Limnology (2014) 15: 185-190 DOI 10. 1007/s 10201 -013-0420- 1 Across-population variation in sex ratio in invasive Japanese P otamopy rgus antip o darum (caenogastropoda : Rissooidea : Hydrobiidae) Yuki Tatara. Kana Hamada. Misako Urabe. The Biology Club of Kojo High School Received: 27 Februuy 2013/Accepted: 10 December 2013/Published online: 28 December 2013 @ The Iapanese Society of Limnology 2013 Abstract Potamopyrgus antipodarum, a well-known invasive species, has both sexual and asexual forms in its native area, and is generally asexual in exotic areas. pot- amopyrgus antipodarum was sampled from ten locations in central and western Japan, and the sex distribution was analyzed. Males were found in two of the ten localities; the percentages of males in these localities were 7 .2 arrd'l .3 Vo, which is within the range of that observed in asexual populations in native and introduced areas. A flow cytometry analysis showed that populations with a low percentage of males (Kanro) and populations consisting only of females (Banyu Park, Hadano and Yugawara) and perhaps the population reported as having a high male percentage in a previous study (Chiba;29.8 Vo) were trip- loid. Males from Chiba and Kanro produced sperm. Most of the females from Chiba stored sperm in their seminal receptacle, showing that they had copulated, but no females from Kanro stored sperm. Fertilization by males, normal development of fertilized eggs, and the fecundity ofjuve- niles should be evaluated in further studies to demonstrate the sexual reproduction of P. antipodarum in Japan. The Handling Editor: Nisikawa Usio. Y. Tatara Department of Science, Toho University,2-2-l Miyama, Funabashi, Chiba 274-8510, Japan K. Hamada .M. Urabe (X) Department ofEcosystem Studies, School of Environmental Science, The University of Shiga Prefecture, 2500 Hassaka, Hikone, Shiga 522-8533, Japan e-mail: urabe @ ses.usp.ac jp The Biology Club of Kojo High School Kojo High School, 411 Mitsukejima, Isehara, Kanagawa 259-l 185, Japan risk of introduction of sexual P. antipodarum individuals is further discussed in the article. Keywords Potamopyrgus antipodarun . Sex ratio . Sexual reproduction . Invasive species Introduction The New Zealand mudsnail Potamopyrgus antipodarum (Gray) is a well-known invasive species that is spreading across Europe, Australia, North America, Japan, and Turkey (Bondesen and Kaiser 1949; Ponder 1988; Ma- suda et al. 1998; New Zealand Mudsnail Management and Control Working Group 2007; Kalyoncu et al. 2008). The mudsnail was first discovered in Japan in 1990 (Habe 1990) and was reported as an introduced species in 1998 (Masuda et al. 1998). Potamopyrgus antipodarum often reaches high densities in introduced areas (>10,000 ind/ m2; llucas 1959; Shimada and Urabe 2003; Ishiwara et al. 2005), and its effects on native aquatic benthos has been cause for alarm (e.g., Shimada and Urabe 2003; New Zealand Mudsnail Management and Control Work- ing Group 2007; Urabe 2007; Vinson et al.2OO7: Mfrria et al. 2008). Native populations of P. antipodarum include indi- viduals of various ploidies, from diploid to tetraploid or more (Wallace 1992; Neiman et al. 2}ll). In general, populations with a high percentage of males (>20 Vo) were diploid and considered to be sexual (Wallace 1992). In the polyploid populations of New Znaland, morphological males with a penis, which are themselves polyploid, are produced by asexual polyploid females in low frequency (Neiman et al.20ll; Neiman et al.2Ol2). Microsatellite DNA analysis showed that most of the Q Springer