Tracing the tropics across land and sea: Permian to present

The continuity through the past 300 million years of key tropical sediment types, namely coals, evaporites, reefs and carbonates, is examined. Physical controls for their geographical distributions are related to the Hadley cell circulation, and its effects on rainfall and ocean circulation. Climate modelling studies are reviewed in this context, as are biogeographical studies of key fossil groups. Low-latitude peats and coals represent everwet climates related to the Intertropical Convergence Zone near the Equator, as well as coastal diurnal rainfall systems elsewhere in the tropics and subtropics. The incidence of tropical coals and rainforests through time is variable, being least common during the interval of Pangean monsoonal climates. Evaporites represent the descending limbs of the Hadley cells and are centred at 10° to 40° north and south in latitudes that today show an excess of evaporation over precipitation. These deposits coincide with the deserts as well as seasonally rainy climates, and their latitudinal ranges seem to have been relatively constant through time. Reefs also can be related to the Hadley circulation. They thrive within the regions of clear water associated with broad areas of downwelling which are displaced toward the western portions of tropical oceans. These dynamic features are ultimately driven by the subtropical high-pressure cells which are the surface signature of the subsiding branches of the Hadley circulation. Carbonates occupy the same areas, but extend into higher latitudes in regions where terrestrial surface gradients are low and clastic runoff from the land is minimal. We argue that the palaeo-latitudinal record of all these climate-sensitive sediment types is broadly similar to their environments and latitudes of formation today, implying that dynamic effects of atmospheric and oceanic circulation control their distribution, rather than temperature gradients that would expand or contract through time.     

Immunocytochemistry In the Assessment of Ps2 Protein Expression In Fine Needle Aspiration Cytology From Breast Carcinoma

pS2 protein is a cysteine-rich polypeptide, of unknown function, the expression of which is induced in the human cancer cell line MCF-7 by oestrogen. the availability of a murine monoclonal antibody to human pS2 protein has prompted us to evaluate its expression in 47 cases of primary breast carcinoma. Using a double indirect immunoperoxidase technique, we compared the expression of pS2 protein in fine needle aspiration (FNA) cytology smears with that in formalin-fixed, paraffin-embedded sections from subsequently excised tumours from the same patients. We also compared the expression of pS2 protein and oestrogen receptor (ER) status using immunocytochemical assay (ER-ICA) in formalin-fixed, paraffin-embedded sections from 22 primary breast carcinomas. We found the application of immunocytochemistry in the assessment of pS2 protein expression in FNA cytology to be a reliable and cost-effective technique, having a sensitivity of 84% and a specificity of 100%. There was also a good correlation between the expression of pS2 protein and ER status.     

Ecdysteroids in helminths and annelids

Summary

This review focuses on recent research developments in the past three years concerning ecdysteroid biochemistry in helminths and annelids, with emphasis on results reported at the IXth Ecdysone Workshop in Paris, France, in September 1989. During the past three years, most of the research in this area has been concentrated on nematodes, in several species of which the occurrence of ecdysteroids has been demonstrated. Interesting biological effects of exogenously applied ecdysteroids have been discovered on meiotic reinitiation in oocytes of the dog heartworm, Dirofilaria immitis, and on microfilarial production by Brugia pahangi. These effects, together with previous discoveries, demonstrate the feasibility of affecting nematode physiology with exogenously applied ecdysteroids. However, experiments with four species of nematodes in three separate laboratories have failed to demonstrate that nematodes biosynthesize ecdysteroids from cholesterol. Therefore, it remains to be proven whether ecdysteroids are truly endogenous nematode hormones or are merely compounds with strong biological activity. Research with cestodes and trematodes has similarly revealed that ecdysteroids occur in these organisms and that the compounds have possible regulatory roles, but experiments demonstrating endogenous biosynthesis have yet to be performed. Annelids, which are more closely related to insects than helminths, also contain ecdysteroids; recent research has demonstrated the C-20 hydroxylation of ecdysone to 20-hydroxyecdysone, the active moulting hormone of most insects. Experiments to demonstrate this metabolic step in helminths have failed.     

A Nicotiana Gametosomatic Hybrid and its Progenies

A Nicotiana gametosomatic hybrid between N. tabacum and N. glutinosawas studied. It was shown to have a stable somatic chromosomecomplement of 2n=5x=60. Karyotypes and measures of DNA contentshow that there have been no major changes in the parental chromosomenumbers or morphology accompanying hybridization. Forty-eightchromosomes are derived from N. tabacum (2n=4x=48); 12 fromN. glutinosa (2n=2x=24). Homologous pairs of N. tabacum chromosomesusually pair normally at meiosis. Trivalents incorporating aglutinosa chromosome do occur but usually these remain as univalents. The fertility of the hybrid is low but some products of self-pollinationwere obtained. These carry the complete N. tabacum genome witha few glutinosa chromosomes, some of which form supplementarybivalents at meiosis. All derivatives studied were mixoploidbut progressive selfing reduces the extent of abnormality ofmitotic divisions. The study of morphological and developmentaltraits indicates that the addition of even a few chromosomesof N. glutinosa to the N. tabacum complement can modify thetabacum phenotype substantially. There is considerable variationamong the derivatives and scope for fixing desirable qualitiesthrough selection. The presence of only a haploid set of glutinosachromosomes in the original hybrid makes the return to a desirablegenotype more efficient than that achieved through more conventionalbreeding methods. Key words: Nicotiana, gametosomatic hybrid, selfed progeny, cytology     

Regulation of the pentose phosphate pathway at fertilization in sea urchin eggs

Summary

After fertilization of sea urchin eggs, there is a rapid increase in cellular levels of NADPH, a metabolite utilized in a variety of biosynthetic reactions during early development. Recent studies have shown that a dramatic increase in the activity of the pentose phosphate shunt occurs in vivo shortly after fertilization, consistent with the hypothesis mat this metabolic pathway is a major supplier of NADPH in sea urchin zygotes. One mechanism that may account, in part, for this increase in pentose shunt activity is the dissociation of glucose-6-phosphate dehydrogenase (G6PDH), the first enzyme of the shunt, from cell structural elements. In vitro, G6PDH is associated with the insoluble matrix obtained from homogenates of unfertilized eggs, and in this state, the enzyme is inhibited. Within minutes of fertilization, G6PDH is released as an active, soluble enzyme. A similar solubilization and activation of G6PDH occurs after fertilization of eggs of other marine invertebrates and in mammalian cells in culture stimulated by growth factors. The occurrence of this phenomenon in such diverse cell types, in response to different stimuli, suggests that the redistribution of G6PDH between insoluble and soluble locations may be involved in the regulation of the pentose phosphate shunt during cell activation in general.     

Size delays female senescence in a medium sized marsupial: The effects of maternal traits on annual fecundity in the northern brown bandicoot (Isoodon macrourus)

The degree to which females allocate resources between current reproduction, future fecundity and survival is a central theme in life history theory. We investigated two hypotheses proposed to explain patterns of reproductive investment, terminal investment and senescence, by examining the effects of maternal traits (age and maternal mass) on annual fecundity in female northern brown bandicoots, Isoodon macrourus (Marsupialia: Peramelidae). We found that annual fecundity in females declined in their final year of reproduction, indicating reproductive senescence. Maternal mass significantly influenced the rate of senescence and, in turn, a female's lifetime reproductive output. Mass had little effect on fecundity in 1st and 2nd year females, but a positive relationship with fecundity in 3rd year females. This meant that heavy, 3rd year females did not suffer the decline in fecundity shown in light 3rd year females. For 1st year females, mass and leg length increased between their first and second reproductive seasons, indicating a temporary shift, from the allocation of resources to reproduction, to increasing condition or structural size post their first breeding event. There were no net changes to body mass in subsequent years. We suggest that this year of post‐reproductive growth has important consequences for senescent effects on reproduction. Overall, results provided support for the effects of senescence on annual fecundity. Our findings were not consistent with the terminal investment hypothesis; reproductive output did not increase in females' final reproductive season despite a rapid decline in survival. However, this notion cannot be entirely dismissed; other measures of reproductive performance not examined here (e.g. offspring mass) may have provided an indication that females did increase their effort at the end of their lifespan. This study highlights the difficulty of measuring reproductive costs and the importance of understanding the combined effects of specific characteristics of an individual when interpreting reproductive strategies in iteroparous organisms.