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

Discovery and characterization of the α-amylases cDNAs from Enchytraeus albidus shed light on the evolution of "Enchytraeus-Eisenia type" Amy homologs in Annelida

Although enchytraeids have gained popularity in scientific research, fundamental questions regarding their feeding ecology and biology remain largely unexplored. This study investigates α-amylases, major digestive enzymes responsible for hydrolyzing starch and similar polysaccharides into sugars, in Enchytraeus albidus. Genetic data related to α-amylases is currently lacking for the family Enchytraeidae but also for the entire Annelida. To detect and identify coding sequences of the expressed α-amylase genes in COI-monohaplotype culture (PL-A strain) of E. albidus, we used classical "gene fishing" and transcriptomic approaches. We also compared coding sequence variants of α-amylase retrieved from transcriptomic data related to freeze-tolerant strains. Our results reveal that E. albidus possesses two distinct α-amylase genes (Amy I and Amy II) that are homologs to earthworm Eisenia fetida Ef-Amy genes. Different strains of E. albidus possess distinctive alleles of α-amylases with unique SNP patterns specific to a particular strain. Unlike Amy II, Amy I seems to be a highly polymorphic and multicopy gene. The domain architecture of the putative Amy proteins was found the same as for classical animal α-amylases with ABC-domains. A characteristic feature of Amy II is the lack of GHGA motif in the flexible loop region, similarly to many insect amylases. We identified "Enchytraeus-Eisenia type" α-amylase homologs in other clitellates and polychaetes, indicating the ancestral origin of Amy I/II proteins in Annelida. This study provides the first insight into the endogenous non-proteolytic digestive enzyme genes in potworms, discusses the evolution of Amy α-amylases in Annelida, and explores phylogenetic implications.

Polymorphic microsatellite markers demonstrate hybridization and interspecific gene flow between lumbricid earthworm species, Eisenia andrei and E. fetida

The lumbricid earthworms Eisenia andrei (Ea) and E. fetida (Ef) have been used as model organisms for studies on hybridization. Previously they have been identified by species specific sequences of the mitochondrial COI gene of maternal origin ('a' or 'f') and the nuclear 28S gene of maternal/paternal origin ('A' or 'F'). In experimental crosses, these hermaphroditic species produce progeny of genotypes Ea (aAA), Ef (fFF) and hybrids (aAF and fFA) originating by self-fertilization or cross-fertilization. To facilitate studies on new aspects of the breeding biology and hybridization of earthworms, polymorphic microsatellite markers were developed based on 12 Ea and 12 Ef specimens and validated on DNA samples extracted from 24 genotyped specimens (aAA, fFF, aAF and fFA) from three laboratory-raised families and 10 of them were applied in the present study. The results indicate that microsatellite markers are valuable tools for tracking interspecific gene flow between these species.

Genetic diversity and genetic differentiation of Megalobrama populations inferred by mitochondrial markers

BACKGROUND

Megalobrama is economically one of the most important freshwater fish genera in China. However, phylogenetic relationships among M. amblycephala, M. skolkovii, M. hoffmanni and M. pellegrini remain unresolved.

OBJECTIVE

To explore the genetic diversity and phylogenetic relationship of Megalobrama populations belonging to all four species.

METHODS

The concatenated sequences of mitochondrial cytochrome b (Cytb) and control region (CR) were used to analyze the genetic variation, genetic differentiation and population expansion of 15 Megalobrama populations.

RESULTS

The study showed that haplotype diversity and nucleotide diversity of M. hoffmanni and M. skolkovii were high, and that M. hoffmanni was the most genetically divergent of the four species. Haplotype network analysis revealed that M. hoffmanni and M. amblycephala formed a monophyletic group each, while M. skolkovii and M. pellegrini clustered together. There was a high genetic differentiation among the four Megalobrama species, and genetic distance among populations was not affected by geographical distance. Additionally, the results indicated that there was gene flow between the Liangzi Lake (LZL) population and Jinsha River Reservoir (JS) population. Also, Zhaoqing (ZQ) population of M. hoffmanni might have experienced a population expansion.

CONCLUSION

Our study verifies genetic diversity and differentiation of Megalobrama populations, and these findings will represent a significant contribution to the conservation and utilization of germplasm resources of Megalobrama.

Species-specific Cd-detoxification mechanisms in lumbricid earthworms Eisenia andrei, Eisenia fetida and their hybrids

Hermaphroditic lumbricid Eisenia sp. earthworms are ubiquitous and highly resistant to a variety of environmental stressors, including heavy metals. Among the progeny of laboratory mated inter-specific pairs of Eisenia fetida (Ea) and Eisenia andrei (Ef) there are fertile Ha hybrids derived from Ea ova fertilized by Ef spermatozoa and very rare sterile Hf hybrids from Ef ova fertilized by Ea spermatozoa. The aim of the first part of the experiment was to compare the life traits and whole body accumulation of cadmium in adult earthworms from genetically defined Ea, Ef and their hybrids (Ha) exposed for four weeks to commercial soil either unpolluted (control) or cadmium-spiked leading to moderate (M) or high (H) soil pollution (M = 425 and H = 835 mg kg^-1 dry soil weight). Such exposure impaired cocoon production but not affected earthworm viability despite the massive Cd bioaccumulation in the whole earthworm bodies reaching at M and H groups 316-454, 203-338, 114-253, and 377-309 mg kg^-1 dry body weights of Ea, Ef1, Ef2, and Ha, respectively, surprisingly reaching maximum accumulation quantities in hybrids. The second part of the experiment aimed to investigate cadmium-related defense mechanisms at transcriptomic level in coelomocytes non-invasively extruded from coelomic cavities of the new sets of Ea, Ef, Ha, and Hf earthworms exposed to Cd in microcosms for 0 days (control), 2 days, and 7 days (M = 425 mg kg^-1). Expression level of stress-induced Cd-metallothionein (mt) and superoxide dismutase (sod) were gradually up-regulated, while the immune-connected lysenin (lys) was rapidly down-regulated; the expression of glutathione S-transferase (gst) and phytochelatin synthase (pcs) remained unaffected. Mt and sod gene up-regulation and lys gene down-regulation were especially pronounced in Ea-derived hybrids. In sum, capacity of cadmium bioaccumulation and detoxification mechanisms is more efficient in interspecific hybrids than in the pure Ea and Ef species.

The Effects of In Vivo Exposure to Copper Oxide Nanoparticles on the Gut Microbiome, Host Immunity, and Susceptibility to a Bacterial Infection in Earthworms

Nanomaterials (NMs) can interact with the innate immunity of organisms. It remains, however, unclear whether these interactions can compromise the immune functioning of the host when faced with a disease threat. Co-exposure with pathogens is thus a powerful approach to assess the immuno-safety of NMs. In this paper, we studied the impacts of in vivo exposure to a biocidal NM on the gut microbiome, host immune responses, and susceptibility of the host to a bacterial challenge in an earthworm. Eisenia fetida were exposed to CuO-nanoparticles in soil for 28 days, after which the earthworms were challenged with the soil bacterium Bacillus subtilis. Immune responses were monitored by measuring mRNA levels of known earthworm immune genes. Effects of treatments on the gut microbiome were also assessed to link microbiome changes to immune responses. Treatments caused a shift in the earthworm gut microbiome. Despite these effects, no impacts of treatment on the expression of earthworm immune markers were recorded. The methodological approach applied in this paper provides a useful framework for improved assessment of immuno-safety of NMs. In addition, we highlight the need to investigate time as a factor in earthworm immune responses to NM exposure.

Impairment of reproductive capabilities in three subsequent generations of asymmetric hybrids between Eisenia andrei and E. fetida from French, Hungarian and Polish laboratory colonies

Eisenia andrei (Ea) and E. fetida (Ef) lumbricid earthworms are simultaneous hermaphrodites potentially capable of self-fertilization and hybridization. We have shown previously that reproductive isolation in these species is incomplete in Ea and Ef earthworms of French provenance, as viable offspring appeared in inter-specific pairs. Fertile asymmetric hybrids developed from Ea-derived ova fertilized by Ef-derived spermatozoa, as well as Ea or Ef specimens derived after self-fertilization (resulting from admixture of endogenously produced spermatozoa with sperm from a partner), but never Ef-hybrids from Ef-ova fertilized by Ea-spermatozoa. The latter appeared only in backcrosses of Ea-hybrids with the Ef. Here we show that these phenomena are not unique for French Ea/Ef earthworms, but are shared by earthworms from French, Hungarian, and Polish laboratory cultures. Semi-quantitative studies on fertility of Ea-derived hybrids revealed gradually decreasing numbers of offspring in three successive generations, more rapid in backcrosses with Ef than with Ea, and the absence of progeny in pairs of hybrids, despite the presence of cocoons in almost all pairs. Based on species specific mitochondrial and nuclear DNA sequences, we provide the first examples of two unique sterile hybrids with mitonuclear mismatch and potential mitonuclear incompatibility among offspring of one of the hybrid+Ef pairs. Earthworms from the investigated populations did not reproduce when kept from hatching in isolation or with representatives of Dendrobaena veneta but started reproducing upon recognition of a related partner, such as Ea, Ef or their hybrids. The existence of Ea or Ef specimens among offspring of hybrid+Ea/Ef pairs might be explained either by partner-induced self-fertilization of Ea/Ef or hybrid-derived ova, or by cross-fertilization of Ea/Ef /hybrid ova by partner-derived spermatozoa; the latter might contribute to interspecific gene introgression.

Identification of new fluorophores in coelomic fluid of Eisenia andrei earthworms

Coelomic fluid of Eisenia andrei contains a number of UV-fluorescent compounds. In the present study we have found that four of these compounds showed identical fluorescence excitation and emission maxima at 310 nm and 364 nm, respectively, suggesting they share the same chromophore. NMR and HR-MS spectroscopy of the most abundant fluorophore reavealed that its molecule is composed of two quinazoline-2,4-dione rings connected by spermine linker. This compound was earlier indentified in Eisenia andrei as SP-8203. Moreover, we have identified the structure of the two other fluorophores, one differing from SP-8203 by the absence of N-acetyl group, the compound not reported in any other organisms before, and the other already found in E. fetida and regarded as species specific. However, our results indicate that this metabolite is also present in E. andrei in significant amounts. The possible origin and function of these new metabolites is discussed.