Can natural phenotypic variances be estimated reliably under homogeneous laboratory conditions?

The phenotypic variance is assumed to be greater in a more heterogeneous environment. The validity of this assumption is important for microevolutionists to extrapolate results from the laboratory to field environments. We subjected clutches of eggs from common snapping turtles (Chelydra serpentina) to a split-family design to evaluate the variability in incubation time and four size traits of neonates from eggs incubated in the laboratory and those left in situ. Mean size measurements were similar between the laboratory and the field, but incubation time was systematically longer in the field. We found no tendency among clutches for hatchlings resulting from eggs incubated in laboratory or field environments to demonstrate greater variability. Also contrary to expectation, clutches that experienced greater thermal variation in the field did not exhibit greater variation in phenotypic traits. Consequently, extrapolating results from the laboratory to the field may not always be problematic for microevolutionary analyses.     

Can light-saturated photosynthesis in lowland tropical forests be estimated by one light level?

Leaf-level net photosynthesis (A_n) estimates and associated photosynthetic parameters are crucial for accurately parameterizing photosynthesis models. For tropical forests, such data are poorly available and collected at variable light conditions. To avoid over- or underestimation of modeled photosynthesis, it is critical to know at which photosynthetic photon flux density (PPFD) photosynthesis becomes light-saturated. We studied the dependence of A_n on PPFD in two tropical forests in French Guiana. We estimated the light saturation range, including the lowest PPFD level at which A_sat (A_n at light saturation) is reached, as well as the PPFD range at which A_sat remained unaltered. The light saturation range was derived from photosynthetic light-response curves, and within-canopy and interspecific differences were studied. We observed wide light saturation ranges of A_n. Light saturation ranges differed among canopy heights, but a PPFD level of 1,000 µmol m⁻² s⁻¹ was common across all heights, except for pioneer trees species that did not reach light saturation below 2,000 µmol m⁻² s⁻¹. A light intensity of 1,000 µmol m⁻² s⁻¹ sufficed for measuring A_sat of climax species at our study sites, independent of the species or the canopy height. Because of the wide light saturation ranges, results from studies measuring A_sat at higher PPFD levels (for upper canopy leaves up to 1,600 µmol m⁻² s⁻¹) are comparable with studies measuring at 1,000 µmol m⁻² s⁻¹.     

Can secular trends in child growth be estimated from a single cross sectional survey?

OBJECTIVE--To formulate and evaluate a new method to measure secular trends in child growth based on the cross sectional collection of heights of children and young adults. DESIGN--Trends in child growth obtained from comparison of two national surveys made with an interval of 15 years were compared with estimates obtained from comparison of height deficits of children and young adults in the more recent survey. SETTING--Brazil. SUBJECTS--Random sample of children (6 and 7 years old) and young adults (21 and 22 years old) living in Brazil in 1974 and 1989 (a total of 23,271 subjects in 1974 and 5479 in 1989). MAIN OUTCOME MEASURES--Increments in average heights of 6 and 7 year old children in a 15 year period. RESULTS--Mean height of 6 year old children increased 4.0 cm (boys) and 3.3 cm (girls) from 1974 to 1989. Similar results were obtained by subtracting, in the 1989 survey, mean height deficits found at ages 21 and 6 (3.8 cm for males and 3.5 cm for females). Positive changes in the mean height of 7 year old children could also be predicted by subtracting, in the 1989 survey, height deficits found at ages 7 and 22. CONCLUSIONS--Findings of this study support the hypothesis that secular trends in child growth can be estimated by comparing height deficits observed in children and young adults.     

Band reporting rates of waterfowl: does individual heterogeneity bias estimated survival rates?

In capture–recapture studies, the estimation accuracy of demographic parameters is essential to the efficacy of management of hunted animal populations. Dead recovery models based upon the reporting of rings or bands are often used for estimating survival of waterfowl and other harvested species. However, distance from the ringing site or condition of the bird may introduce substantial individual heterogeneity in the conditional band reporting rates (r), which could cause bias in estimated survival rates (S) or suggest nonexistent individual heterogeneity in S. To explore these hypotheses, we ran two sets of simulations (n = 1000) in MARK using Seber''s dead recovery model, allowing time variation on both S and r. This included a series of heterogeneity models, allowing substantial variation on logit(r), and control models with no heterogeneity. We conducted simulations using two different values of S: S = 0.60, which would be typical of dabbling ducks such as mallards (Anas platyrhynchos), and S = 0.80, which would be more typical of sea ducks or geese. We chose a mean reporting rate on the logit scale of −1.9459 with SD = 1.5 for the heterogeneity models (producing a back-transformed mean of 0.196 with SD = 0.196, median = 0.125) and a constant reporting rate for the control models of 0.196. Within these sets of simulations, estimation models where σ_S = 0 and σ_S > 0 (σ_S is SD of individual survival rates on the logit scale) were incorporated to investigate whether real heterogeneity in r would induce apparent individual heterogeneity in S. Models where σ_S = 0 were selected approximately 91% of the time over models where σ_S > 0. Simulation results showed < 0.05% relative bias in estimating survival rates except for models estimating σ_S > 0 when true S = 0.8, where relative bias was a modest 0.5%. These results indicate that considerable variation in reporting rates does not cause major bias in estimated survival rates of waterfowl, further highlighting the robust nature of dead recovery models that are being used for the management of harvested species.     

Can iron be teratogenic?

Several kinds of evidence indicate that elevated iron during the 3–8 week embryonic (organogenesis) period of human gestation may be teratogenic. (1) In the embryonic period, the natural maternal absorption of food iron is 30% below the estimated daily iron loss. (2) As compared with maternal serum, embryonic fetal coelomic fluid contains only one-fourth as much iron but nearly six times the quantity of the iron withholding protein, ferritin. (3) In the embryonic period, intraplacental oxygen pressure is 2–3 times lower than in the subsequent fetal growth period. (4) Iron is a strong inducer of emesis which peaks in the embryonic period. (5) In a murine gestation model, iron was neurotoxic at a sharp peak of 8–9 days. Thus it would be prudent, in human pregnancy, to delay any needed iron supplementation until the embryonic period has been completed.     

Can microbes be patented?

Native microorganisms in their original form cannot be patented. However, microbes like yeasts, bacteria, protozoa, unicellular algae, fungi, actinomycetes and viruses can be patented if they have been genetically modified. The process and the product obtained can also be patented.     

Can genetic engineering of lignin deposition be accomplished without an unacceptable yield penalty?

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Highlights► Manipulation of the phenylpropanoid polymer lignin can improve bioenergy crops but often leads to dwarfing. ► Decreasing lignin leads to vascular collapse, but it is unclear that this is the cause of dwarfing. ► Non-lignin phenylpropanoids may be essential for normal plant growth and development. ► Accumulation of lignin biosynthetic intermediates or byproducts may have toxic effects. ► Dwarfism may be mediated by an active cell wall integrity monitoring pathway.     

Can demographic parameters be estimated from capture-recapture data on small grids? A test with forest rodents

This preliminary study proposes small trapping grids as an alternative to traditional large grids for the simultaneous monitoring of several rodent populations by capture--recapture. Monthly trapping sessions of wood mouse Apodemus sylvaticus (Linnaeus, 1758) and bank vole Clethrionomys glareolus (Schreber, 1780) were carried on over a small area (0.015 ha, 21 traps). The coherence of demographic parameter estimates on such small grids with those obtained on classical large grids was checked by performing two trapping sessions on a larger grid (0.9 ha, 110 traps, 10 m mesh) surrounding the small grid. We compared the two grid designs on the basis of sex ratio upon first capture, trap saturation rate, minimum number alive (MNA), monthly survival, and trappability. These demographic parameters proved to be non-biased by the trapped area, even though the precision was lower on the small grid. Small grids seem therefore to give the same picture of population dynamics as classical large grids except for parameters sensitive to an edge effect (eg density). By decreasing significantly the trapping effort, small grids will be of particular interest whenever the simultaneous operation of several trapping grids is needed (eg to compare different environmental conditions).     

Can calmodulin function without binding calcium?

Calmodulin is a small Ca(2+)-binding protein proposed to act as the intracellular Ca2+ receptor that translates Ca2+ signals into cellular responses. We have constructed mutant yeast calmodulins in which the Ca(2+)-binding loops have been altered by site-directed mutagenesis. Each of the mutant proteins has a dramatically reduced affinity for Ca2+; one does not bind detectable levels of 45Ca2+ either during gel filtration or when bound to a solid support. Furthermore, none of the mutant proteins change conformation even in the presence of high Ca2+ concentrations. Surprisingly, yeast strains relying on any of the mutant calmodulins not only survive but grow well. In contrast, yeast strains deleted for the calmodulin gene are not viable. Thus, calmodulin is required for growth, but it can perform its essential function without the apparent ability to bind Ca2+.     

Can there be an escalating arms race without coevolution? Implications from a host-parasitoid simulation

Summary Under a restricted set of conditions, predator-prey or parasite-host systems may exhibit an escalating arms race over several generations that is not coevolutionary. Preconditions for such a process include high correlation between prey/host quality and defensive capability, and phenotypic plasticity in predator/parasite-counter defenses that responds to quality. We present simulation models based on the parasitoid waspEurytoma gigantea, which lays its egg in the goldenrod gall induced by the flyEurosta solidaginis. For the parasitoid to successfully lay an egg, the gall walls must be thinner than the parasitoid's ovipositor is long. Wall thickness is highly correlated with gall size, so probability of successful attack declines with gall size. However, since the parasitoid eats the gall tissue, individuals developing in small galls have little food and mature with shorter ovipositors than those which develop in large galls. The simulation showed that the population mean parasitoid size is set by mean gall size. Since small galls are more frequently parasitized, there is a selection pressure on the gallmaker to induce larger galls. But, an additional simulation showed that since parasitoid ovipositor length depends on gall size, an evolutionary increase in gall size will also result in a non-evolutionary increase in parasitoid body size and ovipositor length over several generations.