VARIABLE SELECTION ON EUROSTA'S GALL SIZE,I: THE EXTENT AND NATURE OF VARIATION IN PHENOTYPIC SELECTION

Natural fluctuations in environmental conditions are likely to induce variation in the intensity or direction of natural selection. A long-term study of the insect, Eurosta solidaginins Fitch (Diptera; Tephritidae), which induces stem galls on the perennial herb Solidago altissima (Asteraceae) was performed to explore the patterns of variation in phenotypic selection. The intensity of selection imposed by parasitoids and predators on gallmaking larvae, for gall size, was measured across 16 populations over the course of 4 generations, for a total of 64 population-generations. Directional selection was quantified by i, the selection intensity, and variance selection by j‘, a measure of the intensity of selection on phenotypic variance. Size-dependent attack by parasitoids caused upward directional selection (mean i_p = 0.42; SE = 0.023), while size-dependent bird attack favored larvae that induced smaller galls (mean i_b = -0.07; SE = 0.013. The mean net directional selection intensity was 0.35 (SE = 0.030), which indicates that insects inducing larger galls are generally favored by selection. The opposing patterns of size-dependent attack resulted in stabilizing selection in half the population generations, with an overall average. j‘ of -0.11 (SE = 0.078). The magnitude of directional selection was strongly influenced by the population mean gall size and weakly by the optimal gall size. The intensity of variance selection was strongly influenced by the shape of the fitness function, with sigmoidal and Gaussian-like shapes causing greater depletion of phenotypic variance.     

BIOLOGICAL INVASIONS IN EUROPE

Books reviewed:
Kowarik I., Biologische Invasionen: Neophyten und Neozoen in Mitteleuropa .     

Theophylline-induced protection in myoglobinuric acute renal failure: further characterization

We have reported previously that aminophylline has an ameliorating effect on the course and severity of glycerol-induced myoglobinuric acute renal failure in rats. Since aminophylline dissociates into theophylline in biological fluids and since theophylline is an adenosine receptor antagonist, we attributed the ameliorating effects to antagonism of the hemodynamic effects of endogenous adenosine. However, theophylline blocks tubuloglomerular feedback and produces natriuresis, and either of these effects might have accounted for the beneficial effects in acute renal failure. Therefore, this study was designed to further characterize the effects of theophylline in glycerol-induced acute renal failure in rats. Aminophylline had dose-dependent beneficial effects, as judged by the peak serum creatinine during the 3 days following induction of acute renal failure, by the number of animals with peak serum creatinine greater than 1 mg/dL, and by the mortality rate. Both furosemide and theophylline block tubuloglomerular feedback and produce natriuresis, but aminophylline had protective effects, whereas furosemide actually increased mortality, compared with aminophylline, following induction of myoglobinuric acute renal failure. Therefore, aminophylline's protective effects are independent of tubuloglomerular feedback and natriuresis. These results offer further support for the hypothesis that adenosine-induced hemodynamic changes play a pathogenic role in glycerol-induced acute renal failure in rats.     

Chondroid bone arises from mesenchymal stem cells in organ culture of mandibular condyles

Mandibular condyles of fetal mice 19 to 20 days in utero comprising clean cartilage and its perichondrium were cultured for up to 14 days, and their capacity to develop osteoid and to mineralize in vitro was examined. After 3 days in culture the cartilage of the mandibular condyle appeared to have lost its inherent structural characteristics, including its various cell layers: chondroprogenitor, chondroblastic, and hypertrophic cells. At that time interval no chondroblasts could be seen; instead, most of the cartilage consisted of hypertrophic chondrocytes. By that time, the surrounding perichondrium, which contains pluripotential mesenchymal stem cells, revealed the first signs of extracellular matrix enclosing type I collagen, bone alkaline phosphatase, osteonection, fibronectin, and bone sialoprotein as demonstrated by immunofluorescent techniques. Electron microscopic examinations of the newly formed matrix revealed foci of mineralization within and along collagen fibers as is normally observed during bone development. The composition of the latter mineral deposits resembled calcium pyrophosphate crystals. Following 14 days in culture larger portions of the condyle revealed signs of osseous matrix, yet the tissue reacted positively for type II collagen. Hence, the condylar cartilage, a genuine representative of secondary-type cartilage, elaborated in vitro a unique type of bone that would be most appropriately defined as chondroid bone. Biochemical assays indicated that the de novo formation of chondroid bone was correlated with changes in alkaline phosphatase activity and 45Ca incorporation. The findings of the present study imply that mesenchymal stem cells that ordinarily differentiate into cartilage possess the capacity to differentiate into osteogenic cells and form chondroid bone.     

Fish cleaning behaviour of shrimp

Cleaning behaviour of five species of shrimp from three families was studied at three different geographic locations in an effort to gain a quantitative understanding of cleaning behaviour, and to compare a broad cross-section of cleaner shrimp species. Two shrimp from the genus Periclimenes , two from the genus Lysmata , and one from the genus Stenopus were used and 27 hours of recorded laboratory observations were made for each of the five shrimp species.
All shrimp species were inactive most of the observed time, and most spent less than 2% of the observed time cleaning fish hosts. Also, the shrimp spent more time cleaning the ventral rather than the dorsal surface of the fish because they were reluctant to board the fish. However, evenness in cleaning does not appear to be an indicator of overall excellence in cleaning because the two best cleaners (based on number and duration of cleaning bouts) were among the least even in their cleaning.
The fish cleaning behaviour of the shrimp appeared to be strictly stereotypic in form, but the stimulus-response and the total amount of cleaning differed greatly among the five species. A Cleaning Efficiency Index (CEI) was created in an attempt to incorporate significant aspects of the cleaning behaviour. According to this CEI, Lysmata grabhami was by far the most efficient (best) cleaner, CEI = 55–51, compared to the others; Stenopus hispidus , 33–78; Periclimenes pedersoni , 6–29; Periclimenes yucatunicus , 5–60; and Lysmata californien , 2–12.
The cleaners most widely distributed geographically have the highest CEI scores, while the most localized cleaners have the lowest CEIs. This relationship may allow the CEI score to be useful in determining a cleaner shrimp's potential geographical distribution, and may also serve as an indicator for the degree of phylogenetic relationship to other cleaner shrimps.     

The ras oncogene and tumour metastasis: observations on murine cells transfected with activated human c-Ha-ras

Transfection of cells with cloned genes or total genomic DNA offers a means for studying aspects of neoplastic behaviour. We have used this method to examine whether incorporation of the cloned 6.6-kilobase (kb) fragment of DNA containing the mutant c-Ha-ras human oncogene can confer metastatic capability on murine NIH 3T3 cells. Cells co-transfected with the mutated ras gene and the neomycin resistance marker pSV2neo were selected by culture in neomycin. On subcutaneous inoculation into MF 1 nude mice, these cells proved to be tumourigenic with short latent periods (approximately 14 days)--nude mice were used to circumvent immunological rejection of the mouse cells expressing the product of the human oncogene. Transfectants were capable of lung colonisation after intravenous injection, but there was no evidence of spontaneous metastasis at autopsy, or on histological examination of the lungs and other organs, 90 days after inoculation. Incorporation of the transfected oncogene was confirmed by Southern blotting and its expression by dot-blot hybridisation and immunoprecipitation. The results in this experimental system indicate that transfection of a mutated human ras oncogene into non-neoplastic 3T3 cells can confer part of the metastatic phenotype, namely lung colonisation, but is not by itself sufficient to induce spontaneous metastatic behaviour.