Growth of Dipodomys ordii (Rodentia: Heteromyidae)

Growth rates were determined for laboratory - reared Dipodomys ordii pallidus Durrant & Setzer. Instantaneous growth rates were used to express increase of body weight, total length, tail length, ear length and hind foot length as rates between times of measurements and the instantaneous percentage of maximum size. Data were analyzed for growth periods of 1 – 3, 4 – 15, 16 – 29 and 30 – 70 days. All five parameters provided significant correlations of growth with age during all growth periods. Even though all of the growth parameters correlate with age, these parameters cannot be reliably used to predict age.     

Growth and development of the western harvest mouse, Reithrodontomys megalotis megalotis

Growth rates, gestation period, litter size, reproductive age, sex ratios, and development were studied on 198 litters of Reithrodontomys megalotis megalotis (Baird). Growth was characterized by several standard skull and body measurements and was partitioned into four phases of 1 – 3, 4 – 12, 13 – 22, and 23 – 70 days. Growth was best described by measurements of tail length, ear length, and dried eye - lens weight. Reproductive activity began as early as 38 days for females and 59 days for males. The gestation period was 22 days, and the mean litter size was 3.83 (range 1 – 7). Sex ratio was 53.49 percent males to 46.51 percent females. Reproductive efficiency was 53.53 percent. The development of R. m. megalotis was very similar to that of R. m. dychei. Early breeding, postpartum estrous, year - round breeding, high reproductive efficiency, and a short gestation period contribute to a high reproductive potential in R. m. megalotis.       

Quality assessment of the human genome sequence

As the final sequencing of the human genome has now been completed, we present the results of the largest examination of the quality of the finished DNA sequence. The completed study covers the major contributing sequencing centres and is based on a rigorous combination of laboratory experiments and computational analysis.     

An Erigeron from Nevada and a Penstemon from Idaho

Described as new species are Erigeron cavernensis Welsh & Atwood from the Schell Creek Range and Currant Mountain, White Pine County, Nevada, and Penstemon idahoensis Atwood     

Niche pattern in a Great Basin rodent fauna

Niche pattern of a desert rodent community in shrub habitats of central Utah was examined in the canonical space formed by the first four principal components of trapsite, microhabitat. Positions of species centroids differed significantly (P 1 ) increased with niche breadth (v 1 ) and decreased with increasing difference of centroids of a species from the overall mean habitat (d 1 ). V 1 was positively related to d 1 . Differences between niche pattern of this community and that of deciduous forest small mammals are discussed.     

A structural-maintenance-of-chromosomes hinge domain-containing protein is required for RNA-directed DNA methylation

RNA-directed DNA methylation (RdDM) is a process in which dicer-generated small RNAs guide de novo cytosine methylation at the homologous DNA region. To identify components of the RdDM machinery important for Arabidopsis thaliana development, we targeted an enhancer active in meristems for methylation, which resulted in silencing of a downstream GFP reporter gene. This silencing system also features secondary siRNAs, which trigger methylation that spreads beyond the targeted enhancer region. A screen for mutants defective in meristem silencing and enhancer methylation retrieved six dms complementation groups, which included the known factors DRD1 (ref. 3; a SNF2-like chromatin-remodeling protein) and Pol IVb subunits. Additionally, we identified a previously unknown gene DMS3 (At3g49250), encoding a protein similar to the hinge-domain region of structural maintenance of chromosomes (SMC) proteins. This finding implicates a putative chromosome architectural protein that can potentially link nucleic acids in facilitating an RNAi-mediated epigenetic modification involving secondary siRNAs and spreading of DNA methylation.     

Competition between harvester ants and rodents in the cold desert

Local distribution patterns of three rodent species ( Perognathus parvus, Peromyscus maniculatus, Reithrodontomys megalotis ) were studied in areas of high and low densities of harvester ants ( Pogonomyrmex owyheei ) in Raft River Valley, Idaho. Numbers of rodents were greatest in areas of high ant-density during May, but partially reduced in August; whereas, the trend was reversed in areas of low ant-density. Seed abundance was probably not the factor limiting changes in rodent populations, because seed densities of annual plants were always greater in areas of high ant-density. Differences in seasonal population distributions of rodents between areas of high and low ant-densities were probably due to interactions of seed availability, rodent energetics, and predation.