Schärer, L.; Brand, J. N.; Singh, P.; Zadesenets, K. S.; Stelzer, C.; Viktorin, G. (2019). A phylogenetically informed search for an alternative Macrostomum model species, with notes on taxonomy, mating behavior, karyology, and genome size. Journal of Zoological Systematics and Evolutionary Research.

365260

10.1111/jzs.12344 [view]

Schärer, L.; Brand, J. N.; Singh, P.; Zadesenets, K. S.; Stelzer, C.; Viktorin, G.

2019

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The free-living flatworm Macrostomum lignano is used as a model in a range of re- search fields—including aging, bioadhesion, stem cells, and sexual selection—culmi- nating in the establishment of genome assemblies and transgenics. However, the Macrostomum community has run into a roadblock following the discovery of an unu- sual genome organization in M. lignano, which could now impair the development of additional resources and tools. Briefly, M. lignano has undergone a whole-genome duplication, followed by rediploidization 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 organiza- tion. 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 or- ganization; the second, Macrostomum mirumnovem n. sp., has an even more unusual genome organization, with a highly variable karyotype based on a 2n = 9 base pat- tern; and the third, Macrostomum cliftonensis n. sp., does not only show the canonical 2n = 6 karyotype, but also performs well under standard laboratory culture condi- tions and fulfills many other requirements. M. cliftonensis is a viable candidate for re- placing M. lignano as the primary Macrostomum model, being outcrossing and having an estimated haploid genome size of only 231 Mbp.

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