Punctuated equilibrium excused: the original examples fail to support it

The four original stipulations of the definition of punctuated equilibrium (PE; Eldredge & Gould, 1972) are shown to be unsupported, and even contradicted, by the two evidential examples these authors supplied: the trilobite Phacops rana of the Middle Devonian, and the land snail Poecilozonites bermudensis of Late Pleistocene Bermuda.
The additional, much-discussed example of Bellamya unicolor and the accompanying suite of molluscan species of Pliocene-Recent African Lake Turkana, studied by Williamson, also fails to exemplify PE. In particular, the data produced for these cases appear to represent counterexamples to Mayr's paradigm of peripatric speciation , embraced by Eldredge and Gould as the central effective mechanism of PE. The data actually illustrate instead a prevailingly centrifugal pattern of speciation that will accommodate and explain episodic aspects of microevolution in a more realistic way.     

Cyclic Variations in Nitrogen Uptake Rate of Soybean Plants: Effects of External Nitrate Concentration

Net uptake of by non-nodulated soybean plants [Glycine max (L.) Merr.cv. Ransom] growing in flowing hydroponiccultures containing 0–5, 1.0 and 10-0 mol m^–3 was measured daily during a 24-d period of vegetativedevelopment to determine if amplitude of maximum and minimumrates of net uptake are responsive to external concentrations of . Removal of from the replenished solutions during each 24-h period was determinedby ion chromatography. Neither dry matter accumulation nor theperiodicity of oscillations in net uptakerate was altered bythe external concentrations. The maxima of the oscillations in net uptake rate, however, increased nearly3-fold in response to external concentrations. The maxima and minima, respectively, changed from 4.0 and 0–6mmol per gram root dry weight per day at an external solution level of 05 mol m^–3 to 15–2and -2–7 mmol per gram root dry weight per day at an external solution level of 10–0mol m^–3 . The negative values for minimum net uptake rate from10–0 mol m^–3 solutions show that net efflux was occurring andindicate thatthe magnitude of the efflux component of net uptake was responsiveto external concentration of . Key words: Nitrate uptake rate, carbon-nitrogen partitioning, flowing solution culture     

Microfibrillar Structure, Cortical Microtubule Arrangement and the Effect of Amiprophos-methyl on Microfibril Orientation in the Thallus Cells of the Filamentous Green Alga, Chamaedoris orientalis

Microfibrillar structure, cortical microtubule orientation andthe effect of amiprophos-methyl (APM) on the arrangement ofthe most recently deposited cellulose microfibrils were investigatedin the marine filamentous green alga, Chamaedoris orientalis.The thallus cells of Chamaedoris showed typical tip growth.The orientation of microfibrils in the thick cell wall showedorderly change in longitudinal, transverse and oblique directionsin a polar dependent manner. Microtubules run parallel to thelongitudinally arranged microfibrils in the innermost layerof the wall but they are never parallel to either transverseor obliquely arranged microfibrils. The ordered change in microfibrilorientation is altered by the disruption of the microtubuleswith APM. The walls, deposited in the absence of the microtubules,showed typical helicoidal pattern. However, the original crossedpolylamellate pattern was restored by the removal of APM. Thissuggests that cortical microtubules in this alga do not controlthe direction of microfibril orientation but control the orderedchange of microfibril orientation. Amiprophos-methyl, Chamaedoris orientalis, coenocytic green alga, cortical microtubule, microfibrillar structure, tip growth     

Gregarina coronata N. Sp. (Apicomplexa: Eugregarinida) Described from Adults of the Southern Corn Rootworm, Diabrotica undecimpunctata howardi (Coleoptera: Chrysomelidae)

ABSTRACT. Gregarina coronata n. sp. (Apicomplexa: Eugregarinida) is described from the adults of the Southern Corn Root Worm, Diabrotica undecimpunctata howardi (Coleoptera: Chrysomelidae). Measurements given are means, in micrometers, taken from mature gamonts in association. Primite: protomerite hemi-ellipsoidal with basal tumidus, length 47.6, width 44.0, with cytoplasmic granule, apical crown apparent; deutomerite elongate ellipsoidal, length 227.9, width 81.3; epimerite absorbed into anterior in gamont, globular in trophozoite. Satellite: protomerite hemi-ellipsoidal, truncated at association interface to appear trapezoidal, length 39.2, width 49.6, with cytoplasmic granule; deutomerite elongate ellipsoidal, length 240.6, width 80.2; epimerite absorbed into anterior in gamont. Association caudofrontal and often precocious, occurring during growth of trophozoites. Gametocysts spherical, 115.3 in diameter, 132.9 with hyaline coat; producing multiple oocyst chains under moist storage in 24–36 h. Oocysts very uniform in shape and size, dorsad: doliform, length 6.4, equatorial width 3.4, polar width 2.9; pleuron: dorso-ventrally flattened, corpus concave with bicondylic termina; corpus height 0.98, width 4.44; terminus height 1.96, width 0.98.     

Immobilization Antigens from Tetrahymena thermophila Are Glycosyl-Phosphatidylinositol-Linked Proteins

We have studied four strains of Tetrahymena thermophila , each of which expresses a different allele of the SerH gene and produces a distinctive surface protein of the immobilization antigen (i-antigen) class. Following exposure of the strains to [³H]ethanolamine or [³H]myristic acid, a protein corresponding in molecular mass to the characteristic i-antigen for that strain became highly labeled, as determined by mobility in sodium dodecylsulfate-polyacrylamide eiectrophoresis gels. Furthermore, antibodies raised to the i-antigens of the T. thermophila strains selectively immunoprecipitated radioactive proteins having molecular mass identical to that of the i-antigen characteristic for that particular strain. The lipid moieties labeled by [³H]myristate were not susceptible to hydrolysis by exogenous phosphatidylinositol-specific phospholipase C from bacteria. However, when protein extraction was carried out in the absence of phospholipase C inhibitors, radioactive fatty acids derived from [³H]myristate were rapidly cleaved from the putative i-antigens. On the basis of available data, it was concluded that T. thermophila i-antigens contain covalently-Iinked glycosyl-phospha-tidylinositol anchors.     

Negative fire feedback in a transitional forest of southeastern Amazonia

Anthropogenic understory fires affect large areas of tropical forest, particularly during severe droughts. Yet, the mechanisms that control tropical forests' susceptibility to fire remain ambiguous. We tested the widely accepted hypothesis that Amazon forest fires increase susceptibility to further burning by conducting a 150 ha fire experiment in a closed-canopy forest near the southeastern Amazon forest–savanna boundary. Forest flammability and its possible determinants were measured in adjacent 50 ha forest plots that were burned annually for 3 consecutive years (B3), once (B1), and not at all (B0). Contrary to expectation, an annual burning regime led to a decline in forest flammability during the third burn. Microclimate conditions were more favorable compared with the first burn (i.e. vapor pressure deficit increased and litter moisture decreased), yet flame heights declined and burned area halved. A slight decline in fine fuels after the second burn appears to have limited fire spread and intensity. Supporting this conclusion, fire spread rates doubled and burned area increased fivefold in B3 subplots that received fine fuel additions. Slow replacement of surface fine fuels in this forest may be explained by (i) low leaf litter production (4.3 Mg ha⁻¹ yr⁻¹), half that of other Amazon forests; and (ii) low fire-induced tree and liana mortality (5.5±0.5% yr⁻¹, SE, in B3), the lowest measured in closed-canopy Amazonian forests. In this transitional forest, where severe seasonal drought removed moisture constraints on fire propagation, a lack of fine fuels inhibited the intensity and spread of recurrent fire in a negative feedback. This reduction in flammability, however, may be short-lived if delayed tree mortality or treefall increases surface fuels in future years. This study highlights that understanding fuel input rate and timing relative to fire frequency is fundamental to predicting transitional forest flammability – which has important implications for carbon emissions and potential replacement by scrub vegetation.