02432nas a2200277 4500008004100000022001400041245012900055210006900184260001300253300001100266490000800277520163700285653001201922653001601934653001101950653001501961653000901976653001201985653001501997653001702012653001402029100001902043700001802062700002202080856005202102 2014 eng d a1432-088600aTriploid planarian reproduces truly bisexually with euploid gametes produced through a different meiotic system between sex.0 aTriploid planarian reproduces truly bisexually with euploid game c2014 Jun a265-720 v1233 a

Although polyploids are common among plants and some animals, polyploidization often causes reproductive failure. Triploids, in particular, are characterized by the problems of chromosomal pairing and segregation during meiosis, which may cause aneuploid gametes and results in sterility. Thus, they are generally considered to reproduce only asexually. In the case of the Platyhelminthes Dugesia ryukyuensis, populations with triploid karyotypes are normally found in nature as both fissiparous and oviparous triploids. Fissiparous triploids can also be experimentally sexualized if they are fed sexual planarians, developing both gonads and other reproductive organs. Fully sexualized worms begin reproducing by copulation rather than fission. In this study, we examined the genotypes of the offspring obtained by breeding sexualized triploids and found that the offspring inherited genes from both parents, i.e., they reproduced truly bisexually. Furthermore, meiotic chromosome behavior in triploid sexualized planarians differed significantly between male and female germ lines, in that female germ line cells remained triploid until prophase I, whereas male germ line cells appeared to become diploid before entry into meiosis. Oocytes at the late diplotene stage contained not only paired bivalents but also unpaired univalents that were suggested to produce diploid eggs if they remained in subsequent processes. Triploid planarians may therefore form euploid gametes by different meiotic systems in female and male germ lines and thus are be able to reproduce sexually in contrast to many other triploid organisms.

10aAnimals10aChromosomes10aFemale10aGerm Cells10aMale10aMeiosis10aplanarians10areproduction10aTriploidy1 aChinone, Ayako1 aNodono, Hanae1 aMatsumoto, Midori uhttps://continenticola.myspecies.info/node/176601453nas a2200205 4500008004100000022001400041245011600055210006900171260003300240300001200273490000800285520077000293100002201063700002201085700002001107700003001127700002001157700002201177856004801199 2008 eng d a0009-591500aProduction of diploid and triploid offspring by inbreeding of the triploid planarian Dugesia ryukyuensis0 aProduction of diploid and triploid offspring by inbreeding of th bSpringer Berlin / Heidelberg a289-2960 v1173 a

Triploidy has generally been considered to be an evolutionary dead end due to problems of chromosomal pairing and segregation during meiosis. Thus, the formation of tetraploids and diploids from triploid types is a rare phenomenon. In the present study, we demonstrated that inbreeding of the triploid planarian Dugesia ryukyuensis resulted in both diploid and triploid offspring in nature. In the triploids of D. ryukyuensis , chiasmata between homologous chromosomes were observed in both female and male germ lines. This result suggests that both diploid and triploid offspring of this species are produced bisexually by zygotic fusion between sperm and eggs. Hence, this phenomenon may be a novel mechanism in planarian for escaping the triploid state.

1 aKobayashi, Kazuya1 aIshizu, Hirotsugu1 aArioka, Sachiko1 aCabrera, Jocelyn, Padilla1 aHoshi, Motonori1 aMatsumoto, Midori uhttp://dx.doi.org/10.1007/s00412-008-0148-6