Life history traits in Darwinula stevensoni (Crustacea: Ostracoda) from Southern European populations under controlled conditions and their relationship with genetic features

Abstract

We describe life history traits of the ostracod Darwinula stevensoni through laboratory experiments. This small (about 0.7 mm), ancient, obligate parthenogenetic species appeared to be particulary difficult to handle as its long life cycle (up to 3-4 years) has made lab experiments over several generations very difficult. D. stevensoni is an eurythermal and euryhaline species with low variability in size and shape (both of the carapace and the soft parts). Its genetic variability has also been found to be very low. Survival, clutch size, deposition timing and hatching were evaluated in acclimated and non-acclimated females from seven populations: six from Northern Italy and one from Spain. The samples were collected from three different habitats: four lakes, two streams and one spring. A genetic survey using starch gel electrophoresis had previously revealed that only Glucose phosphate isomerase (Gpi) locus was polymorphic. A clone, homozygous at Gpi locus, is the most common in lacustrine and spring habitats in the whole biogeographic range. Surprisingly, two heterozygous clones dominate in Northern Italian lotic environments. Enzymatic activity of heterozygous and homozygous genotypes at Gpi locus was assayed in order to evaluate the relationship between Gpi activity and fitness. Survival and developmental time were not affected by acclimation, while reproductive potential decreased in acclimated females. In females from running waters, reproduction started later and lasted for a shorter time, clutch size was smaller, and hatching percentage lower than females from lakes. These differences are not directly correlated with differences in enzymatic activities at Gpi locus. This does not rule out an overall genetic control of these characteristics since, in a parthenogenetic species, the whole genome is transmitted without recombination. We stress the intriguing case of D. stevensoni in relation to the concept of the "general purpose genotype"

Limnological characteristics and recent ostracods (Crustacea, Ostracoda) of freshwater wetlands in the Parco Oglio Sud (Northern Italy)

“…Nevertheless, D. stevensoni is rare in the study area, where it was collected from April to August only in OG10, usually at low densities. Its disappearance in October is puzzling, because this species is thought to have no resting stages and long life cycles (up to 3-4 years, Ranta 1979), although temporary disappearance of D. stevensoni from typical sampling stations was also reported by Gandolfi et al (2001). Herpetocypris brevicaudata and Ilyocypris gibba were found in only one of the two lotic environments included in this study (OG06).…”

Spatial segregation of Darwinula stevensoni (Crustacea: Ostracoda) genotypes in lentic and lotic habitats of Northern Italy

“…We have described a very high tolerance of both homozygous and heterozygous genotypes from lacustrine and riverine habitats to conductivity variation and to long-term hypoxia (Gandolfi et al 2001c;Rossi et al 2002). Females from lotic habitats have a smaller clutch size and lower hatching percentage than females from lentic habitats (Gandolfi et al 2001b). The reproductive season is delayed and shorter in females from lotic than from lentic habitats.…”

Food selection in Eucypris virens (Crustacea: Ostracoda) under experimental conditions

“…In field conditions, freshwater ostracods usually show a high reproductive potential, a relatively short generation time and the possibility to grow large populations. Despite these characteristics, they have only rarely been used in laboratory experiments (but see Gandolfi et al, 2001;Van Doninck et al, 2003). We argue that this is partly due to the limited knowledge of their ecological requirements, which makes it hard to obtain stable and extensive cultures.…”

“…In contrast, long days result in the production of predominantly resting eggs, which need desiccation before hatching can occur. As culture medium, mineral water can be used (Otero et al, 1998;Gandolfi et al, 2001) or filtered water from the original habitat (Xia et al, 1997;Yin et al, 1999).…”