Climate-driven spatial dynamics of plague among prairie dog colonies.

We present a Bayesian hierarchical model for the joint spatial dynamics of a host-parasite system. The model was fitted to long-term data on regional plague dynamics and metapopulation dynamics of the black-tailed prairie dog, a declining keystone species of North American prairies. The rate of plague transmission between colonies increases with increasing precipitation, while the rate of infection from unknown sources decreases in response to hot weather. The mean annual dispersal distance of plague is about 10 km, and topographic relief reduces the transmission rate. Larger colonies are more likely to become infected, but colony area does not affect the infectiousness of colonies. The results suggest that prairie dog movements do not drive the spread of plague through the landscape. Instead, prairie dogs are useful sentinels of plague epizootics. Simulations suggest that this model can be used for predicting long-term colony and plague dynamics as well as for identifying which colonies are most likely to become infected in a specific year.

Temporal and spatial patterns of Bartonella infection in black-tailed prairie dogs (Cynomys ludovicianus).

We describe the temporal dynamics and spatial distribution of Bartonella in black-tailed prairie dogs (Cynomys ludovicianus) based on a longitudinal study conducted in 20 black-tailed prairie dog (BTPD) colonies in Boulder County, CO from 2003 to 2005. Bartonella infection was widely distributed in all colonies with an overall prevalence of 23.1%, but varied by colony from 4.8% to 42.5% and by year from 9.1 to 39.0%, with a marked increase in Bartonella activity in 2005. Levels of bacteremia varied from 40 to 12,000 colony forming units (CFU) per milliliter of BTPD blood, but were highly skewed with a median of 240 CFU. Bartonella infection rates were unimodal with respect to BTPD body mass, first increasing among growing juveniles, then declining among adults. Infection rates exhibited a sigmoidal response to body mass, such that 700g may prove to be a useful threshold value to evaluate the likelihood of Bartonella infection in BTPDs. Bartonella prevalence increased throughout the testing season for each year, as newly emerged juveniles developed bacteremia. Data from recaptured animals suggest that Bartonella infections did not persist in individual BTPDs, which may explain the relatively low prevalence of Bartonella in BTPDs compared to other rodent species. No association was found between Bartonella prevalence and host population density. Prevalence did not differ between males and females. The spatio-temporal pattern of Bartonella infection among colonies suggests epizootic spread from northern to central and southern portions of the study area. The potential significance of the BTPD-associated Bartonella for public health needs to be further investigated.

Iridoid glycosides ofChelone glabra (Scrophulariaceae) and their sequestration by larvae of a sawfly,Tenthredo grandis (Tenthredinidae).

Analysis ofChelone glabra (Scrophulariaceae) by gas chromatography showed that leaves of this plant contained primarily the iridoid glycoside catalpol, and in a few individuals some aucubin was also detected. There was no difference in the iridoid glycoside content of damaged compared to undamaged plants, nor was there a difference between plants collected from a population in Leverett, Massachusetts, and those from plants in an experimental garden in Cambridge, Massachusetts. Larvae and prepupae of the sawfly,Tenthredo grandis (Tenthredinidae) contained catalpol sequestered from the larval host plant. The exuvia also contained catalpol, whereas the frass contained only aucubin. These results indicate that larvae of this sawfly selectively sequester catalpol, eliminating the aucubin in the frass.

Fate of iridoid glycosides in different life stages of the Buckeye,Junonia coenia (Lepidoptera: Nymphalidae).

The buckeye butterfly,Junonia coenia (Lepidoptera: Nymphalidae), specializes on plants that contain iridoid glycosides. To determine the fate of these compounds in larvae, pupae, and adults of this species, we reared larvae on artificial diets with and without iridoid glycosides, and on leaves of a host plant,Plantago lanceolata (Plantaginaceae). Quantification by gas chromatography showed that newly molted third-, fourth-, and fifth-instar larvae reared on leaves ofP. lanceolata contained means of 5.13, 2.88, and 6.83% dry weight iridoid glycoside. In contrast, the mean iridoid glycoside concentration of actively feeding fifth-instar larvae was 0.28% dry weight, that of pupae was 0.19% dry weight iridoids, and adults contained no detectable iridoids. Feeding experiments suggested that this reduction in actively feeding larvae was due to the metabolism of iridoid glycosides.P. lanceolata leaves in these experiments contained a mean of 1.00% dry weight iridoid glycoside, with a 2:1 ratio of aucubin to catalpol. Calculation of iridoid consumption and utilization indices showed that larvae fed artificial diets consumed, digested, and sequestered aucubin and catalpol in similar ways. When these indices were calculated for larvae fed leaves ofP. lanceolata, catalpol was sequestered twice as efficiently as aucubin.

Influence of plant phenology on the insect herbivore/bittercress interaction.

We tested the hypothesis that generally higher levels of herbivory on bittercress in sun vs in shade, especially by leaf miners, were related to the earlier phenological development of plants in the sun. Naturally-occurring plants in the sun were taller and had longer leaves than did those in the shade during the first three weeks of the growing season, which corresponded with the timing of adult fly oviposition. We divided individual bittercress plants from the sun into three parts: one part was transplanted into willow shade immediately after snow melt; the other two parts were replanted in the sun and one of these was sprayed with insecticide. The transplant experiment had two primary results. First, bittercress transplanted into the shade suffered significantly higher levels of insect damage than either treatment in the sun. Leaf-mining in the shade also increased and equalled that observed in the sun. These results strongly support the phenology hypothesis; higher damage in the sun is due, at least in part, to the earlier development of plants in sun vs in shade early in the season. Second, the ramets with the greatest damage, e.g. the shade treatment, initiated significantly fewer rosettes than did ramets in the other two treatments. The decrease in vegetative reproduction may have been due to the direct effects of increased insect herbivory on these shade plants. This result is particularly interesting because so little information is available on below-ground, vegetative reproductive response to chronic, above-ground foliage loss to native herbs caused by insect herbivores.

Herbivory by leaf miners in response to experimental shading of a native crucifer.

We tested the hypothesis that light intensity was the direct, proximal mechanism causing significantly higher vulnerability of Bittercress (Cardamine cordifolia A. Gray) clones in the sun to herbivory by a leaf-mining fly (Scaptomyza nigrita Wheeler). Clones in the sun were experimentally shaded. Plant performance and losses to leaf miners were compared to controls in the sun and natural willow shade. Leaf-mining damage was significantly higher on artificially-shaded plants (P<0.01), opposite of our expectation. Shading sun plants shifted their growth pattern toward that of naturally-shaded plants. No significant differences were detected in leaf water status or glucosinolate concentrations, eliminating water stress and variation in defensive posture for mediating the between habitat differences in levels of herbivory. Although soluble sugars varied significantly, they were higher in sun than either shade treatment. Total and free amino nitrogen concentrations were highest in the artificially-shaded plants and lowest in naturally-occurring sun plants. Adult flies were more abundant on sun and on artificially-shaded plants than on naturally-shaded plants. Thus, relative abundance of ovipositing flies in the sun-exposed area, combined with the higher nitrogen availability in artificially-shaded plants, form the most plausible hypothesis for factors mediating the experimentally documented pattern of herbivory.

Bioavailability to anemic rats of iron from fresh, cooked or nitrosylated hemoglobin and myoglobin.

Bioavailabilities of heme iron prepared from lyophilized, fresh, cooked, nitrosylated hemoglobin and purified myoglobin in semipurified diets were investigated in two experiments. In experiment 1, the bioavailabilities of porcine and bovine hemoglobins were about one-third that for ferrous sulfate regardless of hemoglobin treatments. The efficiency of hemoglobin regeneration by anemic rats fed nitrosylated pork hemoglobin was significantly depressed compared with that by those fed unnitrosylated products. Cooking did not affect the availability of the heme iron, whereas washing tended to increase it. In experiment 2, the hemoglobin regeneration efficiency of the purified myoglobin diet was lower than reported by others for meat diets, and was even lower than that of the purified hemoglobin diet. The respective efficiency values for the basal, basal + FeSO4, hemoglobin, and myoglobin diets (experiment 2) were 0.073, 0.581, 0.199, and 0.125. The efficiencies of converting hemoglobin and ferrous sulfate iron into hemoglobin by the anemic rats were very similar to reported absorption values for these iron sources by iron-deficient human subjects.