The adaptive significance of electrophoretic mobility in phosphoglucose isomerase (PGI)

Sexual dimorphism in size and plumage was investigated in the lek-breeding Jackson's widowbird Euplectes jacksoni. Size dimorphism was evident from the sexual difference in tarsus length, reflecting skeletal body size. The long tail and the wide collar of breeding plumaged males were obvious secondary sex traits, but the wing was also longer than in subadults and might likewise be sexually selected (i.e. not merely a byproduct of body size). Possibly, the increased wingspan functions to save energy during the jump display. To reveal intrasexual selection, courtholders were compared with floaters (nuptial males captured off the leks), and were found to be larger in body size, wing length, collar and tail. The roles of inter-and intrasexual selection are discussed with reference to previously demonstrated female choice, and new results indicating competition for access to leks: quick reoccupation of deserted display courts, frequent observations of intruders and a finding that central males were more aggressive than peripherals. Observations imply that the collar is an agonistic signal that is neutral with respect to female choice. Possible contributions of natural selection to the sexual dimorphism are also considered.     

Composition of the early Oligocene ocean from coral stable isotope and elemental chemistry

A sectioned and polished specimen of the coral Archohelia vicksburgensis from the early Oligocene Byram Formation (～30 Ma) near Vicksburg, Mississippi, reveals 12 prominent annual growth bands. Stable oxygen isotopic compositions of 77 growth‐band‐parallel microsamples of original aragonite exhibit well‐constrained fluctuations that range between ?2.0 and ?4.8. Variation in δ¹⁸O of coral carbonate reflects seasonal variation in temperature ranging from 12 to 24 °C about a mean of 18 °C. These values are consistent with those derived from a bivalve and a fish otolith from the same unit, each using independently derived palaeotemperature equations. Mg/Ca and Sr/Ca ratios were determined for 40 additional samples spanning five of the 12 annual bands. Palaeotemperatures calculated using elemental‐ratio thermometers calibrated on modern corals are consistently lower; mean temperature from Mg/Ca ratios are 12.5 ± 1 °C while those from Sr/Ca are 5.8 ± 2.2 °C. Assuming that δ¹⁸O‐derived temperatures are correct, relationships between temperature and elemental ratio for corals growing in today's ocean can be used to estimate Oligocene palaeoseawater Mg/Ca and Sr/Ca ratios. Calculations indicate that early Oligocene seawater Mg/Ca was ～81% (4.2 mol mol^?1) and Sr/Ca ～109% (9.9 mmol mol^?1) of modern values. Oligocene seawater with this degree of Mg depletion and Sr enrichment is in good agreement with that expected during the Palaeogene transition from ‘calcite’ to ‘aragonite’ seas. Lower Oligocene Mg/Ca probably reflects a decrease toward the present day in sea‐floor hydrothermal activity and concomitant decrease in scavenging of magnesium from seawater. Elevated Sr/Ca ratio may record lesser amounts of Oligocene aragonite precipitation and a correspondingly lower flux of strontium into the sedimentary carbonate reservoir than today.     

Production of a stream shredder, Peltoperla maria (Plecoptera: Peltoperlidae) in disturbed and undisturbed hardwood catchments

SUMMARY. (1) The average benthic density of Peltoperla maria in an undisturbed southern Appalachian stream was more than twice that of a nearby stream draining a previously clear-cul catchment in its tenth year of natural secondary succession.
(2) Peltoperla production estimates, using three methods, do not show a significant difference in production between streams draining the two catchments. We attribute these results to quicker growth and slightly higher densities of larger nymphs in the disturbed stream. Production estimates for the disturbed stream ranged from 498 to 560 mg (ash free dry weight) m⁻²y⁻¹ while those for the undisturbed stream were 41–4–515 mg m⁻² y⁻¹.
(3) Our results reinforce the view that conclusions based solely upon numerical densities may lead to erroneus interpretations about the roles organisms play in ecosystems.
(4) Annual frass production by this shredder is about 20 times (10 g m⁻² y⁻¹) the secondary production of P. maria.     

Seasonal changes of osmotic pressure, symplasmic water content and tissue elasticity in the blades of dune grasses growing in situ along the coast of Oregon

Abstract Midday water potentials of blades of the dune grasses Ammophila arenaria (L.) Link and Elymus mollis Trin. ex Spreng. growing in situ declined over the summer growing period, indicating a trend of increasing water stress. An analysis of the water relations characteristics of these blades using pressure-volume techniques demonstrated that both species increased bulk osmotic pressure at full hydration () and, therefore, bulk turgor as an acclimation response. In A. arenaria, however, the increase of osmotic pressure (+ 0.35 MPa) was entirely the result of decreasing symplasmic water content. The increase of osmotic pressure (+ 0.54 MPa) observed in E. mollis blades was due to solute accumulation (72% of Δ) and to a lesser degree, decreased symplasmic water content (28% of Δ). Osmotic adjustment in E. mollis blades was accompanied by a significant decrease in tissue elasticity (_max went from 12 to 19 MPa). The elastic properties of A. arenaria blades remained constant over the same period and had a maximum modulus (10 MPa) that was always less than that of E. mollis, As estimated from Höfler plots, these seasonal adjustments of osmotic pressure and differences in tissue elasticity enabled plants in situ to maintain turgor pressure in the range of 0.5–0.6 MPa at the lowest water potentials of mid-August. Laboratorygrown plants exhibited the species-specific differences in osmotic pressure, turgor pressure, and tissue elasticity observed in field plants. Although certain alterations of leaf structure were expected to coincide with the observed changes and species-specific differences in symplasmic water content and tissue elasticity, these could not be detected by measurements of specific leaf weight or the ratio of dry matter to saturated water content.     

Archaeological Inference and Inductive Confirmation

The limitations of the hypothetico-deductive (H-D) method of inductive confirmation are described, and an alternate method, the hypothetico-analog (H-A) method is described in detail. The H-A method can be characterized as a modified and supplemented form of the simple H-D method, and is proposed as being more appropriate for archaeological inference. Aspects of the H-A method that are given particular attention include the establishment of boundary conditions for reference classes, plausibility considerations, multiple working hypotheses, bridging arguments, and criteria for selecting alternative hypotheses . [scientific method, archaeological inference, hypothetico-analog method, inductive confirmation]     

Topography and tectonics of the Taconic outer trench slope as revealed through gradient analysis of fossil assemblages

Similarities in stratigraphic sequence, syndepositional topography and tectonics, and regional tectonic setting between the Mohawk Valley, New York, in the Middle Ordovician and the Australian flank of the Timor Trough today support the idea that the Taconic Foreland Basin orginated in an arc-continent collision. The Trenton Group strata studied - a roughly four million year long sequence correlated by bentonite beds along an 83 km downslope transect in the central Mohawk Valley - represent the continental shelf and outer trench slope. Bank limestones pass upward and downslope into deep water black shales in a manner reminiscent of the lateral and vertical sedimentary sequence on the Sahul Shelf and Australian flank of the Timor Trough. In studying topography, relative depth was measured through reciprocal averaging ordination of benthic macroinvertebrate fossil assemblages. Downslope bathymetric profiles show the development of a horst and graben topography coincident with regional tilting and transgression - a pattern associated with downward flexure of the Australian Plate approaching Timor. The net rate of transgression corresponds to an arc-continent convergence rate on the order of 2 cm per year.     

Clinal variation, episodic evolution, and possible parapatric speciation: the trilobite Flexicalymene senaria along an Ordovician depth gradient

Pygidial segmentation in the trilobite Flexicalymene senaria changes with time (as measured in relation to bentonite beds) and with depth (as measured along downslopc transects along bentomtc beds and as measured by gradient analysis of fossil assemblages) along a 'fossil' depth gradient in the Middle Ordovician Trenton Group in central New York State. The pattern of strictly temporal change resembles a 'punctuation' between 'equilibria'. This evolutionary episode, a 10⁶ year interval of continuous change, may represent parapatric speciation. The clinal gradient is strongest during this episode and is weak or not apparent outside it. Strictly temporal change takes place by way of temporal change in the cline's shape. □ Evolution, geographic variation and dines, gradient analysis. Middle Ordovician, morphometry, speciation, Trilobita.     

The Relationship of the Estrogen Receptor to the Induction of Vitellogenin in Chicken and Xenopus Liver

The mechanisms involved in the regulation of gene expression in eukaryote cells, although an area of active research, are still largely unknown. This is at least partly due to the lack of good experimental model systems. One type of system which is being exploited with some considerable success is the induction of proteins by steroid hormones. Studies on the effects of estrogen and progesterone on the synthesis of the egg white proteins in the chick oviduct, for instance, have yielded substantial insight into both the regulation of protein synthesis by steroid hormones [1] and the arrangement of the DNA sequences coding for these proteins [2, 3].
The need for other good inducible systems clearly exists and the induction of vitellogenin, the precursor of the major egg yolk proteins, by estrogen in the livers of the chicken and frog ( Xenopus laevis ) is one that is attracting increasing interest. In common with the chick oviduct, large amounts of a specific protein are synthesised in response to a well defined hormonal stimulus. However, the induction of vitellogenin also has the advantage that the response is not complicated by the extensive hyperplasia that follows estrogen treatment in the chick oviduct [4, 5] and that vitellogenin may be induced in vitro [6–11].
The aims of this review are first to discuss recent data on the induction of vitellogenin and vitellogenin mRNA both in vivo and in vitro and then to relate this data to the properties of the estrogen receptor, present in chicken and Xenopus liver, which is thought to mediate the induction of vitellogenin by estrogen.