Variation in nuclear genome size within the Eisenia nordenskioldi complex (Lumbricidae, Annelida).

S V Shekhovtsov,T V Poluboyarova,Ya R Efremov,S E Peltek

doi:10.18699/vj21.073

Abstract

The size of the nuclear genome in eukaryotes is mostly determined by mobile elements and noncoding sequences and may vary within wide limits. It can differ signif icantly both among higher-order taxa and closely related species within a genus; genome size is known to be uncorrelated with organism complexity (the so-called C-paradox). Less is known about intraspecif ic variation of this parameter. Typically, genome size is stable within a species, and the known exceptions turn out be cryptic taxa. The Eisenia nordenskioldi complex encompasses several closely related earthworm species. They are widely distributed in the Urals, Siberia, and the Russian Far East, as well as adjacent regions. This complex is characterized by signif icant morphological, chromosomal, ecological, and genetic variation. The aim of our study was to estimate the nuclear genome size in several genetic lineages of the E. nordenskioldi complex using f low cytometry. The genome size in different genetic lineages differed strongly, which supports the hypothesis that they are separate species. We found two groups of lineages, with small (250–500 Mbp) and large (2300–3500 Mbp) genomes. Moreover, different populations within one lineage also demonstrated variation in genome size (15–25 %). We compared the obtained data to phylogenetic trees based on transcriptome data. Genome size in ancestral population was more likely to be big. It increased or decreased independently in different lineages, and these processes could be associated with changes in genome size and/or transition to endogeic lifestyle.

Highlights

The amount of nuclear DNA in eukaryotes varies widely and does not correlate with the complexity of an organism (Cavalier-Smith, 1978; Gregory, 2001)
It is generally believed that genome size and architecture must be common in different populations so they remain genetically and reproductively compatible, i. e. remain a species
Significant variation in genome size not associated with polyploidy could have accumulated in this complex. To elucidate this question we studied genome size in several genetic lineages of E. nordenskioldi using flow cytometry

Summary

Introduction

The amount of nuclear DNA in eukaryotes varies widely and does not correlate with the complexity of an organism (Cavalier-Smith, 1978; Gregory, 2001). This phenomenon was dubbed the “C-paradox” (Thomas, 1971). The patterns of intraspecific diversity are generally less known. The known cases of high variation in intraspecific genome size (Alvarez-Fuster et al, 1991; Marescalchi et al, 1998; Neiman et al, 2011; Stelzer et al, 2011; Jeffery et al, 2016) are often explained by the presence of the so-called cryptic, or sister, species, which were not detected earlier

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