The protective value of the colour and shape of the mountain katydid's antipredator defence

Deimatic behaviour is performed by prey when attacked by predators as part of an antipredator strategy. The behaviour is part of a sequence that consists of several defences, for example they can be preceded by camouflage and followed by a hidden putatively aposematic signal that is only revealed when the deimatic behaviour is performed. When displaying their hidden signal, mountain katydids (Acripeza reticulata) hold their wings vertically, exposing striking red and black stripes with blue spots and oozing an alkaloid-rich chemical defence derived from its Senecio diet. Understanding differences and interactions between deimatism and aposematism has proven problematic, so in this study we isolated the putative aposematic signal of the mountain katydid's antipredator strategy to measure its survival value in the absence of their deimatic behaviour. We manipulated two aspects of the mountain katydid's signal, colour pattern and whole body shape during display. We deployed five kinds of clay models, one negative control and four katydid-like treatments, in 15 grids across part of the mountain katydid's distribution to test the hypothesis that their hidden signal is aposematic. If this hypothesis holds true, we expected that the models, which most closely resembled real katydids would be attacked the least. Instead, we found that models that most closely resembled real katydids were the most likely to be attacked. We suggest several ideas to explain these results, including that the deimatic phase of the katydid's display, the change from a camouflaged state to exposing its hidden signal, may have important protective value.     

Proportional processing of a visual mate choice signal in the green swordtail,Xiphophorus hellerii

During mate choice, receivers often assess the magnitude (duration, size, etc.) of signals that vary along a continuum and reflect variation in signaller quality. It is generally assumed that receivers assess this variation linearly, meaning each difference in signalling trait between signallers results in a commensurate change in receiver response. However, increasing evidence shows receivers can respond to signals non-linearly, for example through Weber's Law of proportional processing, where discrimination between stimuli is based on proportional, rather than absolute, differences in magnitude. We quantified mate preferences of female green swordtail fish, Xiphophorus hellerii, for pairs of males differing in body size. Preferences for larger males were better predicted by the proportional difference between males (proportional processing) than the absolute difference (linear processing). This demonstration of proportional processing of a visual signal implies that receiver perception may be an important mechanism selecting against the evolution of ever-larger signalling traits.     

Chirality differences in amino acid retention and release from the acid-extractable pool of cultured mammalian cells

In previous work, no chiral differences were found between D and L enantiomers of Leu in their ability to displace one another from the acid-extractable pool in mammalian cells. Recent evidence suggested otherwise. Our aim is to examine whether, in physiological range, D-amino acids have an equivalent ability to displace L-amino acids from the acid-extractable pool of HeLa cells, and vice versa. In the millimolar range, D-Leu and L-Leu have similar uptake and displacement properties with regard to the acid-extractable pool in HeLa cells, despite only the latter isomer being incorporated into protein. Below millimolar concentrations however, a distinct difference was found in the displacement of tritium-labelled L-Leu from the pool by unlabelled D-Leu compared with unlabelled L-Leu. Thus, unlabelled L-Leu in the external medium at 10⁻⁴ or 10⁻⁵ M displaced an equivalent amount of label from the pool as D-Leu introduced at a concentration approx. one order of magnitude higher, respectively. Reciprocal experiments, in which the acid-extractable pool was preloaded with ³H-D-Leu, confirmed this finding. The chirality difference was noted whether pool prelabelling was carried out at 37 or 0°C; but in order to avoid the complications of active transport mechanisms, the competition work reported here was done at 0°C. Similar chirality differences were observed with other hydrophobic amino acids, including His, Ile and Phe, such as, preferential displacement by the L-Leu racemer compared with the D-Leu racemer below mM levels. This was also true for the D and L forms of the non-utilisable isomer of Leu, norleucine (nLeu). We conclude that D-forms of hydrophobic amino acids have lower affinity for similar or the same intracellular binding sites involved in the acid-extractable pool than their L-forms. The significance of these chirality findings to amino acid pools in cells, and to the predominance of L-forms of amino acids in the biosphere is considered.     

Purification and characterization of an (Na++K+)-ATPase proteolipid labeled with a photoaffinity derivative of ouabain

Highly purified lamb kidney (Na⁺+K⁺)-ATPase was photoaffinity labeled with the tritiated 2-nitro-5-azidobenzoyl derivative of ouabain (NAB-ouabain). The labeled (Na⁺+K⁺)-ATPase was mixed with unlabeled carrier enzyme. Two proteolipid (γ1 and γ2) fractions were then isolated by chromatography on columns of Sepharose CL-6B and Sephadex LH-60. The two fractions were interchangeable when rechromatographed on the LH-60 column, suggesting that γ1 is an aggregated form of γ2. The total yield was 0.8–1.5 mol of γ component per mol of catalytic subunit recovered. This indicates that the γ component is present in stoichiometric amounts in the (Na⁺+K⁺)-ATPase. The proteolipids that were labeled with NAB-ouabain copurified with the unlabeled proteolipids.     

Defect in macrophage effector function confers Salmonella typhimurium susceptibility on C3H/HeJ mice

The defective allele of the endotoxin response locus (Lps^d) renders mice (e.g., C3H/HeJ strain) both endotoxin hyporesponsive and susceptible to Salmonella typhimurium. In this study, the mechanism of Lps^d-regulated susceptibility to murine typhoid was examined. C3H/ HeJ mice became significantly more resistant to S. typhimurium by reconstitution with bone marrow from syngeneic C3H/HeN mice (Lpsⁿ, salmonella resistant). Thus, the Lps^d resistance defect appeared to reside in a radiosensitive bone marrow-derived cell(s). At least one of the abnormal cell types appeared to be a macrophage because C3H/HeJ mice preinfected with Mycobacterium bovis (BCG) were, in contrast to controls, able to restrict early salmonella replication in their spleens and displayed a signficant increase in mean time to death. In contrast, no deficiency in uptake of salmonellae by C3H/HeJ macrophages was observed. These results indicate that the early deaths of C3H/HeJ mice following S. typhimurium challenge reflect a failure of their macrophages to limit the growth of these gram-negative bacteria.     

EFFECTS OF ICE ON ASCOPHYLLUM NODOSUM WITHIN THE GREAT BAY ESTUARY SYSTEM OF NEW HAMPSHIRE-MAINE12

The, effects of ice on Ascophyllum nodosum (L.) Le Jolis within the Great Bay Estuary System of New Hampshire-Maine, U.S.A. were assessed during the winter of 1980–81. Approximately 50% of the plants late fall standing crop, or an estimated 136 tonnes dry weight, was removed by ice-rafting. Pieces of Ascophyllum removed averaged 22 cm in length, 15 g in fresh weight and generally represented 2–3 years of growth. Although the winter of 1980–81 wax somewhat extreme, a similar pruning process probably occurs each year contributing to the characteristic bushy habit of attached inner estuarine plants. Ascophyllum fragments rafted in ice and deposited into salt marshes are suggested as a major source of the, ecad scorpioides (Hornemann) Hauck.     

Analysis of Pleiotropism at the Dominant White-Spotting (W) Locus of the House Mouse: A Description of Ten New W Alleles

Characterization of the pleiotropic effects of ten new putative W locus mutations, nine co-isogenic and one highly congenic with the C57BL/6J strain, reveals a wide variety of influences upon pigmentation, blood formation and gametogenesis. None of the putative alleles, each of which is closely linked to Ph, a gene 0.1 cM from W, gave evidence of complementation with W³⁹, a new allele previously shown to be allelic to W^v. All W*/W³⁹ genotypes resulted in black-eyed-white anemics with reduced gametogenic activity.¹ Homozygotes for seven of these mutations are lethal during perinatal life; anemic embryos have been identified in litters produced by intercross matings involving each of these alleles.—Phenotypes of mice of several mutant genotypes provide exceptions to the frequent observation that a double dose of dominant W alleles (e.g., W/W^v or W/W) results in defects of corresponding severity in each of the three affected tissues. One viable homozygote has little or no defect in blood formation, and another appears to have normal fertility. The phenotypes of these homozygotes support the conclusion that the three tissue defects are not dependent on each other for their appearance and probably do not result from a single physiological disturbance during the development of the embryo.—Although homozygosity for members of this series results in a wide range of phenotypes, the absence of complementation of any allele with W³⁹, the close proximity of each mutant to Ph, and the fact that all alleles produce detectable (though sometimes marginal) defects in the same tissues affected by W and W^v, support the hypothesis that each new mutant gene is a W allele.     

The Behaviour of Red Kangaroos (Megaleia rufa) on Hot Summer Days

To investigate the functional significance of the behaviour of large mammals in hot, arid conditions, field observations were made of the behaviour of red kangaroos. The behaviour of individual animals was recorded in detail during hot summer days and measurements of the prevailing temperature and radiation environment were made. Changes in the postures adopted by animals during the day are described in relation to environmental conditions; and the occurrence of certain postures and behaviours at periods of greatest heat stress is reported.