Interstitial telomere sequences in chromosomes of Baikal planarians

Thu, 29 Feb 2024 00:00:00 +0800

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.

The detection of three species complexes similar to Diacyclops galbinus, D. versutus and D. improcerus (Copepoda: Cyclopoida) from Lake Baikal

Mayor T.Yu., Zaidykov I.Yu., Kirilchik S.V. — Thu, 29 Feb 2024 00:00:00 +0800

Cyclopoids are an extremely diverse and abundant group of arthropods found in Lake Baikal. Diacyclops Kiefer, 1927 is the most species-rich and highly endemic genus among them. The morphological characteristics of the three Baikal species, D. improcerus, D. galbinus and D. versutus, show considerable differences. Therefore, it is worth considering whether all specimens identified as versutus, galbinus, or improcerus belong to the same species. Molecular and morphological analyzes were conducted on Diacyclops from Lake Baikal, which are similar to D. improcerus, D. galbinus and D. versutus. Three molecular markers of mtDNA (COI, 12S) and nuclear DNA (ITS1) revealed three clusters corresponding to the division of specimens into three groups based on morphological characteristics. Each of these groups comprises multiple genetic lineages. We assume that the improcerus-, galbinus-, and versutus- groups are closely related species complexes. The use of PCA for morphometric indices based on linear measurements, which are widely used in Cyclopoida taxonomy, is limited in separating closely related species within species complexes. Micrographs and line drawings of a fourth swimming leg (P4) and an antenna from specimens of the versutus- and improcerus- groups are provided. These images reveal significant differences in the spinule ornamentation of the coxopodite of P4 and the basipodite of the antenna between specimens of different genetic lineages.

Limnology and Freshwater Biology

Interstitial telomere sequences in chromosomes of Baikal planarians

The detection of three species complexes similar to Diacyclops galbinus, D. versutus and D. improcerus (Copepoda: Cyclopoida) from Lake Baikal