Prevention of potato top-roll by aphicide and its effect on leaf area and photosynthesis

In a field of potatoes, top-roll, which is induced by the aphid Macrosiphum euphorbiae feeding on the leaves, was restricted to two rows of plants which accidentally received no phorate aphicide granules at planting. The photo-synthetic rate per unit leaf area and the ground cover of top-rolled leaves were respectively 50% and 20% less than those of normal plants which may account for the smaller yields of affected plants observed in previous experiments.     

NEMATOCYSTS OF THE SEA ANEMONE METRIDIUM

Six types of nematocysts and their nematocytes in tentaclesand acontia of the sea anemone Metridium senile fimbriatum werestudied by electron microscopy. Microbasic b-mastigophores, microbasic amastigophores, and basitrichshave one fundamental feature in common: a straight, complexly-foldedshaft with dense spines pointing apically. An additional resemblancebetween a b-mastigophore and a basitrich is the possession ofa long, narrow, coiled thread bearing spines. An amastigophoreis characterized by a short, looped, unspined thread and a cup-shapedgranular matrix. Atrich and holotrich nematocysts have a coiled, spined tubeof uniform diameter which lies in an evenly granular matrixfilling the entire capsule. The above five nematocysts have three flaps at the apex of thecapsule which open upon discharge, and each nematocyte possessesa flagellum with which is associated one or two centrioles anda striated rootlet. The long rootlet of the b-mastigophorebearingnematocyte passes through a circular band of fibrils surroundingthe neck region of the capsule, and the short rootlet of theatrich lies in a dense fibrous sheath surrounding all but theapex of the capsule. The spirocyst differs from the other nematocysts in having athin, ridged, singlewalled capsule; an inverted tube containingbundles of tubules; an apical disk covered only by a thin layerof granular material and the nematocyst membrane; and the absenceof a flagellum in its nematocyte. Theories of excitation and mechanism of discharge of nematocystsand the function of spirocysts are discussed in the light ofthis and other recent studies of the fine structure of nematocysts.Special attention is drawn to the probable role of the foldsin the walls of shaft and thread in increasing the length ofthe tube upon discharge.     

Effects of accumulation of 3-O-methylglucose on levels of endogenous osmotic solutes in Chlorella emersonii

Abstract. Regulation of the concentration of osmotic solutes was studied in Chlorella emersonii grown at external osmotic pressures (II) ranging between 0.08 and 1.64MPa. NaCl was used as osmoticum. The total solute content of the cells was manipulated by applying 2 mol m⁻³ 3- O -methylglucose (MG), which was not metabolized, and accumulated at concentrations ranging between 60 and 230 mol m⁻³ within 4 h after its addition to the medium. Methylglucose uptake resulted in decreases in concentrations of proline and sucrose, the two solutes mainly responsible for osmotic adaptation of C. emersonii to high external II. The responses were consistent with the hypothesis that proline and sucrose concentrations are controlled by a system of osmotic regulation, with turgor and/or volume as a primary signal. Short-term experiments showed that even very small increases in turgor and/or volume, due to accumulation of methylglucose, resulted in large decreases in proline and sucrose. Over the first 30-60 min the total solute concentration in the cells increased by at most 15 osmol m⁻³ which would represent an increase in turgor pressure of at most 0.04 M Pa. Yet, the decreases in proline and sucrose were as fast as those in cells exposed to a sudden decrease of 0.25 MPa in external II, when the turgor pressure would have increased by at least 0.15 MPa. High concentrations of methylglucose in cells grown at high II did not affect the rapid synthesis of proline and sucrose which started when the cells were transferred to yet higher II. Thus, methylglucose had no direct effects on proline and sucrose metabolism, and it has been assumed that it acted solely as an inert osmotic solute within the cell.     

Heterophylly in Ranunculus flabellaris Raf.: The Effect of Abscisic Acid

Ranunculus flabellaris Raf., the Yellow Water-Crowfoot, is aheterophyllous semi-aquatic dicotyledonous plant, showing strikingmorphological and anatomical differences between terrestrialleaves and those formed underwater. After plants are submergedin a 25 µM solution of abscisic acid, leaves are producedat a normal rate but they exhibit many of the characteristicsof terrestrial leaves. Ranunculus flabellaris Raf., Yellow Water-Crowfoot, heterophylly, abscisic acid     

Evidence for long-distance dispersal in a sedentary passerine, Gymnorhina tibicen (Artamidae)

Australian magpies (Gymnorhina tibicen) are group-living birds found across much of mainland Australia. Adults commonly remain in a breeding territory until death. Young of the year either remain on the natal (birth) site or are forced by their parents to disperse. Observational studies in south-eastern Australia suggest that most dispersing juveniles settle within 7 km of their natal territory. Therefore, despite potential for considerable gene flow (via flight), social organization predisposes magpies towards local population structuring. In this study, we measured genetic variation at both nuclear (allozyme) and mitochondrial loci and found evidence of substantial gene flow over very large distances (up to 1599 km). Thus, some juvenile magpies may disperse much greater distances than was previously thought. For mtDNA, geographic and genetic distance were strongly correlated, consistent with a pattern of isolation by distance. Therefore, although female gene flow is substantial it is apparently geographically restricted over large distances, in approximately a stepping-stone fashion. We conclude that a strong relationship between gene flow and geographic distance can develop even over large distances if populations have experienced no major historical disturbances to gene flow.     

Assessing Ecoregional-Scale Habitat Suitability Index Models for Priority Landbirds

ABSTRACT Emerging methods in habitat and wildlife population modeling promise new horizons in conservation but only if these methods provide robust population-habitat linkages. We used Breeding Bird Survey (BBS) data to verify and validate newly developed habitat suitability index (HSI) models for 40 priority landbird species in the Central Hardwoods and West Gulf Coastal Plain/Ouachitas Bird Conservation Regions. We considered a species’ HSI model verified if there was a significant rank correlation between mean predicted HSI score and mean observed BBS abundance across the 88 ecological subsections within these Bird Conservation Regions. When we included all subsections, correlations verified 37 models. Models for 3 species were unverified. Rank correlations for an additional 5 species were not significant when analyses included only subsections with BBS abundance >0. To validate models, we developed generalized linear models with mean observed BBS abundance as the response variable and mean HSI score and Bird Conservation Region as predictor variables. We considered verified models validated if the overall model was an improvement over an intercept-only null model and the coefficient on the HSI variable in the model was >0. Validation provided a more rigorous assessment of model performance than verification, and models for 12 species that we verified failed validation. Species whose models failed validation were either poorly sampled by BBS protocols or associated with woodland and shrubland habitats embedded within predominantly open landscapes. We validated models for 25 species. Habitat specialists and species reaching their highest densities in predominantly forested landscapes were more likely to have validated models. In their current form, validated models are useful for conservation planning of priority landbirds and offer both insight into limiting factors at ecoregional scales and a framework for monitoring priority landbird populations from readily available national data sets.     

Microsatellite DNA markers for analysis of population structure in the sea urchin Centrostephanus rodgersii

We describe the development of 13 variable microsatellites developed to investigate population structure and dispersal in the sea urchin Centrostephanus rodgersii. This species is the dominant grazing herbivore in southeast Australian coastal waters and has the ability to modify benthic community structure. The microsatellites we identified showed a range of allele numbers (4–21) and expected heterozygosity (0.32–0.91) in two sampled populations. Contrary to previous findings in free‐spawning marine invertebrates, genotype proportions in neither population deviated significantly from Hardy–Weinberg expectations.     

Microfossils and evidence of land plant evolution

Resolving the question of (1) land plant and (2) vascular land plant evolution is a complex problem. It requires a continued, multidisciplinary effort. We are all grateful to Dianne Edwards and her colleagues (Edwards et al. 1979) for pursuing one such line of research with careful attention to morphology and stratigraphy. Their efforts, however, are confined to one small part of the globe, and they perforce involve only one type of evidence effective with regard to questions of vascular plant evolution once the land estate has been reached. They do not deal with the basic question of vascular and non-vascular land plant origins. The so-called Přídolí benchmark that remained the sine qua nun for vascular plant evolution when Dianne Edwards began her studies has now been irrevocably breached. What other supposedly sacrosanct benchmarks will also crumble as the result of future discoveries, now that vascular plants have been recovered from lower Ludlovian strata? Nevertheless, pre-Devonian plant megafossils are too rare to yield definitive results with regard to the origin of land plants prior to the vascular estate, even though they could in principle (as emphasized by Edwards et al. 1979) provide the least ambiguous evidence. We must look elsewhere than to megafossils for evidence suggesting links in time between green algal ancestors, major groups of living green land Plants, and the many extinct groups of enigmatic higher land plants in the crucial Early Paleozoic time interval.