Population fragmentation may reduce fertility to zero in Banksia goodii — a demonstration of the Allee effect

All individuals of all known populations of Banksia goodii were assessed for seed production. Small populations produced no or only a few seeds per unit canopy area. Effects of population size on seed production per unit area and seed production per plant were present over the whole range of population sizes, indicating that even in large populations seed production may still not be at its maximum. Resource differences could not explain this disproportionate decrease in seed production with decline in population size, because there were no differences in soil properties and understorey or overstorey cover between the small and large populations. Although plants in small and large populations were similar in size, seed production per plant was much lower in small populations. This was not because plants in small populations produced fewer cones but because the fraction of these cones that was fertile was much lower. Five of the nine smallest populations (<200 m²) produced no fertile cones over the last 10 years. The number of seeds per fertile cone did not depend on population size. The results are discussed in relation to pollination biology.     

Isolation of a new paramutagenic allele of thesulfurea locus in the tomato cultivar Moneymaker following in vitro culture

A new allele, SC148, of thesulfurea locus inLycopersicon esculentum was detected in a line derived after repeated selfing of plants that had been regenerated from tissue culture. Like the originalsulf mutant, SC148 displayed two mutant phenotypes: green-yellow speckled plants in which thesulf ^vag allele is present and pure yellow plants homozygous for thesulf ^tpura allele. Although the mutant alleles are recessive to wild-type, an unpredictable number of variegated and pura plants appeared in F₁ progenies that had been derived from crosses between SC148 and wild-type tomato plants. The presence of the wild-typesulf ⁺ allele in these variegated heterozygotes was demonstrated using a cytological marker that is linked tosulf. It is concluded that the mutantsulf allele of SC148, imposes its variegated expression state on the wild-typesulf ⁺ allele present insulf ⁺/sulf^vag heterozygotes. This behaviour, known as paramutation, has also been described for the originalsulf allele. The SC148 allele, however, seems to induce changes at an earlier stage in development. The analogy of this paramutagenic system to dominant position effect variegation inDrosophila is discussed.     

The interaction of the vanadyl(IV) cation with phytic acid

The interactions of VO²⁺ with phytate to form both soluble and insoluble complexes, have been studied by electronic absorption spectroscopy. A soluble 1∶1 VO²⁺: phytate complex is formed at pH <1. At higher pH-values insoluble complexes are produced. Two different solid complexes, obtained respectively at pH=2 and 4, were isolated and characterized. The maximal bonding ratio of VO²⁺: phytate was found to be 4, on the basis of a pH binding profile.     

Size dependent metal concentrations in two marine gastropod species

The effect of size on the accumulation of Cd, Cr, Cu, Mn, Ni, Fe and Zn in the muscle and viscera of the gastropodsMonodonta turbinata andCerithium vulgatum was investigated. The concentration of the essential metals Cr, Mn and Ni and the non-essential metal Cd decreased with increasing size in both of the species and tissues. The concentration of the essential metals Cu, Fe and Zn, showed a less constant relation with size.     

Lattice population dynamics for plants with dispersing seeds and Vegetative propagation

The population dynamics of plants in a lattice structured habitat are studied theoretically. Plants are assumed to propagate both by producing seeds that scatter over the population and by vegetative reproduction by extending runners, rhizomes, or roots, to neighboring vacant sites. In addtion, the seed production rate may be dependent on the local density in the neighborhood, indicating beneficial or harmful crowding effects. Two sets of population dynamical equation(s) are derived: one based onmean-field approximation and the other based onpair approximation (tracing both global and local densities simultaneously). We examine the accuracy of these approximate dynamics by comparing them with direct computer simulation of the stochastic lattice model. Pair approximation is much more accurate than mean-field approximation. Mean-field approximation overestimates the parameter range for persistence if crowding effects on seed production are harmful or weakly beneficial, but underestimates it if crowding effects are highly beneficial. Dynamics may show bistability (both population persistence and extinction) if the effect of crowding is strongly beneficial. If there is a linear trade-off between seed production and vegetative reproduction, the equilibrium abundance of the population may be maximised by a mixture of seed production and vegetative reproduction, rather than by pure seed production or by pure vegetative reproduction. This result is correctly predicted by pair approximation but not by mean-field approximation.     

Isolation of silencer-containing sequences causing a tissue-specific position effect on alcohol dehydrogenase expression in Drosophila melanogaster

A transient expression assay has been used to investigate the cause of a tissuespecific position effect on Adh expression from a transgene insertion in Drosophila. A 15.4-kb genomic clone containing the 3.2-kb Adh insert along with flanking regions of genomic DNA is expressed in this assay in a tissue-specific pattern resembling the abnormal expression pattern of the position effect. The 3.2-kb Adh insert is expressed normally without the flanking sequences. A silencer element is located upstream of the Adh gene within a 2-kb fragment that acts in both orientations and at a distance of at least 6.5 kb from the larval Adh promoter to suppress ADH expression in a nontissue specific fashion. The DNA sequence of the 2-kb fragment indicates that it is a noncoding region. A 17-bp sequence is repeated within this region and may be associated with the silencer activity, since subclones from the 2-kb fragment, each containing one of the repeated regions, both retain full silencer activity. This silencer fails to suppress expression from an α₁-tubulin promoter-LacZ fusion construct or an hsp70 promoter-Ach fusion construct. In addition to the silencer, another element is located downstream of the Adh gene that produces a higher level of anterior than posterior midgut expression. These results suggest that the 5′ silencer and the 3′ element act together to create the tissue specific pcsition effect characteristic of the GC-1 line. © 1994 Wiley-Liss, Inc.     

HBIG,无环鸟苷,干扰素联合对慢性乙型肝炎抗病毒效应观察

本文报道血清ＨＢＶ复制标志阳性的慢乙肝５４例,随机分为治疗组及对照组各２７例进行ＨＢＩＧ、无环鸟苷、干扰素联合近、远期抗病毒效应观察。治疗组为无环鸟苷第一周按２５～２０ｍｇ／ｋｇ／ｄ计后改１７～１５ｍｇ／ｋｇ／ｄ×５３天,共６０天;人白细胞干扰素１×１０６Ｕ肌注每周３次×４周,后改１．０×１０６Ｕ肌注每周２次×６周,共１０周;ＨＢＩＧ４００Ｕ肌注隔日１次,共１０周,对照组仅给予一般“保肝”药物。其中治疗组１８例,对照组１９例进行治后半年到２年追踪观察,结果近、远期ＨＢｃＡｇ、ＤＮＡＰ、ＨＢＶ－ＤＮＡ阴转率治疗组均高于对照组,其中治疗组近、远期ＨＢｃＡｇ,ＨＢＶ－ＤＮＡ阴转率均达４０％以上,明显高于对照组（Ｐ＜０．０５～０．０１）,治疗组近、远期各有４例及２例ＨＢｓＡｇ阴转,而对照组则无一例阴转,从近、远期综合抗病毒效应观察,治疗组全阴率分别为３３．３％、４４．４％,而对照组分别为３．７９％及０％,Ｐ＜０．０１,治疗组无明显毒副反应。对比单用无环鸟苷,全阴率３１．８％;无环鸟苷加干扰素两药联合全阴率３７．５％,均有所提高,达到４４．４％,值得进一步研究。     

Wind chill factor applied to Patagonian climatology

The wind cooling effect determines wind chill equivalent-temperatures, which may be rather different to actual temperature. In a windy region such as Patagonia, this difference may reach a magnitude and persistence to become an important bioclimatic element. This paper quantifies the wind cooling effect in Patagonia by the presentation of equivalent isotherms as an adaptation of the usual isotherm maps to the regional bioclimatic environment. It is concluded that due to seasonal variations in wind speed, the annual equivalent temperature range is smaller than the actual temperature range, thus increasing oceanic features, from a thermal viewpoint, of the Patagonian climate.«Les vents que chassent, à travers une échancrure de la Cordillère des Andes, les hautes pressions du Pacifique, s'étranglent et s'accelèrent dans un étroit couloir de cent kilomètres de front, en direction de l'Atlantique, et raclent tout sur leur passage».Antoine de Saint-Exupéry «Un sens à la vie» (1956)     

GENETIC VARIABILITY OF GELIDIUM CANARIENSIS (RHODOPHYTA) DETERMINED BY ISOZYME ELECTROPHORESIS1

The populations of Gelidium canariensis (Grunow) Seoane-Camba from the Canary Islands were analyzed for genetic variability by isozyme electrophoresis in 1989 and 1990. Each population was divided into sporophytic and gametophytic subpopulations. Twenty-three to 27 putative alleles corresponding to 22 gene loci were analyzed. Sev-enteen loci were monomorphic in all six subpopulations, and five were polymorphic in at least one subpopulation. Significant deviations from Hardy-Weinberg equilibrium were found. The amount of genetic variability (percentage of polymorphic loci, mean number of alleles per locus, and average gene diversity) of haploid subpopulations was lower than that of diploid subpopulations. No correlation between genetic distance and geographical distance was found. Low genetic differentiation between sporophytic and gametophytic subpopulations of the same locality was obsewed in two populations. The low genetic diversity and genetic differentiation suggest that the genetic structure of the populations of G. canariensis from the Canary Islands is due to a combination of founder effects and the predominance of asexual reproduction. Initial differences in gene frequencies may have persisted because of insufficient time to reach a higher level of differentiation.