Comparative genomics of three non-hematophagous leeches (<i>Whitmania</i> spp.) with emphasis on antithrombotic biomolecules

Leeches are well known for blood-feeding habits and are widely used for medicinal purposes as they secrete various antithrombotic substances. However, some leeches exhibit non-hematophagous habits and their significance for medicinal use is controversial. Here we provide the chromosome-level genomes of two non-hematophagous leeches, <i>Whitmania acranulata</i> and <i>Whitmania laevis</i>, and, in combination with previous results from <i>Whitmania pigra</i>, we compared these genomes with an emphasis on antithrombotic biomolecules. All three species had the same chromosome number of 11. The genome size, repeat site percentage, and number of protein-coding genes of <i>W. laevis</i> (173.87 Mb, 28.28%, 23,818) were similar to those of <i>W. pigra</i> (169.37 Mb, 27.02%, 24,156), whereas these values of <i>W. acranulata</i> (181.72 Mb, 29.55%, 27,069) were higher than those of the other two leeches. <i>W. laevis</i> was a monophyletic clade of <i>W. pigra</i>, whereas <i>W. acranulata</i> had a paraphyletic relationship with <i>W. pigra</i>. The number of antithrombotic genes in <i>W. laevis</i> (<i>N</i> = 76) was similar to that of <i>W. pigra</i> (<i>N</i> = 79), whereas <i>W. acranulata</i> (<i>N</i> = 102) had apparently more such genes. Of the 21 gene families, 9 and 11 were differentially expressed in <i>W. acranulata</i> and <i>W. laevis</i> compared to <i>W. pigra</i>, respectively. The expression profiles of the antithrombotic gene families were more similar between <i>W. acranulata</i> and <i>W. laevis</i>. Although there were several cases of gene loss or pseudogenization, most antithrombotic genes of the three <i>Whitmania</i> species were intact and transcribable. These results provide valuable insights into the evolution of non-hematophagous leeches and development of antithrombotic drugs.