letters to nature Narture Rev. gene.4,598-612(2003) parental care is provided. 'Pirate males search for freshly laid .Ham. Genet.65,178-1724(1999) clutches, clasp them as they would do a female and fertilize the 8. Kivisild,Tet al. The emerging limbs and twigs of the East Asian mtDNA tree. Mol Biol Evol 19, eggs that were left unfertilized by the parental male. This 1737-1751(2002 behaviour does not seem to be size-dependent, and some males 19.Roberts, DE&Hioms,RW Methods of analysis of the genetic compos ition ofa hybrid population mate with a female and perform clutch piracy in the same season. 20. Bertorelle, G. Excoffier, L Inferring admixture proportions from molecular data. Mol BioL. EvoL. Piracy affected 84% of the clutches and in some cases increased 1298-1311(1998) the proportion of eggs fertilized, providing direct fitness benefits um-likelithood estimation of admixture proportions from genetic data. Genetics 164. both for the pirate males and the females 7. Sexual selection- 22. Wen, B ct aL Analyses of genetic structure of Tibeto-Burman populations revealed a gender-biased probably caused by a strong male-biased sex ratio--occurs in this admixture in southern Tibeto-Burmans. Am. Hum. Genet 74, 856-865(200 population, as indicated by size-assortative mating; however, 23. Jin, L& Su, B Natives or immigrants modern human origin in East Asia, Nature Rev Genet. 1 clutch piracy may reduce its impact. This provides a good L. The Y Chromosome Consortium, A nomenclature system for the tree of human Y-chromosomal model to explore how alternative mating strategies can affect binary haplogroups. Genome Res. 12, 339-348(2002 the intensity of sexual selection. 25. Excoffier, L Smouse, P. E. Quattro I. M. Analysis of molecular variance inferred from metri Anuran amphibians have a wide diversity of reproductive mod mong DNA haplotypes application to human chondrial DNA restriction data. but external aquatic fertilization without parental care is the Genetics131,479-491(1992 for population genetic analysis. (Genetics and ancestral and most widespread strategy. Only a few instances of Biometry Laboratory, Univ of Geneva, Geneva, 2000) multiple paternity have been demonstrated in frogs and those were 27. Dupanloup. L &t Bertorelle, G Inferring admistureproportions from molecular data extenson to any considered to be the result of polyandrous matings, in which several ort, R. Geme admixture in human populations Models and predictions. Yh Phya Anthropol. males mate simultaneously with a female In the common frog 29,1-43(1986) R temporaria, one of the most widespread Palaearctic amphibians", 29. Sans, M. et aL Unequal contributions of male and female gene pools from parental populations in the multiple paternity has been detected through allozyme analyses of African descendants of the city of Melo, Uruguay. Arm /. Plys. Anthropol. 118, 33-44(2002). tadpole kin groups, and was interpreted as being the consequence of SupplementaryInformationaccompaniesthepaperonwww.nature.com/nature. high concentrations of spermatozoa in the water during simul taneous making this work possible. The data collection R temporaria is an explosive pond breeder that often reproduces and a NSF grant to.J L-RD and R C are immediately after the melting of the ice cover. Breeding is usually supported by NIH nocturnal and males form large breeding aggregations. We Competing interests statement The authors declare that they have no competing financial monitored a high altitude population of common frogs in a als should be addressed to LL(ljinefudaneduce or periods(2001-2003)in the central Pyrenean mountains, Spain li jin@uc. edu). The mtDNA I sequences of 711 individuals from 15 Han populations were (42 49N, 017'w, about 2200 m above sea level). Breeding was submitted to Gen Bank with accession numbers Ay594701-AY595411 exclusively diurnal due to low temperatures at night( Supplementary Information A), which permitted us to conduct detailed beha- vioural observations in the field and to measure and mark most individuals in this population. Males aggregated in a specific area of the pond, where clutches were also laid. Male density at the Post-mating clutch piracy in an amphibian Amplexus Clutch deposition David R. Vieites', Sandra Nieto-Roman", Marta Barlueng Antonio Palanca, Miguel Vences& Axel Meyer Clutch Laboratorio de Anatomia Animal, Departamento de ecoloxia e Bioloxia Animal, Facultade de Ciencias Bioloxicas, Universidade de vigo, Buzon 137, 36201 vigo Lehrstuhl fiir Zoologie und Evoluetionsbiologie, Department of Biology University Parental male of Konstanz, 78457 Konstanz, German parental on by INstitute for Biodiversity and Ecosystem Dynamics and Zoological Museun University of Amsterdam, Mauritskade 61, 1092 AD Amsterdam, The Netherlands b Female Present address Museum of vertebrate Zoology and Department of Integrative Biology, 3101 Valley Life the clutch Sciences Building, Universty of California, Berkeley, California 94720-3160, USA Female multiple mating and alternative mating systems can at→ decrease the opportunity for sexual selectionl-. Spero je males tition is often the outcome of females mating with multipl d has been observed in many animals, and alternative Fertilization by reproductive systems are spread am ong species with exte Parental male nal fertilization and parental careB-lo. Multiple paternity with- out associated complex behaviour related to mating or parental Figure 1 Schematic representation of mating mporaria. a, Females arrive care is also seen in simultaneously spawning amphibians -and at the breeding ponds and are clasped in the ion (amplexus ) by a male (the fishes that release gametes into water. Here we report clutch parental male). The female deposits a single, utah of eggs. The parental male piracy' in a montane population of the common frog Rana simultaneously releases his sperm and thereby fertilizes the eggs extemally temporaria, a reproductive behaviour previously unknown in ntly both parents leave the clutch. b, Pirate males search for freshly vertebrates with external fertilization. Males of this species clasp clasp them and release their sperm, sometimes crawling into the clutch to gain the females and the pair deposits one spherical clutch of eggs. No the internal eggs NatuRejVol43116SepTemBer2004www.nature.com/nature02004NaturePublishingGroup© 2004 NaturePublishingGroup Nature Rev. Genet. 4, 598–612 (2003). 17. Su, B. et al. Y-chromosome evidence for a northward migration of modern humans into eastern Asia during the last ice age. Am. J. Hum. Genet. 65, 1718–1724 (1999). 18. Kivisild, T. et al. The emerging limbs and twigs of the East Asian mtDNA tree. Mol. Biol. Evol. 19, 1737–1751 (2002). 19. Roberts, D. F. & Hiorns, R. W. Methods of analysis of the genetic composition of a hybrid population. Hum. Biol. 37, 38–43 (1965). 20. Bertorelle, G. & Excoffier, L. Inferring admixture proportions from molecular data. Mol. Biol. Evol. 15, 1298–1311 (1998). 21. Wang, J. Maximum-likelihood estimation of admixture proportions from genetic data. Genetics 164, 747–765 (2003). 22. Wen, B. et al. Analyses of genetic structure of Tibeto-Burman populations revealed a gender-biased admixture in southern Tibeto-Burmans. Am. J. Hum. Genet. 74, 856–865 (2004). 23. Jin, L. & Su, B. Natives or immigrants: modern human origin in East Asia. Nature Rev. Genet. 1, 126–133 (2000). 24. The Y Chromosome Consortium, A nomenclature system for the tree of human Y-chromosomal binary haplogroups. Genome Res. 12, 339–348 (2002). 25. Excoffier, L., Smouse, P. E. & Quattro, J. M. Analysis of molecular variance inferred from metric distances among DNA haplotypes: application to human mitochondrial DNA restriction data. Genetics 131, 479–491 (1992). 26. Schneider, S., et al. Arlequin: Ver. 2.000. A software for population genetic analysis. (Genetics and Biometry Laboratory, Univ. of Geneva, Geneva, 2000). 27. Dupanloup, I. & Bertorelle, G. Inferring admixture proportions from molecular data: extension to any number of parental populations. Mol. Biol. Evol. 18, 672–675 (2001). 28. Chakraborty, R. Gene admixture in human populations: Models and predictions. Yb. Phys. Anthropol. 29, 1–43 (1986). 29. Sans, M. et al. Unequal contributions of male and female gene pools from parental populations in the African descendants of the city of Melo, Uruguay. Am. J. Phys. Anthropol. 118, 33–44 (2002). Supplementary Information accompanies the paper on www.nature.com/nature. Acknowledgements We thank all of the donors for making this work possible. The data collection was supported by NSFC and STCSM to Fudan and a NSF grant to L.J. L.J., R.D. and R.C. are supported by NIH. Competing interests statement The authors declare that they have no competing financial interests. Correspondence and requests for materials should be addressed to L.J. (lijin@fudan.edu.cn or li.jin@uc.edu). The mtDNA HVS-1 sequences of 711 individuals from 15 Han populations were submitted to GenBank with accession numbers AY594701–AY595411. .............................................................. Post-mating clutch piracy in an amphibian David R. Vieites1,2*, Sandra Nieto-Roma´n1,3, Marta Barluenga2 , Antonio Palanca1 , Miguel Vences3 & Axel Meyer2 1 Laboratorio de Anatomı´a Animal, Departamento de Ecoloxı´a e Bioloxı´a Animal, Facultade de Ciencias Biolo´xicas, Universidade de Vigo, Buzo´n 137, 36201 Vigo, Spain 2 Lehrstuhl fu¨r Zoologie und Evolutionsbiologie, Department of Biology, University of Konstanz, 78457 Konstanz, Germany 3 Institute for Biodiversity and Ecosystem Dynamics and Zoological Museum, University of Amsterdam, Mauritskade 61, 1092 AD Amsterdam, The Netherlands * Present address: Museum of Vertebrate Zoology and Department of Integrative Biology, 3101 Valley Life Sciences Building, University of California, Berkeley, California 94720-3160, USA ............................................................................................................................................................................. Female multiple mating and alternative mating systems can decrease the opportunity for sexual selection1–3. Sperm compe￾tition is often the outcome of females mating with multiple males and has been observed in many animals1,4–7, and alternative reproductive systems are widespread among species with exter￾nal fertilization and parental care3,8–10. Multiple paternity with￾out associated complex behaviour related to mating or parental care is also seen in simultaneously spawning amphibians11–15 and fishes16 that release gametes into water. Here we report ‘clutch piracy’ in a montane population of the common frog Rana temporaria, a reproductive behaviour previously unknown in vertebrates with external fertilization. Males of this species clasp the females and the pair deposits one spherical clutch of eggs. No parental care is provided. ‘Pirate’ males search for freshly laid clutches, clasp them as they would do a female and fertilize the eggs that were left unfertilized by the ‘parental’ male. This behaviour does not seem to be size-dependent, and some males mate with a female and perform clutch piracy in the same season. Piracy affected 84% of the clutches and in some cases increased the proportion of eggs fertilized, providing direct fitness benefits both for the pirate males and the females17. Sexual selection— probably caused by a strong male-biased sex ratio—occurs in this population, as indicated by size-assortative mating; however, clutch piracy may reduce its impact. This provides a good model to explore how alternative mating strategies can affect the intensity of sexual selection. Anuran amphibians have a wide diversity of reproductive modes, but external aquatic fertilization without parental care is the ancestral and most widespread strategy18. Only a few instances of multiple paternity have been demonstrated in frogs and those were considered to be the result of polyandrous matings, in which several males mate simultaneously with a female11,13,14. In the common frog R. temporaria, one of the most widespread Palaearctic amphibians19, multiple paternity has been detected through allozyme analyses of tadpole kin groups, and was interpreted as being the consequence of high concentrations of spermatozoa in the water during simul￾taneous spawning12. R. temporaria is an explosive pond breeder that often reproduces immediately after the melting of the ice cover. Breeding is usually nocturnal12,20 and males form large breeding aggregations. We monitored a high altitude population of common frogs in a medium-sized pond (540 m2 ) during three consecutive breeding periods (2001–2003) in the central Pyrenean mountains, Spain (428490 N, 08170 W, about 2200 m above sea level). Breeding was exclusively diurnal due to low temperatures at night (Supplementary Information A), which permitted us to conduct detailed beha￾vioural observations in the field and to measure and mark most individuals in this population. Males aggregated in a specific area of the pond, where clutches were also laid. Male density at the Figure 1 Schematic representation of mating systems in R. temporaria. a, Females arrive at the breeding ponds and are clasped in the axillary region (‘amplexus’) by a male (the ‘parental’ male). The female deposits a single, spherical clutch of eggs. The parental male simultaneously releases his sperm and thereby fertilizes the eggs externally. Subsequently both parents leave the clutch. b, ‘Pirate’ males search for freshly laid clutches, clasp them and release their sperm, sometimes crawling into the clutch to gain access to the internal eggs. letters to nature NATURE | VOL 431 | 16 SEPTEMBER 2004 | www.nature.com/nature 305