Genome and Karyotype Evolution after Whole Genome Duplication in Free-Living Flatworms of the Genus Macrostomum

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Kira Zadesenets¹, Nikita Ershov², Dmitry Oshchepkov³, Eugene Berezikov⁴, Lukas SchГ¤rer⁵, Nikolay B. Rubtsov^6
1ICG SB RAS, kira_z@bionet.nsc.ru
²ICG SB RAS, nikotinmail@mail.ru
³ICG SB RAS, diman@bionet.nsc.ru
⁴ERIBA, Groningen, The Netherlands, e.berezikov@umcg.nl
⁵Evolutionary Biology, Zoological Institute, University of Basel, Basel, Switzerland, lukas.scharer@unibas.ch
⁶ICG SB RAS, rubt@bionet.nsc.ru

Whole genome duplication (WGD) is a large-scale evolutionary transformation that took place in genome evolution in many taxa of existing animal species. However, the mechanisms underlying the early stages of genome evolution after a WGD event in animals has remained unclear. The study of genome organization of neopolyploid species may shed light on the processes of genome reorganization leading to its re-diploidization after a recent round of WGD. Earlier we uncovered a group of free-living flatworms in which genomes have likely undergone a recent WGD. We found out that karyotype instability was linked to hidden polyploidy in both species M. lignano (2n = 8) and its sibling species M. janickei (2n = 10). Additional studies of other species of the genus Macrostomum revealed a new species (further called M. mirumnovem) with a highly unstable karyotype. The detailed cytogenetic analyses using a set of different DNA probes (microdissected region- and chromosome specific DNA probes, DNA repeats, unique DNA fragments) revealed the peculiarities of karyotype and genome organization in three Macrostomum species with unstable karyotypes. Similar to M. lignano and M. janickei, our findings suggest that M. mirumnovem arose via whole genome duplication (WGD) followed by considerable reshuffling of its chromosomes. The combined approach allowed us to explore the peculiarity of the M. lignano genome organization, the strategy included bioinformatics analysis of the existed genome assemblies of M. lignano and NGS data for its separate chromosomes. Based on the obtained results, we suggest possible evolutionary scenarios for the emergence and reorganization of the karyotypes and genomes of the post-WGD Macrostomum species.