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Niche segregation may prevent competitive exclusion and promote local coexistence. This typically results in the occupation of different habitats. In the freshwater ostracod Eucypris virens (Jurine, 1820), the distribution of sexual and parthenogenetic populations in the temporary Lake Caracuel, central Spain, was not homogeneous. Parthenogens were found everywhere including the littoral, whereas sexuals were restricted to the centre. We investigated the hypothesis that spatial distribution responded to ecological differences. We studied the ecological significance of this segregation by linking environmental data to male presence, sexual fraction, ploidy, and genetic structure of our model organism in 12 ponds in the lake basin. Hydro-chemical and biological data indicated that the observed segregation is not only spatial but also ecological, with sexual E. virens occurring in ponds with shorter and probably more unpredictable hydroperiod. The correlations between environmental gradients and E. virens population structure suggest that sexual and parthenogenetic lineages are ecologically segregated. Sexual populations appeared restricted to sufficiently unpredictable environments, while parthenogens dominated environments with longer hydroperiods. Local coexistence seems mediated by spatial heterogeneity in habitat stability. Key words: coexistence, niche segregation, sex, parthenogenesis, habitat permanence, polyploidy, egg bank, Eucypris virens. La segregation de niche peut empecher l'exclusion competitive et promouvoir la coexistence locale. En decoule, typiquement, l'occupation d'habitats differents. Chez l'ostracode d'eau douce Eucypris virens (Jurine, 1820), la distribution des populations sexuelles et parthenogenetiques dans le lac temporaire Caracuel, en Espagne Centrale, n'etait pas homogene. Les parthenogenetiques furent trouves partout y compris sur le littoral, alors que les sexuelles etaient restreintes au centre. Nous investiguons l'hypothese que la distribution spatiale reponde a des differences ecologiques. Nous etudions la signification ecologique de cette segregation en mettant les donnees environnementales en relation avec la presence de males, la proportion sexuelle, la ploidie et la structure genetique de notre organisme modele dans 12 mares du bassin lacustre. Nos donnees hydro-chimiques et biologiques indiquent que la segregation observee n'est pas seulement spatiale mais aussi ecologique, les E. virens sexuels se trouvant dans des mares dont l'hydroperiode est plus courte et probablement plus imprevisible. Les correlations entre les gradients environnementaux et la structure de la population d'E. virens suggerent que ses lignees sexuelles et asexuelles sont ecologiquement segreguees. Les populations sexuelles apparaissent restreintes aux environnements suffisamment imprevisibles, alors que les parthenogenetiques dominent dans les hydroperiodes longues. Une coexistence locale semble favorisee par une heterogeneite dans la stabilite de l'habitat. Mots-cles: coexistence, segregation de la niche, sexe, parthenogenese, permanence de l'habitat, polyploidie, reserve d'ceufs, Eucypris virens., Introduction The phenomenon where sexual populations are restricted to a core area while parthenogenetic lineages occupy a wider geographic range is termed geographic parthenogenesis (Vandel 1928). It has been described [...]

A study assesses primary (after hatching) and secondary (after juvenile mortality) outcrossing rates of two mixed-mating snail populations in order to investigate the variation in mating-system parameters and estimate significance of inbreeding depression for secondary outcrossing rate. Results show that outcrossing rate is much more variable among families in the population with the lower average outcrossing rate, suggesting that individuals differ considerably in the mating system.

The South Anchorage Snow Disposal and Sedimentation Basin in Alaska was developed to treat water discharges from commercial, industrial and residential areas including runoff from snow-disposal sites. The project was developed in compliance with EPA's National Pollutant Discharge Elimination System program requiring a permit for a separate stormwater sewer system to control urban runoff. The sedimentation basin and wetland complex was expected to minimize the turbidity observed in local streams.

The adult and metacercaria life stages of a new species of the microphallid genus Atriophallophorus Deblock & Rosé, 1964 are described from specimens collected at Lake Alexandrina (South Island, New Zealand). In addition to molecular analyses of ribosomal and mitochondrial genes, metacercariae of Atriophallophorus winterbourni n. sp. from the snail host Potamopyrgus antipodarum (Gray) were grown in vitro to characterize internal and external morphology of adults using light and scanning electron microscopy and histological techniques. Atriophallophorus winterbourni n. sp. is readily distinguishable from Atriophallophorus coxiellae Smith, 1973 by having a different structure of the prostatic chamber, sub-circular and dorsal to genital atrium, rather than cylindrical, fibrous, elongate and placed between the seminal vesicle and the genital atrium. The new species is most similar to Atriophallophorus minutus (Price, 1934) with regards to the prostatic chamber and the morphometric data, but possesses elongate-oval testes and subtriangular ovary rather than oval and transversely oval in A. minutus. Phylogenetic analyses including sequence data for A. winterbourni n. sp. suggested a congeneric relationship of the new species to a hitherto undescribed metacercariae reported from Australia, both forming a strongly supported clade closely related to Microphallus and Levinseniella. In addition, we provide an amended diagnosis of Atriophallophorus to accommodate the new species and confirm the sinistral interruption of the outer rim of the ventral sucker caused by the protrusion of the dextral parietal atrial scale at the base of the phallus. [ABSTRACT FROM AUTHOR]