A comparative analysis reveals little evidence for niche conservatism in aquatic macrophytes among four areas on two continents

One of the most intriguing questions in current ecology is the extent to which the ecological niches of species are conserved in space and time. Niche conservatism has mostly been studied using coarse‐scale data of species' distributions, although it is at the local habitat scales where species' responses to ecological variables primarily take place. We investigated the extent to which niches of aquatic macrophytes are conserved among four study regions (i.e. Finland, Sweden and the US states of Minnesota and Wisconsin) on two continents (i.e. Europe and North America) using data for 11 species common to all the four study areas. We studied how ecological variables (i.e. local, climate and spatial variables) explain variation in the distributions of these common species in the four areas using species distribution modelling. In addition, we examined whether species' niche parameters vary among the study regions. Our results revealed large variation in both species' responses to the studied ecological variables and in species' niche parameters among the areas. We found little evidence for niche conservatism in aquatic macrophytes, though local environmental conditions among the studied areas were largely similar. This suggests that niche shifts, rather than different environmental conditions, were responsible for variable responses of aquatic macrophytes to local ecological variables. Local habitat niches of aquatic macrophytes are mainly driven by variations in local environmental conditions, whereas their climate niches are more or less conserved among regions. This highlights the need to study niche conservatism using local‐scale data to better understand whether species' niches are conserved, because different niches (e.g. local versus climate) operating at various scales may show different degrees of conservatism. The extent to which species' niches are truly conserved has wide practical implications, including for instance, predicting changes in species' distributions in response to global change.     

Association mapping for phenological, morphological, and quality traits in canola quality winter rapeseed (Brassica napus L.)

QTL mapping by association analysis has recently gained interest in plant breeding research as an alternative to QTL mapping in segregating populations from biparental crosses. In a first experiment on whole-genome association analysis in rapeseed, 684 mapped AFLP markers were tested for association with 14 traits in a set of 84 canola quality winter rapeseed cultivars. For association analysis a general linear model was used. By testing significance of marker-trait associations against a false discovery rate of 0.2, between 1 and 34 associated markers were found for 10 of the 14 traits. Taking into account linkage disequilibrium between the significant markers, these markers represent between 1 and 22 putative QTL for the respective traits. The minimum phenotypic variance explained by the QTL for the different traits ranged from 15% to 53%. A subset of 27 markers were significantly associated with two or more traits. These markers were predominantly shared between traits that were significantly correlated at the phenotypic level. The results show clearly that in rapeseed, QTL mapping by association analysis is a viable alternative to QTL mapping in segregating populations.     

Mobile actin clusters and traveling waves in cells recovering from actin depolymerization

At the leading edge of a motile cell, actin polymerizes in close apposition to the plasma membrane. Here we ask how the machinery for force generation at a leading edge is established de novo after the global depolymerization of actin. The depolymerization is accomplished by latrunculin A, and the reorganization of actin upon removal of the drug is visualized in Dictyostelium cells by total internal reflection fluorescence microscopy. The actin filament system is reorganized in three steps. First, F-actin assembles into globular complexes that move along the bottom surface of the cells at velocities up to 10 microm/min. These clusters are transient structures that eventually disassemble, fuse, or divide. In a second step, clusters merge into a contiguous zone at the cell border that spreads and gives rise to actin waves traveling on a planar membrane. Finally, normal cell shape and motility are resumed. These data show that the initiation of actin polymerization is separated in Dictyostelium from front protrusion, and that the coupling of polymerization to protrusion is a later step in the reconstitution of a leading edge.