Lipid content of terrestrial arthropods in relation to body size,phylogeny, ontogeny and sex

Energy storage in arthropods has important implications for survival and reproduction. The lipid content of 276 species of adult arthropods with wet mass in the range 0.2–6.13 g is determined to assess how lipid mass scales with body mass. The relative contribution of lipids to total body mass is investigated with respect to phylogeny, ontogeny and sex. The lipid content of adult insects, arachnids, and arthropods in general shows an isometric scaling relationship with respect to body mass (M) (M_{arthropod lipid} = ?1.09 ×M_dry^1.01 and M_{arthropod lipid} = ?1.00 ×M_lean^0.98). However, lipid allocation varies between arthropod taxa, as well as with sex and developmental stage within arthropod taxa. Female insects and arachnids generally have higher lipid contents than males, and larval holometabolous insects and juvenile arachnids have higher lipid contents than adults.     

Estimates of gene flow, genetic substructure and population heterogeneity in bracken (Pteridium aquilinum)

Bracken [ Pteridium aquilinum (L.) Kuhn] is a cosmopolitan species and is a noxious weed in many areas. Because of its abundance, particularly in Britain, bracken affords an ideal system for investigating various aspects of population genetics and evolution. High mobility of dispersal units (spores) suggests that rates of gene flow among distant populations should be high. Gene flow is a major evolutionary force that influences the genetic structure of populations. To examine the effects of gene flow on population heterogeneity and population substructuring in bracken, starch gel electrophoresis of enzymes was used to provide the necessary genetic database. Allele frequency data at 21 loci were obtained for seven British populations, one Majorcan and one from the eastern United States. A model was employed to estimate the amount of gene flow ( Nm ) at several levels. Gene flow among British populations was extremely high ( Nm = 36.51), one of the highest estimates reported for plants. Among eight European populations gene flow was lower (but still considered high) at Nm = 2.47. Trans-Atlantic gene flow was low ( Nm = 0.0926).
F -statistics were used to assess population heterogeneity and substructuring. The data indicate that, compared with other species, there is very little genetic differentiation among British populations of bracken. Indeed, it appears that the whole island is behaving as a single randommating population. This result is consistent with high levels of gene flow. Only one population (on the Isle of Arran) showed statistically significant genetic substructuring. Habitat heterogeneity on the island and age structure are hypothesized as possible causes of this result.
The data reported here support previous studies demonstrating that bracken is genetically polymorphic and is an outcrossing species.     

Elemental distribution in striated muscle and the effects of hypertonicity: Electron probe analysis of cryo sections

A method of rapid freezing in supercooled Freon 22 (monochlorodifluoromethane) followed by cryoultramicrotomy is described and shown to yield ultrathin sections in which both the cellular ultrastructure and the distribution of diffusible ions across the cell membrane are preserved and intracellular compartmentalization of diffusabler ions can be quantitated. Quantitative electron probe analysis (Shuman, H., A.V. Somlyo, and A.P. Somlyo. 1976. Ultramicros. 1:317-339.) of freeze-dried ultrathin cryto sections was found to provide a valid measure of the composition of cells and cellular organelles and was used to determine the ionic composition of the in situ terminal cisternae of the sarcoplasmic reticulum (SR), the distribution of CI in skeletal muscle, and the effects of hypertonic solutions on the subcellular composition if striated muscle. There was no evidence of sequestered CI in the terminal cisternae of resting muscles, although calcium (66mmol/kg dry wt +/- 4.6 SE) was detected. The values of [C1](i) determined with small (50-100 nm) diameter probes over cytoplasm excluding organelles over nuclei or terminal cisternae were not significantly different. Mitochondria partially excluded C1, with a cytoplasmic/ mitochondrial Ci ratio of 2.4 +/- 0.88 SD. The elemental concentrations (mmol/kg dry wt +/- SD) of muscle fibers measured with 0.5-9-μm diameter electron probes in normal frog striated muscle were: P, 302 +/- 4.3; S, 189 +/- 2.9;C1, 24 +/- 1.1;K, 404 +/- 4.3, and Mg, 39 +/- 2.1. It is concluded that: (a) in normal muscle the "excess CI" measured with previous bulk chemical analyses and flux studies is not compartmentalized in the SR or in other cellular organelles, and (b) the cytoplasmic C1 in low [K](0) solutions exceeds that predicted by a passive electrochemical distribution. Hypertonic 2.2 X NaCl, 2.5 X sucrose, or 2.2 X Na isethionate produced: (a) swollen vacuoles, frequently paired, adjacent to the Z lines and containing significantly higher than cytoplasmic concentrations of Na and Cl or S (isethionate), but no detectable Ca, and (b) granules of Ca, Mg, and P = approximately (6 Ca + 1 Mg)/6P in the longitudinal SR. It is concluded that hypertonicity produces compartmentalized domains of extracellular solutes within the muscle fibers and translocates Ca into the longitudinal tubules.     

Shoot-Dependent Regulation of Sodium and Potassium Fluxes in Roots of Whole Barley Seedlings

Unidirectional fluxes and the cytoplasmic and vacuolar contentsof potassium and sodium in root cells of intact barley seedlings(Hordeum vulgare L., cv. Villa) were determined by use of compartmentalanalysis. In addition, the net vacuolar accumulation J_cv andthe xylem transport ø_cx of K⁺ and Na⁺ were measured.Both of these data were needed for the evaluation of the effluxdata. Fluxes and compartmental contents of K⁺ and Na⁺ were comparableto data obtained with excised roots. The effect of the shoot-to-rootratio—as varied by partial excision of the seedlings seminalroots—on the fluxes and contents was investigated. Highershoot-to-root ratios induced an increase in xylem transport,in plasmalemma influx, and also in the cytoplasmic content ofK⁺ and Na⁺. With potassium the plasmalemma efflux was almostunaltered while the tonoplast fluxes and vacuolar content weredecreased (in presence of Na⁺). With sodium, on the other hand,the plasmalemma efflux and the tonoplast fluxes were also increasedin the plants having one root and a high shoot-to-root ratio.These changes occurred even under conditions of low humidity,when transpiration was low and guttation occurred. The latterwas also increased at the high shoot-to-root ratio. The observedchanges could be due to a relieved feedback control of ion fluxesby the shoot and mediated in part by a relatively higher supplyof photosynthates in the plants having one root In addition,hormonal signals were suggested to participate. In particulara possibly decreased level of cytokinins in the plants havingonly one root could contribute to the signal. The observed changesappear to be responses of the plant to an alteration that canoccur under natural conditions when the root system is damaged.