We compare data from a survey of ostracode species carried out during 1994-1998 from Northern Italian ricefields with data from the same area collected in the ’60s. Twenty-five species were recorded during a survey of 19 ricefields in 1994-98 as against 46 species found in 16 ricefields over thirty years ago. Three of these species (Ilyocypris biplicata, Chlamydotheca incisa and Chrissia sp.), as well as six among the 27 species found in the '60s but not recorded during 1994-1998, were found in Italy only in the ricefield habitat. Three species were recorded for the first time in Italy: Hemicypris dentatomarginata, Ilyocypris monstrifica and Chrissia sp. Eight taxa (Chlamydotheca incisa, Chrissia sp., Cypretta turgida, Dolerocypris sinensis, H. dentatomarginata, Isocypris beauchampi, Strandesia spinulosa and Tanycypris pellucida) were considered endemic to South America, Africa or Asia and are thought to have been introduced to Italy with useful plants, notably rice varieties. The recording of these species indicates once again the importance of man as an agent for passive dispersal of ostracode and the role of ricefields as a suitable habitat for new exotic colonising species. Heterocypris incongruens is the most widespread species and several other species (D. sinensis, Cypridopsis vidua, Ilyocypris gibba and Isocypris beauchampi cicatricosa) were found in more than 50% of the ricefields sampled: 40% of the species occur in just one or two ricefields. In Northern Italy today, species similarity between ricefields is inversely related to their geographic distance but is not spatially structured. This may be due to the fact that, in ostracodes, the production of passive dispersal resting eggs constrains regional differentiation. Species richness is significantly related to the amount of cultivated area. The decrease in species richness observed over the last thirty years or so may be related to the widespread use of pesticides in local current agricultural practices

We analysed the genetic structure of five populations of Heterocypris from small temporary ponds on the islands of Lampedusa and Linosa (Isole Pelagie, South of Sicily) where we have observed two different adult females morphotypes. The most genetically-differentiated population, Cavallo Bianco, is made up by females only showing a morphology typical of H. incongruens. All other populations, from both islands, are bisexual and their adult females present a lobe-like expansion of the selvage (lamella hyalina) on the posterior margin of the left valve. In one locality, Vallone della Forbice, both female morphotypes occur. The analyses of individuals raised in the laboratory microcosms confirmed the genetic differentiation between morphotypes and their different reproductive modes. The adult females without a lamella hyalina are apomictic, whereas females with this feature are amphimictic. Genetic differentiation of the two female morphotypes is compatible with the hypothesis that the two morphotypes represent different species of Heterocypris although, such a morphological differentiation is not unusual in populations of the same parthenogenetic species, and we found evidence of hybridisation between males and parthenogenetic females.

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The hatching phenology of Heterocypris resting eggs was investigated in laboratory controlled conditions. Microcosms were set up using dry sediments from three freshwater temporary ponds (Cavallo Bianco, Aria Rossa and Vallone della Forbice) of the island of Lampedusa (Sicily) and kept at different temperatures and photoperiods. Hatching time was modulated by different environmental factors. Initial anoxia, induced by the decomposition of the sediment's organic matter, delayed hatching in the microcosm set up with sediments from Vallone della Forbice which has a high organic matter content. Temperature and photoperiod in isolation did not seem to affect hatching significantly, while their interaction did. The coexistence of two female morphotypes with different reproductive modes could not be explained by a differential response to temperature and photoperiod. Coexistence was probably due to disturbance events, such as drying up of ephemeral pools. Some resting eggs (in different percentages in different microcosms) hatched only after a second hydration (after microcosms dried up). Hatching phenology is discussed in relation to genetic differences in egg responsiveness to hatching stimuli and to a bet-hedging strategy in a year-to-year highly variable environment such as the ephemeral ponds of Lampedusa.

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Differences exist in the population structure of Heterocypris in five temporary ponds on the islands of Lampedusa and Linosa (Isole Pelagie, south of Sicily). In a temporary pond on Lampedusa (Cavallo Bianco) we found only H. incongruens females. All the other populations were bisexual, with the female/male sex ratio varying from 1 to 18. We analysed and measured a sub-sample from each population and observed, as a typical morphological feature of adult females in the bisexual populations, a lobe-like expansion of the selvage (lamella hyalina) on the posterior margin of the left valve. In another temporary pond from Lampedusa (Vallone della Forbice) both females with this lamella and others without it occur. We discuss the possible coexistence of two lineages of H. incongruens each having a different reproductive mode. The parthenogenetic lineage comprises females without a lamella hyalina whereas the bisexual females possess this feature. Alternatively, we hypothesise the sympatry of two different species of Heterocypris: H. incongruens and H. barbara. In this hypothesis, H. incongruens is parthenogenetic and H. barbara is amphimictic. Differences in mean body size between the adult females with and without the lamella hyalina are in accordance with values reported in the literature for niche differentiation among sympatric taxa.

Acute toxicity of parathion, dichlobenil and TPBS to Biomphalaria glabrata and Brachydanio rerio was evaluated. Parathion resulted the most toxic substance to the two animals, and Biomphalaria the less sensitive organism, thus confirming that Brachydanio is, within fishes, the least sensitive to toxic agents. The results of the tests are discussed not only in relation to the toxicity of the substances, but also in relation to the mode of manifestation of biological variability, which shows different temporal dynamics depending on the toxic.

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