Genetic evidence of multiple introductions and mixed reproductive strategy in the peregrine earthworm Pontoscolex corethrurus

Abstract

Pontoscolex corethrurus is a well-known invasive earthworm in tropical zone which is believed to have originated from the Guayana Shield in South America and was described as parthenogenetic. A recent phylogenetic study revealed four cryptic species in the P. corethrurus complex (L1, L2, L3 and L4), among them L1 was particularly widespread and was proposed as P. corethrurus sensu stricto. Here, our aims were to investigate the genetic variation of P. corethrurus L1 in its presumed native and introduced ranges and to examine its reproductive strategy. An extensive dataset of 478 cytochrome oxidase I gene (COI) sequences, obtained in specimens sampled all around the world, revealed a weak COI haplotype diversity with one major haplotype (H1) present in 76% of the specimens. Analyses of the genetic variation of 12 L1 populations were done using both nuclear (226 AFLP profiles) and mitochondrial (269 COI sequences) genetic information. The high AFLP genotype diversity at the worldwide scale and the fact that no genotype was shared among populations, allowed to reject the ‘super-clone’ invasion hypothesis. Moreover, a similar level of mean genetic diversity indices were observed between the introduced and native ranges, a pattern explained by a history of multiple introductions of specimens from different parts of the world. At last, occurrence of identical AFLPs genotypes (i.e. clones) in several population confirmed asexual reproduction, but recombination was also revealed by gametic equilibrium analysis in some populations suggesting that P. corethrurus L1 may have a mixed reproductive strategy.