Coevolution between parasite virulence and host life-history traits

Epidemiological models generally explore the evolution of parasite life-history traits, namely, virulence and transmission, against a background of constant host life-history traits. However, life-history models have predicted the evolution of host traits in response to parasitism. The coevolution of host and parasite life-history traits remains largely unexplored. We present an epidemiological model, based on resource allocation theory, that provides an analysis of the coevolution between host reproductive effort and parasite virulence. This model allows for hosts with either a fixed (i.e., genetic) or conditional (i.e., a phenotypically plastic) response to parasitism. It also considers superinfections. We show that parasitism always favors increased allocation to host reproduction, but because of epidemiological feedbacks, the evolutionarily stable host reproductive effort does not always increase with parasite virulence. Superinfection drives the evolution of parasite virulence and acts on the evolution of the host through parasite evolution, generally leading to higher host reproductive effort. Coevolution, as opposed to cases where only one of the antagonists evolves, may generate correlations between host and parasite life-history traits across environmental gradients affecting the fecundity or the survival of the host. Our results provide a theoretical framework against which experimental coevolution outcomes or field observations can be contrasted.     

The value of 'bat boxes' for attracting hollow-dependent fauna to farm forestry plantations in southeast Queensland

Summary Small artificial nest/roost boxes, originally designed for microbats, were deployed in three farm forest plantations and at one native forest site in southeast Queensland in order to assess their use by vertebrates and their contribution toward enhancing biodiversity in plantation forests through the provision of habitat. Two sites were located in a relatively 'intact' forest landscape (SF 351 and Strano) and two sites in a more 'fragmented' or 'variegated' landscape (Askham and Thomas). Twenty-four boxes were placed at each site over an area covering approximately 1.2–1.8 ha. Each site was checked from five (SF 351) to nine (Askham) times between April 1996 and November 2000. The artificial nest/roost boxes were attractive to a range of small fauna that included Feathertail Gliders ( Acrobates pygmaeus ), Sugar Gliders ( Petaurus breviceps ), Squirrel Gliders ( Petaurus norfolcensis ) and the Yellow-footed Marsupial Mouse ( Antechinus flavipes ), all of which constructed nests inside boxes. Gould's Long-eared Bats ( Nyctophilus gouldi ) used boxes primarily as roosts and maternity sites. In general, fewer animals were recorded in boxes at the two sites located within a relatively 'intact' landscape, while the highest numbers of animals were recorded in boxes in two farm forest plantations within 'variegated' landscapes. The availability of alternative natural hollows and landscape factors appear to be important determinants of the extent to which boxes are occupied. The present study indicates that the biodiversity of farm forests can be enhanced through simple habitat manipulation utilizing artificial roosting or nesting boxes.
Key words Antechinus, biodiversity, farm forestry, glider, marsupial, microbat, nest box, roost.     

A serum-free culture system for stydying solute exchanges in the choroid plexus

Summary Organ cultures of choroid plexus tissues from the lateral ventricle of juvenile rats have been maintained for periods up to 7 wk in a chemically defined, serum-free media. Of several media and various supplements evaluated, the best growth and survival was obtained with the Pasadena Foundation for Medical Research-4 media supplemented with three hormones: epidermal growth factor, insulin, and hydrocortisone. Autoradiographic studies demonstrated that the epithelial cells incorporated [³H]leucine and [³H]thymidine indicating active protein and DNA synthesis, respectively. The organ cultures were characterized by bulbous, vesicular outgrowths from the choroidal villi explants. The fluid-filled lumina of the vesccles reached diameters of 900 μm and were easily accessed by micropipettes. The walls of the vesicles were composed of single layers of epithelial cells in which the ultrastructural features in the in vivo tissue were well maintained. The in vivo polarity (apical end toward the media and basilar end of the cells toward the luminal cavity) was also maintained. This morphologically stable in vitro system seems to be a promising model for investigation of secretory mechanisms of choroidal tissue. This work was supported in part by National Institutes of Health Grant NS 12906-06.     

muI Na+ channels expressed transiently in human embryonic kidney cells: biochemical and biophysical properties.

We describe the transient expression of the rat skeletal muscle muI Na+ channel in human embryonic kidney (HEK 293) cells. Functional channels appear at a density of approximately 30 in a 10 microns 2 patch, comparable to those of native excitable cells. Unlike muI currents in oocytes, inactivation gating is predominantly (approximately 97%) fast, although clear evidence is provided for noninactivating gating modes, which have been linked to anomalous behavior in the inherited disorder hyperkalemic periodic paralysis. Sequence-specific antibodies detect a approximately 230 kd glycopeptide. The majority of molecules acquire only neutral oligosaccharides and are retained within the cell. Electrophoretic mobility on SDS gels suggests the molecules may acquire covalently attached lipid. The channel is readily phosphorylated by activation of the protein kinase A and protein kinase C second messenger pathways.     

Virulence reaction norms across a food gradient

Host-parasite interactions involve competition for nutritional resources between hosts and the parasites growing within them. Consuming part of a host's resources is one cause of a parasite's virulence, i.e. part of the fitness cost imposed on the host by the parasite. The influence of a host's nutritional conditions on the virulence of a parasite was experimentally tested using the mosquito Aedes aegypti and the microsporidian parasite Vavraia culicis. A condition-dependent expression of virulence was found and a positive relation between virulence and transmissibility was established. Spore production was positively influenced by host food availability, indicating that the parasite's within-host growth is limited by host condition. We also investigated how the fitness of each partner varied across the nutritional gradient and demonstrated that the sign of the correlation between host fitness and parasite fitness depended on the amount of nutritional resources available to the host.     

Elephants and human color-blind deuteranopes have identical sets of visual pigments

Being the largest land mammals, elephants have very few natural enemies and are active during both day and night. Compared with those of diurnal and nocturnal animals, the eyes of elephants and other arrhythmic species, such as many ungulates and large carnivores, must function in both the bright light of day and dim light of night. Despite their fundamental importance, the roles of photosensitive molecules, visual pigments, in arrhythmic vision are not well understood. Here we report that elephants (Loxodonta africana and Elephas maximus) use RH1, SWS1, and LWS pigments, which are maximally sensitive to 496, 419, and 552 nm, respectively. These light sensitivities are virtually identical to those of certain "color-blind" people who lack MWS pigments, which are maximally sensitive to 530 nm. During the day, therefore, elephants seem to have the dichromatic color vision of deuteranopes. During the night, however, they are likely to use RH1 and SWS1 pigments and detect light at 420-490 nm.     

Multiplexed fluorescence detection of phosphorylation, glycosylation, and total protein in the proteomic analysis of breast cancer refractoriness

The Multiplexed Proteomics (MP) technology is a new approach that permits quantitative, multicolor fluorescence detection of proteins in one-dimensional or two-dimensional gels. This methodology allows for multiplexed identification and differential analysis of phosphoproteins, glycoproteins, and total proteins within a single gel electrophoresis experiment. Here the MP system was applied to the differential proteomic analysis of pregnancy-induced refractoriness to breast cancer using a rat model system. Differential analyses identified multiple proteins with altered phosphorylation, glycosylation, or protein expression patterns.     

Associations between stress reactivity and sexual and nonsexual risk taking in young adult human males

Release of the hormone cortisol represents a distress response to novel or stressful situations. Individual differences in such reactivity have been conceptualized as representing a relatively enduring, generalizable trait. In this study, cortisol responses to two experimentally manipulated "sexual" and "nonsexual" stressors were used to examine whether stress reactivity is related to sexual and nonsexual risk behavior in young adult males. Analyses were based on 150 males 18 to 25 years old; risk behavior was assessed in confidential, self-administered questionnaires. Analyses indicated that both stressors effectively elicited cortisol increases. Generalized reactivity, defined as a cortisol response to both stressors, was inversely associated with deviance (e.g., theft, substance use) and with two indicators of sexual risk taking (lifetime number of intercourse partners and frequency of condom use). Findings are discussed in terms of cross-situational consistency of stress responses, the utility of stress reactivity for understanding individual differences in risk taking, and the interpretive limitations imposed by study design.