Abstract
Lumbricid earthworms Eisenia andrei (Ea) and E. fetida (Ef) are simultaneous hermaphrodites with reciprocal insemination capable of self-fertilization while the existence of hybridization of these two species was still debatable. During the present investigation fertile hybrids of Ea and Ef were detected. Virgin specimens of Ea and Ef were laboratory crossed (Ea+Ef) and their progeny was doubly identified. 1 –identified by species-specific maternally derived haploid mitochondrial DNA sequences of the COI gene being either ‘a’ for worms hatched from Ea ova or ‘f’ for worms hatched from Ef ova. 2 –identified by the diploid maternal/paternal nuclear DNA sequences of 28s rRNA gene being either ‘AA’ for Ea, ‘FF’ for Ef, or AF/FA for their hybrids derived either from the ‘aA’ or ‘fF’ ova, respectively. Among offspring of Ea+Ef pairs in F1 generation there were mainly aAA and fFF earthworms resulted from the facilitated self-fertilization and some aAF hybrids from aA ova but none fFA hybrids from fF ova. In F2 generation resulting from aAF hybrids mated with aAA a new generations of aAA and aAF hybrids were noticed, while aAF hybrids mated with fFF gave fFF and both aAF and fFA hybrids. Hybrids intercrossed together produced plenty of cocoons but no hatchlings independently whether aAF+aAF or aAF+fFA were mated. These results indicated that Ea and Ef species, easy to maintain in laboratory and commonly used as convenient models in biomedicine and ecotoxicology, may also serve in studies on molecular basis of interspecific barriers and mechanisms of introgression and speciation. Hypothetically, their asymmetrical hybridization can be modified by some external factors.
Highlights
IntroductionBecause the molecular-genetic platforms used in these studies are both sensitive and especially specific, it is crucial that the two eco-physiologically similar commonly used species, Eisenia andrei (Ea; ‘red worms’) and E. fetida (Ef; ‘tiger worms’ or ‘brandlings’) are reliably identified
Reproductive output was most efficient in E. andrei, lower in E. fetida, whilst it was very low in inter-specific pairings (Table 1)
The better reproductive performance of E. andrei than E. fetida demonstrated in earthworms from the present experiment was described by other scientists who investigated these species derived from other localities [18, 19, 40]
Summary
Because the molecular-genetic platforms used in these studies are both sensitive and especially specific, it is crucial that the two eco-physiologically similar commonly used species, Eisenia andrei (Ea; ‘red worms’) and E. fetida (Ef; ‘tiger worms’ or ‘brandlings’) are reliably identified. These two species were considered as pigmentation morphs of E. foetida, later as its subspecies. [22]) including findings from our own pilot studies showing that these two species can potentially inter-breed to yield hybrids and fertile hybrid offspring This calls for special care to avoid potential source of error and misinterpretation of data collected during work with specimens of unclear genetic origin
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