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Resea ch a icle
Island selec ion on mammalian li e-his o ies: gene ic di e en ia ion
in o sp ing size
Tapio Mappes*1, Alessand o G appu o2, Ha i Hakka ainen3, Esa Huh a4,
Esa Koskela5, Raimo Saunanen1 and Pe i Suo sa3
Add ess: 1Cen e o Excellence in E olu iona y Resea ch, Uni e si y o Jy äskylä, P.O. Box 35, FIN-40014 Jy äskylä, Finland, 2Depa men o
Biology, Uni e si y o Pado a, 58/B 35121 Pado a, I aly, 3Sec ion o Ecology, Depa men o Biology, Uni e si y o Tu ku, FIN-20014 Tu ku,
Finland, 4Finnish Fo es Resea ch Ins i u e, Kola i Resea ch S a ion, FIN-95900 Kola i, Finland and 5Depa men o Biological and En i onmen al
Science, P.O. Box 35, FIN-40014 Jy äskylä, Finland
Email: Tapio Mappes* - mappes@by l.jyu. i; Alessand o G appu o - alessand o.g appu [email protected] ; Ha i Hakka ainen - [email p o ec ed];
Esa Huh a - [email p o ec ed]; Esa Koskela - esa[email p o ec ed]; Raimo Saunanen - [email protected]; Pe i Suo sa - pe i.suo sa@u u. i
* Co esponding au ho
Abs ac
Backg ound: Since Da win's pionee ing wo k, e olu iona y changes in isola ed island popula ions
o e eb a es ha e con inued o p o ide he s onges e idence o he heo y o na u al selec ion.
Besides mac o-e olu iona y changes, mic o-e olu iona y changes and he ela i e impo ance o
na u al selec ion s. gene ic d i a e unde in ense in es iga ion. Ou s udy ocuses on he gene ic
di e en ia ion in mo phological and li e-his o y ai s in insula popula ions o a small mammal he
bank ole Myodes gla eolus.
Resul s: Ou esul s do no suppo he ea lie indings o la ge adul size o lowe ep oduc i e
e o in insula popula ions o small mammals. Howe e , he indi iduals li ing on islands p oduced
la ge o sp ing han indi iduals li ing on he mainland. Gene ic di e en ia ion in o sp ing size was
u he con i med by he analyses o quan i a i e gene ics in lab. In insula popula ions, gene ic
di e en ia ion in o sp ing size simul aneously dec eases he addi i e gene ic a ia ion (VA) o ha
ai . Fu he mo e, ou analyses o di e en ia ion in neu al ma ke loci (Fs ) indica e ha VA is less
han expec ed on he basis o gene ic d i alone, and hus, a lowe VA in insula popula ions could
be caused by na u al selec ion.
Conclusion: We belie e ha di e en selec ion p essu es (e.g. highe in aspeci ic compe i ion)
in an insula en i onmen migh a ou la ge o sp ing size in small mammals. Island selec ion o
la ge o sp ing could be he p elimina y mechanism in a p ocess which could e en ually lead o a
smalle li e size and lowe ep oduc i e e o equen ly ound in insula e eb a es.
Backg ound
Popula ion gene ics models [1] emphasise he impo -
ance o di e en s ochas ic p ocesses ela ed o geog aph-
ical isola ion, such as he ounde e ec and gene ic d i ,
on he di e en ia ion o small popula ions. Se e e educ-
ions o gene ic a iabili y and popula ion size a e sug-
ges ed o a ou d i and cons ain na u al selec ion [2].
Howe e , ecen s udies [3,4] ha e shown ha na u al
selec ion could be he dominan di e si ying agen in he
e olu ion o quan i a i e ai s. I espec i e o whe he we
Published: 27 Oc obe 2008
BMC E olu iona y Biology 2008, 8:296 doi:10.1186/1471-2148-8-296
Recei ed: 21 Decembe 2007
Accep ed: 27 Oc obe 2008
This a icle is a ailable om: h p://www.biomedcen al.com/1471-2148/8/296
© 2008 Mappes e al; licensee BioMed Cen al L d.
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 (h p://c ea i ecommons.o g/licenses/by/2.0),
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 wo k is p ope ly ci ed.
BMC E olu iona y Biology 2008, 8:296 h p://www.biomedcen al.com/1471-2148/8/296
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conside na u al selec ion o andom d i as he majo
causa i e agen in e olu ion, oge he hey may allow
popula ions on isola ed islands o e ol e a collec ion o
ai s ha dis inguish hem om hei mainland ela i es.
Di e ences be ween mainland and island popula ions o
mammals ha e o en been e e ed o as he Island ule o
Island Synd ome [5-11]. The mos amilia pa e n on
islands is he e olu ion o la ge -bodied species owa ds a
smalle size and smalle -bodied species owa ds a la ge
size [12]. In small mammals, he pa e n also includes
educed ep oduc i e ou pu , highe su i al a e, and di -
e ences in beha iou (see e iews in [9,13]). Recen ly he
gene ali y o he island ule has been c i icized by Mei i
and colleagues [14,15]. Acco ding o hei phylogene ic
analyses, he inc ease in body size migh only hold ue in
some mammalian g oups (e.g. mu id oden s). They
a gued ha ea lie e iews we e biased by a ew ex eme
examples in some mammalian g oups (e.g. elephan s),
and hese e iews migh ha e igno ed many examples
whe e body size has no changed. Fu he mo e, i has
been sugges ed [15,16] ha u u e s udies should be
ocused mo e clea ly on he possible di e ences in na u al
selec ion caused by island cha ac e s (size and isola ion)
[17], ecological mechanisms (e.g. p eda ion a e and
in e /in aspeci ic compe i ion) [18] and species speci ic
mechanisms (e.g. e olu iona y cons ain s caused by
addi i e gene ic a ia ion).
He e we ocused on he possible gene ic di e en ia ion in
mo phological and li e-his o y ai s be ween insula and
mainland popula ions o a small mammal, he bank ole
Myodes gla eolus. Ou p e ious s udies ha e indica ed a
la ge addi i e gene ic a ia ion in ep oduc i e ai s (e.g
size and numbe o o sp ing) in he mainland popula-
ion o ou s udy species [19]. Fu he mo e, we ha e
shown ha he apid selec ion caused by in aspeci ic
compe i ion can signi ican ly egula e he p opo ion o
gene ic ep oduc i e ac ics (high o low ep oduc i e
e o ) in mainland popula ions [20]. In he p esen s udy,
we es ed he hypo hesis ha he selec ion o ep oduc-
i e ac ics migh di e in an insula en i onmen , causing
gene ic di e en ia ion o insula popula ions om main-
land ones. We also es ed he ela i e impo ance o na u-
al selec ion and andom d i on gene ic di e en ia ion.
In hese analyses i ness- ela ed addi i e gene ic a ia ion
was compa ed o neu al gene ic a ia ion (neu al gene ic
ma ke s) [21].
Resul s
We obse ed nei he mo phological di e en ia ion in he
b eeding emales, no a signi ican di e ence in hei
ep oduc i e e o be ween insula and mainland popu-
la ions o he bank ole. By con as , emales ha o igi-
na ed om he islands p oduced signi ican ly la ge
o sp ing han hose om he mainland (Fig 1, Table 1),
indica ing ei he en i onmen al o gene ic esponses o
mo he s o he insula en i onmen . The size o island o
dis ance o mainland did no a ec he b eeding cha ac-
e s o insula emales (see Addi ional ile 1).
As he pheno ypic di e ences in neona e size do no nec-
essa ily imply mic o-e olu iona y di e en ia ion, he
gene ic basis o o sp ing size was u he analysed in he
labo a o y using pa e nal hal sib analyses. Males o igina -
ing om island popula ions a he ed signi ican ly hea ie
o sp ing a bi h han mainland a he s (Fig 1, Table 2),
when bo h we e ma ed o a common s ock o emales.
Mo eo e , he analyses indica ed signi ican addi i e
gene ic a iance only among he mainland a he s (VA ±
S.E. = 0.047 ± 0.020 and h2 ± S.E = 0.96 ± 0.41), whe eas
gene ic a iance was ze o o e y low among island a he s
(Table 3). He i abili y es ima es di e ed signi ican ly
be ween he mainland and island a he s ( = 3.67, d =
26, P < 0.002) (Table 3).
The ela i e impo ance o na u al selec ion and andom
d i on o sp ing size di e gence can be es ed by compa -
ing among-island di e ences based on addi i e gene ic
a ia ion and measu es based on neu al ma ke genes
(Fs ) [21]. He e he island popula ions we e di e en
acco ding o neu al ma ke s (Fs ± S.E. = 0.177 ± 0.021; P
< 0.001) bu no acco ding o he addi i e gene ic a iance
(VA ≈ 0) (Table 3). This means ha he VA was less han
Island o sp ing we e signi ican ly hea ie han mainland ones in he ield (see s a is ics in Table 1)Figu e 1
Island o sp ing we e signi ican ly hea ie han main-
land ones in he ield (see s a is ics in Table 1). In u -
he lab analyses, males o igina ing om island popula ions
a he ed signi ican ly hea ie o sp ing han mainland a he s
(pa e nal e ec s) (see s a is ics in Table 2). (■, island; 䊐,
mainland).
In he ield Pa e nal e ec s
in he lab
Mean (¢s.e)
body mass o
o sp ing (g)
2.00
1.95
1.90
1.85
1.80
1.75
1.70
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expec ed on he basis o gene ic d i alone. Mainland
popula ions (locali ies) did no di e acco ding o neu al
ma ke s (Fs ± S.E. = 0.008 ± 0.006; n.s.). Fs alues di e ed
signi ican ly be ween mainland and island popula ions (P
= 0.001).
Discussions and conclusion
The p esen esul s a e in ag eemen wi h ea lie sugges-
ions ha o sp ing size migh be he i s li e-his o y cha -
ac e is ic o e ol e in insula popula ions o e eb a es
[22,23]. La ge neona e size can be a local adap a ion o an
insula en i onmen , whe e many ecological selec ion
p essu es, e.g. in a- and in e -speci ic compe i ion and
p eda ion, di e om la ge mainland popula ions [9].
He e we could no di ec ly es he biological signi icance
o la ge o sp ing size (0.11 g di e ence be ween he
island and mainland popula ions), bu acco ding o ou
p e ious esea ch, he inc ease in emale o sp ing size
om 1.74 g o 1.85 g may ha e an impo an impac on
he u u e i ness o bank ole o sp ing [19]. Fo example,
he age o i s b eeding would dec eased by 5 days, calcu-
la ed by a linea eg ession model (y = -46.11x + 181; Fig
1b in [19]), and he p obabili y o b eeding was inc eased
om 0.68 o 0.78, calcula ed by a logis ic eg ession
model (ln(y/1-y) = 4.87x - 7.70; Fig. 2a in [19]).
The b eeding densi y o e i o ial bank ole emales
seems o be lowe in open popula ions (app ox. 10
emales/ha maximum) [24] compa ed o he a i icially
enclosed popula ions (e.g. o e 20 emales/ha) [25]. I
in a-speci ic compe i ion be ween b eeding emales is
simila ly inc eased on (enclosed) islands, i could be an
impo an selec i e o ce o he la ge o sp ing size a
bi h. In gene al, he p ecise mechanisms o selec ion and
when in a-speci ic compe i ion may a ou he i ness o
la ge o sp ing o adul size ha e no ye been es ed in
insula popula ions [18]. The e exis s only indi ec e i-
dence ha compe i ion is lowe on la ge islands, dec eas-
ing selec ion o body size in mammals [17]. He e we did
no ind any e ec o island a ea o isola ion on he meas-
u ed mo phological o li e-his o y ai s. We sugges ha
compa ed o he ea lie s udies, he p esen islands we e
ela i ely small and a ia ion in size migh be oo low o
ind he signi ican e ec s o island cha ac e s. Howe e ,
ou indings a e in ag eemen wi h mos o he ea lie
s udies, which do no suppo he impo ance o island
cha ac e s o he di e en ia ion o insula indi iduals
om hei mainland descendan s [26-30].
The phenomenon o p oduce la ge o sp ing can also be
linked o he gene ic dispe sal ac ics o indi iduals
[22,31]. The indi iduals which a e mo e p one o ake
isks, e.g. by dispe sing o e la ge open ice o islands,
migh also gene ically di e acco ding o many o he
ai s besides o sp ing size. The change in o sp ing size
could hen be a by-p oduc o selec ion on o he ai s.
This possibili y canno be uled ou be o e knowing mo e
abou popula ion gene ics and he beha iou o indi idu-
als (e.g. ex inc ions, dispe sal and mu a ion a es) in ou
island sys em. E en he loss o addi i e gene ic a ia ion
in o sp ing body mass ha we ha e shown he e can be
explained by non-adap i e gene ic p ocesses, e.g. andom
d i . Howe e , ou analyses o di e en ia ion in neu al
ma ke loci (Fs ) indica e ha VA is less han expec ed on
he basis o gene ic d i alone [21]. He e, we we e no able
o analyse addi i e gene ic a iance o a iance in neu al
ma ke s wi hin single islands, as ou es ima es o addi i e
gene ic a iance we e based on a ew indi iduals pe loca-
Table 1: Cha ac e is ics (mean ± SE) o b eeding emales om mainland and island popula ions.
island (n = 51) mainland (n = 33) Fnd , dd p- alue
Body mass o o sp ing (g) 1.85 ± 0.01 1.74 ± 0.02 4.541,23.3 0.044
Li e size 5.0 ± 0.2 5.6 ± 0.3 3.091,82 0.083
Li e mass (g) 9.25 ± 0.37 9.74 ± 0.44 0.8131,80 0.370
Rep oduc i e e o (1) 0.76 ± 0.03 0.81 ± 0.04 1.201,82 0.277
Rep oduc i e e o (2) 0.40 ± 0.02 0.42 ± 0.2 1.201,29.1 0.392
Pos -pa um head wid h o mo he (mm) 13.2 ± 0.1 13.3 ± 0.1 0.401,33.9 0.529
Pos -pa um body mass o mo he (g) 23.2 ± 0.4 23.2 ± 0.4 0.021,32.1 0.896
Only he es s a is ics o o igin a e p esen ed om he mixed model analyses (SPSS 14.0). O igin o mo he was used as a ixed ac o and
popula ion as a andom ac o in he analyses. Mo he was also used as a andom ac o in he analysis o o sp ing body mass. Rep oduc i e e o
(1) = L × Mo0.75/Mm0.75, and Rep oduc i e e o (2) = L × Mo/Mm; whe e L is li e size; Mo is mean pup mass a bi h, and Mm is weigh o he emale
a e deli e y. nd = nume a o deg ees o eedom, dd = denomina o deg ees o eedom.
Table 2: Mixed Model Analyses (SPSS) o di e ences in body
mass o o sp ing a he ed ei he by mainland o island males.
Sou ce nd dd F Wald Z P
O igin o si e 1 6.8 10.488 0.015
Si e 27 48.3 1.828 0.033
Dam (si e) 48 278 14.631 < 0.001
Popula ion 0.240 0.810
O igin o si e, si e and dam (wi hin si e) we e used as ixed ac o s
and popula ion as a andom ac o . nd = nume a o deg ees o
eedom, dd = denomina o deg ees o eedom.
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ion. The e o e, comp ehensi e compa isons o di e en i-
a ion in neu al ma ke loci and addi i e gene ic a ia ion
in quan i a i e ai s a e s ill lacking [21].
In con as o he island popula ions, addi i e gene ic a -
ia ion in o sp ing body mass has been obse ed in main-
land popula ions [[19] and he e]. Addi i e gene ic
a ia ion was also highe han expec ed by he a ia ion in
neu al ma ke s. Simila ly, a la ge addi i e gene ic a ia-
ion has also been show in se e al o he li e-his o y ai s
in di e en sys ems [32-34]. In ag eemen wi h ou ind-
ings, he addi i e gene ic a ia ion is also usually highe
han he a ia ion in neu al ma ke s [21]. Addi i e
gene ic a ia ion in li e-his o y ai s can be main ained
by a ade-o (nega i e gene ic co ela ion) be ween wo
ai s [35], in his case be ween he size and numbe o o -
sp ing [19], especially when na u al selec ion a ou s one
ai unde cu en condi ions and ano he a a la e da e
[36]. S ong annual and mul i-annual densi y luc ua ions
(cyclici y) a e sugges ed o main ain addi i e gene ic a i-
a ion and e en gene ic polymo phism in li e-his o y
ai s, pa icula ly in oden popula ions [37]. In ac , ou
ecen indings wi h he bank ole indica e ha densi y-
and nega i e equency-dependen selec ion a ou he
gene ically di e en alloca ion ac ics be ween he size
and numbe o o sp ing [20].
We supposed ha i densi y luc ua ions and o he ecolog-
ical pa ame e s ela ed o hem a e mo e s able in insula
en i onmen s, selec ion o la ge o sp ing size could also
be s able long e m. Theo e ically, s ong selec ion migh
dec ease addi i e gene ic a ia ion ound in ou islands
[34,38,39]. Mo eo e , selec ion o la ge o sp ing size
migh simul aneously dec ease li e size [19]. A u u e
goal would be o show whe he la ge neona e size is an
adap a ion o insula en i onmen s, and also how gene ic
di e en ia ion in his pa icula ai is ela ed o o he
li e-his o y and beha io al ai s (e.g. li e size, ep oduc-
i e e o , adul size, longe i y, dispe al) as well as hei
e olu ion.
Me hods
S udy species
The bank ole is a common mammal in coni e ous o es s
o no he n Eu ope [40]. The b eeding pe iod in cen al
Finland las s om May o Sep embe [25]. P egnancy las s
o 19–20 days and pups a e weaned un il he age o h ee
weeks [41]. In addi ion o ema kably la ge pheno ypic
[25] and addi i e gene ic a ia ion [19] in li e size (2–
10) and o sp ing size (1.3–2.5 g), a ade-o (i.e. bo h
nega i e pheno ypic and gene ic co ela ions) also exis s
be ween hese ai s [19]. Fu he mo e, a la ge size a
bi h [19,24] and a weaning [41] inc eases he p obabil-
i y o ma u a ion (i.e. b eeding in summe hey a e bo n)
in ju enile emales. Rep oducing bank ole emales a e
e i o ial, while home anges o males and non-b eeding
indi iduals o e lap [42-44]. The densi y o b eeding
emales is limi ed due o hei e i o iali y [45].
Field sample
The s udy was ca ied ou in cen al Finland (62° 37'N,
26° 20'E). The da a a e based on 898 indi iduals caugh
om 37 islands (0.12–70 ha) in lake Konne esi and om
20 mainland locali ies wi hin 5 km o he lake du ing he
summe 1999. P egnan emales we e caugh om 20
islands and all mainland a eas, and hus only hese popu-
la ions we e included in he p esen s udy. The sho es
dis ance be ween neighbou ing s udy islands a ied
be ween 50 o 500 m and he mean dis ance om islands
o he mainland was 631 m (S.E. = 75 m). Dispe sal
be ween islands du ing summe is e y low, indica ed by
a sepa a e s udy du ing he au umn whe e we ecap u ed
106 island indi iduals ( h ee o i e mon hs om he i s
cap u e); none o hese indi iduals le hei home
islands. The mainland apping a eas we e su icien ly a
apa (mean ± S.E = 832 ± 129 m, ange 300 – 2 000 m)
o dec ease dispe sal be ween di e en mainland locali-
ies. We we e no able o es ima e dispe sal a e be ween
mainland locali ies, bu acco ding o ea lie s udies [25],
i should be e y low especially among e i o ial b eeding
emales. The indi iduals we e caugh using Ugglan mul i-
Table 3: Gene ic basis o he bi h mass o o sp ing si ed by a he s om wo di e en o igins.
Sou ce d MS F P VPVA ± S.E. h2 ± S.E.
Mainland
Si e 7 0.298 2.384 0.047 0.049 0.047 ± 0.020* 0.96 ± 0.41*
Dam (si e) 28 0.140 13.010 < 0.001
E o 171 0.011
Island
Si e 5 0.328 1.676 0.186 0.081 0.012 ± 0.012n.s.. 0.14 ± 0.24n.s..
Dam (si e) 19 0.294 16.918 < 0.001
E o 107 0.017
Pheno ypic a iances (VP), addi i e gene ic a iances (VA) and he i abili ies (h2) o body mass we e es ima ed by hal -sib analyses om he a iance
componen s among si es sepa a ely o he di e en en i onmen s. S anda d e o s o VA and h2 we e es ima ed using he o mula in [59]. The
e ec o popula ion (P > 0.39 in bo h o igins) was included o he models as a andom ac o .* P < 0.05, n.s.= non-signi ican .
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ple-cap u e li e- aps. On he smalle islands (< 3.5 ha),
ap lines we e se a c. 20 m in e als (25 aps/ha). On
he la ge islands (> 3.5 ha) and in he mainland locali-
ies, indi iduals we e apped using he small quad a
sampling me hod (modi ied om [46]: each quad a a ea
(side = 15 m) con ained ou ap si es (4 aps/a ea). P e-
bai ed aps we e le open o wo nigh s, a e which hey
we e se and checked o e h ee consecu i e days. T ap-
pings we e ca ied ou om ea ly May o he end o he
b eeding season in Sep embe .
All apped oles we e aken in o he labo a o y whe e
each indi idual was sexed, weighed o he nea es 0.1 g,
and measu ed o maximum head wid h o he nea es 0.1
mm wi h a digi al callipe [47]. Males and non-p egnan
emales we e hen eleased back o he ield. 51 p egnan
emales om 20 islands and 33 p egnan emales om 20
mainland locali ies we e kep in he labo a o y p io o
p oducing a li e [41]. Immedia ely a e bi h, pups we e
weighed wi h an elec onic balance o he nea es 0.01 g,
and wid h o head was measu ed using a s e eomic o-
scope. The mo he s we e eleased wi h hei pups a hei
poin o cap u e [41]. The p opo ion o b eeding emales
did no di e be ween he islands (21.2%, n = 241) and
mainland (26.8%, n = 123)(G = 1.45, d = 1, P = 0.229).
The ep oduc i e e o o emales was es ima ed using
wo o mulas. Fi s , we used he o mula:RE(1) = L ×
Mo0.75/Mm0.75, whe e L is li e size; Mo is pup mass a bi h,
and Mm is weigh o he emale a e deli e y [22,48]. In
his o mula, ene gy equi emen s o p oduce o sp ing is
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) [48-51]. The mo he s
we e eleased wi h hei pups a hei poin o cap u e
[41]. Since he heo e ical and empi ical basis o 0.75 scal-
ing is s ill unde deba e in he li e a u e o animal me ab-
olism (see e.g. [52,53]), we also used a mo e simple
o mula: RE(2) = L × Mo/Mm, whe e li e mass was
di ided by mo he body mass.
Analyses o quan i a i e gene ics and neu al ma ke s
The gene ic basis o o sp ing cha ac e is ics was analyzed
in he labo a o y. In he analyses, we compa ed he e ec
o male o igin (island/mainland) on he cha ac e is ic o
hei o sp ing. Bank ole males do no ea hei o sp ing
and male quali y does no a ec he amoun o ma e nal
ca e [54], hence we can assume ha he gene ic analyses
a e no biased by co a iances be ween non-gene ic ma e -
nal e ec s and gene ic pa e nal e ec s.
We ma ed a andom sample o males om he mainland
and island popula ions wi h wo o h ee andomly cho-
sen emales ha o igina ed om a sepa a e lab colony
(Fig. 1, Table 2). The emales ma ed wi h he island males
did no di e om he emales ma ed wi h mainland
males (head wid h: ( = 0.255, d = 73, P = 0.800; body
mass: = 1.651, d = 73, P = 0.103). Body mass and head
wid h o he males ha o igina ed om islands did no
di e om he males ha o igina ed om he mainland
(Mixed model analyses (SPSS);o igin ixed and popula-
ion andom ac o ; head wid h: F1,15.7 = 1.21, P = 0.287;
body mass: F1,10.9 = 1.13, P = 0.311). To ob ain an es i-
ma e o he i abili y (h2) and addi i e gene ic a iance
(VA) o he body mass o o sp ing in he mainland and
island popula ions, we pe o med s anda d hal -sib anal-
yses (Table 3). The analyses included 16 si es, 44 dams
and 216 p ogeny om mainland popula ions and 12
si es, 31 dams and 140 p ogeny om island popula ions.
We we e only able o include one o h ee males pe island
o mainland loca ion o he analyses, so ou es ima es o
gene ic a iance indica e he a iance among he whole
island sys em, no a iance wi hin single islands.
Indi iduals we e geno yped wi h six mic osa elli e loci,
which a e highly a iable in he bank ole [55]. To ob ain
compa able analyses, we used ma u e males om he
same islands (62 males om 9 islands) and mainland
locali ies (75 males om 10 a eas) as we used in he anal-
yses o quan i a i e gene ics. An es ima e o popula ion
s uc u e was ob ained using Fs [56], calcula ed using
FSTAT e 2.9.3 [57]. S anda d e o was ob ained wi h
Jackni ing o e loci. The signi icance o popula ion di e -
en ia ion was es ed by log-likelihood G-s a is ics and he
es was based on 1000 andomiza ion o geno ypes
wi hin samples [58].
Au ho s' con ibu ions
TM, HH, EH, EK, RS and PS planned he s udy and pe -
o med he ield appings. TM pe o med he analyses o
quan i a i e gene ics. AG was esponsible o he analyses
o molecula gene ics.
Addi ional ma e ial
Acknowledgemen s
We a e g a e ul o Leena Linds öm, Johanna Mappes, Juha Me ilä, Mikael
Mökkönen, Suzanne C. Mills, Tuula A. Oksanen and Tanja Poikonen o
cons uc i e commen s on he manusc ip , and Rii a Ahonen and Taba ha
Addi ional ile 1
Mixed Model Analyses (SPSS) o he e ec s o island size and island
dis ance o mainland on he b eeding cha ac e s o insula emales.
Size o island and dis ance o mainland we e used as ixed ac o s (co a i-
a es) and popula ion as a andom ac o in he analyses. nd = nume a o
deg ees o eedom, dd = denomina o deg ees o eedom.
Click he e o ile
[h p://www.biomedcen al.com/con en /supplemen a y/1471-
2148-8-296-S1.doc]

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Lamon h o hei ield assis ance. The s udy was inancially suppo ed by
he Academy o Finland (g an no. 118603, 109165, 204284 o T.M; 78794
o HH; 115961, 119200 o EK) and he Tu ku Uni e si y Founda ion o PS,
and Finnish Biological Socie y "Vanamo" and Socie as p o Fauna e Flo a
Fennica o RS and Cen e o Excellence in E olu iona y Resea ch 2006–
2011 (Academy o Finland).
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