Introduced populations of Dendrodrilus rubidus ssp. (oligochaeta:lumbricidae) at Crozet, Kerguelen and Amsterdam islands: effects of temperature on growth patterns during the juvenile stages

Abstract

Dendrodrilus nibidus (Savigny, 1826), one of the worldwide distributed Lumbricidae, is present in many subantarctic islands. D. r. tenuis (Eisen, 1874) occurs at Possession Island (Crozet archipelago) and at Amsterdam Island while D. r. norvegicus (Eisen, 1874) is present at Kerguelen Islands. Individuals of these three populations have been bred in order to compare their growth patterns at different temperatures and to demonstrate their parthenogenetic or self-fertilization abilities. Analysis of features of the juvenile stage, from hatching to maturity, is provided. We show that parthenogenesis, growth and reproductive abilities over a wide range of temperature (8–20°C) are the mean features which may explain the success of colonization and establishing D. rubidus ssp. in the French subantarctic islands. At 2°C, D. r. tenuis is active and grows slowly but it is still juvenile after 300 days. The biological parameters studied provide a means to clearly discriminate the two subspecies D. r. norvegicus and D. r. tenuis. D. r. norvegicus shows a lower growth rate and a lower weight of individuals at every developmental stage and the total duration of the juvenile stage is about one third longer than those of D. r. tenuis at Crozet. On the other hand, the D. r. tenuis populations from Crozet and Amsterdam show close growth patterns even if some biological parameters, such as the specific growth rate or the duration of the juvenile stage, differ significantly between the two populations.