The natural history of a fugitive prairie plant (Mirabilis hirsuta (Pursh) MacM.)

Summary Some perennial fugitive plants that colonize badger disturbances in xeric prairies have a limited dispersal capacity, and consequently propagules are dispersed over a small area. I hypothesized that high density-dependent mortality might occur early in the life history of such species, and thus increased survival might occur in subsequent age classes because intraspecific competition would be reduced. These hypotheses were tested using natural and experimental cohorts of Mirabilis hirsuta (Pursh) MacM. From these data and field observations, inferences were obtained concerning selective forces operating upon life history characteristics of this species.The distance between individuals of M. hirsuta increases in successive age classes; the greatest decrease in density occurs between the propagule and seedling age classes. Mortality of propagules due to predation by ants and mice was density-dependent. Predation rates were highest at high propagule densities and predation upon propagules located on badger disturbances was higher than the mortality of propagules at similar densities in undisturbed prairie. The results of mortality in the propagule age class are seedlings present only at low densities and located away from parent plants. Seedlings survive to maturity only if they are located on badger disturbances; this species apparently can not successfully compete with plants present in undistrubed prairie. On badger disturbances seedlings present at low densities have much higher survival (roughly 50%) to maturity than do seedlings present at high densities (essentially zero). Thus, if high densities of propagules occur on a disturbance, predation upon propagules results, indirectly, in increased survival of seedlings to maturity. Such predation potentially could have important effects upon interspecific competition of M. hirsuta with other fugitives also colonizing badger disturbances.Reproductive success of M. hirsuta on the Cayler Prairie Preserve is contingent upon successful colonization of disturbance sites. It would appear that selection has operated upon the life history characteristics to favor both successful immigration onto new sites and establishment of seedlings on those sites. Relatively few, but large propagules are produced annually over a long adult life span. While large propagules enhance seedling establishment on xeric sites, production of few propagules annually for a number of years increases the likelihood of immigration onto sites that are variable in the time of appearance within the dispersal range of the plant.     

The condensed tannins of pasture legume species

Condensed tannins have been isolated from legume pasture species and purified by gel chromatography on Sephadex G-50 and LH-20 media. Molecular size di     

The molecular structure of (10R)-17β-hydroxy-5-methylene-4,10-cyclo-19-nor-4,5-seco-17α-pregn-20-YN-1-one

The crystal and molecular structure of (10R)-17β-hydroxy-5-methylene-4,10-cyclo-19-nor-4,5-seco-17α -pregn-20-YN-1-one has been determined by X-ray analysis in order to ascertain the configuration at C(10). As observed in most other 17α-pregn-20-yn-17β-ol structures, atom 0(17B) participates as a donor in a hydrogen bond trans to the C(16)-C(17) bond, and there is a short C(21)…0 intermolecular contact.     

Structural gene sets active in embryos and adult tissues of the sea urchin

Structural gene sequences active in a variety of sea urchin adult and embryo tissues are compared. A single-copy ³H-DNA fraction, termed mDNA, was isolated, which contains sequences complementary to the messenger RNA present on gastrula stage polysomes. Gastrula message sequences are 50 fold concentrated in the mDNA compared to total single-copy DNA. mDNA reactions were carried out with excess mRNA from blastula, pluteus, exogastrula, adult ovary, tubefoot, intestine, and coelomocytes, and with excess total mature oocyte RNA. A single-copy ³H-DNA fraction totally devoid of gastrula message sequences, termed null mDNA, was also reacted with these RNAs. Large differences in the extent of both mDNA and null mDNA reaction with the various RNAs were observed, indicating that in each state of differention a distinct set of structural genes is active, generally characterized by several thousand specific sequences. The complexity of gastrula mRNA was shown in previous work to be about 17 × 10⁶ nucleotides. In units of 10⁶ nucleotides, the complexities of the RNA sequence reacting with mDNA and with null mDNA in each tissue are, respectively, as follows: intestine mRNA; 2.1 and 3.7; coelomocyte mRNA: 3.5 and ≤1.4; tubefoot mRNA: 2.7 and ≤0.4; ovary mRNA: 13 and 6.7; oocyte total RNA: 17 and 20; blastula mRNA: 12 and 15; pluteus mRNA: 14 and ≤0.6; exogastrula mRNA: 14 and ≤0.6. The total complexity of each mRNA population is the sum of these values, as verified for several cases by reactions with total single-copy DNA. A relatively small set of mRNAs, the complexity of which is about 2.1 × 10⁶ nucleotides, appears to be shared by several of the tissues studied.     

An electron microscope study of the relative positions of the 4S and ribosomal RNA genes in HeLa cell mitochondrial DNA

The 4S RNA genes in HeLa mitochondrial DNA (mtDNA) have been mapped by electron microscopy using the electron-opaque label ferritin. This method is based on the high affinity interaction between the protein, avidin, and biotin. 4S RNA, covalently coupled to biotin, was hybridized to single-stranded mtDNA. The hybrids were then labeled with ferritin-avidin conjugates. The positions of ferritin-labeled 4S RNA genes were determined relative to the rRNA genes on both heavy (H) and light (L) strands of mtDNA. This region was recognized as a duplex segment after hybridization either with rRNA in the case of H strands or with DNA complementary to rRNA in the case of L strands.Our studies suggest that at least nineteen 4S RNA genes are present in the HeLa mitochondrial genome. On the H strand, we have confirmed the nine map positions found in a previous electron microscope mapping study (Wu et al., 1972) and obtained evidence for three additional 4S RNA genes. On the L strand, seven 4S RNA genes have been mapped. The nineteen genes are distributed more or less uniformly around the genome. There is a pair of closely spaced genes, approximately 150 nucleotides apart, on the H strand, and another closely spaced pair on the L strand.     

A radioimmunoassay for the Gm(b0) allotype of human immunoglobulins

A radioimmunoassay for the human allotype Gm(b⁰) which provides a sensitive and quantitative measurement of the level of this IgG3 genetic marker has been developed. The assay system can detect 15 nanograms of Gm(b⁰) IgG3 protein and is not inhibited by immunoglobulins of other allotypes and isotypes. Using this assay, good correlation was found between IgG3 and Gm(b⁰) levels in homozygous Gm(f, b⁰) sera and gene dosage effects could be confirmed. The correlation between Gm(b⁰) levels and IgG3 in Negroid Gm(a, b⁰) sera was not as good. This reduced correlation has been attributed to antigen differences in the IgG3 Gm markers characteristic of some Negroid Gm(a, b⁰) sera.     

Water and sodium balance in the estuarine diamondback terrapin (Malaclemys)

Summary Total body water decreased significantly in terrapins exposed to sea water (SW). Although the intracellular fluid decreased somewhat upon SW exposure, the decline in extracellular fluid was almost twice as great. Under conditions of voluntary drinking after salt loading, terrapins substantially increased the volume of the extracellular fluid while maintaining the intracellular fluid near the freshwater (FW) control levels. FW terrapins were consistently heavier than animals of the same plastron length exposed to SW. Thus expression of body fluid volumes as ml/cm plastron length rather than as % body weight is necessary to correct for the loss of total body water with progressive dehydration. Fasted terrapins in SW lost weight at 0.32% weight/day, whereas the rate in FW was 0.21%/day. Water influx and efflux in SW were 0.17 and 0.16 ml/100 g·h respectively. When the efflux was increased by the calculated value for unmeasured respiratory loss, it exceeded the influex by 0.01 ml/100 g·h. Consequently the net water loss determined with radiotracers (equivalent to 0.24% weight/day) was similar to the difference between the weight losses in SW and FW (0.11%/day). Partitioning studies indicated that the majority of water exchange between the terrapin and SW occurs through the integument. Terrapins in SW underwent a concentration of the body fluids, most of which can be attributed to water loss, not electrolyte gain. The rates of Na influx and efflux were quite low (usually ranging from 6–10 moles/100 g·h). In two terrapins the injection of NaCl loads resulted in eight- to 19-fold increases in Na efflux. The uptake of Na from SW occurred orally. The skin was virtually impermeable to Na. The salt gland and possibly the cloaca were the major routes of Na efflux. The injection of NaCl loads resulted in an increase in cephalic Na excretion from a mean of 3.2 moles/100 g·h to 32.5 moles/100 g·h. Terrapins in SW exhibited a significant increase in bladder urine [K] over the FW controls. There was a direct relationship between plasma [Na], urine [K], and lachrymal salt gland Na–K ATPase content. In comparing SW terrapins with FW painted turtles (Chrysemys) exposed to SW radiotracer studies demonstrated a similarity in Na influx, but there was at least a four-fold increase in water exchange in the painted turtle. It seems likely that the skins of many aquatic reptiles (marine, estuarine and FW) are impermeable to Na but differ markedly in water permeability.     

On the role of olfaction in sexual and interspecies recognition in crickets (Acheta and Gryllus)

Crickets appear to rely less upon olfactory communication than do their non-acoustical relatives, but males and females of house (Acheta) and field (Gryllus) crickets can determine sex by odour, and males can distinguish odours of conspecific and heterospecific females. In the presence of female odours, female-deprived males groom more vigorously and are more aggressive.