Allolobophora chlorotica (Savigny, 1826): Evidence for classification as two separate species

Abstract

Breeding experiments have questioned the status of the green (g) and pink (p) colour morphs of Allolobophora chlorotica. Should they become regarded as separate species, the name Allolobophora virescens (Savigny, 1826) is available for the pink form of this earthworm.

Breeding experiments were established to investigate the status of this species utilising previously unmated laboratory-reared adults. Pairs were set up for 10 days to facilitate mating, separated and then maintained in isolation for 28 days to obtain individual reproduction results. Cocoon production and viability were first determined from intra-morphic (p×p and g×g) and inter-morphic (p×g) pairings. All p×p and g×g pairings bred true with mean cocoon production in g×g (4.6 cocoons/worm/28 days) significantly greater (P<0.05) than in p×p (3.2 cocoons/worm/28 days). In p×g pairings, both pink and green individuals produced cocoons (3.9 and 5.9 cocoons/worm/28 days, respectively). However here, viability of cocoons produced by g was very low at 6%, compared with 59% for p.

In a second experiment, previously unmated offspring from inter-morphic pairings (pg) were paired with like individuals (pg×pg) and also paired with pure bred pink (p1) and green (g1) individuals (p1×pg and g1×pg, respectively). All crosses produced cocoons. All cocoons produced by pg×pg crosses were non-viable. In p1×pg and g1×pg crosses the pg parent produced viable cocoons (64% and 79% viability, respectively) but cocoons produced by p1 and by g1 parents from these matings were 100% non-viable.

It is suggested that severely restricted viability of cocoons produced by the green morph in p×g pairings provides evidence for genetic divergence of the 2 morphs. Furthermore, back-crossing of hybrids (pg) with pure bred morphs has indicated that hybrids are male sterile.