Effects of genotype and environment on phenotypic variability in Limnocythere inopinata (Crustacea : Ostracoda)

Limnocythere inopinata (Baird) is a Holarctic species, widely distributed i n non-marine waters, and mainly occurring in unisexual populations. It disp lays polymorphic traits which could be useful for taxonomical and (palaeo)e cological purposes, if the origin of these traits could be better understoo d. Three clones of L. inopinata were cultured in the laboratory under vario us temperature and salinity conditions (i.e. temperature 15, 20 and 25 degr ees C, salinity expressed as electrical conductivity 400, 2000, 5000 and 80 00 mu S cm(-1)). Morphological traits for both the valves (shape and size) and soft parts (11 limb setae) were observed. Field populations from Chines e salt lakes and from Austrian lakes were also compared. The freshwater pop ulation from Mondsee and its derived clone M develop larger valves than tho se of the other two clones, clone N (from Neusiedlersee) and clone S (from Seewinkel, Oberer Stinkersee), which live exclusively in saline (alkaline) water. Parthenogenetic specimens from the freshwater lake Mondsee and sexua lly reproducing females from the Chinese salt lakes both have sub-rectangul ar valves with straight dorsal margin; the saline clones and populations ha ve highly arched valves with rounded dorsal margin. No direct effects of te mperature or salinity on valve ornamentation (reticulation, nodation) have been found. At least for nodation, a genetic factor seems apparent, as the saline clones N and S are never nodose, while the freshwater animals from M ondsee and the sexual animals from the Chinese salt lakes can be both with or without nodes. In the former case, number and position of nodes are vari able. Both absolute and relative length of limb setae can be affected by en vironmental factors and by genotype, and this is the first time that this h as been demonstrated in non-marine ostracods. Based on the present observat ions and experiments, it is concluded that L. inopinata is a variable, poly morphic species, consisting of a (semi-) continuous morphological cluster, in which both clonal genotypes and sexual haplotypes are nested. Therefore, Limnocythere sappaensis Staplin and L. binoda Huang are considered synonym s of L. inopinata; L. mongolica Daday is a possible synonym; L. sanctipatri cii sensu Huang and L. dubiosa sensu Huang from Lake Qinghai are most likel y erroneous identifications. Apparently recognisable clones with typical ec ologies cannot be allocated a taxonomic rank, as this does not reflect a ph ylogenetic reality. Such links between recognisable morphologies and typica l ecological ranges are useful for palaeoenvironmental reconstructions, but are applicable at a regional scale only.