The role of silk in courtship and chemical communication of the false widow spider, <Emphasis Type="Italic">Steatoda grossa</Emphasis> (Araneae: Theridiidae)

In spiders, sex pheromones are often associated with silk produced by females, and function in mate attraction, recognition, and evaluation. Silk-bound pheromones typically elicit courtship behaviour in web-building spiders. Here we (1) describe courtship interactions of Steatoda grossa males with virgin or mated females, and (2) show that silk and methanol extracts of silk produced by virgin females trigger courtship behaviour (silk production) by males, whereas silk of mated females does not. Our results indicate that (1) virgin females produce a silk-bound sex pheromone, (2) males discriminate between virgin and mated females based on silk cues, and (3) male silk likely functions in sexual communication.     

Controlled Biomineralization of Magnetite (Fe(inf3)O(inf4)) and Greigite (Fe(inf3)S(inf4)) in a Magnetotactic Bacterium

A slowly moving, rod-shaped magnetotactic bacterium was found in relatively large numbers at and below the oxic-anoxic transition zone of a semianaerobic estuarine basin. Unlike all magnetotactic bacteria described to date, cells of this organism produce single-magnetic-domain particles of an iron oxide, magnetite (Fe(inf3)O(inf4)), and an iron sulfide, greigite (Fe(inf3)S(inf4)), within their magnetosomes. The crystals had different morphologies, being arrowhead or tooth shaped for the magnetite particles and roughly rectangular for the greigite particles, and were coorganized within the same chain(s) in the same cell with their long axes along the chain direction. Because the two crystal types have different crystallochemical characteristics, the findings presented here suggest that the formation of the crystal types is controlled by separate biomineralization processes and that the assembly of the magnetosome chain is controlled by a third ultrastructural process. In addition, our results show that in some magnetotactic bacteria, external environmental conditions such as redox and/or oxygen or hydrogen sulfide concentrations may affect the composition of the nonmetal part of the magnetosome mineral phase.     

Reconciliation of evolution and nomenclature among the higher taxa of protists*

Existing taxonomic schemes for the protists at the highest levels are confusing owing to insensitivity to evolutionary data, lack of stability, evolutionary misleading terminology and multiple, contradictory systems. We propose a system which circumvents these problems by recognizing the largest monophyletic groups possible, and creating a nomenclature for these by appending the suffix ‘protista’ onto an already recognizable prefix: for example, euglenoprotista, cilioprotista, chytridioprotista. This system provides a high degree of stability while also allowing for the further clustering of these groups and inclusion of their descendant groups, such as the plants, as more evolutionary data become available.     

ASSOCIATIONS BETWEEN ALLOZYME FREQUENCIES AND SOIL CHARACTERISTICS IN GAILLARDIA PULCHELLA (COMPOSITAE)

Selection favoring different alleles in different environments frequently has been suggested as an explanation for allozyme variation within and among populations. This hypothesis predicts that allozyme frequencies will be correlated with environmental variables. Previous studies on allozyme frequency-environment covariation in plants often have relied on qualitative assessments of the environment and have emphasized highly autogamous species. We have examined allozyme frequency-soil associations in Gaillardia pulchella, an obligately outcrossed annual plant, by regressing the frequencies of 15 common allozymes representing six polymorphic enzyme loci on principal components from a set of 20 quantitative soil variables. Fifty-one populations, representing four taxonomic varieties, were included in the analysis. Among the 26 populations representing the var. pulchella, allozymes Adh-2f and Pgm-1c were significantly associated with a block of highly inter-correlated soil characteristics which serve to discriminate between soils derived from calcareous vs. non-calcareous rock types. This geographically complex pattern of allozyme frequency-soil covariation is not likely to be spurious and, thus, indicates the presence of adaptively differentiated soil races, or ecotypes. However, these results are not sufficient to conclude that the allozyme frequency divergence between ecotypes was mediated by selection, either directly or through genetic hitchhiking. The pattern of allozyme frequency-soil covariation within var. pulchella was not found among the other taxonomic varieties. Patterns of genotype-environment covariation often may be recognizable only within geographically or environmentally restricted groups of populations because of the confounding influences of other environmental variables.     

Lamin B1 and lamin B2 are long-lived proteins with distinct functions in retinal development

Lamin B1 and lamin B2 are essential building blocks of the nuclear lamina, a filamentous meshwork lining the nucleoplasmic side of the inner nuclear membrane. Deficiencies in lamin B1 and lamin B2 impair neurodevelopment, but distinct functions for the two proteins in the development and homeostasis of the CNS have been elusive. Here we show that embryonic depletion of lamin B1 in retinal progenitors and postmitotic neurons affects nuclear integrity, leads to the collapse of the laminB2 meshwork, impairs neuronal survival, and markedly reduces the cellularity of adult retinas. In stark contrast, a deficiency of lamin B2 in the embryonic retina has no obvious effect on lamin B1 localization or nuclear integrity in embryonic retinas, suggesting that lamin B1, but not lamin B2, is strictly required for nucleokinesis during embryonic neurogenesis. However, the absence of lamin B2 prevents proper lamination of adult retinal neurons, impairs synaptogenesis, and reduces cone photoreceptor survival. We also show that lamin B1 and lamin B2 are extremely long-lived proteins in rod and cone photoreceptors. OF interest, a complete absence of both proteins during postnatal life has little or no effect on the survival and function of cone photoreceptors.     

Orientation of repeating units in Xenopus chromosomal ribosomal DNA: A test of a stochastic model for maintaining intraspecies homogeneity

The orientation of repeating units in chromosomal ribosomal DNA of Xenopus was determined by denaturation mapping in order to test a model for gene rectification. The model postulates an alternating orientation that will allow the formation of pallindromic loops between adjacent repeats. Mutations would then be lost or driven to fixation by random correction of one sequence by another, following genetic homogeneity among the repeats. Head-to-tail orientation was found, ruling out the model for this system.     

The localization of a tcRNA102 gene near the 3' OH terminus of a fast myosin heavy chain gene. A comparison between normal and dystrophic chickens

Two genomic fragments were isolated from a normal and a dystrophic library containing the 3'OH terminus of the fast isoform of myosin heavy chain gene. Restriction map analysis confirmed that the genes were similar. The sequences coding for myosin were defined and shown to be the same in each genomic fragment. However, using a cDNA clone for tcRNA102 and two specific oligomers for tcRNA102 sequences, we determined that only the genomic fragment from normal chick contained homologous sequences to tcRNA102. Dystrophic chick DNA did not contain these regions of homology. In addition, the normal genomic fragment transcribes tcRNA102 in vitro via RNA polymerase III while the corresponding fragment of DNA from dystrophic chick was inactive. These results suggest that there are detectable differences between the normal and dystrophic genomes in this regard.     

NUTRITIONAL STUDIES ON THE CHLOROMONADOPHYCEAE: VACUOLARIA VIRESCENS AND GONYOSTOMUM SEMEN12

Unialgal, nonaxenic cultures of Vacuolaria virestcens Cienkowsky were grown in soil-water medium, in simple salt solutions with added peat and soil extract, and in synthetic medium. Doubling times in different media were determined: maximum growth rate (doubling time = 46.0 hr) was obtained in continuous light (210 ft-c) at 24 ± I C. Gonyostomum semen (Ehrenberg) Diesing was isolated from a natural population and grown in soil-water medium and a synthetic medium. Other techniques that have been used for culturing chloromonadophycean algae are reviewed.     

Organ-specific crystalline structures of ferritin cores inβ-thalassemia/hemoglobin E

Summary The cores of ferritins isolated from different organs of human subjects with-thalassemia/hemoglobin E (-thal/HbE) disease have different size distributions and crystallinities depending on the source organ. These patients have not been treated by hypertransfusion regimen or iron chelation therapy.-Thal/HbE spleens and livers yield ferritin cores which are less crystalline than those isolated from normal spleens and livers, reflecting the more rapid deposition of iron in the diseased state. Ferritins isolated from the hearts and pancreases of-thal/HbE subjects were found to have larger, more crystalline cores than those from the-thal/HbE livers and spleens, possibly as a consequence of the role of the heart and pancreas as long-term iron deposition sites in this iron overload pathology.