Sperm competition represents an important component of post-copulatory sexual selection. It has been argued that the level of sperm competition declines in birds towards the equator. However, to date, sperm competition estimates have been available mainly for avian species inhabiting the northern temperate zone. Here we apply a novel approach, using the coefficient of between-male variation (CV(bm)) in sperm size as an index for sperm competition risk, in a comparative analysis of 31 Afrotropical and 99 northern temperate zone passerine species. We found no difference in sperm competition risk between the two groups, nor any relationship with migration distance. However, a multivariate model indicated that sperm competition risk was highest in species with a combination of low body mass and few eggs per clutch. The effect of clutch size was most pronounced in tropical species, which indicates that sperm competition risk in tropical and temperate species is differently associated with particular life-history traits. Although tropical species had lower sperm competition risk than temperate zone species for overlapping clutch sizes, the idea of a generally reduced risk of sperm competition in tropical birds was not supported by our analysis.

Institute of Vertebrate Biology vvi Academy of Sciences of the Czech Republic Kvetna 8 Brno 603 65 Czech Republic

See more in PubMed

Birkhead TR, Møller AP. 1998. Sperm competition and sexual selection. London, UK: Academic Press

Albrecht T, Vinkler M, Schnitzer J, Polakova R, Munclinger P, Bryja J. 2009. Extra-pair fertilizations contribute to selection on secondary male ornamentation in a socially monogamous passerine. J. Evol. Biol. 22, 2020–203010.1111/j.1420-9101.2009.01815.x (doi:10.1111/j.1420-9101.2009.01815.x) PubMed DOI

Webster M, Pruett-Jones S, Westneat D, Arnold S. 1995. Measuring the effects of pairing success, extra-pair copulations and mate quality on the opportunity for sexual selection. Evolution 49, 1147–115710.2307/2410439 (doi:10.2307/2410439) PubMed DOI

Pizzari T, Parker GA. 2006. Sperm competition and sperm phenotype. In Sperm biology: an evolutionary perspective (eds Birkhead TR, Hosken DJ, Pitnick S.), pp. 207–245 Oxford, UK: Academic Press

Birkhead TR, Møller AP. 1992. Sperm competition in birds: evolutionary causes and consequences. London, UK: Academic Press

Griffith S, Owens IPF, Thuman K. 2002. Extra pair paternity in birds: a review of interspecific variation and adaptive function. Mol. Ecol. 11, 2195–221210.1046/j.1365-294X.2002.01613.x (doi:10.1046/j.1365-294X.2002.01613.x) PubMed DOI

Westneat D, Stewart I. 2003. Extra-pair paternity in birds: causes, correlates, and conflict. Annu. Rev. Ecol. Evol. Syst. 34, 365–39610.1146/annurev.ecolsys.34.011802.132439 (doi:10.1146/annurev.ecolsys.34.011802.132439) DOI

Skutch A. 1949. Do tropical birds rear as many young as they can nourish? Ibis 91, 430–45810.1111/j.1474-919X.1949.tb02293.x (doi:10.1111/j.1474-919X.1949.tb02293.x) DOI

Ricklefs R, Wikelski M. 2002. The physiology/life-history nexus. Trends Ecol. Evol. 17, 462–46810.1016/S0169-5347(02)02578-8 (doi:10.1016/S0169-5347(02)02578-8) DOI

Stutchbury BJM, Morton ES. 2001. Behavioral ecology of tropical songbirds. London, UK: Academic Press

Stutchbury B, Morton E. 1995. The effect of breeding synchrony on extra-pair mating systems in songbirds. Behaviour 132, 675–69010.1163/156853995X00081 (doi:10.1163/156853995X00081) DOI

Mauck R, Marschall E, Parker P. 1999. Adult survival and imperfect assessment of parentage: effects on male parenting decisions. Am. Nat. 154, 99–10910.1086/303216 (doi:10.1086/303216) PubMed DOI

Arnold K, Owens IPF. 2002. Extra-pair paternity and egg dumping in birds: life history, parental care and the risk of retaliation. Proc. R. Soc. Lond. B 269, 1263–126910.1098/rspb.2002.2013 (doi:10.1098/rspb.2002.2013) PubMed DOI PMC

Bennett PM, Owens IPF. 2002. Evolutionary ecology of birds. Oxford, UK: Oxford University Press

Peach W, Hanmer D, Oatley T. 2001. Do southern African songbirds live longer than their European counterparts? Oikos 93, 235–24910.1034/j.1600-0706.2001.930207.x (doi:10.1034/j.1600-0706.2001.930207.x) DOI

Wiersma P, Munoz-Garcia A, Walker A, Williams JB. 2007. Tropical birds have a slow pace of life. Proc. Natl Acad. Sci. USA 104, 9340–934510.1073/pnas.0702212104 (doi:10.1073/pnas.0702212104) PubMed DOI PMC

Stutchbury B. 1998. Female mate choice of extra-pair males: breeding synchrony is important. Behav. Ecol. Sociobiol. 43, 213–21510.1007/s002650050483 (doi:10.1007/s002650050483) DOI

Spottiswoode C, Møller A. 2004. Extrapair paternity, migration, and breeding synchrony in birds. Behav. Ecol. 15, 41–5710.1093/beheco/arg100 (doi:10.1093/beheco/arg100) DOI

Govaty PA. 1996. Battle of the sexes and origins of monogamy. In Partnerships in birds: the study of monogamy (ed. Black JM.), pp. 21–52 Oxford, UK: Oxford University Press

Mulder RA, Dunn PO, Cockburn A, Lazenby-Cohen KA, Howell MJ. 1994. Helpers liberate female fairy-wrens from constraints on extra-pair mate choice. Proc. R. Soc. Lond. B 255, 223–22910.1098/rspb.1994.0032 (doi:10.1098/rspb.1994.0032) DOI

Ghalambor CK, Martin TE. 2001. Fecundity–survival trade-offs and parental risk-taking in birds. Science 292, 494–49710.1126/science.1059379 (doi:10.1126/science.1059379) PubMed DOI

Jetz W, Sekercioglu CH, Boehning-Gaese K. 2008. The worldwide variation in avian clutch size across species and space. PLoS Biol. 6, 2650–265710.1371/journal.pbio.0060303 (doi:10.1371/journal.pbio.0060303) PubMed DOI PMC

McNamara JM, Barta Z, Wikelski M, Houston AI. 2008. A theoretical investigation of the effect of latitude on avian life histories. Am. Nat. 172, 331–34510.1086/589886 (doi:10.1086/589886) PubMed DOI

Macedo RH, Karubian J, Webster MS. 2008. Extrapair paternity and sexual selection in socially monogamous birds: are tropical birds different? Auk 125, 769–77710.1525/auk.2008.11008 (doi:10.1525/auk.2008.11008) DOI

Calhim S, Immler S, Birkhead TR. 2007. Postcopulatory sexual selection is associated with reduced variation in sperm morphology. PLoS ONE 2, e413.10.1371/journal.pone.0000413 (doi:10.1371/journal.pone.0000413) PubMed DOI PMC

Pitnick S, Hosken DJ, Birkhead TR. 2006. Sperm morphological diversity. In Sperm biology: an evolutionary perspective (eds Birkhead TR, Hosken DJ, Pitnick S.), pp. 69–149 Oxford, UK: Academic Press

Lifjeld JT, Laskemoen T, Kleven O, Albrecht T, Robertson RJ. 2010. Sperm length variation as a predictor of extrapair paternity in passerine birds. PLoS ONE 5, e13456.10.1371/journal.pone.0013456 (doi:10.1371/journal.pone.0013456) PubMed DOI PMC

Birkhead T, Pellatt E, Brekke P, Yeates R, Castillo-Juarez H. 2005. Genetic effects on sperm design in the zebra finch. Nature 434, 383–38710.1038/nature03374 (doi:10.1038/nature03374) PubMed DOI

Parker G, Begon M. 1993. Sperm competition and sperm games: sperm size and number under gametic control. Proc. R. Soc. Lond. B 253, 255–26210.1098/rspb.1993.0111 (doi:10.1098/rspb.1993.0111) PubMed DOI

Hunter F, Birkhead T. 2002. Sperm viability and sperm competition in insects. Curr. Biol. 12, 121–12310.1016/S0960-9822(01)00647-9 (doi:10.1016/S0960-9822(01)00647-9) PubMed DOI

Fitzpatrick JL, Baer B. 2011. Polyandry reduces sperm length variation in social insects. Evolution 65, 3006–301210.1111/j.1558-5646.2011.01343.x (doi:10.1111/j.1558-5646.2011.01343.x) PubMed DOI

Immler S, Calhim S, Birkhead TR. 2008. Increased postcopulatory sexual selection reduces the intramale variation in sperm design. Evolution 62, 1538–154310.1111/j.1558-5646.2008.00393.x (doi:10.1111/j.1558-5646.2008.00393.x) PubMed DOI

Kleven O, Laskemoen T, Fossøy F, Robertson RJ, Lifjeld JT. 2008. Intraspecific variation in sperm length is negatively related to sperm competition in passerine birds. Evolution 62, 494–49910.1111/j.1558-5646.2007.00287.x (doi:10.1111/j.1558-5646.2007.00287.x) PubMed DOI

Pitcher T, Dunn P, Whittingham L. 2005. Sperm competition and the evolution of testes size in birds. J. Evol. Biol. 18, 557–56710.1111/j.1420-9101.2004.00874.x (doi:10.1111/j.1420-9101.2004.00874.x) PubMed DOI

Dunn P, Whittingham L, Pitcher T. 2001. Mating systems, sperm competition, and the evolution of sexual dimorphism in birds. Evolution 55, 161–17510.1554/0014-3820 (doi:10.1554/0014-3820) PubMed DOI

Lindstedt SL, Calder WA. 1976. Body size and longevity in birds. Condor 78, 91–14510.2307/1366920 (doi:10.2307/1366920) DOI

Wolfson A. 1952. The cloacal protuberance: a means for determining breeding condition in live male passerines. Bird Banding 23, 159–16510.2307/4510381 (doi:10.2307/4510381) DOI

Laskemoen T, Kleven O, Fossøy F, Lifjeld JT. 2007. Intraspecific variation in sperm length in two passerine species, the Bluethroat Luscinia svecica and the Willow Warbler Phylloscopus trochilus. Ornis Fenn. 84, 131–139

Lessells CM, Boag PT. 1987. Unrepeatable repeatabilities: a common mistake. Auk 104, 116–12110.2307/4087240 (doi:10.2307/4087240) DOI

Sokal RR, Rohlf FJ. 1981. Biometry: the principles and practice of statistics in biological research, 2nd edn New York, NY: W. H. Freeman and Co

Cramp S, Simmons KEL, Perrins CM. 1978–1994. The birds of the Western Palearctic. Oxford, UK: Oxford University Press

Fry CH, Keith S, Newman K, Urban EK. 1982–2004. The birds of Africa. Princeton, NJ: Princeton University Press

Ridgely SR, Tudor G. 2009. Birds of South America: passerines.  London, UK: Christopher Helm

Bakken V, Runde O, Tjørve E. 2006. Norsk ringmerkingsatlas, vol. 2 Stavanger, Norway: Stavanger Museum

Cepák J, Klvaňa P, Škopek J, Schröpfer L, Jelínek M, Hořák D, Formánek J, Zárybnický J. 2008. Czech and Slovak bird migration atlas [in Czech]. Prague, Czech Republic: Aventinum

Fraser KC, Kyser TK, Ratcliffe LM. 2008. Detecting altitudinal migration events in neotropical birds using stable isotopes. Biotropica 40, 269–27210.1111/j.1744-7429.2008.00408.x (doi:10.1111/j.1744-7429.2008.00408.x) DOI

R Development Core Team 2011. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing

Paradis E, Claude J, Strimmer K. 2004. APE: analyses of phylogenetics and evolution in R language. Bioinformatics 20, 289–29010.1093/bioinformatics/btg412 (doi:10.1093/bioinformatics/btg412) PubMed DOI

Pagel M. 1999. Inferring the historical patterns of biological evolution. Nature 401, 877–88410.1038/44766 (doi:10.1038/44766) PubMed DOI

Freckleton R, Harvey P, Pagel M. 2002. Phylogenetic analysis and comparative data: a test and review of evidence. Am. Nat. 160, 712–72610.1086/343873 (doi:10.1086/343873) PubMed DOI

Crawley MJ. 2007. The R book. Chichester, UK: John Willey & Sons Ltd

Schielzeth H. 2010. Simple means to improve the interpretability of regression coefficients. Methods Ecol. Evol. 1, 103–11310.1111/j.2041-210X.2010.00012.x (doi:10.1111/j.2041-210X.2010.00012.x) DOI

Calhim S, Birkhead TR. 2007. Testes size in birds: quality versus quantity—assumptions, errors, and estimates. Behav. Ecol. 18, 271–27510.1093/beheco/arl076 (doi:10.1093/beheco/arl076) DOI

Griffith S, Stewart I, Dawson D, Owens I, Burke T. 1999. Contrasting levels of extra-pair paternity in mainland and island populations of the house sparrow (Passer domesticus): is there an ‘island effect’? Biol. J. Linnean Soc. 68, 303–31610.1111/j.1095-8312.1999.tb01171.x (doi:10.1111/j.1095-8312.1999.tb01171.x) DOI

Hau M, Ricklefs RE, Wikelski M, Lee KA, Brawn JD. 2010. Corticosterone, testosterone and life-history strategies of birds. Proc. R. Soc. B 277, 3203–321210.1098/rspb.2010.0673 (doi:10.1098/rspb.2010.0673) PubMed DOI PMC

Petrie M, Doums C, Møller A. 1998. The degree of extra-pair paternity increases with genetic variability. Proc. Natl Acad. Sci. USA 95, 9390–939510.1073/pnas.95.16.9390 (doi:10.1073/pnas.95.16.9390) PubMed DOI PMC

Arnqvist G, Kirkpatrick M. 2005. The evolution of infidelity in socially monogamous passerines: the strength of direct and indirect selection on extrapair copulation behavior in females. Am. Nat. 165, S26–S3710.1086/429350 (doi:10.1086/429350) PubMed DOI

Albrecht T, Kreisinger J, Pialek J. 2006. The strength of direct selection against female promiscuity is associated with rates of extrapair fertilizations in socially monogamous songbirds. Am. Nat. 167, 739–74410.1086/502633 (doi:10.1086/502633) PubMed DOI

Ashmole NP. 1963. The regulation of numbers of tropical oceanic birds. Ibis 103, 458–473

Garamszegi LZ, Hirschenhauser K, Bokony V, Eens M, Hurtrez-Bousses S, Møller AP, Oliveira RF, Wingfield JC. 2008. Latitudinal distribution, migration, and testosterone levels in birds. Am. Nat. 172, 533–54610.1086/590955 (doi:10.1086/590955) PubMed DOI

Fitzpatrick S. 1994. Colourful migratory birds: evidence for a mechanism other than parasite resistance for maintenance of good genes sexual selection. Proc. R. Soc. Lond. B 257, 155–16010.1098/rspb.1994.0109 (doi:10.1098/rspb.1994.0109) DOI

Stutchbury B. 1998. Breeding synchrony best explains variation in extra-pair mating system among avian species. Behav. Ecol. Sociobiol. 43, 221–22210.1007/s002650050485 (doi:10.1007/s002650050485) DOI

Weatherhead P, Yezerinac S. 1998. Breeding synchrony and extra-pair mating in birds. Behav. Ecol. Sociobiol. 43, 217–21910.1007/s002650050484 (doi:10.1007/s002650050484) DOI

Slagsvold T, Lifjeld JT. 1997. Incomplete knowledge of male quality may explain variation in extra-pair paternity in birds. Behaviour 134, 353–37110.1163/156853997X00584 (doi:10.1163/156853997X00584) DOI

Stutchbury BJM, Morton ES. 2008. Recent advances in the behavioral ecology of tropical birds: the 2005 Margaret Morse Nice Lecture. Wilson J. Ornithol. 120, 26–3710.1676/07-018.1 (doi:10.1676/07-018.1) DOI

Gut microbiota variation between climatic zones and due to migration strategy in passerine birds

Feather growth and quality across passerines is explained by breeding rather than moulting latitude

Evolution of female promiscuity in Passerides songbirds

Postcopulatory sexual selection reduces Z-linked genetic variation and might contribute to the large Z effect in passerine birds

Variation in apical hook length reflects the intensity of sperm competition in murine rodents