densi ies we e high
and ini ial equency was low ( a e ac ic) ( = 23.7, d =2,
P= 0.002), and simul aneously he equency o low RE emales
(common and high densi y) dec eased signi ican ly (Fig. 3).
Discussion
Ou esul s indica e clea nega i e equency-dependen and
densi y-dependen selec ion on di e en b eeding ac ics in bank
oles. Females wi h low ep oduc i e e o we e especially a o ed in
low densi ies. Mo eo e , emales wi h high ep oduc i e e o we e
mos success ul when hey we e a e in high densi y popula ions. The
di e en successes o RE ac ics we e con i med by bo h he b eeding
success and su i al o mo he s. When s udying how selec ion a he
indi idual le el a ec ed he equencies o ac ics a he popula ion
le el, we ound ha he equency o he a e high e o ac ic
inc eased signi ican ly in high densi ies (Fig. 3).
Acco ding o hese esul s, we hypo hesize ha a e he c ash o
a ole popula ion, low RE emales ha e he highes b eeding
success un il he popula ion size inc eases, a which ime high RE
emales ob ain a a e ac ic ad an age. Ano he c ucial phase o
he li e his o y occu s du ing and a e he win e c ash phase,
which migh be bene icial o indi iduals wi h low RE. This idea
p edic s ha he equencies o opposi e b eeding ac ics change
acco ding o he seasonal o mul i-annual densi y a ia ions in ole
popula ions.
Nega i e equency-dependen selec ion e iden ly shows com-
pe i ion be ween ac ics [28]; he e i is in aspeci ic compe i ion
be ween he b eeding ac ics. In bank oles, high RE emales
Table 1. The e ec s o equency and densi y on numbe o o sp ing weaned, and p opo ion o o sp ing su i ing un il weaning
in di e en ac ics o ep oduc i e e o .
Low ep oduc i e e o
Numbe o o sp ing weaned P opo ion o o sp ing su i ing
d
1
d
2
FPd
1
d
2
FP
Indi idual le el F equency 1 18.2 0.19 0.669 1 34.0 0.01 0.935
Densi y 1 18.2 7.24 0.015 1 34.0 11.04 0.002
F eq * Den 1 18.2 2.58 0.126 1 34.0 2.13 0.154
Popula ion le el F equency 1 9 0.23 0.642 1 9 0.01 0.919
Densi y 1 9 8.89 0.015 1 9 17.72 0.002
F eq * Den 1 9 3.17 0.109 1 9 3.42 0.098
High ep oduc i e e o
Numbe o o sp ing weaned P opo ion o o sp ing su i ing
d
1
d
2
FPd
1
d
2
FP
Indi idual le el F equency 1 30 2.19 0.149 1 30 4.35 0.046
Densi y 1 30 0.08 0.783 1 30 0.01 0.930
F eq * Den 1 30 4.53 0.042 1 30 6.79 0.014
Popula ion le el F equency 1 9 2.33 0.161 1 9 3.44 0.097
Densi y 1 9 0.82 0.781 1 9 0.01 0.939
F eq * Den 1 9 4.82 0.056 1 9 5.38 0.046
No es: The analyses o gene alized linea mixed models a e pe o med bo h a he indi idual le el (indi idual alues o med he dependen a iables) and a he
popula ion le el (popula ion means o med he dependen a iables). A he indi idual le el, he andom e ec o popula ion (enclosu e) is included in he models
(Es ima e,0.006, P.0.989 in all cases). d
1
= nume a o d , d
2
= denomina o d
doi:10.1371/jou nal.pone.0001687. 001
F equency-Dependen Selec ion
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seems o be dominan o e he low RE emales. As he compe i ion
o space is he mos impo an ac o a ec ing b eeding success o
e i o ial emale bank oles [22,29–31], he high RE emales
migh ha e a g ea e abili y o occupy and de end hei e i o ies
especially agains low RE emales in high densi ies. In small
mammals, e i o iali y unc ions o de end ood esou ces and/o
o sp ing agains in an icide [32,33]. The ask o u u e s udies is o
de e mine he impo ance o hese wo unc ions o he RE ac ics
in di e en densi ies.
In he cu en s udy, emales wi h high ep oduc i e e o ha e
lowe su i al as p edic ed by he heo y o ep oduc i e cos s
[34,35]. These esul s a e consis en wi h hose o ou ea lie
expe imen al s udies, which epo a ade-o be ween ep oduc-
i e e o (li e size) and mo he su i al [20,36]. In e es ingly,
he ep oduc i e cos s o a mo he can be a ec ed by o he
mo he s as well as hei b eeding ac ic in he popula ions. High
su i al cos s o high RE emales a e e iden especially when hey
compe e agains he mo he s wi h he same (common) ac ic
(Table 2). This could be caused by la ge ood equi emen s o
high RE emales. Unde in ense compe i ion hey migh no be
able o alloca e bo h o ep oduc ion and hei own su i al.
The densi y luc ua ion causing i ness di e ences in RE ac ics
can be annual o mul i-annual. I has been hypo hesized ha e en
he popula ion dynamics (e.g. popula ion cycles) in small mammals
a e de e mined by he luc ua ions in geno ypes [37]. This
hypo hesis o in insic egula ion has no ecei ed clea e idence,
and so he dynamics o cyclici y (e.g. popula ion c ashes) a e mo e
e iden ly a ec ed by ex e nal ac o s e.g. p eda o s and/o ood
[38–40] S ill, he ‘‘so ’’ hypo hesis o Chi y, ha gene ic a ia ion
is a consequence and no a cause o popula ion cycles, could be
alid. Howe e , e en a e ex ensi e esea ch, his idea is
suppo ed only by a ew gene ic s udies in cyclic mammals [41,42]
In conclusion, we would like o emphasize ha i emains o be
de e mined whe he he o igin o gene ic a iance in li e-his o y
ai s is causally ela ed o densi y a ia ion (e.g. popula ion cycles).
Ne e heless, ou s udy demons a es ha selec ion on al e na i e
Figu e 1. Numbe o o sp ing weaned o low (a) and high RE
emales (b) in di e en densi ies and equencies. Closed ci cles:
a e ac ic; Open ci cles: common ac ic in he popula ions.
doi:10.1371/jou nal.pone.0001687.g001
Table 2. Su i al di e ences be ween he high and low RE
emales and whe he he ac ic was a e o common in he
popula ion.
Pe cen age (N) o emales su i ing o he end o b eeding season
Tac ic Ra e Common All
Low RE 42.9 (7) 63.0 (27) 58.8 (34)
High RE 66.7 (9) 19.0 (21) 33.3 (30)
Indi idual le el
d
1
d
2
FP
RE ac ic 1 57 0.89 0.348
F equency 1 57 0.75 0.391
Densi y 1 26.7 0.57 0.458
RE ac ic * F equency 1 23.6 6.02 0.022
RE ac ic *Densi y 1 57 0.29 0.595
F equency * Densi y 1 57 1.64 0.206
Popula ion le el
d
1
d
2
FP
RE ac ic 1 15 0.40 0.536
F equency 1 15 0.40 0.536
Densi y 1 15 0.24 0.631
RE ac ic * F equency 1 15 4.79 0.045
RE ac ic *Densi y 1 15 0.09 0.772
F equency * Densi y 1 15 0.94 0.347
No es: The analyses o gene alized linea mixed models a e pe o med bo h a
he indi idual le el (indi idual alues o med he dependen a iable) and
popula ion le el (popula ion means o med he dependen a iable). A he
indi idual le el, he andom e ec o popula ion (enclosu e) is included in he
models (Es ima e = 0.046, P= 0.339). d
1
= nume a o d , d
2
= denomina o d
doi:10.1371/jou nal.pone.0001687. 002
F equency-Dependen Selec ion
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li e-his o y s a egies would a ise om he ac ion o densi y and
equency cycles.
Ma e ials and Me hods
S udy species
The s udy species, he bank ole (Myodes gla eolus), is a small oden
species common in no he n Eu ope [43]. The main habi a s a e
o es s and ields, and he die consis s o o bs, shoo s, seeds, be ies
and ungi [44]. The densi y o b eeding emales is limi ed h ough
hei e i o iali y [29], and in high densi ies he ma u a ion o young
emales is supp essed by social in e ac ion among emales [45]. The
pa e ns and ampli ude o densi y a ia ion show conside able
geog aphical a iabili y, and bo h s able and cyclic popula ions a e
ound [46]. In ou s udy a ea, emales gi e bi h o a maximum o
ou li e s du ing he b eeding season, which las s om la e Ap il o
Sep embe . In addi ion o la ge pheno ypic [20] and gene ic
a ia ion in li e size (2–10) and o sp ing size (1.3–2.5 g), a nega i e
gene ic co ela ion also exis s be ween hese ai s [19]. P egnancy
las s o 19–20 days and pups a e weaned un il he age o h ee weeks
[47]. Bank oles ha e good appabili y, and hey a e no sensi i e o
dis u bance, which allows moni o ing popula ions by li e- apping.
S udy p ocedu es
Expe imen al animals o igina ed om a i icial selec ion lines a
he Uni e si y o Jy a¨skyla¨. Founde animals o he selec ion lines
we e caugh in cen al Finland (62u379N, 26u209E). In he
unca ion selec ion expe imen , wo lines we e selec ed acco ding
o li e size o emales (see de ails Sch ode us e al. 2007,
submi ed manusc ip ). The selec ion expe imen was based on he
be ween amily selec ion p ocedu e [48], which p e en s he
possibili y o inb eeding.
Rep oduc i e e o o emales is de e mined he e by he
o mula o [49]: RE = (li e size * mean o sp ing mass
0.75
)/
mo he s pos -pa um mass
0.75
). In his o mula ene gy equi e-
men s o p oduce o sp ing a e calcula ed ela i e o he allome ic
equi emen o he mo he (assuming s anda d me abolism
inc eases o he 0.75 powe o mass o mammals [50]).
The s udy s a ed by ma ing a ac ion o he emales (n= 91)
ob ained om he selec ion expe imen wi h andomly chosen
males o he same line o emale (low RE: mean6SE = 0.6760.02,
n= 49; High RE: mean6SE = 0.8460.02, n= 42). We u he
inc eased he di e ence be ween he wo g oups by choosing only
he emales wi h lowes RE (n= 39) and highes RE (n= 33) o he
p esen expe imen . All emales we e a he same age and in
simila ep oduc i e s a e. Cha ac e is ic o hese mo he s and
hei o sp ing and s a is ical es s a e p esen ed in he Table 3.
These 72 emales ga e bi h in he labo a o y in ea ly July, and
a e ha he emales wi h hei new-bo n indi idually ma ked
pups we e eleased o 13 la ge ou doo enclosu es (each 0.2 ha)
[47]. None o he mo he s abandoned hei pups du ing he
eleasing p ocess. Fou males we e in oduced o each enclosu e o
keep emales in ep oduc i e condi ion. These males migh ma e
wi h he emales, bu we we e no able o measu e he success o
he possible subsequen b eeding e en s.
In he enclosu es, bo h he densi ies (4 o 8 emales/0.2 ha) and
equencies (1:3 (4 enclosu es); 3:1 (4), 2:6 (2), 6:2 (3)) o di e en
ep oduc i e ac ics (low o high RE) we e manipula ed (see he
design in Table 4). The choice o 4 and 8 emales pe enclosu e o
low and high expe imen al densi ies espec i ely, was based on ou
ea lie s udies showing ha 4–6 emales can gain a e i o y and
b eed simul aneously in he same enclosu e [51].
The b eeding success o all 72 emales was s udied du ing one
b eeding in July. B eeding success was de e mined by moni o ing
he numbe and he p opo ion o o sp ing su i ing o he
weaning age (abou 25 days old). Fo moni o ing indi idual oles,
20 mul i-cap u e li e aps we e dis ibu ed in each enclosu e in a
465 a ay wi h 10 m be ween he ap s a ions. Mo he s and
Figu e 2. Densi y-dependen selec ion o ep oduc i e e o
among a e ac ics. In he analyses o selec ion g adien s, he ela i e
i ness (numbe o o sp ing weaned/mean numbe o o sp ing
weaned in he popula ion) was es ima ed in ela ion o s anda dized
ep oduc i e e o ((RE
i
–RE
mean
)/RE
SD
). Selec ion g adien s indica e
di ec ional selec ion owa ds highe ep oduc i e e o in high
densi ies (closed ci cles and solid line: b6SE = 0.6060.15, P= 0.004)
bu no in low densi ies (open ci cles and dashed line:
b6SE = 20.0860.21, P= 0.726) (S anda dized RE * Densi y in e ac ion:
F
1,14
= 7.34, P= 0.017). The selec ion g adien among common ac ics
was non-signi ican (b6SE = 0.3360.44, P= 0.453) and densi y-indepen-
den (S anda dized RE * Densi y in e ac ion: F
1,50
= 0.02, P= 0.904).
doi:10.1371/jou nal.pone.0001687.g002
Figu e 3. Change in equencies o low and high RE ac ics in he
di e en ea men popula ions du ing he b eeding season.
F equency o high RE ac ics inc eased signi ican ly when densi ies we e
high and ini ial equency was low ( a e ac ic), which simul aneously
dec eased he equency o low RE (common ac ic). Open ci cles: low RE;
Closed ci cle: high RE. N = numbe o eplica es (popula ions).
doi:10.1371/jou nal.pone.0001687.g003
F equency-Dependen Selec ion
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o sp ing we e apped a weaning and a he end o he
expe imen (o sp ing abou h ee mon hs old) (see de ails o
apping p ocedu e [24,52]).
Su i al o only 64 emales was de e mined om he beginning
o he expe imen (ea ly July) o he end o he expe imen (ea ly
Oc obe ), as all he indi iduals in wo enclosu es escaped be o e
he end o he expe imen . The emales escaped a e he i s li e
was weaned, so we we e able o include all emales o he analyses
o he b eeding success (Table 1 and Fig. 1A,B). Only he
success ul enclosu es (see numbe o eplica es in Fig. 3) we e
included in o he analyses o equency changes in he popula ion
le el (see below). No o he indica ions o unsuccess ul eplica es
we e ound du ing he expe imen .
Selec ion o ep oduc i e e o was s udied using he analyses
o selec ion g adien s [48,53]. Selec ion g adien s (b) we e
es ima ed om he linea eg ession coe icien s o ela i e i ness
on he s anda dized ai . He e he ela i e i ness (numbe o
o sp ing weaned/mean numbe o o sp ing weaned in he
popula ion) was es ima ed in ela ion o s anda dized ep oduc i e
e o ((RE
i
–RE
mean
)/RE
SD
).
The su i al o mo he s (Table 2) and hei o sp ing was
moni o ed un il he end o he b eeding season o es ima e he
changes in equencies o RE ac ics a he popula ion le el (Fig. 3).
Change in equency was de e mined by he equency o he
ce ain b eeding ac ic (su i ed mo he s and hei o sp ing) a he
end o b eeding season minus he ini ial equency o he b eeding
ac ic in he enclosu e.
S a is ical analyses
The da a we e analysed using SPSS 14.0 o Windows and SAS
e sion 9.1 so wa e. In he gene alized linea mixed model
analysis (GLMM), he numbe o o sp ing weaned, p opo ion o
o sp ing su i ing o mo he su i al we e explained by RE
ac ic, equency, densi y and hei in e ac ions. The analyses o
GLMM we e pe o med bo h a he indi idual le el (indi idual
alues o med he dependen a iables) and popula ion le el
(popula ion means o med he dependen a iables). A he
indi idual le el, GLMM allows o he popula ion (enclosu e) o
be included as a andom e ec in he models [54].
Suppo ing In o ma ion
Figu e S1
Found a : doi:10.1371/jou nal.pone.0001687.s001 (5.22 MB TIF)
Acknowledgmen s
We hank Johanna Mappes, Suzanne C. Mills, Mikael Mo¨kko¨nen, Tanja
Poikonen and F. S ephen Dobson o aluable commen s.
Au ho Con ibu ions
Concei ed and designed he expe imen s: BS TM MK EK TO. Pe o med
he expe imen s: TM MK EK TO TS. Analyzed he da a: TM.
Con ibu ed eagen s/ma e ials/analysis ools: TM. W o e he pape : TM.
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Sou ce o a iance (
F
1,64
)
Low RE (
n
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ns
1.91
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Li e size 3.8260.14 6.1560.18 76.36 *** 0.10
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ns
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Mean head wid h o o sp ing (mm) 8.2860.05 8.0960.04 6.81 * 0.00
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Pos -pa um head wid h o mo he (g) 13.860.07 13.860.06 0.07
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doi:10.1371/jou nal.pone.0001687. 003
Table 4. The design o he expe imen .
Low densi y Low densi y o al High densi y High densi y o al O e all o al
Ra e Low RE +Common High RE 1+3 (4) 4+12 2+6(2) 4+12
Ra e High RE +Common Low RE 1+3 (4) 4+12 2+6 (3) 6+18
To al (Low Re+High RE) 16+16 = 32 22+18 = 40 32+40 = 72
Numbe o emales pe enclosu e, numbe o enclosu es (in pa en hesis) and o al numbe o indi iduals in each ea men .
doi:10.1371/jou nal.pone.0001687. 004
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