Jumping performance and short-term repeatability of newly metamorphosed hybrid and parental leopard frogs ( Rana sphenocephala and Rana blairi )

1999 ◽  
Vol 77 (5) ◽  
pp. 748-754 ◽  
Author(s):  
Raymond D Semlitsch ◽  
Joyce Pickle ◽  
Matthew J Parris ◽  
Richard D Sage
Keyword(s):  
Parental Species ◽  
High Density ◽  
Low Density ◽  
Locomotor Performance ◽  
Rana Sphenocephala ◽  
Short Term ◽  
Jumping Performance ◽  
Leopard Frogs ◽  
Backcross Hybrid ◽  
Rana Blairi

Differential fitness between hybrid and parental genotypes plays a critical role in explaining the maintenance of natural hybrid zones as well as the production of novel genetic variation that may lead to diversification. Because locomotor performance is a reliable and practical measure of potential fitness related to morphological variation, we tested for differences in jumping performance among parental and hybrid genotypes of newly metamorphosed leopard frogs (Rana sphenocephala and Rana blairi). Tadpoles of the parental species and primary and backcross hybrid tadpoles, generated from artificial crosses (a total of five genotypes), were reared at two initial larval densities. Locomotor performance of newly metamorphosed frogs, as measured by jumping ability, was tested three times over 6 days in the laboratory at 24-25°C. Maximum and average jump lengths were greater for metamorphs reared at low larval density than for those reared at high density. Regression analyses indicated that 70-79% of the variation in jump length was due to body mass. When reared at low density, metamorphs of two F1 backcross genotypes (HB and HS) and one primary hybrid genotype (SB) jumped shorter distances than either parental species. When reared at high density, hybrid performance was indistinguishable from that of the parentals, except for one backcross hybrid (HB). Moderately high short-term repeatabilities (0.47-0.66) of metamorphs reared at the high density indicate that measures of performance in newly metamorphosed frogs can be predictive. We suggest that, owing to poor jumping performance, some hybrid frogs would be at a selective disadvantage relative to their parental species in the terrestrial environment and thus would partially reinforce mechanisms of reproductive isolation in this leopard frog system. Yet equivalent performance of some hybrids relative to the parentals, at least when reared at low density, suggests that hybrid lineages also have the potential to evolve independently in some environments.

Hybridization in leopard frogs (Rana pipiens complex): terrestrial performance of newly metamorphosed hybrid and parental genotypes in field enclosures

2001 ◽  
Vol 79 (9) ◽  
pp. 1552-1558 ◽  
Author(s):  
Matthew J Parris
Keyword(s):  
Growth Rates ◽  
Life Histories ◽  
Parental Species ◽  
Natural Populations ◽  
Life Cycles ◽  
Natural Hybridization ◽  
Evolutionary Potential ◽  
Leopard Frogs ◽  
Rana Blairi ◽  
Advanced Generation

Terrestrial ecology has been largely neglected in the study of amphibian life histories because it is difficult to manipulate most species during the terrestrial stage. I examined the terrestrial performance of Rana blairi, Rana sphenocephala, and four hybrid (two F1 and two advanced generation) genotypes in replicated experimental enclosures to test for differences in traits related to juvenile terrestrial fitness. I produced all genotypes by means of artificial fertilizations using frogs collected from natural populations in central Missouri, and juvenile frogs were obtained from larvae reared in experimental ponds. Following metamorphosis, froglets were raised in single-genotype groups in terrestrial enclosures through the first overwintering. The proportion surviving did not vary among genotypes, but the power to detect significant differences was low. F1 hybrid genotypes BS and SB demonstrated significantly higher growth rates than either parental species or advanced-generation hybrid genotypes. Observation of growth rates of advanced-generation hybrids equal to those of the parental species, and heterosis in F1 hybrids for growth rate, suggests that natural hybridization between R. blairi and R. sphenocephala can produce novel and relatively fit hybrid genotypes. Direct measurement of multiple fitness components for hybrid and parental genotypes is critical for assessing the evolutionary potential of natural hybridization in organisms with complex life cycles.

Quantitative defect studies in semiconductor TEM samples prepared by low angle ion milling

1995 ◽  
Vol 53 ◽  
pp. 512-513
Author(s):  
L. Mulestagno ◽  
J.C. Holzer ◽  
P. Fraundorf
Keyword(s):  
Sample Preparation ◽  
Milling Time ◽  
High Density ◽  
Low Density ◽  
Ion Milling ◽  
High Quality ◽  
Variable Angle ◽  
Major Disadvantage ◽  
Induced Defects

Due to the wealth of information, both analytical and structural that can be obtained from it TEM always has been a favorite tool for the analysis of process-induced defects in semiconductor wafers. The only major disadvantage has always been, that the volume under study in the TEM is relatively small, making it difficult to locate low density defects, and sample preparation is a somewhat lengthy procedure. This problem has been somewhat alleviated by the availability of efficient low angle milling.Using a PIPS® variable angle ion -mill, manufactured by Gatan, we have been consistently obtaining planar specimens with a high quality thin area in excess of 5 × 104 μm2 in about half an hour (milling time), which has made it possible to locate defects at lower densities, or, for defects of relatively high density, obtain information which is statistically more significant (table 1).

Scanning Electron Microscopic and Electrophoretic Observations on Barium Sulphate Used to Adsorb Clotting Factors

1975 ◽  
Vol 33 (02) ◽  
pp. 256-270
Author(s):  
R. M Howell ◽  
S. L. M Deacon
Keyword(s):  
Electron Microscopy ◽  
Factor Xa ◽  
Barium Sulphate ◽  
High Density ◽  
Low Density ◽  
Factor X ◽  
Clotting Factors ◽  
Electron Microscopic ◽  
Complementary Techniques ◽  
Scanning Electron

SummaryElectron microscopy and particle electrophoresis were found to be complementary techniques with which to complete the physical data from an earlier study on barium sulphates used to adsorb clotting factors from serum. The differences revealed by scanning electron microscopy (S. E. M.) in the physical shape of low and high density grades of barium sulphate particles appear to be of greater significance than charge as expressed by electrophoretic mobility, in determining whether or not precursor or preformed factor Xa is eluted.This conclusion was based on the finding that at pH values close to 7, where the adsorption from serum occurs, all samples with the exception of natural barytes were uncharged. However as the high-density, or soil-grade, was found by S. E. M. to consist of large solid crystals it was suggested that this shape might induce activation of factor X as a result of partial denaturation and consequent unfolding of the adsorbed protein. In contrast, uptake of protein into the centre of the porous aggregates revealed by S. E. M. pictures of low-density or X-ray grade barium sulphate may afford protection against denaturation and exposure of the enzyme site.The porous nature of particles of low-density barium sulphate compared with the solid crystalline forms of other grades accounts not only for its lower bulk density but also for its greater surface/gram ratio which is reflected by an ability to adsorb more protein from serum.Neither technique produced evidence from any of the samples to indicate the presence of stabilising agents sometimes used to coat particles in barium meals.

scholarly journals Low-Temperature Mechanical Properties of High-Density and Low-Density Polyethylene and Their Blends

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1821
Author(s):  
Ildar I. Salakhov ◽  
Nadim M. Shaidullin ◽  
Anatoly E. Chalykh ◽  
Mikhail A. Matsko ◽  
Alexey V. Shapagin ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Low Temperature ◽  
Impact Strength ◽  
Relative Elongation ◽  
High Density ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Elongation At Break ◽  
Subzero Temperatures ◽  
Izod Impact

Low-temperature properties of high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and their blends were studied. The analyzed low-temperature mechanical properties involve the deformation resistance and impact strength characteristics. HDPE is a bimodal ethylene/1-hexene copolymer; LDPE is a branched ethylene homopolymer containing short-chain branches of different length; LLDPE is a binary ethylene/1-butene copolymer and an ethylene/1-butene/1-hexene terpolymer. The samples of copolymers and their blends were studied by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), 13С NMR spectroscopy, and dynamic mechanical analysis (DMA) using testing machines equipped with a cryochamber. It is proposed that such parameters as “relative elongation at break at −45 °C” and “Izod impact strength at −40 °C” are used instead of the ductile-to-brittle transition temperature to assess frost resistance properties because these parameters are more sensitive to deformation and impact at subzero temperatures for HDPE. LLDPE is shown to exhibit higher relative elongation at break at −45 °C and Izod impact strength at −20 ÷ 60 °C compared to those of LDPE. LLDPE terpolymer added to HDPE (at a content ≥ 25 wt.%) simultaneously increases flow properties and improves tensile properties of the blend at −45 °C. Changes in low-temperature properties as a function of molecular weight, MWD, crystallinity, and branch content were determined for HDPE, LLDPE, and their blends. The DMA data prove the resulting dependences. The reported findings allow one to understand and predict mechanical properties in the HDPE–LLDPE systems at subzero temperatures.

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