Body size increase in insular rodent populations: a role for predators?

Insular mammalian populations living in areas of small size are often characterized by a drastic change in body mass compared to related continental populations or species. Generally, small mammals (less than 100 g) evolve into giant forms while large mammals (up to 100 g) evolve into dwarf forms. These changes, coupled with changes in other life, behavioural, physiological or demographic traits are referred to generally as the insular syndrome. We tested in this study the relative contribution of three factors — area of island, numbers of competitor species and number of predator species — to changes in body size of the woodmouse (Apodemus sylvaticus) in the Western Mediterranean Sea. Our results, based on a comparative analysis using the phylogenetic independent contrasts method, indicate that the increase in body size is related both to the decrease of island size and to the lower number of predator species. A decrease of competitor species does not seem to have an important effect.     

Präadaptation, Wirtskreiserweiterung and Parallel-Cladogenese in der Evolution von phytophagen Insekten1, 2

Preadaptation, host shifts and parallel cladogenesis in the evolution of phytophagous insects In this contribution we investigate the possibilities to apply concepts developed for the evolution of animal parasites to insect-plant systems. We compare host parasite systems in animals with plant-herbivore systems and list similarities and differences. The terms preadaptation, predisposition, expansion and contraction of host ranges, and parallel cladogenesis are discussed. We enumerate general preadaptations for the evolution of herbivory in insects and preadaptations for shifts between herbivory and entomophagy. Examples are given for expansions of host ranges based on phytochemical or structural characters of host plants. Cases of parallel cladogenesis in herbivoreparasitoid systems and plant-herbivore systems are compiled from the literature. An analysis of the insect fauna of the “thistles” (Cynaroideae) in the Palearctic and Nearctic demonstrates the importance of the evolutionary history of the plant taxa and of the existence of preadapted pools of herbivores for the evolution of guilds of specialized herbivores. The members of the Curculionid taxon Cleoninae provide examples for multiple colonizations and radiations of herbivores on the Cynaroideae. The taxonomic and biological relationships of the weevil genera Rhinocyllus, Bangasternus and Larinus which exploit the flower heads of Cynaroideae, can be interpreted as result of a basic parallel cladogenesis between herbivore and host. A gelelectrophoretic analysis of Larinus spp. supports this hypothesis.     

Genetic diversity among progenitors and elite lines from the Iowa Stiff Stalk Synthetic (BSSS) maize population: comparison of allozyme and RFLP data

Summary Data for restriction fragment length polymorphisms (RFLPs) of 144 clone-enzyme combinations and for 22 allozyme loci from 21 U.S. Corn Belt maize (Zea mays L.) inbreds were analyzed. The genetic materials included 14 progenitors of the Iowa Stiff Stalk Synthetic (BSSS) maize population, both parents of one missing BSSS progenitor, four elite inbreds derived from BSSS, and inbred Mo17. Objectives were to characterize the genetic variation among these 21 inbreds for both allozymes and RFLPs, to compare the results from both types of molecular markers, and to estimate the proportion of unique alleles in the BSSS progenitors. Genetic diversity among the 21 inbreds was substantially greater for RFLPs than for allozymes, but the percentages of unique RFLP variants (27%) and unique allozyme alleles (25%) in the BSSS progenitors were similar. Genetic distances between inbreds, estimated as Rogers' distance (RD), were, on average, twice as large for RFLP (0.51) as for allozyme data (0.24). RDs obtained from allozyme and RFLP data for individual line combinations were only poorly correlated (r = 0.23); possible reasons for discrepancies are discussed. Principal component analysis of RFLP data, in contrast to allozyme data, resulted in separate groupings of the ten BSSS progenitors derived from the Reid Yellow Dent population, the four BSSS elite lines, and Mo17. The remaining six BSSS progenitors were genetically rather diverse and contributed a large number of rare alleles to BSSS. The results of this study corroborate the fact that RFLPs are superior to allozymes for characterizing the genetic diversity of maize breeding materials, because of (1) the almost unlimited number of markers available and (2) the greater amount of polymorphisms found. In particular, RFLPs allow related lines and inbreds with common genetic background to be identified, but a large number of probe-enzyme combinations is needed to estimate genetic distances with the precision required.Joint contribution from Cereal and Soybean Research Unit, USDA, Agricultural Research Service, and Journal Paper No. J-14236 of the Iowa Agricultural and Home Economics Experiment Station, Projects 2818 and 2778     

Removal of zero-quantum interference in NOESY spectra of proteins by utilizing the natural inhomogeneity of the radiofrequency field

Summary A single scan method for the suppression of signals arising from zero-quantum coherences (ZQC) is analysed with respect to its application to NMR experiments on proteins. The ZQC are dephased during a spinlock period due to the natural RF inhomogeneity of a commercial probe. A quantitative analysis of a ZQC-compensated NOESY experiment is given. Although the build-up curve for the cross peaks in ZQC-compensated NOESY experiments differ from those in uncompensated experiments, interproton distances in medium-sized proteins can be evaluated with high accuracy. The proposed method is compared with other techniques for ZQC suppression.     

Isozyme studies in provenance research of forest trees

Summary The nature and origin of the isozymes and the techniques for their detection in forest trees are briefly reviewed. The theories used to interpret the isozyme variation are summarized. Recent isozyme variation studies in provenance research are discussed in relation to known variation pattern detected by classical nursery and field tests. The populations of a tree species can be sometimes, but not always, distinguished by their isozyme patterns. For a number of species, relationships between environment of origin of the provenances and some isozyme frequencies have been statistically established. In one case (Picea sitchensis) where direct comparison between the variation pattern detected by isozymes and the genetic variation of silviculturally important traits was possible, no meaningful relationships between both patterns could be detected. Nei's genetic distances and indices of gene diversity do not appear to be useful in provenance research. The concept of genetic distance based on gene frequencies is probably not very useful in provenance research either.     

The extension reached by the minimization of the polarity distances during the evolution of the genetic code

Summary The level reached by the optimization of the polarity distances during the evolution of the genetic code was investigated. The results, although not conclusive, indicate that this optimization level is higher than the data reported in the literature. The results seem compatible with the reaching of an evolutionary minimum, with respect to the optimization of the polarity distances, by the genetic code during its formation.     

Inferring landscape resistance to gene flow when genetic drift is spatially heterogeneous

In connectivity models, land cover types are assigned cost values characterizing their resistance to species movements. Landscape genetic methods infer these values from the relationship between genetic differentiation and cost distances. The spatial heterogeneity of population sizes, and consequently genetic drift, is rarely included in this inference although it influences genetic differentiation. Similarly, migration rates and population spatial distributions potentially influence this inference. Here, we assessed the reliability of cost value inference under several migration rates, population spatial patterns and degrees of population size heterogeneity. Additionally, we assessed whether considering intra-population variables, here using gravity models, improved the inference when drift is spatially heterogeneous. We simulated several gene flow intensities between populations with varying local sizes and spatial distributions. We then fit gravity models of genetic distances as a function of (i) the ‘true’ cost distances driving simulations or alternative cost distances, and (ii) intra-population variables (population sizes, patch areas). We determined the conditions making the identification of the ‘true’ costs possible and assessed the contribution of intra-population variables to this objective. Overall, the inference ranked cost scenarios reliably in terms of similarity with the ‘true’ scenario (cost distance Mantel correlations), but this ‘true’ scenario rarely provided the best model goodness of fit. Ranking inaccuracies and failures to identify the ‘true’ scenario were more pronounced when migration was very restricted (<4 dispersal events/generation), population sizes were most heterogeneous and some populations were spatially aggregated. In these situations, considering intra-population variables helps identify cost scenarios reliably, thereby improving cost value inference from genetic data.     

Sieving experiment: the controlled recovery of charred plant remains from modern and archaeological samples

Results of experimental retrieval of plant remains (both charred modern and fossil) from three sediment types (clay, gravel and sandy loam) carried out by environmental archaeologists from the Ancient Monuments Laboratory and the Central Archaeology Service, English Heritage, are reported. For each sediment type, six different treatments were carried out using three flotation machines of the Siraf type, two other machines in use in two archaeological units and one experimental machine. The results show that there is invariably considerable discrepancy between the amount of plant material present and that recovered, that the Serif-type machine is among the best currently available and that pretreatment of particular mineral soils may improve recovery of plant macrofossil material.     

Uncertain branch lengths, taxonomic sampling error, and the egg to body size allometry in temperate butterflies (Lepidoptera)

The allometry of egg to body size in temperate butterflies, and the relationships between egg size and larval host structure, taxonomy, voltinism, and duration of the egg stage, are investigated using cross-species analysis and the comparative analysis of independent contrasts. In addition, the effect of two sources of uncertainty that may affect continuous data when treated under a statistical, comparative, framework, is assessed: (1) unknown evolutionary distances, and (2) taxonomic representativity (proportion of species of a given taxon, from which data are available). It is suggested that the effects of taxonomic under-representation could be important in comparative, quantitative studies, but this problem may be tempered by means of weighted regression. Under the assumption that taxonomy represents butterfly phylogeny, egg and adult body size are related by negative allometry (i.e. the slope of the line fitted to the logarithmically transformed data is lower than 1.0). However, the precise slope (0.2-0.9) depends on the method used, branch lengths, and taxonomic sampling. There is evidence for a relationship between a species' voltinism and the number of days it spends in the egg stage, as well as between adult butterfly size and the gross structure of the plants used as larval hosts (woody plants or herbs). Egg size proves to be related to foodplant taxonomy, voltinism, and duration of the egg stage when the data are analysed using species means, but these relationships become non-significant when the comparative method is employed.