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Arendt J.D.,University of California at Riverside | Reznick D.N.,University of California at Riverside | Lopez-Sepulcre A.,CNRS Ecology and Environmental Sciences Institute of Paris | Lopez-Sepulcre A.,University of Jyvaskyla
Evolution | Year: 2014

There are many theoretical and empirical studies explaining variation in offspring sex ratio but relatively few that explain variation in adult sex ratio. Adult sex ratios are important because biased sex ratios can be a driver of sexual selection and will reduce effective population size, affecting population persistence and shapes how populations respond to natural selection. Previous work on guppies (Poecilia reticulata) gives mixed results, usually showing a female-biased adult sex ratio. However, a detailed analysis showed that this bias varied dramatically throughout a year and with no consistent sex bias. We used a mark-recapture approach to examine the origin and consistency of female-biased sex ratio in four replicated introductions. We show that female-biased sex ratio arises predictably and is a consequence of higher male mortality and longer female life spans with little effect of offspring sex ratio. Inconsistencies with previous studies are likely due to sampling methods and sampling design, which should be less of an issue with mark-recapture techniques. Together with other long-term mark-recapture studies, our study suggests that bias in offspring sex ratio rarely contributes to adult sex ratio in vertebrates. Rather, sex differences in adult survival rates and longevity determine vertebrate adult sex ratio. © 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution. Source

Tully T.,CNRS Ecology and Environmental Sciences Institute of Paris | Tully T.,Paris-Sorbonne University | Potapov M.,Moscow State Pedagogical University
PLoS ONE | Year: 2015

We describe and compare the external morphology of eleven clonal strains and one sexual lineage of the globally distributed Folsomia candida, known as "standard" test Collembola. Of the 18 morphological characters studied, we measured 14 to have significant between-strains genetic variations, 9 of these had high heritabilities (>78%). The quantified morphological polymorphism was used to analyse the within-species relationships between strains by using both a parsimony analysis and a distance tree. These two detailed morphological phylogenies have revealed that the parthenogenetic strains grouped themselves into two major clades. However the exact position of the sexual strain remains unclear and further analysis is needed to confirm its exact relationship with the parthenogenetic ones. The two morphologically based clades were found to be the same as the ones previously described using molecular analysis. This shows that despite large within-strain variations, morphological characters can be used to differentiate some strains that have diverged within a single morphospecies. We discuss the potential evolutionary interpretations and consequences of these different levels of phenotypic variability. © 2015 Tully, Potapov. Source

Vergnes A.,CNRS Ecology and Environmental Sciences Institute of Paris | Vergnes A.,French Natural History Museum | Pellissier V.,French Natural History Museum | Rollard C.,French Natural History Museum | Clergeau P.,French Natural History Museum
Biodiversity and Conservation | Year: 2014

Urban densification is often considered has a green planning policy. However, its effects on woodland arthropods have been rarely analysed. To fill this gap, a multi-taxa approach using three ground-dwelling arthropod assemblages was conducted on 11 woodlands located along an urbanisation gradient. The gradient range from rural areas to one of the most urbanized cities in the world: Paris (France). Spiders, ground beetles and rove beetles were sampled with pitfall traps. We addressed the two following questions: (i) do the responses to urbanisation differ between taxa and/or between trait groups (habitat affinity to woodlands and dispersal capability) along the gradient? (ii) do the richness and abundance show a linear or an intermediate response? Our results showed a replacement of forest and non-flying species by generalist species and flying species with an increasing level of urbanisation. In term of species richness and abundance, the response varied between taxonomical and also trait groups. Some groups showed a strong linear decrease like forest carabids but other groups like spiders showed maximum values at intermediate levels of urbanisation. However, after a threshold of 70 % of built-in area, urbanisation negatively affected the species richness of all taxa and almost all trait groups, with a stronger effect on forest species. We suggest that the urban densification strongly impacted the assemblages of ground-dwelling arthropods by modifying both landscape and local properties of woodlands. To be considered as a green planning policy, the deleterious effects of urban densification should be mitigated. © 2014 Springer Science+Business Media Dordrecht. Source

Raynaud X.,Paris-Sorbonne University | Nunan N.,CNRS Ecology and Environmental Sciences Institute of Paris
PLoS ONE | Year: 2014

Despite an exceptional number of bacterial cells and species in soils, bacterial diversity seems to have little effect on soil processes, such as respiration or nitrification, that can be affected by interactions between bacterial cells. The aim of this study is to understand how bacterial cells are distributed in soil to better understand the scaling between cell-to-cell interactions and what can be measured in a few milligrams, or more, of soil. Based on the analysis of 744 images of observed bacterial distributions in soil thin sections taken at different depths, we found that the inter-cell distance was, on average 12.46 μm and that these inter-cell distances were shorter near the soil surface (10.38 μm) than at depth (>18 μm), due to changes in cell densities. These images were also used to develop a spatial statistical model, based on Log Gaussian Cox Processes, to analyse the 2D distribution of cells and construct realistic 3D bacterial distributions. Our analyses suggest that despite the very high number of cells and species in soil, bacteria only interact with a few other individuals. For example, at bacterial densities commonly found in bulk soil (108 cells g-1 soil), the number of neighbours a single bacterium has within an interaction distance of ca. 20 mm is relatively limited (120 cells on average). Making conservative assumptions about the distribution of species, we show that such neighbourhoods contain less than 100 species. This value did not change appreciably as a function of the overall diversity in soil, suggesting that the diversity of soil bacterial communities may be species-saturated. All in all, this work provides precise data on bacterial distributions, a novel way to model them at the micrometer scale as well as some new insights on the degree of interactions between individual bacterial cells in soils. © 2014 Raynaud, Nunan. Source

Leibold M.A.,University of Texas at Austin | Loeuille N.,CNRS Ecology and Environmental Sciences Institute of Paris
Ecology | Year: 2015

Metacommunity theory indicates that variation in local community structure can be partitioned into components including those related to local environmental conditions vs. spatial effects and that these can be quantified using statistical methods based on variation partitioning. It has been hypothesized that joint associations of community composition with environment and space could be due to patch dynamics involving colonization-extinction processes in environmentally heterogeneous landscapes but this has yet to be theoretically shown. We develop a two-patch, type-two, species competition model in such a "harlequin" landscape (where different patches have different environments) to evaluate how composition is related to environmental and spatial effects as a function of background extinction rate. Using spatially implicit analytical models, we find that the environmental association of community composition declines with extinction rate as expected. Using spatially explicit simulation models, we further find that there is an increase in the spatial structure with extinction due to spatial patterning into clusters that are not related to environmental conditions but that this increase is limited. Natural metacommunities often show both environment and spatial determination even under conditions of relatively high isolation and these could be more easily explained by our model than alternative metacommunity models. © 2015 by the Ecological Society of America. Source

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