Clonal and morphological variation in marginal populations of parthenogenetic earthwormsOctolasion tyrtaeumandO. cyaneum(Oligochaeta, Lumbricidae) from eastern Fennoscandia

Abstract

Clone pool diversity was studied in two parthenogenetic Octolasion species in South Finland belonging to the region of Fennoscandia where the species occur at the northern margin of their European range. In spontaneously dispersing O. tyrtaeum we recorded 24 clones (238 individuals/8 localities), but in anthropochorously dispersing O. cyaneum only two clones (134 ind./4 locs.) were found. In O. tyrtaeum the clone pools of the East ( = sample region) and the North were more similar to each other than to that in the West. Clone groups showed a clinal distribution pattern, which suggests that they may be adapted to regional environments. The low clonal heterogeneity of O. cyaneum is attributed to a small founder population and clonal drift. Morphological variability showed that characters related to reproductive organs vary extremely little in the two species. Considering somatic characters, segment number seemed to be mostly controlled by the genotype, whereas body size varied mostly according to the locality and region implying the role of environmental variables. In the North, O. tyrtaeum adults were larger than their counterparts in the East and the West.

Features of the genetic structure of the earthworms Aporrectodea (Superspecies) Caliginosa (Oligochaeta: Lumbricidae) complex in Ukraine

“…In fact, the genus Ostolasium, the individual Lumbricidae of which are large in size, exhibit a far lower level of clonal diversity [5,10] than those found in A. trapezoides in the present investigation. For example, in Fennoscandia the number of clones in O. Tyrtaeum amounted to 24 in a set of 238 individuals, while in O. cyaneus there were only 2 clones among 138 individuals.…”

“…According to these studies, some of these species are capable of forming a series of even-and odd-numbered polyploid forms, which correspondingly reproduce by means of amphi-or apomixis (parthenogenesis). The application of methods of biochemical gene marking has demonstrated that the polyploid forms of earthworms form a set of clones and are polyphyletic [4][5][6][7][8][9][10][11][12][13][14][15]. Even in an insignificantly small fraction of the habitat, the number of these forms may be counted in the tens and even hundreds of thousands, depending on the particular species.…”

Dispersal and clonal diversity of North-European parthenogenetic earthworms

“…By doing this we have aimed at relating observed variability to clone diversity in North Europe. Our surveys often revealed significant differences in somatic and Biol Invasions (2006) 8:1205-12181207 reproductive characters between local populations but with few exceptions we have not recorded any regular pattern of geographical variability (Terhivuo 1988a;Terhivuo and Saura 1993a, b, 1996, 1997. This emphasizes the key role of local environmental factors on the genotype of the worm that ultimately determine the structural characteristics of the species.…”

Variability of sexual organ possession rates and phylogenetic analyses of a parthenogenetic Japanese earthworm, Amynthas vittatus (Oligochaeta: Megascolecidae)

“…Previous studies discussed the correlation between morphological traits and genetics in parthenogenetic earthworms. In some Lumbricidae earthworms, the morphological traits, such as body size and the number of segments, differed in each clone (Terhivuo, 1988;Terhivuo and Saura, 1993b), but in other species, morphological differences did not correlate with genotypic ones (Terhivuo and Saura, 1990, 1993a, 1993b, 2003. Presence of male pores did not correlate with genotype (Terhivuo andSaura, 1993a, 2006).…”

“…However, parthenogenesis with degradation of reproductive organs is not uncommon. Many studies examined the ecology and genetics of parthenogenetic earthworms, including two families of Lumbricidae and Megascolecidae (Lumbricidae: Jaenike and Selander, 1979;Terhivuo, 1988;Terhivuo and Saura, 1990, 1993a, 1993b, 2003Mezhzherin et al, 2008;Megascolecidae: Gates, 1956). Parthenogenetic earthworms evolutionarily trend towards reduction of reproductive organs, especially male organs (e.g.…”