Reproductive pair correlations and the clustering of organisms.

Clustering of organisms can be a consequence of social behaviour, or of the response of individuals to chemical and physical cues. Environmental variability can also cause clustering: for example, marine turbulence transports plankton and produces chlorophyll concentration patterns in the upper ocean. Even in a homogeneous environment, nonlinear interactions between species can result in spontaneous pattern formation. Here we show that a population of independent, random-walking organisms ('brownian bugs'), reproducing by binary division and dying at constant rates, spontaneously aggregates. Using an individual-based model, we show that clusters form out of spatially homogeneous initial conditions without environmental variability, predator-prey interactions, kinesis or taxis. The clustering mechanism is reproductively driven-birth must always be adjacent to a living organism. This clustering can overwhelm diffusion and create non-poissonian correlations between pairs (parent and offspring) or organisms, leading to the emergence of patterns.     

Effects of habitat fragmentation and differing mobility on the population structures of a Great Basin dragonfly ( Sympetrum corruptum ) and damselfly ( Enallagma carunculatum )

The population structure of 2 Great Basin odonate species was assessed using protein electrophoresis. Analyses included 7 populations of Sympetrum corruptum (suborder Anisoptera), a migratory and highly mobile dragonfly, and 8 populations of Enallagma carunculatum (suborder Zygoptera), a weak flier that is not known to migrate far from natal water sources. Though we expected the damselfly ( E. carunculatum ) to show greater genetic isolation than the dragonfly ( S. corruptum ), both species apparently had high levels of gene flow (theta = 0.0604 for S. corruptum , theta = 0.0485 for E. carunculatum ) and showed no evidence for isolation by distance. These results suggest that both species are highly vagile and that the most important factors affecting population structure of these odonates may be ecological conditions such as habitat patchiness and the ephemerality of water sources.     

Stable transmission of reversible modifications: maintenance of epigenetic information through the cell cycle

Even though every cell in a multicellular organism contains the same genes, the differing spatiotemporal expression of these genes determines the eventual phenotype of a cell. This means that each cell type contains a specific epigenetic program that needs to be replicated through cell divisions, along with the genome, in order to maintain cell identity. The stable inheritance of these programs throughout the cell cycle relies on several epigenetic mechanisms. In this review, DNA methylation and histone methylation by specific histone lysine methyltransferases (KMT) and the Polycomb/Trithorax proteins are considered as the primary mediators of epigenetic inheritance. In addition, non-coding RNAs and nuclear organization are implicated in the stable transfer of epigenetic information. Although most epigenetic modifications are reversible in nature, they can be stably maintained by self-recruitment of modifying protein complexes or maintenance of these complexes or structures through the cell cycle.     

Distribution of the Shoshone scuplin ( Cottus greenei: Cottidae) in the Hagerman Valley of south central Idaho

Cottus greenei, a potentially threatened species endemic to Idaho, was collected from 49 localities in 25 springs/streams in south central Idaho. Most localities were along the north bank of the Snake River in waters of the Thousand Springs formation, Gooding County. One population was found in a spring in the main Snake River. Another sculpin, Cottus bairdi, was collected with C. greenei at 23 locations in 16 springs/streams. Confusion concerning the type locality of Cottus greenei is discussed.        

Identification of a bacterial inhibitor against g-type lysozyme

Lysozymes are antibacterial effectors of the innate immune system in animals that hydrolyze peptidoglycan. Bacteria have evolved protective mechanisms that contribute to lysozyme tolerance such as the production of lysozyme inhibitors, but only inhibitors of chicken (c-) and invertebrate (i-) type lysozyme have been identified. We here report the discovery of a novel Escherichia coli inhibitor specific for goose (g-) type lysozymes, which we designate PliG (periplasmic lysozyme inhibitor of g-type lysozyme). Although it does not inhibit c- or i-type lysozymes, PliG shares a structural sequence motif with the previously described PliI and MliC/PliC lysozyme inhibitor families, suggesting a common ancestry and mode of action. Deletion of pliG increased the sensitivity of E. coli to g-type lysozyme. The existence of inhibitors against all major types of animal lysozyme and their contribution to lysozyme tolerance suggest that lysozyme inhibitors may play a role in bacterial interactions with animal hosts.     

Molecular basis of parathyroid hormone receptor signaling and trafficking: a family B GPCR paradigm

The parathyroid hormone (PTH) receptor type 1 (PTHR), a G protein-coupled receptor (GPCR), transmits signals to two hormone systems—PTH, endocrine and homeostatic, and PTH-related peptide (PTHrP), paracrine—to regulate different biological processes. PTHR responds to these hormonal stimuli by activating heterotrimeric G proteins, such as G_S that stimulates cAMP production. It was thought that the PTHR, as for all other GPCRs, is only active and signals through G proteins on the cell membrane, and internalizes into a cell to be desensitized and eventually degraded or recycled. Recent studies with cultured cell and animal models reveal a new pathway that involves sustained cAMP signaling from intracellular domains. Not only do these studies challenge the paradigm that cAMP production triggered by activated GPCRs originates exclusively at the cell membrane but they also advance a comprehensive model to account for the functional differences between PTH and PTHrP acting through the same receptor.     

Relaxin family peptide systems and the central nervous system

Since its discovery in the 1920s, relaxin has enjoyed a reputation as a peptide hormone of pregnancy. However, relaxin and other relaxin family peptides are now associated with numerous non-reproductive physiologies and disease states. The new millennium bought with it the sequence of the human genome and subsequently new directions for relaxin research. In 2002, the ancestral relaxin gene RLN3 was identified from genome databases. The relaxin-3 peptide is highly expressed in a small region of the brain and in species from teleost to primates and has both conserved sequence and sites of expression. Combined with the discovery of the relaxin family peptide receptors, interest in the role of the relaxin family peptides in the central nervous system has been reignited. This review explores the relaxin family peptides that are expressed in or act upon the brain, the receptors that mediate their actions, and what is currently known of their functions.     

Number and condition of seeds in ponderosa pine cones in central Arizona

Ponderosa pine cones from 10 areas in Arizona were collected prior to natural seed dispersal and dissected to determine the number of sound, hollow, and insect-damaged seeds in each cone. Total and sound seed yields per cone did not vary significantly among areas but did vary significantly among trees within each area. Numbers of hollow and Megastigmus -infested (Hymenoptera: Torymidae) seeds varied significantly among areas and trees within areas. Numbers of sound seed increased significantly with increasing cone length but did not change with increasing numbers of cones per cluster. The percentages of Megastigmus -infested seed did not change significantly with increasing cone length or number of cones per cluster.     

On Cowania and its intergeneric hybrids in Arizona

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Habitat use of leatherside chub ( Gila copei ) in the presence of predatory brown trout ( Salmo trutta )

The objectives of this study were to (1) examine distribution and habitat use of leatherside chub ( Gila copei ) in a creek with high densities of predatory brown trout ( Salmo trutta ), and (2) compare study results with published accounts of leatherside chub habitat use in streams with few or no brown trout. A 14-km section of Diamond Fork Creek, Utah, was point-shocked to determine macrohabitat (main channel and lateral habitat) and microhabitat (current, depth, substrate, and cover) use of leatherside chug. At the macrohabitat level, leatherside chub were most common in lower reaches of Diamond Fork Creek where the channel was braided and lateral habitats (cutoff pools and backwaters) were abundant. Only a single leatherside chub was found in the main channel of Diamond Fork. Investigations in other systems lacking brown trout indicated that leatherside chub occupy main channel habitats. At the microhabitat level, we found significant positive associations between presence of leatherside chub and both habitat depth and silt. In addition, we found a significant negative association between presence of leatherside chub and number of brown trout. Our results suggest predation by brown trout may limit leatherside chub to lateral habitats that could provide refugia against predation. The introduction of brown trout to systems with little lateral habitat could have serious effects on persistence of resident leatherside chub populations.