The change in genetic diversity down the core‐edge gradient in the eastern spadefoot toad (Pelobates syriacus)

Several hypotheses are available to predict change in genetic diversity when approaching peripheral populations. We used the eastern spadefoot toad in Israel as a model system to examine these hypotheses using population genetics analyses and network theory. Our results contradicted most of the predictions from the ‘abundant centre’ model, that edge populations should have lower density and lower genetic diversity than core populations. Furthermore, dispersal rate between core and peripheral populations is expected to be asymmetric, mostly directed outwards from the core population, but we did not detect such a trend. Our data did not support the hypothesis of no change or a non‐linear change in genetic diversity towards the range edge. However, our results did fit the Fisher (The Genetical Theory of Natural Selection, Clarendon Press, Oxford, 1930) hypothesis, which predicts increase in genetic variability from core to edge of distribution. We attributed this finding to the much harsher climatic and abiotic conditions at the edge, which must be tolerated over generations by both tadpoles and post‐metamorphic individuals in this region. Finally, our results have significant conservation implications for the survival of this species in Israel, where it is critically endangered. We identified two distinct communities, which are genetically linked through two specific rain pools in the Upper Galilee. Details on the spatial subdivision of this species are cardinal for future management and restoration of temporary wetlands in Israel.     

Leaf and root degeneration in early maturing onions: A physiological disorder

Three onion cvs., four sowing dates, two plant densities and two photoperiod regimes were employed to elucidate the factor(s) responsible for leaf and root degeneration which occur frequently in crops of early maturing onions in the Arava valley, Israel, causing heavy economic losses. It was found that the symptoms developed in early maturing genotypes which showed the abnormal sequence of early bulbing in the autumn, followed by the reversal of bulbing later in the season. At this time of season root regrowth is restrained due to low soil temperatures and therefore mineral and water supply to the sprouting foliage is likely to be limited. These interpretations appear to be correct for the problem has been avoided in several seasons by the prevention of early bulbing by sowing later, by keeping population density at standard rates, and by the prevention of mineral deficiency by application of extra nitrogen.     

Isolation and characterization of polymorphic microsatellite markers in Zabrotes subfasciatus Boheman (Coleoptera: Bruchidae)

Bruchid beetles of the genus Zabrotes (Coleoptera: Bruchidae) are important worldwide pests of legume seeds. Samples of Zabrotes subfasciatus and Z. sylvestris were collected from seeds of two Phaseolus species throughout Mexico to assess the role of host plant variation and plant domestication on the evolution of host use in this species. For this purpose six polymorphic microsatellite loci were isolated and characterized for the bruchid Z. subfasciatus. Cross‐species amplification tests were performed on Z. sylvestris and revealed that three loci amplified successfully and were polymorphic in this closely related species.     

Functional anatomy controls ion distribution in banana leaves: significance of Na+ seclusion at the leaf margins

Typical salt stress symptoms appear in banana ( Musa sp., cv. 'Grand Nain' AAA) only along the leaf margins. Mineral analysis of the dry matter of plants treated with increasing concentrations of KCl or NaCl revealed significant accumulation of Na⁺, but not of K⁺ or Cl^-, in the affected leaf margins. The differential distribution of the three ions suggests that water and ion movement out of the xylem is mostly symplastic and, in contrast to K⁺ and Cl^-, there exists considerable resistance to the flow of Na⁺ from the xylem to the adjacent mesophyll and epidermis. The parallel veins of the lamina are enclosed by several layers of bundle sheath parenchyma; in contrast, the large vascular bundle that encircles the entire lamina, and into which the parallel veins merge, lacks a complete bundle sheath. Xylem sap containing a high concentration of Na⁺ is 'pulled' by water tension from the marginal vein back into the adjacent mesophyll without having to cross a layer of parenchyma tissue. When the marginal vein was dissected from the lamina, the pattern of Na⁺ distribution in the margins changed markedly. The distinct anatomy of the marginal vein plays a major role in the accumulation of Na⁺ in the margins, with the latter serving as a 'dumping site' for toxic molecules.