Cyanophyten aus oberjurassischen Algen—Schwamm-Riffen

Blue-green algae of the families Rivulariaceae, Oscillatoriaceae, Stigonemataceae and Nostochopsidaceae have been identified by scanning electron microscopy in Upper Jurassic (Malm δ) sponge reefs near Solnhofen-Eichstätt, southern Franconia. Algal growth may account for 50–75% of the volume of the reef limestone. 'Hollow-sphere' algal structures up to 500 µm predominate. Rivulariaceae are the typical form and act as main reef-building biotic component. Pellets, intraclasts and oncolites as well as stromatolitic and cryptalgal crusts are of blue-green algal origin. These observations introduce new aspects regarding the evolution of the siliceous-sponge reefs of the Upper Jurassic in Southern Germany.
Mit dem Rasterelektronenmikroskop wurden in der jurassischen Schwammfazies des Malm δ bei Solnhofen-Eichstätt Blaugrün-Algen der Familien Rivulariaceae, Oscillatoriaceae, Stigonemataceae und Nostochopsidaceae nachgewiesen. 50–75% des Riffkalkes ist direkt auf Algen zurückzuführen. Vorherrschend sind Hohlkugelkolonien bis 500 µm, die zu den Rivulariaceae gestellt werden und die wichtigste riffbildende Biogenkomponente darstellen. Pellets, Intraklasten, Onkoide, Stromatolithen und strukturlose Krusten auf den Schwämmen sind Algenprodukte. Es ergeben sich neue ökologische Aspekte für die Kieselschwamm-Riffe des Oberen Jura in Süddeutschland.     

Age-specific patterns of reproduction in White-tailed and Willow Ptarmigan Lagopus leucurus and L. lagopus

Although many studies report a difference in reproductive success between old and young birds, little is known about how, why and when productivity changes as individuals age. We examined age-dependent reproduction in two bird species that inhabit harsh tundra environments: White-tailed Ptarmigan Lagopus leucurus in alpine areas and Willow Ptarmigan Lagopus lagopus in subarctic Canada. We evaluated reproductive performance in the light of three hypotheses: constraint, restraint and selection. Using cross-sectional and longitudinal data, we observed significant age effects in seven of the eight life history and behavioural traits examined for the two species. However, the pattern of age effects variedconsiderably across life history stages; younger birds generally had smaller clutches, later laying dates and poorer spring body condition, but the nesting success did not vary with age. Brood-rearing and renesting abilities were greater for older parents. The oldest age class of White-tailed Ptarmigan showed reproductive senescence for laying date and clutch size but fledged such a large proportion of the brood that they had the highest overall production of any class. It thus appears that parental experience can compensate for reduced physical ability to produce eggs. Annual mortality rates for breeding females were U-shaped for White-tailed Ptarmigan, with higher rates for young and old birds, but mortality did not change with age in Willow Ptarmigan. Overall, the two species differed in the presence of age dependence for only two traits (renesting ability and annual survival). Age-dependent effects were generally greater for White-tailed Ptarmigan than for Willow Ptarmigan. The patterns of mortality and fecundity we observed in ptarmigan provide general support for the constraint hypothesis of reproductive performance. By examining discrete stages of reproduction, we identified the life history stages where age effects occur and propose proximate mechanisms responsible for these effects.     

Gibberellins, Amylase, and the Onset of Heterosis in Maize Seedlings

Rood, S. B. and Larsen, K. M. 1988. Gibberellins, amylase, andthe onset of heterosis in maize seedlings.—J. exp. Bot.39: 223–233. The possible involvement of gibberellins and amylase in heterosisof maize seedlings was investigated in two parental inbreds,CM7 and CM49, and their single cross F₁ hybrid, CM7xCM49. Germinationof all three genotypes was complete within 36 h after the onsetof imbibition. By 48 h, heterosis (hybrid vigour) for increasedshoot and root length was consistently observed. The endogenousconcentration of gibberellin A₁ (GA₁) was measured in 48 h seedlingsby gas chromatography-mass spectrometry with selected ion monitoring(GC-SIM) using [²H₂]-GA₁ as an internal standard. The GA₁ concentrationwas highest in the hybrid (59 ng g^–1 dry wt.), intermediatein CM49 (9.0 ng g^–1), and lowest in CM7 (<5.0 ng g^–1).Amylase activities in all three genotypes were very low at 24h, but increased during the next 24 h, after which time amylaseactivity in the hybrid was significantly higher than that ofeither parental inbred. Inhibitors of gibberellin (GA) biosynthesis,AMO-1618 or CCC, inhibited germination, shoot and root growth,and amylase activity in all three genotypes. Conversely, exogenousgibberellic acid (GA₃) increased amylase activity, particularlyin the inbred CM7. Amylase isozymes were separated through polyacrylamidegel electrophoresis and generally similar profiles of starchdegrading enzymes were observed in the three genotypes. SinceGA is known to control a-amylase biosynthesis in some cereals,these results are consistent with the hypothesis that GAs areinvolved in the regulation of heterosis in maize. A higher endogenousGA₁ concentration in the hybrid could result in increased amylaseactivity in the hybrid seedlings and consequently, more rapidstarch hydrolysis which fuels heterosis for early growth. Key words: Amylase, germination, gibberellic acid, Gibberellin A₁, heterosis, hybrid vigour, Zea mays     

Genetics and Molecular Biology of Mouse Pigmentation

The formation of mouse coat color is a relatively complex developmental process that is affected by a large number of mutations, both naturally occurring and induced. The cloning of the genes in which these mutations occur and the elucidation of the mechanisms by which these mutations disrupt the normal pigmentation pattern is leading to an understanding of the way interactions between gene products lead to a final phenotype.     

Sap flow in wheat under free-air CO2 enrichment

The effects of elevated carbon dioxide (CO₂) concentration on plant water use are best evaluated on plants grown under field conditions and with measurement techniques that do not disturb the natural function of the plant. Heat balance sap flow gauges were used on individual main stems of wheat (Triticum aestivum L. cv Yecora rojo) grown under normal ambient conditions (control) and in a free-air CO₂ enrichment (FACE) system in Arizona with either high (control + high H₂O = CW; FACE + high H₂O = FW) or low (control + low H₂O = CD; FACE + low H₂O = FD) irrigation regimens. Over a 30d period (stem elongation to anthesis), combinations of treatments were monitored with,10–40 gauges per treatment. The effects of increased CO₂ on tiller water use were inconsistent in both the diurnal patterns of sap flow and the statistical analyses of daily sap flow (F_tot). Initial results suggested that the reductions in F_tot, from CO₂ enrichment were small (,0–10%) in relation to the H₂O treatment effect (,20–30%). For a 3d period, F_tot of FW was,19–26% less than that of CW (P = 0.10). Examination of the different sources of variation in the study revealed that the location of gauges within the experimental plots influenced the variance of the sap flow measurements. This variation was probably related to positional variation in subsurface drip lines used to irrigate plots. A sampling design was proposed for use of sap flow gauges in FACE systems with subsurface irrigation that takes into account the main treatment effects of CO₂ enrichment and the other sources of variation identified in this study. Despite the small and often statistically non-significant differences in F_tot between the CW and FW treatments, cumulative water use of the FW treatment at the end of the first three test periods ranged from 7 to 23% lower than that of the CW treatment. Differences in sap flow between FW and CW compared well with treatment differences in evapotranspiration. The results of the study, based on the first reported sap flow measurements of wheat, suggest that irrigation requirements for wheat production, in the present climatic regimen of the south-western US, may be predicted to decrease slightly because of increasing atmospheric CO₂.     

Changing Patterns of Infant Mortality and Maternal Fertility among Pumé Foragers and Horticulturalists

National census data show that the modern demographic transition—the recent trend toward declining mortality and fertility—is well underway in most countries. A different picture emerges when data from small-scale societies in unindustrialized parts of the world are considered. Many of these small-scale societies are also adapting to rapid changes in their subsistence economies. In this article, we examine the relationship between the pace of acculturation, infant mortality, and fertility levels among Pumé foragers and horticulturalists, two related groups of native South Americans. During the earliest stages of acculturation, Pumé horticulturalists experience not only a rapid drop in infant mortality but also a rise in birth rates. An anthropological view of demographic transitions provides important insight into how small-scale societies are affected by exposure to the labor market economy and has practical applications to effective development initiatives and public health policies.     

Light (Blt), a Mutation That Causes Melanocyte Death,Affects Stria Vascularis Function in the Mouse Inner Ear

The Light mutation (B^lt) is a dominant allele of the b-locus on mouse chromosome 4 which causes progressive dilution of coat colour. Melanocytes within the hair follicles of mutant mice develop normally but later degenerate, due to the accumulation of a toxic product, so that the hair becomes lighter with age. Previous studies on W-locus spotting mutants, from which melanocytes are absent, have shown that melanocytes in the stria vascularis of the inner ear are essential for the development and/or maintenance of the endocochlear potential (EP) which is normally around 100 mV. In this study, physiological recordings from the ears of Light mutants were correlated with strial ultrastructure. EPs recorded from all b/b controls and young homozygous and heterozygous mutants (20–22 days old) were normal (77 to 113 mV), but were reduced (19 to 59 mV) in about 30% of ears from older mutants (B^lt/B^lt and B^lt/b). Strial function therefore appears to develop normally but later degenerates in some mutants. This suggests that strial melanocytes are affected by the Light allele and that the continued presence of melanocytes is necessary for strial function. There was no obvious association between the recorded EP value and the ultrastructural appearance of the stria. No structural abnormalities of the stria were noted in control or mutant mice aged 20 days to 4 months including those which had a reduced EP. Strial atrophy was common in old controls and mutants (1–2 years), and appeared to be an age-related process rather than an effect of the Light mutation. Similarly, pigment build-up was common in all strial cells of old mice. However, the accumulations of lipofuscin-like pigment were much larger and more abundant in aged brown non-agouti mice than those observed in old agouti mice, which suggests that this age-related process also has a genetic component.     

Liverwort genomes display extensive structural variations

PIKE, L. M., HU, A., RENZAGLIA, K. S. & MUSICH, P. R., 1992. Liverwort genomes display extensive structural variations. Analyses of the total genomic DNA of eight species of liverworts and two species of green algae by thermal denaturation and CsCl buoyant density gradient centrifugation reveal a high degree of structural complexity and interspecific heterogeneity. The hepatic taxa exhibit two or more DNA components of varying base composition. Average G4-C contents of total cellular DNA calculated from melting profiles are similarly variable, ranging from 38% to 53% G + C. The green alga Chara , a member of the ancestral line to land plants, shows similarities with liverworts in possessing multiple DNA components of comparable complexity, whereas Hydrodiciyon DNA displays a single component. Detailed hybridization analyses of individual density gradient fractions using α-tubulin, rRNA and ribulose 1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL) gene probes were performed to locate the low-copy number and moderately repetitive nuclear genes, and the chloroplast chromosome, respectively. The location of each gene within the density gradient is highly variable among the organisms examined; a-tubulin occurs in fractions ranging from 44–64% G + C, rDNA in 50–64% G + C fractions, and the RbcL gene is located in fractions from 30–59% G + C. For a given species, the two nuclear genes normally overlap in their distributions within the gradient. In most instances, neither gene occurs in the major DNA components, indicating that these components may contain repetitive DNAs. The observed variation in the density of the rbcL gene implies substantial reorganization of the chloroplast genome. The overall differences in the genomic components within and between taxa provide insight into the dynamics of DNA structure that have occurred during the extended evolutionary history of these organisms.     

Breeding dispersal of Northern Flickers Colaptes auratus in relation to natural nest predation and experimentally increased perception of predation risk

After nest predation, breeding dispersal can be an effective strategy to avoid local nest predators. Furthermore, encounters with predators at a nest during the pre-laying stage may be used by parents to judge future risk, such that they may abandon a nest when a nest predator has been encountered. We studied whether the between- and within-year breeding dispersal of Northern Flickers Colaptes auratus was dependent upon the outcome of the previous nesting attempt. We also tested whether pairs presented with a model predator prior to egg-laying were more likely to abandon their nests than were pairs presented with a control model. Between years, males moved significantly further after having their nest depredated than did successful males, and females showed the same trend. However, these movements did not result in greater reproductive success. More pairs switched sites within years after having their nest depredated, but those that remained and those that moved had equal subsequent nest success. Stressful encounters with predators involving nest defence may trigger dispersal both between and within years, although reproductive benefits are unclear. The proportion of pairs abandoning nests did not differ between parents presented with control or predator models, suggesting that a single encounter with a predator is not a sufficient deterrent against continued use of a particular nest.