Interstitial telomere sequences in chromosomes of Baikal planarians

Abstract

The presence of internal telomeric sequences (ITSs) in chromosomes typically indicates instances of genome reorganization. Changes in morphology and chromosome number can be sources of intraspecific polymorphism and also lead to speciation. Both variants are found in flatworms, but ITSs are rare in chromosomes, as is common in other invertebrate animals. Out of 23 flatworm species ITSs has been identified in only three parasitic species. Using FISH with telomeric probes, we found that ITSs are also present in the chromosomes of the endemic Baikal planarians Baikalobia Kenk, 1930 (Tricladida, Continenticola, Dendrocoelidae). This is the first time that ITSs has been identified in free-living flatworms. Like Shistosoma Weinland, 1858, the appearance of ITSs in the Baikal planarians could be associated with the process of speciation. There is no data yet on ITSs in other dendrocoelids, and the question remains whether ITSs are a specific feature of Baikal planarians or a special feature of all dendrocoelids.