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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 [...]

Research has been conducted on seabird ectoparasite Ixodes uriae. The authors have investigated the local genetic structure patterns within this population in the effort to examine the importance of hosts' spatial subdivision for the parasite population functioning, and they report the results.

Parental environments could play an important role in controlling insect outbreaks, provided they influence changes in physiological, developmental or behavioural life-history traits related to fluctuations in population density. However, the potential implication of parental influence in density-related changes in life-history traits remains unclear in many insects that exhibit fluctuating population dynamics, particularly locusts. In this study, we report a laboratory experiment, which enabled us to characterize the life-history trait modifications induced by parental crowding of female individuals from a frequently outbreaking population of Locusta migratoria (Linnaeus) (Orthoptera: Acrididae). We found that a rearing history of crowding led to reduced female oviposition times and increased offspring size but did not affect the developmental time, survival, fecundity, and the sex-ratio and the number of offspring. Because all studied females were raised in a common environment (isolation conditions), these observed reproductive differences are due to trans-generational effects induced by density. We discuss the ecological and evolutionary implications of the observed density-dependent parental effects on the life-history of L. migratoria. [ABSTRACT FROM AUTHOR]

An understanding of the role of factors intrinsic to a species’ life history in structuring contemporary genetic variation is a fundamental, but understudied, aspect of evolutionary biology. Here, we assessed the influence of the propensity to outbreak in shaping worldwide genetic variation in Locusta migratoria, a cosmopolitan pest well known for its expression of density-dependent phase polyphenism. We scored 14 microsatellites in nine subspecies from 25 populations distributed over most of the species’ range in regions that vary in the historical frequency and extent of their outbreaks. We rejected the hypothesis that L. migratoria consists of two genetically distinct clusters adapted to habitats either rarely (nonoutbreaking) or cyclically (outbreaking) favourable to increases in population density. We also invalidated the current subspecific taxonomic classification based on morphometrics. Bayesian inferences indicated evidence of a homogenizing effect of outbreaks on L. migratoria population structure. Geographical and ecological barriers to gene flow in conjunction with historical events can also explain the observed patterns. By systematically assessing the effects of null alleles using computer simulations, we also provide a template for the analysis of microsatellite data sets characterized by a high prevalence of null alleles. [ABSTRACT FROM AUTHOR]

We develop a simple mathematical model to explain the lower than expected levels of infection of wild perennial ryegrass populations in France by endophytic Neotyphodium fungi (formerly named Acremonium). Indeed, seed-borne Neotyphodium endophytes are considered as mutualistic symbionts, because they increase survival, growth and flowering rates of their hosts, and should therefore be present at very high frequencies in all host populations. However, recent surveys have shown that 70% of wild populations of perennial ryegrass harbour such endophytes in France. Moreover, most infected populations exhibit a low level of infection. Our simple model, taking into account the life-cycles of the host and the fungus, shows that these patterns can be satisfactorily explained if the vertical transmission of the fungus is imperfect. Such imperfect transmission, though never measured in natural populations, is likely because of the reported mortality of the endophyte in stored seeds. This process, analogous to the mutation-selection balance of classical population genetics theor, may explain the observed patterns even better when we consider random fluctuations of selection coefficients over time and genetic drift. [ABSTRACT FROM AUTHOR]

The genetic structure of wild populations of Colletotrichum lindemuthianum was evaluated for virulence and molecular markers. Forty-five isolates were collected from five wild common bean populations located in their South-Andean centre of origin. The five pathogen populations were monomorphic in their ITS regions, but 45 polymorphic markers were identified using RAPDs. Polymorpbism for virulence was also observed; 15 pathotypes were characterized on an international set of 12 differentials. A molecular variance analysis (AMOVA) showed that a very large part of the total genetic variation was within populations. Statistical analysis showed that there was a weak though significant differentiation among the five populations for the RAPD and virulence markers. A positive and significant correlation was found between geographic distance and the distances from RAPD and virulence data, suggesting migration between adjacent populations along the Argentinian transect. Our results suggest that the Andean wild isolates of C. lindemuthianum do not reflect all the putative diversity found in the isolates from cultivated common bean. [ABSTRACT FROM AUTHOR]