Island selection on mammalian life-histories: genetic differentation in offspring size

BioMed Cen al Page 1 o 7 (page numbe no o ci a ion pu poses) BMC E olu iona y Biology Open Access 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 Page 2 o 7 (page numbe no o ci a ion pu poses) 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 BMC E olu iona y Biology 2008, 8:296 h p://www.biomedcen al.com/1471-2148/8/296 Page 3 o 7 (page numbe no o ci a ion pu poses) 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. BMC E olu iona y Biology 2008, 8:296 h p://www.biomedcen al.com/1471-2148/8/296 Page 4 o 7 (page numbe no o ci a ion pu poses) 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 . BMC E olu iona y Biology 2008, 8:296 h p://www.biomedcen al.com/1471-2148/8/296 Page 5 o 7 (page numbe no o ci a ion pu poses) 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] BMC E olu iona y Biology 2008, 8:296 h p://www.biomedcen al.com/1471-2148/8/296 Page 6 o 7 (page numbe no o ci a ion pu poses) 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). Re e ences 1. W igh S: E olu ion o Mendelian popula ions. Gene ics 1931, 16:97-159. 2. F ankham R, Ballou JD, B iscoe DA: In oduc ion o conse a ion gene ics. Camb idge: Camb idge Uni e si y P ess; 2002. 3. Clegg SM, Degnan SM, Mo i z C, Es oup A, Kikkawa J, Owens PF: Mic oe olu ion in island o ms: he oles o d i and di ec- ional selec ion in mo phological di e gence o passe ine bi d. E olu ion 2002, 56:2090-2099. 4. Koskinen MT, Haugen TO, P imme CR: Con empo a y Fishe ian li e-his o y e olu ion in small salmonid popula ion. Na u e 2002, 419:826-830. 5. Cope E: P ima y ac o s o o ganic e olu ion. Chicago: Uni e - si y P ess; 1886. 6. Damu h J: Cope's ule, he island ule and scaling o mamma- lian popula ion densi y. Na u e 1993, 365:748-750. 7. Fos e JB: The e olu ion o mammals in islands. Na u e 1964, 202:234-235. 8. Lomolino MV: Body size o mammals on islands: he island ule e-examined. Ame ican Na u alis 1985, 125:310-316. 9. Adle GH, Le ins R: The island synd ome in oden popula- ions. The Qua e ly Re iew o Biology 1994, 69:473-490. 10. Lomolino MV: Body size e olu ion in insula e eb a es: gen- e ali y o he island ule. Jou nal o Biogeog aphy 2005, 32(10):1683-1699. 11. an Valen L: A new e olu iona y law. E olu iona y Theo y 1973, 1:1-30. 12. Whi ake RJ, Fe nández-Palacios JM: Island Biogeog aphy. Ox o d Uni e si y P ess; 2007. 13. Be y RJ: E olu ion o small mammals. In E olu ion on islands Edi ed by: G an PR. Ox o d: Ox o d Uni e si y P ess; 1998:35-50. 14. Mei i S, Dayan T, Simbe lo D: The gene ali y o he island ule eexamined. Jou nal o Biogeog aphy 2006, 33(9):1571-1577. 15. Mei i S, Coope N, Pu is A: The island ule: made o be b o- ken? P oceedings: Biological Sciences 2008, 275(1631):141-148. 16. Lomolino MV, Sax DF, Riddle BR, B own JH: The island ule and a esea ch agenda o s udying ecogeog aphical pa e ns. Jou - nal o Biogeog aphy 2006, 33(9):1503-1510. 17. Heaney LR: Island A ea and Body Size o Insula Mammals: E idence om he T i-Colo ed Squi el (Callosciu us p e os i) o Sou heas Asia. E olu ion 1978, 32(1):29-44. 18. Dayan T, Simbe lo D: Size pa e ns among compe i o s: eco- logical cha ac e displacemen and cha ac e elease in mammals, wi h special e e ence o island popula ions. Mam- mal Re iew 1998, 28(3):99-124. 19. Mappes T, Koskela E: Gene ic basis o he ade-o be ween o - sp ing numbe and quali y in he bank ole. E olu ion 2004, 58:645-650. 20. Mappes T, Koi ula M, Koskela E, Oksanen TA, Sine o B: F e- quency- and densi y dependen selec ion on ep oduc i e e o s a egies. PLoS ONE 2008, 3:e1687. 21. Me ilä J, C nok ak P: Compa ison o gene ic di e en ia ion a ma ke loci and quan i a i e ai s. Jou nal o E olu iona y Biology 2001, 14:892-903. 22. Ebenha d T: A coloniza ion s a egy in he ield ole (Mic o us ag es is): ep oduc i e ai s and body size. Ecology 1990, 71:1833-1848. 23. Wiggins DA, Mølle AP, Sø ensen MFL, B and LA: Island biogeog- aphy and he ep oduc i e ecology o g ea i s Pa us majo . Oecologia 1998, 115:478-482. 24. Oksanen TA, Koi ula M, Koskela E, Mappes T: The cos o ep o- duc ion induced by body size a bi h and b eeding densi y. E olu ion 2007, 61:2822-2831. 25. Koi ula M, Koskela E, Mappes T, Oksanen TA: Cos s o ep oduc- ion in he wild: manipula ion o ep oduc i e e o in he bank ole. Ecology 2003, 84:398-405. 26. Millien V, Damu h J: Clima e change and size e olu ion in an island oden species: New pe spec i es on he island ule. E olu ion 2004, 58(6):1353-1360. 27. Lawlo TE: Compa a i e biogeog aphy o mammals on islands. Biological Jou nal o he Linnean Socie y 1986, 28(1–2):99-125. 28. Raia P, Mei i S: The island ule in la ge mammals: Paleon ology mee s ecology. E olu ion 2006, 60(8):1731-1742. 29. Mei i S, Dayan T, Simbe lo D: A ea, isola ion and body size e o- lu ion in insula ca ni o es. Ecology Le e s 2005, 8(11):1211-1217. 30. Mel on RH: Body size and island Pe omyscus: a pa e n and a hypo hesis. E ol Theo 1982, 6:113-126. 31. Ebenha d T: High ac i i y in Bank Voles in ela ion o coloni- za ion abili y. Oikos 1987, 49:297-302. 32. Me ilä J, K uuk LEB, Sheldon BC: C yp ic e olu ion in a wild bi d popula ion. Na u e 2001, 412:76-79. 33. Mousseau TA, Ro DA: Na u al selec ion and he he i abili y o i ness componen s. He edi y 1987, 59:181-198. 34. Ro DR: Li e his o y e olu ion. U.S.A.: Sinaue ; 2002. 35. Rose MR: Li e his o y e olu ion wi h an agonis ic pleio opy and o e lapping gene a ions. Theo Popul Biol 1985, 28:342-358. 36. Coulson T, K uuk LEB, Ta ecchia G, Pembe on JM, Clu on-B ock TH: Es ima ing selec ion on neona al ai s in ed dee using elas ici y pa h analysis. E olu ion 2003, 57:2879-2892. 37. Chi y D: Do lemmings commi suicide? Beau i ul hypo heses and ugly ac s. Ox o d Uni P ess; 1996. 38. Fishe RA: The Gene ical Theo y o Na u al Selec ion. Ox o d: Cla endon P ess; 1930. 39. Gus a sson L: Li e ime ep oduc i e success and he i abili y: empi ical suppo o Fishe 's undamen al heo em. Am Na 1986, 128:761-764. 40. S ense h NC: Geog aphic dis ibu ion o Cle h ionomys spe- cies. Annales Zoologici Fennici 1985, 22:215-219. 41. Mappes T, Koskela E, Ylönen H: Rep oduc i e cos s and li e size in he bank ole. P oceedings o Royal Socie y o London, Biological Sciences 1995, 261:19-24. 42. Bond up-Nielsen S, Ka lsson F: Mo emen s and spa ial pa e ns in popula ions o Cle h ionomys species: A e iew. Annales Zoologici Fennici 1985, 22:385-392. 43. Jonsson P, Ha ikainen T, Koskela E, Mappes T: De e minan s o ep oduc i e success in oles: space use in ela ion o ood and li e size manipula ion. E olu iona y Ecology 2002, 16:455-467. 44. Koskela E, Mappes T, Ylönen H: Te i o ial beha iou and ep o- duc i e success o bank ole Cle h ionomys gla eolus emales. Jou nal o Animal Ecology 1997, 66:341-349. 45. Bujalska G: Rep oduc ion s abilizing elemen s in island popu- la ions o Cle h ionomys gla eolus. Ac a The iologica 1970, 15:381-412. 46. Myllymäki A, Paasikallio A, Pankakoski E, Kane o V: Remo al expe imen s on small quad a s as a means o apid assess- men o he abundance o small mammals. Annales Zoologici Fennici 1971, 8:177-185. 47. Koskela E, Jonsson P, Ha ikainen T, Mappes T: Limi a ion o ep oduc i e success by ood a ailabili y and li e size in he bank ole Cle h ionomys gla eolus. P oceedings o he Royal Soci- e y o London, Biological Sciences 1998, 265:1129-1134. 48. Milla JS: Adap i e ea u es o mammalian ep oduc ion. E o- lu ion 1977, 31:370-386. 49. Kleibe M: The i e o li e. New Yo k: John Wiley & Sons Publ; 1961. 50. Gould SJ: On he Scaling o Too h Size in Mammals. Ame Zool 1975, 15(2):353-362. 51. Symonds MRE, Elga MA: Phylogeny a ec s es ima ion o me a- bolic scaling in mammals. E olu ion 2002, 56(11):2330-2333. 52. Whi e CR, Seymou RS: Allome ic scaling o mammalian me abolism. Jou nal o Expe imen al Biology 2005, 208:1611-1619. 53. Glazie DS: E ec s o me abolic le el on he body size scaling o me abolic a e in bi ds and mammals. P oc R Soc B 2008, 275(1641):1405-1410. 54. Oksanen TA, Ala alo RV, Ho ne TJ, Koskela E, Mappes J, Mappes T: Ma e nal e o and male quali y in he bank ole, Cle h ion- omys gla eolus. P oceedings o Royal Socie y o London, Biological Sci- ences 1999, 266:1495-1499. 55. Gockel J, Ha B, Schö e e C, A nold W, Ge lach G, Tau z D: Iso- la ion and cha ac e iza ion o mic osa elli e loci om Apo- Publish wi h BioMed Cen al and e e y scien is can ead you wo k ee o cha ge "BioMed Cen al will be he mos signi ican de elopmen o dissemina ing he esul s o biomedical esea ch in ou li e ime." Si Paul Nu se, Cance Resea ch UK You esea ch pape s will be: a ailable ee o cha ge o he en i e biomedical communi y pee e iewed and published immedia ely upon accep ance ci ed in PubMed and a chi ed on PubMed Cen al you s — you keep he copy igh Submi you manusc ip he e: h p://www.biomedcen al.com/in o/publishing_ad .asp BioMedcen al BMC E olu iona y Biology 2008, 8:296 h p://www.biomedcen al.com/1471-2148/8/296 Page 7 o 7 (page numbe no o ci a ion pu poses) demus la icollis ( oden ia, mu idae) and Cle h ionomys gla eolus ( oden ia, c ice idae). Molecula Ecology 1997, 6:597-599. 56. W igh S: The gene ical s uc u e o popula ions. Annals o Eugenics 1951, 15:323-354. 57. Goude J: Fs a ( e s. 1.2): a compu e p og am o calcula e F-s a is ics. Jou nal o He edi y 1995, 86:485-486. 58. Goude J, Raymond M, De Meeues T, Rousse F: Tes ing di e en- ia ion in diploid popula ions. Gene ics 1996, 144:1933-1940. 59. Robe son A: Expe imen al design in he e alua ion o gene ic pa ame e s. Biome ics 1959, 15:219-226.