Extrapair paternity and maternity in the three-toed woodpecker, Picoides tridactylus : insights from microsatellite-based parentage analysis

Ex apai Pa e ni y and Ma e ni y in he Th ee-Toed Woodpecke , Picoides idac ylus : Insigh s om Mic osa elli e-Based Pa en age Analysis Meng-Hua Li 1 *, Kaisa Va ¨lima ¨ki 1 , Ma kus Piha 2 , Timo Pakkala 2 , Juha Me ila ¨ 1 1Ecological Gene ics Resea ch Uni , Depa men o Biological and En i onmen al Sciences, Uni e si y o Helsinki, Helsinki, Finland, 2Finnish Museum o Na u al His o y, Uni e si y o Helsinki, Helsinki, Finland Abs ac Molecula echniques ha e e ealed ha a ian ma ing sys ems a e mo e di e se and complex han p e iously hough . We used mic osa elli e ma ke s o de e mine gene ic pa en age, he p e alence o ex apai pa e ni y and quasi-pa asi ism (i.e. si ua ions whe e a male’s ex apai ma e lay in his nes ) in a socially monogamous popula ion o h ee- oed woodpecke s (Picoides idac ylus) in sou he n Finland. A o al o 129 adul s and nes lings, ep esen ing 5–9 amilies annually om 2004– 2007, we e geno yped a up o en mic osa elli e loci. The esul s o gene ic assignmen es s con i med ha monogamous pa en age cha ac e ized he majo i y (84.6%, 22/26) o b oods, and ha mos (93.8%, 75/80) nes lings we e he o sp ing o hei social pa en s. Two o 80 nes lings (2.5%) in wo o 26 b oods (7.7%) we e si ed by ex apai males and quasi-pa asi ism occu ed in 3.8% (3/80) o nes lings and 7.7% (2/26) o b oods. Hence, he le els o ex apai pa en age we e low, possibly because bo h gene ic polygyny and polyand y a e cons ained by he high pa e nal e o equi ed o pa en al ca e. The co-occu ence o low le els o ex apai pa e ni y and quasi-pa asi ism a e discussed in ligh o ecological and beha iou al ac o s cha ac e izing he species biology. Ci a ion: Li M-H, Va ¨lima ¨ki K, Piha M, Pakkala T, Me ila ¨J (2009) Ex apai Pa e ni y and Ma e ni y in he Th ee-Toed Woodpecke , Picoides idac ylus: Insigh s om Mic osa elli e-Based Pa en age Analysis. PLoS ONE 4(11): e7895. doi:10.1371/jou nal.pone.0007895 Edi o : Tom Pizza i, Uni e si y o Ox o d, Uni ed Kingdom Recei ed Sep embe 25, 2009; Accep ed Oc obe 23, 2009; Published No embe 18, 2009 Copy igh : ß2009 Li 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: This wo k was suppo ed by he g an (No.118673) om he Uni e si y o Helsinki (h p://www.helsinki. i/uni e si y). 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: menghua.li@helsinki. i In oduc ion Ex a-pai e iliza ions, which can esul om emales engaging in copula ions wi h ex a-pai males (ex apai pa e ni y; EPP), o om males copula ing wi h ex a-pai emales ha lay eggs in he male’s nes (ex a-pai ma e ni y; EPM o quasi-pa asi ism, QP) [1], is known om app oxima ely 90% o he a ian species (see [2]). EPPs a e known o be common in passe ines and less so in non-passe ines [3]. Despi e i s ubiqui y ac oss a ian species, he p e alence o EPP a ies conside ably wi hin and among species (see [2]). In con as o EPP, QP is a e and has been desc ibed in only a ew bi d species. Howe e , a close examina ion o hese s udies e ealed ha unequi ocal e idence o QP is slim due o possibili y o apid ma e-swi ching and/o insu icien molecula wo k [4]. Hence, i emains unclea whe he QP is gene ally a e, o whe he i s appa en sca ci y e lec s he di icul y o iden i ying i when occu ing. Gene ic pa en age s udies ha e been conduc ed only in ou ou o mo e han 200 woodpecke species (see [5]). One o hese is he h ee- oed woodpecke (Picoides idac ylus) which is ypically socially monogamous [6], al hough occasional cases o simul aneous social polyand y ha e been eco ded [5], [7]. Howe e , mo e accu a e pa en age analysis ools o he h ee- oed woodpecke s would be needed o add ess ques ions ela ing o he gene ic bene i s o ma e choice, inb eeding a oidance and he ac ual b eeding sys em in his species (c . [8]). Likewise, addi ional da a om non-passe ine bi ds will be also use ul in unde s anding he e olu iona y signi icance and li e-his o y co ela es o p omiscui y in bi ds. In compa ison wi h he mul ilocus DNA inge p in ing analyses p e iously conduc ed in h ee- oed woodpecke s [5], applica ion o high- esolu ion mic o- sa elli es would ep esen a mo e e icien and s aigh o wa d echnique o pa en age assignmen and kinship analyses [9]. The main pu pose o he p esen s udy was o es ima e he p e alence o EPP and QP in he h ee- oed woodpecke . Since he males o his species alloca e signi ican ly mo e ime o e i o y de ence, ca i y exca a ion and eeding o he young han emales [5], we p edic ed ha his should esul in low equency o EPP and possible occu ence o QP. The s udy was conduc ed in a popula ion b eeding in sou he n Finland, which has been s udied since he la e 1980s and has been a subjec o a i e-yea (2003–2007) in ensi e popula ion s udy (e.g. [10], [11]). To his end, we applied a se o 10 polymo phic mic osa elli e loci de eloped o he species [12]. In addi ion, gi en he s a is ical limi a ions acing mos pa en age s udies (e.g. [13]), we u he applied an app oach which was implemen ed in p og am CERVUS and has been p o en o be wi h high con idence in pa en age assignmen in an open ma ing sys em [14]. Me hods E hics S a emen The me hods we e app o ed by he ins i u ion ha coo dina es inging ac i i y in Finland (Finnish Museum o Na u al His o y), based on he egula ion by he Minis y o he En i onmen (No. 17/5713/2002). PLoS ONE | www.plosone.o g 1 No embe 2009 | Volume 4 | Issue 11 | e7895 S udy Species The h ee- oed woodpecke (Picoides idac ylus) is a ca i y nes ing habi a specialis inhabi ing coni e ous aiga o es s in he no h, and high ele a ion alpine coni e ous o es a he sou he n edge o he bo eal zone [5]. They exhibi nes -si e ideli y o e yea s [7], ma e gua ding [15], long du a ion o ca i y exca a ion, bi- pa en al ca e, and in pa icula , a e y high deg ee o pa e nal ca e due o exclusi e incuba ion/b ooding a nigh by he males [5]. The a e age b eeding densi y a ies a lo depending on he incidence o i e acciden s [16] and he quali y o o es landscape, habi a s and spa ial scale conside ed, and has been es ima ed o a y be ween 0.1 and 1.5 e i o ies/km 2 in an in ensi e s udied a ea o 150 km 2 in sou he n Finland [10], [11]. S udy Si e and Popula ion The s udy was conduc ed in he E o a ea (ca.61u119N, 25u069E) in sou he n Finland in an a ea o 150 km 2 . The s udy a ea has been desc ibed in mo e de ail in [10], [11]. The e i o y numbe s and nes si es o he h ee- oed woodpecke popula ion inhabi ing he E o a ea ha e been s udied since 1987 [11]. An in ensi e s udy on b eeding biology, including indi idual ma king o bi ds wi h colou ings, was s a ed in 2004. Du ing yea s 2004–2007 e i o ies and nes s we e sea ched in he s udy a ea by using me hods desc ibed in [11]. Ten o 25 nes s wi h nes lings we e ound annually. Fo each nes possible, he adul s we e apped and nes lings we e pulled ou om he nes ca i ies wi h a special ool (so ongs) ha is in gene al use in he woodpecke inging p ojec s in Finland. The adul s we e apped using mis ne s o a ne designed o ca ching bi ds coming ou om he nes ca i y. Each bi d was agged wi h an indi idual combina ion o colou ings, measu ed, aged, sexed (adul s only) using he mo phological c i e ia gi en in [6], and body ea he samples we e collec ed om he bi ds. Two o i e ea he s we e plucked wi h a pai o weeze s om he en al body ea he ac s in case any ea he s did no all away du ing he handling o he bi ds. No ad e se e ec s on bi ds we e obse ed du ing o a e he ca ching, inging, measu ing and ea he emo al. Finally he nes lings we e pu back in he nes and adul s we e eleased. Due o cha ac e is ics o ees, ca i ies o si es, all ound nes s could no be sampled comple ely. In addi ion, some nes s we e ound oo la e in he cou se o he b eeding season he e o e pulling he la ge nes lings ou om he ca i y was no longe sa e o he indi iduals. Al oge he 26 nes s we e sampled adequa ely o u he analyses. DNA Ex ac ion, Molecula Sexing and Mic osa elli e Geno yping Genomic DNA was isola ed om he body ea he sha s using he Chelex-based ex ac ion p o ocol (Bio-Rad, Helsinki, Finland) ollowing he manu ac u e ’s ins uc ions. The sex o all samples was iden i ied ollowing a simple and uni e sal me hod o molecula sexing o non- a i e bi ds using PCR ampli ica ion o he CHD1 gene as de ailed in [17]. In hose cases whe e bi ds we e sexed on he basis o c own ea he colo a ion (e.g. [6]) in he ield, he esul s o ield and molecula sex iden i ica ion me hods ma ched each o he pe ec ly. A o al o 10 polymo phic mic osa elli es de eloped o he h ee- oed woodpecke [12] we e included in his in es iga ion (Table 1). The PCR geno yping p o ocols a e a ailable om [12]. All geno ypes we e double checked independen ly by wo pe sons. Mic osa elli e Va ia ion De ia ions om Ha dy-Weinbe g equilib ium (HWE) o each locus and om linkage equilib ium be ween all pai s o loci we e es ed wi h Fishe ’s exac es s based on he app oach o [18] using GENEPOP e sion 3.4 [19] wi h 100 000 s eps in he Ma ko chain (100 ba ches wi h 1000 i e a ions). Basic di e si y indices, including he numbe o alleles, obse ed he e ozygosi y, Nei’s [20] unbiased es ima es o expec ed he e ozygosi y, wi hin- popula ion inb eeding coe icien (F IS ; [21]), and equency o null alleles we e es ima ed a each locus as well as o e all loci using GENEPOP. S anda d exclusion p obabili ies o each locus and o he selec ed loci combined (Table 1) we e es ima ed wi h he p og am CERVUS 3.0 [14]. The dis ibu ion o geno ypes a he en loci con o med o he expec a ion o HWE and all he locus pai s we e in linkage equilib ium (Table 1; P.0.05; da a no shown o he esul s o es s o linkage disequilib ium). The cumula i e exclusion p obabili ies o he se o loci used in he pa en age analysis we e high: 0.9935 o he i s pa en and 0.9998 o he second pa en (assuming he i s pa en was assigned co ec ly; Table 1). Pa en age Analysis We i s checked misma ch dis ibu ions be ween he pu a i e pa en s and he nes lings. The ac ha mos o sp ing ma ched he pu a i e mo he o a he exac ly, o misma ched a a single locus, s ongly sugges s ha mos o he pu a i e pa en s we e ue gene ic pa en s. O he cases whe e misma ches occu ed, i e misma ched by mo e han one epea a wo o mo e loci (Figu e 1). The pa en age analysis o gene ic da a om he ield-collec ed samples was u he pe o med using he compu e so wa e CERVUS e sion 3.0 [14]. By using a likelihood-based app oach desc ibed in [14], CERVUS calcula es pa en age in e ence likelihood a ios and gene a es a s a is ic, DLOD, de ined as he di e ence in posi i e log likelihood a ios (LOD) be ween he op wo candida e pa en s. A o al o 10,000 es s, which is hough o be su icien in mos cases [14], we e used he e. We de ine ‘candida e pa en s’ as adul s o he popula ion in a speci ic yea . Bo h male and emale h ee- oed woodpecke s we e assumed o be capable o p oducing o sp ing in hei second calenda yea (one yea old) and, Table 1. Summa y s a is ics o he 10 mic osa elli e loci used in his s udy. Locus nN A H O H E F IS F Null P (Ex1 ) P ( Ex2 ) P H-W P i13 129 11 0.767 0.768 0.001 20.002 0.372 0.549 0.1761 P i17 126 11 0.817 0.845 0.033 0.027 0.525 0.692 0.5625 P i20 129 3 0.101 0.097 20.036 20.016 0.005 0.049 1 P i22 129 11 0.829 0.806 20.029 20.013 0.448 0.623 0.2304 P i23 123 7 0.715 0.662 20.081 20.045 0.264 0.448 0.1574 P i24 129 7 0.69 0.655 20.054 0.028 0.232 0.392 0.2489 P i30 127 15 0.827 0.864 0.044 0.020 0.57 0.728 0.0346 P i31 125 6 0.864 0.8 20.081 20.044 0.422 0.6 0.4087 P i36 129 11 0.783 0.844 0.073 0.036 0.519 0.687 0.1451 P i38 127 9 0.732 0.782 0.064 0.032 0.426 0.609 0.0493 O e all 127.3 8.7 0.713 0.712 0.0001 – 0.9935 0.9998 – Numbe o bi ds sc eened (n), numbe o alleles (N A ), obse ed he e ozygosi y (H O ), expec ed he e ozygosi y (H E ), Wei and Cocke ham’s (1984) wi hin- popula ion inb eeding coe icien (F IS ), equency o null alleles (F Null ), exclusion p obabili y o he locus o he i s pa en (P Ex1 ), exclusion p obabili y o he locus o he second pa en wi h he i s assigned (P Ex2 ), and he exac p obabili y o de ia ion om Ha dy-Weinbe g equilib ium (P H–W ). doi:10.1371/jou nal.pone.0007895. 001 Ma ing Sys em o a Woodpecke PLoS ONE | www.plosone.o g 2 No embe 2009 | Volume 4 | Issue 11 | e7895 he e o e, su i ing males o emales om ea lie coho s we e included as candida e pa en s o o sp ing bo n in la e yea s. The numbe o candida e emales was 10, 21, 34, and 42 and he numbe o candida e males was 13, 32, 48, and 59 o he 2004– 2007 coho s, espec i ely. The sampling o pa en s in he s udy a ea was no exhaus i e, and i was es ima ed ha ca. 25–40% o he adul s we e sampled depending on he yea (M. Piha, pe sonal obse a ion). Thus, a sampling a e o 25% was used o he 2004 coho and 40% o he 2005–2007coho s. The p opo ion o success ully geno yped loci was on a e age 98.5% as es ima ed om he gene ic da a (see esul s). A yping e o a e o 1.2% was inco po a ed in o he simula ion o ma e ni y and pa e ni y assignmen s. Assignmen s we e ca ied ou a a elaxed le el o 80% and a s ic le el o 95%. We assigned pa en age unde wo scena ios o s eps. (i) Fo comple e amilies in which bo h pu a i e pa en s we e sampled (N= 46 nes lings in 14 b oods), we i s assigned ma e ni y wi h unknown pa e ni y using he p og am CERVUS. Once a emale was assigned, we hen a emp ed o assign pa e ni y o ei he he pu a i e a he o a po en ial b eeding male om he popula ion wi h known ma e ni y; o he wise, pa e ni y assignmen s we e implemen ed wi h unknown ma e ni y. We included he pu a i e pa en s when possible and all po en ial emales/males in he popula ion as possible candida es o ma e ni y/pa e ni y. (ii) Fo amilies which he e was sample a ailable o only he pu a i e a he (N= 34 nes lings in 12 b oods) we again a emp ed o assign pa e ni y using CERVUS wi h unknown ma e ni y. The e we e no cases whe e a DNA sample was a ailable o jus he pu a i e mo he . The dis ibu ion o he LOD sco es o assigned and excluded pa en s is shown in Figu e 2. The LOD sco es o unequi ocal wi hin-pai o sp ing (i.e. assigned o pu a i e pa en s) assigned on he basis o ma ching eigh o mo e loci a e all posi i e and he majo i y o hem a e g ea e han h ee (Figu e 2a,b), bu his is no ue o he i e ex apai o sp ing assigned wi h ex apai pa en age (Figu e 2c). The Dc i e ion calcula ed o assignmen o pa en age was be ween 1.44 and 5.14 in di e en yea s o 95% con idence, and be ween 0 and 2.94 o 80% con idence whe e one pa en was known (Table 2). Resul s Ac oss he yea s, we assigned 56.5% (26/46) o o sp ing o he pu a i e mo he wi h a high deg ee o con idence (P.95%) in he 14 comple e amilies. Mo eo e , he pu a i e mo he s we e con i med as he gene ic mo he s o o sp ing o he as majo i y o cases (93.5%, 43/46) wi h .80% con idence (Table 3). O he 14 b oods, 12 wi h wo o mo e chicks, all o sp ing we e assigned o he same pu a i e mo he . O he h ee unassigned nes lings, ma e ni y o one could no be assigned wi h .80% con idence and i was om a b ood o ou nes lings. Since he a he o he ma e nally unassigned nes ling was con i med in he la e pa e ni y analysis, addi ional ma e ni y analysis wi h known a he did no assign i any gene ic mo he wi h .80% con idence ei he . In bo h analyses wi h unknown and known a he s, he nes ling could no be assigned o any ma e ni y, nei he he pu a i e mo he , no o any o he candida e adul emales in he popula ion. The pu a i e mo he / o sp ing pai , iden i ied as ha ing mo e han wo geno ype misma ches, we e cha ac e ized by nega i e LOD sco es. Thus, he ma e ni y o he nes ling could no be esol ed and he ue gene ic mo he s we e unlikely o ha e been sampled as all candida e emales we e excluded a leas on basis o misma ches in Figu e 2. LOD sco e dis ibu ions om CERVUS analyses o pa en age in h ee- oed woodpecke s. (a) LOD sco e o he candida e males ha ha e been unequi ocally assigned as a he s (&) and o candida e males ha we e he second mos likely candida e excluded (%)(N= 80); (b) LOD sco e o he candida e emales ha ha e been unequi ocally assigned as mo he s (&) and o candida e emales ha we e he second mos likely candida e excluded (%) (N= 46); (c) LOD sco e o pai male wi h o sp ing assigned o ex apai a he (&) and pai emale wi h o sp ing assigned o ex apai mo he (%)(N= 5). doi:10.1371/jou nal.pone.0007895.g002 Figu e 1. His og am showing he equency dis ibu ion o misma ches be ween each h ee- oed woodpecke nes ling and i s pu a i e a he (&) and mo he (%). doi:10.1371/jou nal.pone.0007895.g001 Ma ing Sys em o a Woodpecke PLoS ONE | www.plosone.o g 3 No embe 2009 | Volume 4 | Issue 11 | e7895 wo loci. These esul s also do no exclude he possibili y ha he o sp ing may ha e esul ed om ex apai e iliza ion. Nex , we a emp ed o assign pa e ni y o he 46 o sp ing om 14 comple e amilies including he o sp ing wi h unassigned ma e ni y. In he assignmen analyses, he pu a i e a he was no success ully assigned o wo o 46 o sp ing in wo o 12 b oods, while he emaining o sp ing could be assigned o a candida e male wi h .95% con idence (Table 3). Fo he 12 amilies (34 Table 2. C i ical DLOD sco es and ac ual and p edic ed success a e o en mic osa elli e loci used o assign pa en age. Ma e ni y assignmen Pa e ni y assignmen 95% con idence 80% con idence 95% con idence 80% con idence Yea DLOD Ra e DLOD Ra e DLOD Ra e DLOD Ra e 2004 1.79 55 (60) 0 100 (100) 1.53 89 (95) 0 100 (100) 2005 1.44 67 (75) 0 100 (100) 1.92 88 (94) 0 100 (100) 2006 2.01 57 (67) 0 100 (100) 2.66 87 (94) 0 100 (100) 2007 2.33 49 (53) 0 75 (100) 5.14 85 (90) 2.94 95 (100) Calcula ions we e pe o med ac oss he samples, exp essed as pe cen age o o al numbe o indi iduals analysed (p edic ed success a es in pa en heses). doi:10.1371/jou nal.pone.0007895. 002 Table 3. De ails o pa en age assignmen analysis using CERVUS, including he sampling yea , he nes iden i y, he numbe o nes lings in he nes (n), he a ailabili y (+) and una ailabili y (2) o social a he s (=) and social mo he s (R), he numbe o nes lings assigned o he social a he s and social mo he s using CERVUS wi h 80% con idence, he a es o ex a-pai ma e ni y (QP) and ex a-pai pa e ni y (EPP). CERVUS Yea Nes iden i y n =R Ma e ni y assigned o RPa e ni y assigned o =QP EPP 2004 E o13 4 ++4/4 4/4 22 E o14 2 +22 2/2 22 E o15 4 ++4/4 4/4 22 E o16 3 ++3/3 3/3 22 E o19 3 ++3/3 3/3 22 E o20 3 +23/3 3/3 22 E o21 4 ++4/4 4/4 22 E o22 2 +22 2/2 22 E o23 3 ++3/3 3/3 22 2005 E o24 4 ++2/4 4/4 2/4 E o25 3 ++3/3 3/3 22 E o27 2 +22 2/2 22 E o28 2 ++2/2 2/2 22 E o34 3 +22 3/3 22 E o37 3 ++3/3 3/3 22 2006 E o40 3 ++3/3 2/3 21/3 E o41 4 +22 4/4 22 E o42 3 +22 3/3 2 E o44 3 ++3/3 3/3 22 E o45 2 +22 2/2 22 2007 E o48 3 +22 3/3 22 E o49 3 ++22/3 21/3 E o51 4 ++3/4 4/4 1/4 2 E o52 4 +22 4/4 22 E o53 3 +22 3/3 22 E o54 3 +22 3/3 22 To al 26 80 26 14 43/46 78/80 3/80 2/80 doi:10.1371/jou nal.pone.0007895. 003 Ma ing Sys em o a Woodpecke PLoS ONE | www.plosone.o g 4 No embe 2009 | Volume 4 | Issue 11 | e7895 nes lings) om which he pu a i e a he s alone had been sampled, pu a i e a he s we e assigned o all o sp ing wi h a .80% con idence. Thus, he pu a i e a he was excluded o wo (2.5%) o 80 nes lings in wo (7.7%) o 26 b oods. When all o he po en ial candida e adul males we e es ed agains he wo ex a-pai chicks wi h known mo he s, he ue gene ic a he o one chick was de ec ed wi h .95% con idence. Howe e , no male eme ged as a likely candida e a he o he o he nes ling - none me e en an 80% con idence c i e ion. O he nes lings, wo we e ound o be unassigned o any ma e ni y o pa e ni y. Gene ic sampling o adul males and emales a he s udy a ea was no comple e in he yea s, and we suspec — by analogy wi h o he published s udies (e.g. [22], [23]) - ha he gene ic pa en s o he wo ex a-pai nes lings we e esiden , unsampled e i o ial adul s. Discussion The main aim o his s udy was o gain insigh in o he ma ing sys em o he h ee- oed woodpecke s wi h he aid o igo ous s a is ical analyses ( iz. he ex emely high cumula i e exclusion p obabili y, dis inc misma ch be ween social pa en s and ex a- pai o sp ing and he powe ul likelihood-based app oach) o gene ic da a. The esul s p o ide he i s gene ic e idence o he co-occu ence o polyand y and polygamy in he h ee- oed woodpecke . To his end, hey add o ou unde s anding o b eeding beha iou o non-passe ine bi ds, and o an inc easing numbe o s udies epo ing occu ence o ex a-pai e iliza ions in na u al bi d popula ions (see [2], [4]). Ex apai Pa e ni y o Th ee-Toed Woodpecke s This is he i s gene ic s udy showing ha EPP and QP occu wi hin a single woodpecke species. O e all, howe e , his species is p edominan ly gene ically monogamous. Since ma e swi ching wi hin a b eeding season has ne e been isually obse ed in his species (see [5], [7]), EPPs and QPs p edominan ly esul om ex apai copula ions. Ma e swi ching can, howe e , occu o example when male o emale dies acciden ally du ing he ea ly b eeding season. The equency o ex apai pa e ni y a ies ma kedly wi hin and be ween species (see [2]). Ou poin es ima e o he p opo ion o EPP is 2.5% which is much less han he a e age o ca. 11% in passe ines, bu mo e equen han in some o he gene ically monogamous species such as he New Zealand saddlebacks Philes u nus ca uncula us and obins Pe oica aus alis whe e no EPP has e e been de ec ed [24]. Compa a i e s udies sugges ha many ac o s such as phylogene ic his o y, b eeding synch ony and b eeding densi y, demands o pa e nal ca e, he a e o adul mo ali y as well as he in ensi y o sexual con lic s all in luence he cos s and bene i s o ex apai copula ions, and he e o e, con ibu e o he a ia ion in EPC equency among species (see [2]). In he con ex o his s udy he ques ion becomes: wha migh keep ex a-pai e iliza ion a es low in h ee- oed woodpecke s as compa ed o he a e age ex apai pa e ni y a e o ca. 11% o e.g. passe ines [2]? We p edic ha he g ea es po en ial o he need o pa e nal ca e hypo hesis will be in explaining he di e ences in he le el o EPP among he species because he high male in es men in b ood ca e is essen ial o emale ep oduc i e success. In h ee- oed woodpecke s, males alloca e signi ican ly mo e ime o e i o y de ence, ca i y exca a ion and eeding young han emales [5]. Noc u nal incuba ion and b ooding as well as nes cons uc ion also cons ain males wi h espec o social polygamy (e.g. [6]). In addi ion, since he e a e signi ican sex di e ences in he p o ision o a ious ypes o ca e and he o al du a ion o di e en componen s o ca e, hese di e ences could be ano he possible beha iou al explana ion [25] o he low ex apai pa e ni y obse ed he e. In aspeci ic a ia ion in he equency o EPP can occu a bo h a he spa ial (e.g. he house spa ow Passe domes icus, [26]) and empo al le els (e.g. he ed-winged blackbi d Agelaius phoeniceus, [27]). Recen s udies o ex apai pa e ni y ound a somewha bu no signi ican ly (Fishe ’s exac es ; P= 0.37) highe a e o EPP (3.625.5%) in a Ge man popula ion o h ee- oed woodpecke s [5], [7]. Al hough ecological ac o s could explain di e en le els o EPP in h ee- oed woodpecke s obse ed in his and ea lie s udies [5], [7], some addi ional po en ial explana ions may be e oked. Fi s ly, he ea lie s udies may ha e lowe s a is ical powe due o he smalle sample size (n= 55 chicks, 95% CI: 41.79263.21), he lowe - esolu ion molecula ools (mul i-locus DNA inge p in ing) and s a is ical me hods (exclusion-based analysis) employed (see [28]). Secondly, oppo uni ies o adop al e na i e ep oduc i e s a egies may di e be ween popula ions (see [29]), o ins ance due o habi a di e ences be ween he Ge man and Finnish popula ions: s udy a ea o he Ge man popula ion is 60022700 me e s abo e sea le el [5], while he a e age al i ude o he s udy a ea o he Finnish popula ion is ca. 130 me e s [5], [7], [10]. Thi dly, spa io empo al luc ua ions in popula ion densi y and esou ces a e likely o induce empo al a ia ion in EPP equency. Howe e , u he s udies a e needed o inden i y p oxima e and ul ima e de e minan s o EPP occu ence in he species. Quasi-Pa asi ism o Th ee-Toed Woodpecke s We ound a low (3.8%) equency o ex apai ma e ni y esul ing om quasi-pa asi ism. This has a ely been epo ed in he ela ed woodpecke s such as he lesse spo ed woodpecke Dend ocopos mino [30]. A numbe o explana ions ha e been pu o wa d o explain he occu ence o QP [31]. The ‘ emale-d i en QP’ sugges s ha a emale may choose, o assen a e an app oach, o copula e wi h an ex apai male and goes on o lay one o mo e o he eggs in his nes . This op ion implies ha emales selec ‘high quali y’ males o e ilize hei eggs, and ei he a oid he cos s o pa en al ca e associa ed wi h p o isioning some young o bene i om he chosen males’ ‘good genes’ o di ec ly om beha iou al o o he con ibu ions such as e i o y quali y (e.g. [32]). Ano he one o he main hypo hesis sugges s ha QP in non-passe ine bi ds is an insu ance mechanism agains he po en ial de imen al e ec o inb eeding, o mo e simply, males’ own low quali y ma e [31]. Ne e heless, gi en he low le el o QP in his s udy popula ion i seems unlikely ha QP is an inb eeding a oidance s a egy as high le els o ex apai copula ions would be expec ed in such a case (c . [33]). Fu he mo e, ou da a is hin abou he ac ual ela edness be ween pa ne s, making i di icul o es he inb eeding a oidance hypo hesis wi h much con idence. In e es ingly, he a e o QP o he emales in h ee- oed woodpecke s (3.75%) is a he lowe ange o es ima es epo ed o many sho ebi ds (e.g. Common sandpipe . Ac i is hypoleucos, 5.7%, [1]) and passe ines (e.g. Sand ma in Ripa ia ipa ia, 2.4%, [31]). The limi s o QP could a ise om he species cha ac e is ics such as a high deg ee o male pa en al ca e, long du a ion o ca i y exca a ion (and hus a na ow ime ame o e iliza ion), long day- ime incuba ion and b ooding shi s (mo e han 3 hou s, [34]), and ew e-ma ing oppo uni ies [5], all o which a e likely o cons ain bo h males and emales in hei abili y o ob ain addi ional ma es, and also limi hei abili y o seek ex apai pa ne s. Howe e , he es ima es o bo h EPP and QP ob ained he e should be conside ed wi h cau ion. One po en ial ca ea is ha we did no sample unha ched eggs o dead chicks. This a ec s Ma ing Sys em o a Woodpecke PLoS ONE | www.plosone.o g 5 No embe 2009 | Volume 4 | Issue 11 | e7895 he es ima es by making hem conse a i e unde he assump ion ha mo ali y be o e sampling is andom in espec o EPP and QP. Ano he possible bias in he es ima es comes om he idea ha nes s wi h QP may be mo e hea ily p eda ed i emales de end hem less igo ously. I is also wo h no ing ha since he es ima ed a es o EPP and QP a e jus based on ela i ely ew nes lings sampled, he con idence limi s o hese es ima es a e p obably b oad and hence he es ima es a e po en ially imp ecise. We de ec ed no case o conspeci ic b ood pa asi ism (CBP) due o egg dumping in his s udy while a single case o CBP, as a esul o egg-dumping o QP, has been epo ed om a Ge man popula ion o h ee- oed woodpecke s [5]. This sugges s ha he CBP s emming om egg dumping mus be a e in ou s udy popula ion. O e all, he wo popula ions did no di e signi ican ly in he equency o ex apai o sp ing (Fishe ’s exac es ; P= 0.41) o p opo ion o b oods con aining one o mo e ex apai young (Fishe ’s exac es ; P= 0.61). In conclusion, ou esul s o gene ic analysis ound he co- occu ence o low le els o EPP and QP in he h ee- oed woodpecke s. Al hough al e na i e explana ions may exis o he obse a ions in ou s udy species (see [2], [4]), ou da a a e consis en wi h he hypo hesis ha a high deg ee o male pa en al ca e play an impo an ole in explaining low a es o EPP and QP ac oss species. The in o ma ion p o ided in his s udy u he allows us o examine he success o male and emale ma ing pa e ns, as well as o unde s and he e olu iona y signi icance and li e-his o y co ela es o p omiscui y in bi ds. Acknowledgmen s We hank Toni Nu mi, Johanna Lakka, Ja mo Pii oinen and Ville Vepsa¨la¨inen o hei in aluable help in collec ing he ield da a. 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