GENETIC CONTROL OF VERY EARLY MAMMALIAN DEVELOPMENT

The overall picture of mammalian preimplantation development is one of complex but integrated molecular activity. As development progresses from the 1 cell stage, blastomeres acquire properties that differ from those of cells of previous stages and eventually differ from one another even at the same stage. The evidence concerning the role of the embryonic genome during this process can be summarized under two headings:
(1) Expression of embryonic genome
(a) Quantitative and qualitative changes in RNA and protein synthesis begin to occur soon after fertilization.
(b) Changes in structural proteins (enzyme activities, transport systems and intercellular junctions) occur throughout early development.
(c) Paternal gene products can be detected as early as the 2-cell stage.
(2) The need for expression of the embryonic genome
(a) Inhibitors of RNA and protein synthesis result in abnormal and lethal development.
(b) Several mutations ( T/t, A^y, Os, c^25H, Om, Ts ) are lethal during early development.
(c) Chromosomal imbalance (monsomy, haploidy, nullisomy) has adverse effects on early development.
Even though studies in vitro on the inhibition of translation indicate that stable maternal messenger RNAs are present in the developing mouse embryo, the evidence outlined in this article strongly supports the belief that embryonic gene expression occurs very early in development (at least by the 2 cell stage) and that this expression is required for normal development.     

Tigers and Telazol®: The Unintended Evolution of Caution to Contraindication

Abstract: Scientific writing depends on citing accurate sources. There can be real-world consequences for failing to do so. As an example, several authors have stated that tiletamine-zolazepam (Telazol®) is contraindicated for tiger (Panthera tigris) immobilization. This admonition has virtually evolved into dogma in the field of wildlife chemical immobilization and was recently used to challenge field research. However, a literature review revealed that no author cited the primary reference that raised concern about the use of Telazol in tigers. We conducted an internet-based inquiry of zoo veterinarians combined with personal communications and other field reports to gather data on the use of Telazol in tigers. These data indicated that the mortality rate (1.3%) of tigers given Telazol was similar to other immobilization regimens in other species, which suggested that, although adverse reactions may still occur, tiletamine-zolazepam should not be contraindicated in tigers. This investigation emphasized the need to conduct thorough literature reviews before making unsubstantiated claims.     

Direct Effects of Ca2+-Channel Blockers on Plasma Membrane Cation Channels of Amaranthus tricolor Protoplasts

Ca²⁺-channel blockers at concentrations greater than 1 mmolm^–3, directly affect the activity of K ⁺selective channelsin the plasma membrane of Amaranthus tricolor protoplasts. Theseeffects are not mediated by the blockade of Ca²⁺ channels. Blockers tested included 1, 4-dihydropyridines (nifedipine,nicardipine), verapamil, bepridil, Gd³⁺ and La³⁺, applied towhole-cell and detached outside-out patches of plasma membraneat concentrations from 50µmol m^–3 to 100 mmol m^–3.For certain experiments the concentration of Ca²⁺ on the cytoplasmicside of the plasma membrane ([Ca²⁺]cyt) was buffered at either50ftmol m^–3 or 500 µmol m^–3. The principal currents observed in whole-cells flowed throughcation outward rectifier (OR) channels. Each blocker causedan immediate reduction of time-dependent outward currents atdoses down to 1 mmol m^–3 and produced a different, reversible,kinetic block of the outward current, independent of the levelof [Ca²⁺]cyt. Verapamil also activated a sustained inward cationcurrent at negative p.d. The same effects were found with individualchannels in detached outside-out patches. Conductance and selectivityof the cation OR channels were unchanged by the drugs. [Ca²⁺]ex, was varied over a range from 0 to 10 mol m^–3.Progressively lower [Ca²⁺]eI, increasingly enhanced the maximumamplitude of the time-dependent currents. Time-constants fordecay of inward tail currents were increased at low [Ca²⁺]eit.These effects were rapidly reversible. Although there was noevidence that the cation ORs in plasma membrane of Amaranthustricolor were dependent on [Ca²⁺]cyl for their activation, theywere sensitive to the concentration of free Ca²⁺ in the extracellularmedium. Key words: Verapamil, blocker, cation channels, Amaranthus, protoplasts     

Effect of Water Stress on the Temperature Optima of Net CO2 Exchange for Two Desert Species

The temperature dependence of net CO₂ exchange was determined at various soil water potentials for two sympatric desert species. Notholaena parryi D. C. Eat. (Pteridaceae) and Encelia farinosa Gray (Compositae). As water stress increased, the temperature optimum of apparent (net) photosynthesis shifted 7 to 10°C downward and the maximum rate decreased for both species. The downward shift in temperature optimum with water stress was the result of a greater fractional stomatal closure with increasing temperature and a lowering of the temperature where maximal CO₂ residual conductance of the mesophyll cells occurred. This lowering of the temperature for maximal CO₂ residual conductance appears to reflect (1) a greater effect of water stress on gross photosynthesis than on respiration plus photorespiration and (2) the higher temperature optimum for respiration plus photorespiration than for gross photosynthesis. The downward shift in the temperature optimum of apparent photosynthesis can have a significant effect on the predicted carbon balance of plants as the soil water potential decreases.     

Raptor and Corvid Response to Power Distribution Line Perch Deterrents in Utah

Abstract: Increased raptor and corvid abundance has been documented in landscapes fragmented by man-made structures, such as fence posts and power lines. These vertical structures may enhance raptor and corvid foraging and predation efficiency because of increased availability of perch, nesting, and roosting sites. Concomitantly, vertical structures, in particular power distribution lines, have been identified as a threat to sage-grouse (Centrocercus spp.) conservation. To mitigate potential impacts of power distribution lines on sage-grouse and other avian species, the electrical power industry has retrofitted support poles with perch deterrents to discourage raptor and corvid use. No published information is available regarding efficacy of contemporary perch deterrents on avian predator use of lower-voltage power distribution lines. We evaluated efficacy of 5 perch deterrents mounted on support poles of an 11-km section of a 12.5-kV distribution line that bisected occupied Gunnison sage-grouse (Centrocercus minimus) habitat in southeastern Utah, USA. Perch deterrents were mounted on the line in November–December 2006 following a random replicated block design that included controls. During 168 hours and 84 hours of direct observation in 2007 and 2008, respectively, we recorded 276 and 139 perching events of 7 potential avian predators of sage-grouse. Golden eagles (Aquila chrysaetos) were the dominant species we recorded during both years. We did not detect any difference in perching events by perch deterrent we evaluated and controls (P > 0.05). Perch deterrents we evaluated were not effective because of inherent design and placement flaws. Additionally, previous pole modifications that mitigated avian electrocutions provided alternative perches. We did not record any raptor or corvid electrocutions or direct predation on Gunnison sage-grouse. The conclusions of this study can be applied by conservation groups and power companies to future management of power distribution lines within areas inhabited by species sensitive to man-made vertical structures.     

Achieving Better Estimates of Greater Sage-Grouse Chick Survival in Utah

Abstract: Declining sage-grouse (Centrocercus urophasianus) populations may be characterized by poor recruitment largely attributed to low chick survival. However, few published studies have explicitly examined factors that influence chick survival. We used a suture method to radiomark 1-2-day-old sage-grouse chicks (n = 150) in 2005-2006 on Parker Mountain in south-central Utah, USA, and monitored their survival to 42 days. We modeled effects of year, hatch date, chick age, brood-female age, brood-mixing, and arthropod abundance on chick survival. Our best model revealed an average survival estimate of 0.50 days to 42 days, which is the highest level ever documented for this long-lived species. Brood-mixing occurred in 21% (31/146) of chicks and 43% (18/42) of broods we studied. Moreover, yearling females had more chicks leave their broods than did adults. We found that survival may be higher among chicks that switch broods compared to those that stayed with their natal mother until fledging. Thus, brood-mixing may be an adaptive strategy leading to increased sage-grouse chick survival and higher productivity, especially among chicks born to yearling females. Our findings also indicate that arthropod abundance may be an important driver of chick survival, particularly during the early brood-rearing period and, therefore, sage-grouse populations may benefit from a management strategy that attempts to increase arthropod abundance via brood habitat management.     

Ecological effects of river ice break-up: a review and perspective

1. Abiotic disturbances strongly modify spatial and temporal patterns of lotic ecosystem community structure and function. Such effects are produced because disturbances alter organic matter, nutrient and contaminant dynamics and the distribution and abundance of bacterial, algal, macroinvertebrate and fish communities. 2. River ice break-up is a seasonal disturbance in rivers at high altitudes and latitudes world-wide and is characterized, in part, by large increases in current velocity, stage, water temperature, concentrations of suspended materials and substrate scouring. 3. These abiotic factors are likely to have important effects on primary producers, consumers, and food-web dynamics of river biota. Despite the potential importance of river ice break-up on community structure and function, detailed information describing the magnitude of their effects and underlying causal mechanisms is scarce. 4. The objective of this paper is to provide a hydrological and ecological review and perspective on the potential effects of ice break-up on lotic ecosystems. Specifically, the potential importance of break-up on water temperature, river sediments and geomorphology, riverine energy sources, contaminants, and its effects on river biota and food-web dynamics are evaluated.     

Natural history of the non-solitary sheetweaving spider Anelosimus jucundus (Araneae: Theridiidae)

Field observations were made on one Panamanian population of Anelosimus jucundus. Almost all webs were found in a relatively exposed area, on small shrubs and composites. This is in contrast to A. eximius , a colonial congeneric which in our study site built its large webs along moist, fern-covered banks. Web structure varied with different plant substrates; for example, only some of the webs incorporated a clearly defined lower sheet. Webs were built by penultimate instar females, and perhaps by adult females and males. In some cases, several adult females inhabited a web, but they remained under separate leaf canopies; during census observations co-operative efforts were not noted. Prey consisted mainly of winged insects. Juvenile sex ratio was about equal. The degree of sociality demonstrated by A. jucundus is discussed.     

Preferential feeding and damage to cultivars of Nigerian cassava by the variegated grasshopper (Zonocerus variegatus)

Large populations of Zonocerus variegatus invaded a cassava crop established during the dry season. The resultant damage was severe, certain cultivars being totally destroyed. The grasshoppers exhibited a statistically significant preference for certain cultivars the defoliation of which shifted attacks to less preferred ones. On a particular variety (Isunikankiyan), populations increased and persisted even after defoliation, probably due to