Uncertainty in ensemble forecasting of species distribution

Species distribution modelling has been widely applied in order to assess the potential impacts of climate change on biodiversity. Many methodological decisions, taken during the modelling process and forecasts, may, however, lead to a large variability in the assessment of future impacts. Using measures of species range change and turnover, the potential impacts of climate change on French stream fish species and assemblages were evaluated. Our main focus was to quantify the uncertainty in the projections of these impacts arising from four sources of uncertainty: initial datasets (Data), statistical methods [species distribution models (SDM)], general circulation models (GCM), and gas emission scenarios (GES). Several modalities of the aforementioned uncertainty sources were combined in an ensemble forecasting framework resulting in 8400 different projections. The variance explained by each source was then extracted from this whole ensemble of projections. Overall, SDM contributed to the largest variation in projections, followed by GCM, whose contribution increased over time equalling almost the proportion of variance explained by SDM in 2080. Data and GES had little influence on the variability in projections. Future projections of range change were more consistent for species with a large geographical extent (i.e., distribution along latitudinal or stream gradients) or with restricted environmental requirements (i.e., small thermal or elevation ranges). Variability in projections of turnover was spatially structured at the scale of France, indicating that certain particular geographical areas should be considered with care when projecting the potential impacts of climate change. The results of this study, therefore, emphasized that particular attention should be paid to the use of predictions ensembles resulting from the application of several statistical methods and climate models. Moreover, forecasted impacts of climate change should always be provided with an assessment of their uncertainty, so that management and conservation decisions can be taken in the full knowledge of their reliability.     

Ultrastructural investigations of the female genital system of Epiperipatus biolleyi ( Bouvier 1902) (Onychophora,Peripatidae)

Brockmann, C., Mummert, R., Ruhberg, H. and Storch, V. 1999. Ultrastructural investigations of the female genital system of Epiperipatus biolleyi (Bouvier 1902) (Onychophora, Peripatidae). — Acta Zoologica (Stockholm) 80: 339–349. The female genital system of the neotropical peripatid Epiperipatus biolleyi was examined using transmission and scanning electron microscopy. Special attention is given to the two accessory organs of the paired oviducts: the receptacula seminis and the ovarian funnels (Ovarialtrichter). The latter occur only in the Peripatidae, whereas receptacula seminis may also be present in the Peripatopsidae, the only other family in the Onychophora. The ovarian funnels of E. biolleyi are thin-walled and closed from the haemocoel. This trait has also been reported from Epiperipatus trinidadensis, Macroperipatus torquatus, and Eoperipatus weldoni, whereas other peripatids have ovarian funnels which have been reported to open into the haemocoel. The occurrence of artificially opened ovarian funnels, caused by tissue rupture during specimen preparation, is discussed. The presence of spermatozoa both in the receptaculum seminis and in parts of the uterus of the female examined in this study supports the hypothesis that in E. biolleyi insemination of juvenile females occurs directly via the genital opening. The female contained one unstalked cleavage embryo in each uterus horn. Two features of the uterus were found to be unique to E. biolleyi: (1) a second cell layer overlying the uterine epithelium with a pronounced secretory activity (2) embryos are enclosed in a noncellular coat interspersed with numerous transport vesicles.     

Molecular coevolution among cryptically simple expansion segments of eukaryotic 26S/28S rRNAs

The set of "expansion segments" of any eukaryotic 26S/28S ribosomal RNA (rRNA) gene is responsible for the bulk of the difference in length between the prokaryotic 23S rRNA gene and the eukaryotic 26S/28S rRNA gene. The expansion segments are also responsible for interspecific fluctuations in length during eukaryotic evolution. They show a consistent bias in base composition in any species; for example, they are AT rich in Drosophila melanogaster and GC rich in vertebrate species. Dot-matrix comparisons of sets of expansion segments reveal high similarities between members of a set within any 28S rRNA gene of a species, in contrast to the little or spurious similarity that exists between sets of expansion segments from distantly related species. Similarities among members of a set of expansion segments within any 28S rRNA gene cannot be accounted for by their base-compositional bias alone. In contrast, no significant similarity exists within a set of "core" segments (regions between expansion segments) of any 28S rRNA gene, although core segments are conserved between species. The set of expansion segments of a 26S/28S gene is coevolving as a unit in each species, at the same time as the family of 28S rRNA genes, as a whole, is undergoing continual homogenization, making all sets of expansion segments from all ribosomal DNA (rDNA) arrays in a species similar in sequence. Analysis of DNA simplicity of 26S/28S rRNA genes shows a direct correlation between significantly high relative simplicity factors (RSFs) and sequence similarity among a set of expansion segments. A similar correlation exists between RSF values, overall rDNA lengths, and the lengths of individual expansion segments. Such correlations suggest that most length fluctuations reflect the gain and loss of simple sequence motifs by slippage-like mechanisms. We discuss the molecular coevolution of expansion segments, which takes place against a background of slippage-like and unequal crossing-over mechanisms of turnover that are responsible for the accumulation of interspecific differences in rDNA sequences.      

Differences in optical trapping prompt investigations of Agrobacterium surface characteristics

Comparison of the optical trapping efficiency of Agrobacterium rhizogenes and A. tumefaciens strains indicates the A. rhizogenes strain, ATCC 11325, is significantly less efficiently trapped than A. rhizogenes A4, ATCC 15834, and the A. tumefaciens strain LBA4404. Differences were also found in capsule generation, growth media viscosity, and transmission electron microscopy negative staining. These observations imply a difference in surface structure exists. Calcofluor fluorescence suggests the difference involves an exopolysaccharide. Received 1 July 1998/ Accepted in revised form 5 October 1998