Hiatal shell concentrations, sequence analysis, and sealevel history of a Pleistocene coastal alluvial fan, Punta Chueca, Sonora

Richly fossiliferous marine sediments exposed along the Sonoran coastline of the Gulf of California near Punta Chueca provide an excellent setting in which to test (a) the strength of the association of skeletal concentrations with sedimentary hiatuses, (b) the utility of taphonomic evidence for reconstructing detailed histories of those non-depositional episodes, and thus (c) the largely unexploited potential of skeletal concentrations in the identification and interpretation of lithologically obscure unconformities and condensed sequences in shallow marine deposits. Sequence analysis based on discontinuity surfaces is possible in the complex, alluvial fan-to-shallow marine transition at Punta Chueca despite rapid facies changes. Progradation of depositional sequences that contain cobbles reworked from older terrace deposits indicates accumulation during a fall in eustatic sea level. The supratidal to subtidal conglomerates and sands contain a variety of predominantly molluscan shell concentrations that, on the basis of postmortem histories of shells, formed during periods of low net sedimentation (i.e. depositional hiatuses); the majority of these shell beds lie along discontinuity surfaces identified by independent physical stratigraphic evidence. Although not all discontinuity surfaces in the terrace are paved by shell material. and not all relative concentrations of shells indicate distinct discontinuities, the strength of the association between skeletal concentrations and stratigraphic hiatuses reveals the high degree of control on fossil occurrence by sedimentation rates, and indicates that skeletal concentrations can provide good clues to stratigraphically significant surfaces. Moreover, the detailed dynamics of non-depositional episodes are reliably revealed by taphonomic analysis of the associated fossil assemblages, improving interpretations of non-depositional episodes in local sedimentary history.     

Phorbol esters as probes of the modulatory site on protein kinase G–an overview

Phorbol esters as probes of the modulatory site on protein kinase C–an overview. The phorbol esters, diterpene derivatives produced by members of the family Euphorbiaceae, are of major scientific importance as tumour promoters. Their primary site of action is protein kinase C, an enzyme involved in the message transduction pathway for a large class of hormones which cause enhanced phosphatidylinositol turnover. Heterogeneity in the response of biological systems to the phorbol esters may be explained in part by heterogeneity in the phospholipids associated with protein kinase C, in its subcellular localization, and by proteolytic processing, as well as by isoforms of the enzyme. Development of other classes of activators of protein kinase C through computer modelling and natural product isolation suggests possible new approaches for intervention in the pathway.     

Isospora petrochelidon sp. n. (Protozoa: Eimeriidae) from the Cliff Swallow, Petrochelidon pyrrhonota

SYNOPSIS. Isospora petrochelidon sp. n. (Protozoa: Eimeriidae) is described from the cliff swallow, Petrochelidon pyrrhonota , from Douglas County, Colorado. Oocysts were passed primarily between 4 and 9 p.m. Sporogony was completed by 24 hr in 3% aqueous potassium dichromate at 21–28 C. The ellipsoid to ovoid oocysts averaged 25.2 × 22.2 μm. The oocyst wall was smooth, colorless, and single-layered. The 2 polar granules were disc-shaped, each adjoining a sporocyst. The lemon-shaped sporocysts averaged 18.4 × 10.8 μm. There was no membrane enclosing the sporocyst residuum and sporozoites. Two fledgling Isospora -free swallows fed sporulated oocysts began passing them on day 4 and died with massive infections on day 5. Data from these birds indicate that schizogony occurred during nighttime hours, gametogony during the day. Endogeny was found throughout the intestine distal to the gizzard, with schizogony confined to the convoluted glands of the subvillar mucosa and gametogony to the villar epithelium. Sporocysts released from mechanically ruptured oocysts excysted in 2% pancreatin within 5 min. Sporulated oocysts fed to a pigeon squab, duckling and cockerel produced no infections.     

Heterophylly in Ranunculus flabellaris: The Effect of Abscisic Acid on Leaf Ultrastructure

Ranunculus flabellaris Rafin., an aquatic buttercup, exhibitsheterophylly at the level of cellular ultrastructure. Comparedto terrestrial leaves, underwater leaves have thinner epidermalcell walls and more numerous paramural bodies per epidermaland mesophyll cell cross-section. The number of chloroplastsand mitochondria in cell cross-sections also contrasts betweenthe two leaf types. Despite within-and between-leaf variations,different patterns of organelle distribution for the two leafforms were found using principal coordinates analysis. In addition,underwater leaf chloroplasts are smaller, have fewer grana,a greater number of thylakoids/granum, and less starch comparedto chloroplasts from terrestrial leaves. At the ultrastructurallevel, submergence in ABA solution does not produce a leaf withas many characteristics of the terrestrial environment, as shownin previous studies of leaf morphology and anatomy. While numberand distribution of organelles in ABA-treated leaves are similarto terrestrial leaves, some features of chloroplast internalstructure and paramural body number and distribution resembleunderwater leaves. It is postulated that ABA acts as a morphogeninvolved in guiding the irreversible processes of leaf development,but certain subcellular characteristics may be determined directlyby the physical environment. Difficulties encountered in quantitativeanalyses of cellular ultrastructure are discussed. Ranunculus flabellaris, ABA, heterophylly, leaf ultrastructure, principal coordinates analysis     

Phenology of nutritional differences between new and mature leaves and its effect on caterpillar growth

Abstract. 1. We determined the phenology of the shrub Spiraea latifolia Ait. Bork. (Rosaceae), which has indeterminate shoot growth, and the effects of phenological changes in leaf quality on growth rate of the early-spring feeding buckmoth caterpillars, Hemileuca lucina Hy. Edw. (Saturniidae).
2. Leaves, regardless of whether they were newly expanded or several weeks old, were tougher later in the growth season (mid-June) than similarly aged leaves collected earlier; correspondingly, water and nitrogen content for leaves of all ages declined through the larval period. By July, newly expanded leaves had no more nitrogen than mature leaves.
3. Relative growth rate of third instar larvae fed new leaves or a mixture of new and mature leaves in early June was higher than that of those fed mature leaves, and efficiency of conversion of digested food to biomass was higher for larvae fed new leaves than for those fed mature leaves or a mixture.
4. In another experiment, larvae were reared on new leaves through the fourth instar and then fed a diet of new, mature or a combination of new and mature leaves, a regimen that was similar to the phenologies of both plants and caterpillars in the field. There was no difference in time to pupation or pupal weights among these treatments.     

Anther culture in Brussels sprouts (Brassica oleracea var. gemmifera)

In Brussels sprouts, yields of up to 357 embryos per 100 anthers cultured were obtained using a thermal shock treatment of 16 h at 35°C at the start of the culture period. Treatments of 48 h at 35°C and 14 days at 30°C gave no embryos. The F₁ hybrid cv. Gower consistently gave higher embryo yields than the F₁ hybrid cv. Nym, the differences being 3 to 10-fold. Differences in embryo yield of 3-fold or less were usually not statistically significant because of great variation within a treatment. This variation was less with donor plants raised in a growth room than with those raised in a glasshouse, where temperature and light intensity could not be so accurately controlled. From 842 embryos cultured, 270 plants were regenerated, mostly via hypocotyl explants, which developed from the anther-derived embryos. Most of the regenerants were haploid or diploid, with a few of higher ploidy.     

Pollination activity by blowflies and honeybees on onions in breeders' cages

Honeybees (Apis mellifera) and three species of blowflies (Calliphora vomitoria, Lucilia caesar and L. sericata) were observed on mass-pollinated populations of onions (Allium cepa) in 4·4 × 3·6 m × 2-2·5 m cages in June-August 1977. Pollination activity at temperatures from 14° to 28°C was compared on the basis of mean time per flower touched on each umbel visit. Honeybees did not forage below 16°C. Above 16°C their mean time per flower was short (1·4 s) and varied little with temperature. For blowflies, it decreased markedly from 12·1 s at 14–15·5°C to 2·7 s at 26°C and above, largely because at low temperatures flies spent long periods quiescent or grooming rather than actively feeding. When flowering was not completely synchronous between cultivars, honeybees were more selective than blowflies, but where flowering was synchronous, both types of pollinator visited the two cultivars at random. For the size of cage used, neither type of insect had a distinct advantage as a pollinator of onions, despite their different behaviour patterns.     

Onion pollination by blowflies and honeybees in large cages

Three experiments to investigate the effect of pollination by blowflies (Calliphora and Lucilia spp.) and honeybees (Apis mellifera) on seed yield and crossing level were made using a mixture of plants from two open-pollinated cultivars of onions (Allium cepa) in breeders' cages. No consistent differences were found between pollinators. In two experiments, fly pollination gave significantly higher yields than bee pollination but in the third, bee pollination gave slightly more seed. Crossing between cultivars, assessed by progeny testing on one cultivar, varied between 22-7 and 55-9%. Differences in crossing level attributable to the pollinators were not consistent and were not or only just statistically significant, but there were significant and substantial differences between the experiments themselves. Where more umbels were produced by the red-bulbed cultivar than by the yellow, higher crossing levels were found in the yellow cultivar. The highest crossing levels were found in the only experiment where insects were not introduced until peak flowering time, but where seed yield was comparatively low. Crossing levels were lowest where the umbel numbers were approximately equal. Individual umbels studied showed that while seed set was usually heaviest at and just before the mid-flowering date, this period could correspond with the lowest levels of crossing during the flowering period, particularly if flowering of the two cultivars was not completely synchronous. In field plots, approximately 75% of crossed seeds sown survived to give harvestable bulbs, but fewer than 50% of selfed seeds did so. In an experiment in which crossing levels from different pollinators were similar but survival levels differed significantly, it was deduced that bees performed more crossing within a cultivar than flies.     

THE DETERMINATION OF THE COLI-AEROGENES CONTENT OF MILK AND DAIRY EQUIPMENT BY PLATING ON VIOLET RED BILE AGAR INCUBATED AT 30°

SUMMARY: Violet red bile agar (VRB) incubated at 30° for 20–24 hr was as good an indicator of coli-aerogenes bacteria in milk as MacConkey's broth. A high proportion (82%) of the large, deep red colonies considered to be formed by coli-aerogenes bacteria were confirmed as such. A British brand of dehydrated VRB agar was as suitable as an American brand of this medium for determining the coli-aerogenes content of milk. All the strains of typical coli-aerogenes bacteria tested formed red colonies. In a small proportion of cases the diameter was less than 0·5 mm. The only other milk bacteria which formed colonies resembling those of coli-aerogenes organisms were some acid forming strains of Gram-negative rods. Coli-aerogenes bacteria, determined on VRB agar at 30°, generally constituted only a small proportion of the microflora of fresh raw milk and of farm dairy equipment.