Cytochemistry and Ultrastructure of Hyphae and Haustoria of Peronospora parasitica (Pers. ex Fr.) Fr.

The uniform distribution of nuclei, mitochondria, lipid material,protein, and RNA in the hyphae and haustoria of Peronosporaparasitica was demonstrated by staining techniques. Glycogenwas not detected, the only insoluble carbohydrate material detectedby the periodic acid-Schiff reaction being in the fungal wall.The host cell walls reacted more intensely to this stain thanthe hyphal walls. The reaction of haustorial walls varied betweenthe slight staining reaction characteristic of the fungal walls,and the strong reaction of the host cell wall. Callose sheathswere occasionally seen. Fine structure was found to be similar to that of other Oomycetes.Welldeveloped sheaths of a vesicular nature, possibly synonymouswith callose sheaths, were occasionally seen partly surroundinghaustoria.     

Kinetic Analysis of Chemokinesis of Paramecium1

Paramecia detect and accumulate in or disperse from some chemicals. Cells do this by changing frequency of turning and speed of swimming. There are at least two mechanisms by which cells respond: one dependent on ability to turn, one dependent on speed modulation. There are also two classes of chemicals: those that require the cells' ability to turn in order to cause accumulation and dispersal (type I), and those that apparently require only speed modulation (type II). Attractants of type I cause qualitatively similar changes in behavior to repellents of type II and the converse; therefore, assays are needed to distinguish between these two classes of chemicals, despite qualitatively similar behavior of some attractants and repellents. We examined two assays of paramecium chemoresponse, T-maze assay and well test, to understand how the T-maze distinguishes between attractants of type I and repellents of type II and why the well test does not.     

Using space‐for‐time substitution and time sequence approaches in invasion ecology

1. Invasion biologists use two main approaches to evaluate the effects of non‐native species (NNS) on diversity of native species (DNS), namely space‐for‐time and time approaches. These approaches have pitfalls related to lack of controls: the former lacks pre‐invasion data, while the latter often lacks data from non‐invaded sites. 2. We propose a framework that combines space‐for‐time and time approaches and which should result in more focused mechanistic hypotheses and experiments to test the causes of invasibility and the effects of NNS on DNS. We illustrate the usefulness of our framework using two case studies: one with the submersed macrophyte, Hydrilla verticillata, in reservoir and the other with the fish, Geophagus proximus, in a large river–floodplain system. 3. Hydrilla verticillata invaded sites with DNS similar to that found in non‐invaded sites, indicating that biotic and/or abiotic factors did not influence invasion success; however, DNS increased over time in invaded sites compared with non‐invaded sites, suggesting that H. verticillata facilitated natives. In contrast, G. proximus invaded sites with higher DNS than non‐invaded sites, suggesting that biotic and/or abiotic factors favouring natives were important for invasion success, but DNS increased in invaded and non‐invaded sites over time, indicating that an independent factor contributed to DNS increases. 4. Conclusions from both studies would have been inaccurate or incomplete if the space‐for‐time and time approaches had not been used in combination as proposed in our framework.     

Drilling by Octopus vulgaris(Mollusca: Cephalopoda) in the Mediterranean

Octopus vulgaris drills holes in the shells of a variety of molluscs. The walls of the cavities drilled exhibit dissolution of mineral and organic material. The features which characterize the cavities have been described. The composition and structure of the shell itself is important in determining the size, shape and form of the cavity drilled, and not the size of the octopus. Capture, drilling the shell, and eating the occupant may take less than one hour.     

Callitriche Stem Elongation is controlled by Ethylene and Gibberellin

Callitriche platycarpa is a freshwater plant characterized by floating rosettes of leaves connected to the water-bed by threadlike (diameter < 1 mm) stems. The internodes within the rosettes are immature and short (< 2 mm). If they mature at the water surface, they become 10 to 30 mm long, but if the rosette is submerged the internodes elongate faster and to a greater extent (25–60 mm). This method of growth rate control is of interest.     

PRIMARY PEPTIDE SEQUENCES FROM SQUID MUSCLE AND OPTIC LOBE MYOSIN IIs: A STRATEGY TO IDENTIFY AN ORGANELLE MYOSIN

The squid giant axon provides an excellent model system for the study of actin-based organelle transport likely to be mediated by myosins, but the identification of these motors has proven to be difficult. Here the authors purified and obtained primary peptide sequence of squid muscle myosin as a first step in a strategy designed to identify myosins in the squid nervous system. Limited digestion yielded fourteen peptides derived from the muscle myosin which possess high amino acid sequence identities to myosin II from scallop (60–95%) and chick pectoralis muscle (31–83%). Antibodies generated to this purified muscle myosin were used to isolate a potential myosin from squid optic lobe which yielded 11 peptide fragments. Sequences from six of these fragments identified this protein as a myosin II. The other five sequences matched myosin II (50–60%, identities), and some also matched unconventional myosins (33–50%). A single band that has a molecular weight similar to the myosin purified from optic lobe copurifies with axoplasmic organelles, and, like the optic lobe myosin, this band is also recognized by the antibodies raised against squid muscle myosin II. Hence, this strategy provides an approach to the identification of a myosin associated with motile axoplasmic organelles.     

Population genomics of the inbred Scandinavian wolf

The Scandinavian wolf population represents one of the genetically most well-characterized examples of a severely bottlenecked natural population (with only two founders), and of how the addition of new genetic material (one immigrant) can at least temporarily provide a 'genetic rescue'. However, inbreeding depression has been observed in this population and in the absence of additional immigrants, its long-term viability is questioned. To study the effects of inbreeding and selection on genomic diversity, we performed a genomic scan with approximately 250 microsatellite markers distributed across all autosomes and the X chromosome. We found linkage disequilibrium (LD) that extended up to distances of 50 Mb, exceeding that of most outbreeding species studied thus far. LD was particularly pronounced on the X chromosome. Overall levels of observed genomic heterozygosity did not deviate significantly from simulations based on known population history, giving no support for a general selection for heterozygotes. However, we found evidence supporting balancing selection at a number of loci and also evidence suggesting directional selection at other loci. For markers on chromosome 23, the signal of selection was particularly strong, indicating that purifying selection against deleterious alleles may have occurred even in this very small population. These data suggest that population genomics allows the exploration of the effects of neutral and non-neutral evolution on a finer scale than what has previously been possible.