Magnetic resonance microscopy: in vivo sectioning of a developing insect

Summary The utility of magnetic resonance imaging vis-a-vis insect morphology and development was investigated. MRI is a noninvasive technique that distinguishes between tissues based on proton content and proton environment. At present a resolution of 100 m is achievable. The technique avoids fixation artifacts and allows the detection of motion within the organism.     

Light is a dominant mouse mutation resulting in premature cell death.

Light is a dominant mutant allele of the mouse brown locus which results in hairs pigmented only at their tips. The phenotype is due to premature melanocyte death. We have sequenced the tyrosinase-related protein-1 cDNA encoded at this locus from Light mice and found that it contains a single base alteration from wild-type, causing an Arg to Cys change in the protein. To further elucidate the mutant phenotype, we studied the expression of melanocyte specific genes in the skin of Light mice. We have demonstrated premature melanocyte death, but only in pigmented mice, indicating that the cell death is mediated through the inherent cytotoxicity of pigment production.     

Estimating root biomass and distribution after fire in a Great Basin woodland using cores and pits

Quantifying root biomass is critical to an estimation and understanding of ecosystem net primary production, biomass partitioning, and belowground competition. We compared 2 methods for determining root biomass: a new soil-coring technique and traditional excavation of quantitative pits. We conducted the study in an existing Joint Fire Sciences demonstration area in the central Great Basin. This area is representative of a shrub (sagebrush) ecosystem exhibiting tree (pinyon and juniper) encroachment. The demonstration area had a prescribed burn implemented 4 years prior to our study, and we sampled both control and burned plots. The samples were stratified across 3 microsites (interspace, under shrub, and under tree) and 4 soil depths (0–8, 8–23, 23–38, and 38–52 cm) to determine the effects of plant life form and burning on root biomass. We found that estimates of total root biomass were similar between quantitative pits and our soil cores. However, cores tended to show a more even distribution of root biomass across all microsites and depths than did pits. Overall, results indicated that root biomass differs significantly among microsites and soil depths and that the amount of root biomass at a given depth differs among microsites. Burning reduced root biomass in our study by 23% and altered the spatial distribution of root mass.     

Mycorrhization of ponderosa pine in a second-growth Sierra Nevada forest

Ectomycorrhizal colonization and rooting characteristics were quantified in a mature ponderosa pine ( Pinus ponderosa Dougl. ex Laws.) stand in the western Sierra Nevada. Root length totaled 3835.9 m · m –2 of forest floor surface area, with 96% consisting of the fine-root fraction. Total root dry weight and volume were 2230.4 g · m –2 and 5807.4 cm 3 · m –2 of forest floor area, respectively, with 69% of the former and 75% of the latter accounted for by the coarse fraction. Fine roots were most prevalent in the upper 15 cm of the mineral soil profile, and their abundance declined with increasing depth. Coarse roots were most abundant at a depth of 15–30 cm. Ectomycorrhizal counts totaled 26,814 · m –2 of forest floor area, and an overwhelming preponderance was associated with the fine-root fraction. More than three-quarters of mychorrhizae resided in the upper 15 cm of mineral soil, with an overall trend of declining numbers with increasing depth. Roots and mycorrhizae were exceedingly scarce at a depth of 45–60 cm, and neither was found in the organic soil layer above the mineral profile. A necessary step in understanding the ecophysiological role of mycorrhizae in mature forests is to quantify their abundance in such settings, and the results of this study contribute such information for ponderosa pine.     

Characterizing a first occurrence of bison deposits in southeastern Nevada

Late Holocene bison bones eroding from the badlands topography of Cathedral Gorge State Park in southeastern Nevada have been identified as the remains of Bison and date between approximately 400 and 850 years old. The bones were originally thought to be turn-of-the-century cattle and then early bison, so park personnel had need to solve this interpretive problem. A multidisciplinary team sought information on archaeology, geomorphology, paleontology, and paleoenvironment to document the 1st established occurrence of bison in this part of Nevada and to develop a hypothesis explaining their demise.     

Feeding by the Great Basin spadefoot toad ( Spea intermontana ) (Anura: Pelobatidae)

The present study analyzed the stomach contents of 65 Great Basin spadefoot toads, Spea intermontana (Cope), collected in an area of irrigation runoff in south central Washington State. Toads were collected by pitfall trapping. Traps were maintained for 1 year beginning in April 2002. Toads consumed at least 56 different arthropod taxa belonging to the orders Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, Neuroptera, Orthoptera, Trichoptera, Collembola, and Araneae. Ants and darkling beetles were among the most common prey. Feeding appeared to be very generalized with the toads accepting almost anything they could capture and subdue.     

Herbivorous and parasitic insect guilds associated with Great Basin wildrye ( Elymus cinereus ) in southern Idaho

Insects inhabiting Great Basin wildrye ( Elymus cinereus Scribn. & Merr.) were surveyed at two sites on the Snake River Plain in southern Idaho during 1982 and 1983. Forty-six species of phytophagous insects were observed. In addition, eight parasitoid species were reared from insect hosts in the plant culms and identified. Lifestage, abundance, plant part utilized, and study site were recorded for each insect species collected. Insect guilds at the two sites were compared based on species presence utilizing Sorensen's similarity index. Overall, 26 insect species were common to both sites, yielding a moderate similarity index of 0.62. The majority of the species that constitute the wildrye herbivore guilds were oligophagous (restricted to grasses). Many of these insects feed on grain crops as well as other native and introduced grasses. The relatively high diversity of phytophages on wildrye may be due to its tall, bunchgrass growth form, its abundance within its habitat, its broad geographic range, and the large number of related species of grasses in the region.     

Notes on the genus Bombylius Linnaeus in Utah, with key and descriptions of new species (Diptera: Bombyliidae)

A key to the Utah species of Bombylius is presented. Bombylius heximaculatus, nigriventris, montanus, abdominalis, aestivus, and auriferoides, new species, and lancifer kanabensis, subspecies new, are described from Utah. Bombylius lassenensis, new name, is proposed to replace the preoccupied B. pallescens Johnson and Maughan.         

Field acetylene reduction rates of Lupinus argenteus along an elevational gradient

The effects of elevation and environmental parameters associated with elevation on the dinitrogen fixation rates, N 2 [C 2 H 2 ], of a North American lupine species were evaluated. Lupinus argenteus Pursh plants growing at five elevations on Francis Peak, Utah, were sampled weekly throughout the growing season. The highest elevation site had the greatest frequency of nodulated plants. Influence of the environmental and physiological variables on fixation activity varied with elevation and the mean time of sampling. Soil moisture, nodule dry weight, and air temperature were important. Less than one-half of the observed variation in fixation rates, N 2 [C 2 H 2 ], was accounted for by variation in the associated independent variables. Nevertheless this study documented that nodulated plants of L. argenteus were capable of actively fixing nitrogen at a range of elevations on Francis Peak.