02465nas a2200181 4500008004100000245015400041210006900195300001200264490000700276520181500283100002002098700002402118700001802142700002502160700002502185700002102210856005202231 2020 eng d00aA phylogenetically informed search for an alternative Macrostomum model species, with notes on taxonomy, mating behavior, karyology, and genome size.0 aphylogenetically informed search for an alternative Macrostomum  a41–650 v583 a

The free-living flatworm Macrostomum lignano is used as a model in a range of research fields—including ageing, bioadhesion, stem cells, and sexual selection—leading to the recent establishment of genome assemblies and transgenics. However, the Macrostomum community has run into a roadblock following the discovery of an unusual genome organization in M. lignano, which could impair the development of essential resources and tools. Briefly, M. lignano has undergone a whole-genome duplication, followed by rediploidisation into a 2n=8 karyotype (distinct from the canonical 2n=6 karyotype in the genus). Although this karyotype appears visually diploid, it is in fact a hidden tetraploid (with rarer 2n=9 and 2n=10 individuals being pentaploid and hexaploid, respectively). Here we report on a phylogenetically-informed search for close relatives of M. lignano, aimed at uncovering alternative Macrostomum models with the canonical karyotype and a simple genome organization. We taxonomically describe three new species: the first, Macrostomum janickei n. sp., is the closest known relative of M. lignano, and shares its derived genome organization; the second, Macrostomum mirumnovem n. sp., has an even more unusual genome organization, with a highly variable karyotype based on a 2n=9 base pattern; and the third, Macrostomum cliftonensis n. sp., does not only show the canonical 2n=6 karyotype, but also performs well under standard laboratory culture conditions and fulfils many other requirements. M. cliftonensis is a viable candidate for replacing M. lignano as the primary Macrostomum model, being outcrossing and having an estimated haploid genome size of only 231 Mbp.

1 aSchärer, Lukas1 aBrand, Jeremias, N.1 aSingh, Pragya1 aZadesenets, Kira, S.1 aStelzer, Claus-Peter1 aViktorin, Gudrun uhttps://macrostomorpha.myspecies.info/node/4774