Preparative fractionation of lignin by gel-permeation chromatography

The combination of an agarose gel (Bio-Gel A) and a dioxane–water (1:1) solvent system allowed the fractionation, on a preparative scale, of a very polydisperse, non-derivatized lignin preparation (enzymatically liberated lignin prepared from sweetgum sapwood with Lenzites trabea). Three fractions differing markedly in molecular weight were obtained. A gel of crosslinked alkylated dextran (Sephadex LH-20) with the same solvent system allowed division of the lowest molecular weight fraction into two fractions. These materials were characterized by measurements of intrinsic viscosity and number-average molecular weights in dimethylformamide and dioxane–water. It was established that the two highest molecular weight fractions were associated in an average trimeric form in dioxane-water (1:1) as compared to the form (considered to be molecular) that occurred in dimethylformamide. Molecular size distributions and eluant volumes of the fractions were determined with a Sephadex G-100–formamide system, the latter being one of the most powerful nonaqueous solvents for lignin. Adsorption effects were known to be absent in this case, and the lignin molecules were considered to be unassociated in formamide. The four fractions were distinguishable with the formamide–G-100 system, thus indicating that the original fractionation was based on molecular size. The enzymatically liberated lignin contained molecules that comprised a continuum of molecular weights from approximately monomeric to molecules that were at the limit of the solvating power of dioxane–water (1:1) and dimethylformamide. Limited physicochemical data were consistent with a compact, approximately spherically symmetric shape of the lignin in solution.     

Do temperature and social environment interact to affect call rate in frogs (Crinia signifera)?

Abstract Acoustic displays are pervasive and conspicuous forms of sexual advertisement used by animals to attract mates. Evidence suggests that individuals may use environmental cues and/or the presence of other displaying animals to select the best times for display to optimize the chances of mating. Less well‐known is how the physical and social environment might interact to affect the actual content of the display itself. We examined the effects of social environment and temperature on calling rate in a frog Crinia signifera. We found that both variables interacted to affect call rate but only among continuous callers. Call rate increased with temperature in individuals calling continuously on their own but no relationship was found in frogs calling continuously in the presence of others, either in a duet or in a group calling situation. We suggest that the temperature sensitivity of calling rate in frogs could depend on the social environment of the caller. As such, we suggest caution in generalizing about the way temperature affects calling rates in frogs and encourage greater consideration of how physical and social environments might interact to influence the signal content of acoustic displays.     

Effect of galvanically induced surface potentials on marine fouling

This paper reports the effect of a galvanically produced negative surface potential on the accumulation of marine biofouling. The potential was created by connecting pieces of copper or stainless steel to a layer of Indium/Tin Oxide semiconductor deposited on glass. It was shown that the negative potential significantly reduced the accumulation of biofouling. As the conductive layer is transparent, the technique was used to protect the windows of commercial optical instruments. This technology could provide an inexpensive way of extending deployment times for marine instruments.     

Lottery coexistence models extended to plants with disjoint generations

Abstract. Neither conventional niche theory nor current lottery models offer a satisfactory theoretical scope for modelling coexistence of species with disjoint generations. South-African fynbos and Australian kwongan include many species which are killed by, and recruit only after, fire. We propose a density-dependent lottery model which accommodates the unusual demographics of these species. We show that coexistence requires density dependence in recruitment. The result applies to a wider class of populations than the one considered here. It is applied to non-resprouting species in fynbos and kwongan. We show that the lottery assumption of recruitment in proportion to propagules is often satisfied, while the production of such propagules is often density-dependent, and we discuss some evidence of mechanisms whereby this may occur.