Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Reproduction without cross-fertilisation in the invasive Asian leech Barbronia weberi (Blanchard, 1897) (Hirudinea: Arhynchobdellida).

Abstract

Evidence is presented in this paper for the first time that reproduction without crossfertilisation can occur in the arhynchobdellid leech Barbronia weberi (Blanchard, 1897). The discovery of "virgin birth" in this invasive Asian species was serendipitous in that a single unmated hatchling reared in isolation to maturity unexpectedly laid viable cocoons. In order to confirm unequivocally that this reproduction was indeed non-sexual the experiment was repeated rigorously for five successive generations. The formal possibility that cross-fertilisation may have occurred in the cocoon prior to hatching was specifically investigated by isolating embryos at the earliest stages of viability, well before reproductive structures developed. The cocoons and eggs of each successive generation were carefully quantified. No evidence of diminution of fertility was found in spite of severe inbreeding by the fifth generation. In fact fecundity of the inbred laboratory leeches was comparable to that of the original wild population. A total of 1,147 cocoons containing 4,455 eggs were laid during this year-long study. This was undoubtedly an underestimate of reproductive potential in that a number of healthy individuals had to be culled for pragmatic reasons. That a single individual is capable of producing thousands of progeny in one year, without mating, is sufficient to explain the success of B. weberi as an invasive species. In recent years this alien leech has become established on every inhabited continent. The mechanism of reproduction without cross-fertilisation in B. weberi is unknown but is probably attributable to self-fertilisation linked to its hermaphroditism. Taxonomic and phylogenetic implications of self-fertilisation in B. weberi are discussed.