Asymmetrical hybridization and gene flow between Eisenia andrei and E. fetida lumbricid earthworms

• Published in: PloS one Vol. 13; no. 9; p. e0204469
• Main Authors: Plytycz, Barbara, Bigaj, Janusz, Panz, Tomasz, Grzmil, Paweł
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 21-09-2018; Public Library of Science (PLoS)
• Subjects: Alleles; Analysis; Animals; Bacteria; Banding; Biochemistry; Biology and Life Sciences; Biomarkers; Biomedical research; Cross-fertilization; Deoxyribonucleic acid; DNA; Eisenia (Earthworms); Eisenia andrei; Eisenia fetida; Fertilization; Fluorescence; Gene Flow; Gene sequencing; Genes; Genetic aspects; Genetic crosses; Genetic research; Genetic testing; Genomes; Genotype; Genotyping; Hermaphrodites; Hermaphroditism; Hybridization; Hybridization, Genetic; Hybrids; Hypotheses; Immunology; Laboratories; Metabolic pathways; Mitochondria; Offspring; Oligochaeta - genetics; Oligochaeta - metabolism; Phenotype; Phenotypes; Physical Sciences; Pigmentation; Pigmentation - genetics; Progeny; RNA; RNA, Ribosomal, 28S; rRNA; Self-fertilization; Species Specificity; Worms; Zoology; Poland
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0204469

Uniformly pigmented Eisenia andrei (Ea) and striped E. fetida (Ef) lumbricid earthworms are hermaphrodites capable of self-fertilization, cross-fertilization, and asymmetrical hybridization. The latter was detected by genotyping of F1 and F2 progeny of the controlled Ea+Ef pairs by species-specific sequences of maternal mitochondrial COI genes and maternal/paternal nuclear S28 rRNA genes. Among F1offspring there were self-fertilized Ea (aAA), Ef (fFF), and cross-fertilized fertile Ea-derived hybrids (aAF); the latter mated with Ea and gave new generation of Ea and hybrids, while mated with Ef gave Ea, Ef, Ea-derived hybrids and sterile Ef-derived hybrids (fFA). Coelomic fluid of Ea exhibits unique fluorescence spectra called here the M-fluorescence considered as a molecular biomarker of this species. Since similar fluorescence was detected also in some Ef (hypothetical hybrids?), the aim of present investigations was to identify the M-positive earthworms among families genotyped previously. It was assumed that factor/s responsible for metabolic pathways leading to production of undefined yet M-fluorophore might be encoded/controlled by alleles of hypothetical nuclear gene of Eisenia sp. segregating independently from species-specific S28 rRNA nuclear genes, where 'MM' or 'Mm' alleles determine M-positivity while 'mm' alleles determine M-negative phenotypes. Spectra of M-fluorescence were detected in all 10 Ea (aAAMM) and 19 Ea-derived hybrids (aAFMm), three of four Ef-derived hybrids (fFAMm) and one 'atypical' Ef (fFFMm) among 13 Ef earthworms. Among progeny of 'atypical' M-positive Ef (fFFMm) reappeared 'typical' M-negative Ef (fFFmm), confirming such hypothesis. Alternatively, the M-fluorescence might be dependent on unknown gene products of vertically-transmitted Ea-specific symbiotic bacteria sexually transferred to the Ef partner. Hypotheses of intrinsic and external origin of M-fluorescence might complement each other. The presence/absence of M-fluorophore does not correspond with body pigmentation patterns; Ef-characteristic banding appeared in posterior parts of hybrids body. In conclusion, Ea/Ef hybridization may serve for further studies on bi-directional gene flow.