Island biogeography of a North European parthenogenetic earthworm: Fugitive clones of Eiseniella tetraedra (Sav.) (Lumbricidae)

A survey of the obligate parthenogenetic lumbricid Eiseniella tetraedra (Sa v.) in the Skeppsvik archipelago and in sites by the River Savaran near the city of Umea in northern Sweden revealed 94 'clones' among the 449 worms c ollected, The clones were defined through allozyme combinations in four pol ymorphic enzyme systems. We recorded 18 clones in common to the island and the riverside sample sets in 1996 and/or 1997, but, their proportion was si gnificantly higher on the islands. Five (28%) of these clones were recorded on the islands in both years. Moreover, in 1996 the individuals of the lat ter five clones made up 50% of the sample catch of the islands whereas in 1 997 the corresponding proportion was 74%. Accordingly, there seems to be di spersing 'fugitive' clones that are able to establish themselves on the isl ands and even increase in relative numbers there. About 81% of the E. tetra edra individuals from the islands in 1996-97 represented clones also presen t by the River Savaran, which flows to the Skeppsvik archipelago. In the ri verside sample catch, however, only 35% of the individuals belonged to thes e clones. This and the high annual turnover rate of the clones (> 80%) in t he archipelago imply the wide inland basin of the River Savaran to be the m ain source of clones to the Skeppsvik archipelago. Low clone pool diversity , impact of fugitive clones and high turnover rate of clones indicate a gra dual shift of the island clone pool away from that of the mainland. This sh ift is opposed by a flow of mainland clones by the River Savaran.