Speciation and chromosomal evolution of the Baikalian endemic chironomids of the genus Sergentia Kief. (Diptera, Chironomidae): Karyotype divergence and chromosomal polymorphism in the populations of eurybathic species Sergentia flavodentata Tshern. and littoral species Sergentia baicalensis Tshern

Abstract

Specific karyotype structure and chromosomal polymorphism was investigated in the populations of the Baikalian endemic chironomid species, eurybathic Sergentia flavodentata Tshernovskij, 1949 and littoral Sergentia baicalensis Tshernovskij, 1949. In addition to two fluctuating homozygous inversions in arms A and E, both species were characterized by species-specific karyotype features, namely, nucleolar organizer in the region 1 of chromosome IV in S. flavodentata, and inversion in arm F in S. baicalensis. Moreover, S. baicalensis demonstrated the presence of intraspecific population polymorphism. The populations differing in the presence of secondary overlapping inversion in arm A were found. The highest number of chromosomal rearrangements (7) was detected in S. flavodentata. Most of these rearrangements (six) were found in the population from the underwater thermal spring at a depth of 420 to 430 m (Northern Baikal, Frolikha Bay). In the populations from Middle and Southern Baikal, a rare pericentric inversion in chromosome I was described. In S. baicalensis, in addition to two common heterozygous inversions in arms C and F, disturbance of homologous pairing in different regions of the remaining arms were often detected. Stable chromosomal polymorphism preserved during 13 years in the population of S. flavodentata from the region of hydrothermal venting, serves as an evidence of high genetic plasticity of the species, which favors successful colonization of different Baikal depths and biotopes.