Morphological and Molecular-Genetic Characterization of the Nematode Aplectana acuminata Schrank, 1788 (Nematoda: Cosmocercidae) in Uzbekistan

In this article, the partial nucleotides of the ribosomal DNA (rDNA) ITS region gene of A. acuminata nematodes were studied molecular-genetically. To conduct morphological and molecular-genetic research, 264 amphibian specimens were helminthologically examined from southern (Qashqadaryo and Surxondaryo regions) and central (Bukhara and Navoi regions) territories of Uzbekistan during 2023-2025.
Morphological analyses revealed that the body length of male A. acuminata nematodes is 1.5- 3.6mm, while that of females is 3.3- 5.2mm; the muscular part of the esophagus forms a bulb, with the excretory pore located around it and opening after 0.26-0.37mm from the anterior part of the body. Comparative studies of our data and those of other authors determined that the width of the esophagus-intestine junction and the morphometric dimensions of the bulb circumference of A. acuminata nematodes are slightly larger. According to the results of molecular-genetic studies based on Kimura’s K2P model, transition substitutions (A↔G and C↔T) showed high frequencies, with an average distance of 13.6233. Transversion substitutions (A↔C, A↔T, G↔C, G↔T) demonstrated lower values, with an average result of 5.6883. The transition/transversion (Ti/Tv) ratio was ≈2.4. Neutrality test results based on 42 ITS sequences identified a total of 648 polymorphic sites. The calculated Tajima’s D value was 0.659444, indicating no significant deviation from neutral evolution. The phylogenetic tree of A.  acuminata_uzb specimens belonging to the genus Aplectana Railliet & Henry, 1916, along with closely related representatives available in the NCBI database, formed 5 monophyletic groups with bootstrap values ranging from 51.2 to 100%. For the first time in Uzbekistan, the nucleotide sequence of the ITS region of rDNA belonging to A. acuminata_uzb nematodes was extracted and uploaded to the National Center for Biotechnology Information (NCBI) database by us. Based on morphological and molecular-genetic research results, this nematode species was confirmed to be a distinct, stable species.