Impact of feather molt on ectoparasites: looks can be deceiving

Animals possess a variety of well-documented defenses against ectoparasites, including morphological, behavioral, and immune responses. Another possible defense that has received relatively little attention is the shedding of the host's exterior. The conventional wisdom is that ectoparasite abundance is reduced when birds molt their feathers, mammals molt their hair, and reptiles shed their skin. We carried out an experimental test of this hypothesis for birds by manipulating molt in feral pigeons (Columba livia) infested with feather lice (Phthiraptera: Ischnocera). We used two standard methods, visual examination and body washing, to quantify the abundance of lice on the birds. The visual data indicated a significant effect of molt on lice. However, the more robust body washing method showed that molt had no effect on louse abundance. Two factors caused visual examination to underestimate the number of lice on molting birds. First, molt replaces worn feathers with new, lush plumage that obscures lice during visual examination. Second, we discovered that lice actively seek refuge inside the sheath that encases developing feathers, where the lice cannot be seen. The apparent reduction in louse abundance caused by these factors may account for the conventional wisdom that feather molt reduces ectoparasite abundance in birds. In light of our experimental results, we argue that it is necessary to reinterpret the conclusions of previous studies that were based on observational data. Additional experiments are needed to test whether shedding of the host's exterior reduces ectoparasites in other birds, mammals, and reptiles, similar to the impact of facultative leaf drop on herbivorous insects on trees.

     

Patterns of accumulation resulting from Taxes and changes in motility of micro-organisms

Summary An analysis is made of the development of patterns of accumulation of micro-organisms, as governed by tactic responses, changes in motility, and the effects of diffusion.When a soluble crystal is placed in a suspension of micro-organisms, the first manifestation is the development of a clear zone surrounding the crystal. This effect is a physical one, produced by a transfer of momentum from the solute molecules to the organisms.As the solute spreads and its boundary moves more slowly, the organisms are distributed in patterns which depend upon the occurrence of tactic responses and the influence of the solute upon motility. A congregation in the zone occupied by the solute can correspond either to a positive chemotaxis or to an inhibition of motility by the solute. Conversely, a withdrawal from the solute can signal either a negative chemotaxis or an enhancement of motility by the solute.The proper interpretation of the patterns described in Figs. 10 and 11 requires a microscopic study of individual organisms, in which the effect of the reagent upon motility is noted.     

Risk assessment method for submerged weeds in New Zealand hydroelectric lakes

The latent potential for problematic weed growth in a hydro-lake is proportional to water level fluctuation, water clarity, lake shape, littoral gradient and exposure to wave action. These five factors were used to assess a score for measuring the latent potential for weed impact and each factor was allocated a score of 1–5, with a theoretical maximum of 25. Any hydro-lake scoring above 15 could be expected to present potential inconvenience to power generation, given the presence of suitable submerged weed species. Assessment of potential impact arising from weed invasion must firstly determine what species are already established, and whether it is possible for a weed species of greater potential impact to be introduced. The risk of this occurring is dependent upon a number of factors, including public accessibility, proximity to sources of those species and the desirability of the waterbody to potential weed vectors. Once these factors are quantified, appropriate surveillance strategies in high-risk hydro-lakes may then be developed.     

The allelic isozymes of hexose-6-phosphate dehydrogenase isolated from Fundulus heteroclitus: physical characteristics and kinetic properties

Hexose-6-phosphate dehydrogenase (H6PDH-A2; beta-D-glucose:NAD(P)+ oxido-reductase; E.C. 1.1.1.47) of the teleost Fundulus heteroclitus (L.) shows clinal allelic variation along the east coast of North America. Three of the major allelic isozymes have been purified and compared for native molecular weight, subunit molecular weight, isoelectric point, thermal stability, and steady-state kinetic properties (pH 8.0 and 25 degrees C). Significant differences were found among the allelic isozymes for isoelectric point, thermal stability, and some kinetic parameters. The predominant allelic isozyme in northern populations (H6PDH-AcAc) was found to be more sensitive to heat denaturation than were the predominant homozygous allelic isozymes isolated from southern populations (H6PDH-AaAa and H6PDH-AbAb). The H6PDH-AcAc allelic isozyme had both a significantly greater Km for glucose-6-phosphate than did either of the southern phenotypes and a significantly greater Km for NADP+ and Ki of NAD+ than did one of the southern phenotypes (H6PDH-AaAa). While the allelic isozymes are functionally nonequivalent, it is not yet known whether these differences are reflected at higher levels of biological organization.      

Aerobiosis and the hemoprotein content of photosynthetic bacteria

Summary Rhodospirillum rubrum and Rhodopseudomonas spheroides, grown under various degrees of illumination, aeration, and iron deprivation, have been assayed for their content of cytochrome c, RHP, catalase, total iron, bacteriochlorophyll, and carotenoids.Concentrations of bacteriochlorophyll and carotenoids were consistent with the findings of Cohen-Bazire et al. (1957).Total iron content, which ranged from 0.017 to 0.04% of the dry weight, reflected the content of the principal hemoproteins but exceeded the amount of iron in these hemoproteins.The catalase content of R. rubrum, on a dry weight basis, was 0.0005% for cells grown anaerobically in the light, and 0.0028% for cells grown in darkness with vigorous aeration; that of Rps. spheroides was 0.006% and 0.25%, respectively. The catalase content in both species rose with increasingly vigorous aeration.Cytochrome c in both species, and RHP in R. rubrum, attained the same levels in cells grown under vigorous aeration as in cells grown anaerobically in the light. In cells grown under limited aeration the levels of these substances were about 50% higher. In Rps. spheroides the RHP content was greatest in cells grown anaerobically, falling under gentle aeration and declining further under more vigorous aeration.Iron deficiency caused a decrease in the catalase content of cells grown anaerobically in the light but not in cells grown aerobically. The content of cytochrome c and of RHP was diminished by iron depletion in aerobic cultures, but not in anaerobic cultures.operated by Union Carbide Corporation for the U.S.Atomic Rnergy Commission.     

Association of serum lipid components and obesity with genetic ancestry in an admixed population of elderly women

The prevalence of metabolic disorders varies among ethnic populations and these disorders represent a critical health care issue for elderly women. This study investigated the correlation between genetic ancestry and body composition, metabolic traits and clinical status in a sample of elderly women. Clinical, nutritional and anthropometric data were collected from 176 volunteers. Genetic ancestry was estimated using 23 ancestry-informative markers. Pearsons correlation test was used to examine the relationship between continuous variables and an independent samples t-test was used to compare the means of continuous traits within categorical variables. Overall ancestry was a combination of European (57.49%), Native American (25.78%) and African (16.73%). Significant correlations were found for European ancestry with body mass index (r = 0.165; p = 0.037) and obesity (mean difference (MD) = 5.3%; p = 0.042). African ancestry showed a significant correlation with LDL (r = 0.159, p = 0.035), VLDL (r = −0.185; p = 0.014), hypertriglyceridemia (MD = 6.4%; p = 0.003) and hyperlipidemia (MD = 4.8%; p = 0.026). Amerindian ancestry showed a significant correlation with triglyceride levels (r = 0.150; p = 0.047) and hypertriglyceridemia (MD = 4.5%; p = 0.039). These findings suggest that genetic admixture may influence the etiology of lipid metabolism-related diseases and obesity in elderly women.