REPRODUCTIVE ISOLATION AND DISTINCT POPULATION STRUCTURES IN TWO TYPES OF THE FRESHWATER SHRIMP PALAEMON PAUCIDENS

Twenty local populations of the Japanese freshwater shrimp Palaemon paucidens were electrophoretically and morphologically surveyed. Based on the diagnostic distributions of some alleles at Gpi, Mpi, Mdh-1, and Mdh-2, these populations were largely classified into two types (A and B). The A type occurred in lakes, ponds, and rivers, while the B type was observed only in rivers. Average Nei's genetic distance (D) between the two types fell into the subspecies range . The coefficient of gene differentiation, G_ST, varied considerably between the two types. In 12 populations of the A type, with a G_ST value of 0.281, nine pond and lake populations showed a higher G_ST (0.246) than the three river populations (0.151). On the other hand, G_ST was 0.036 for the eight local populations of the B type. The lower rostrum tooth number had a mode of two in type A and three in type B. Type-A populations largely varied in the upper rostrum tooth number and egg size but type B did not. Under laboratory conditions, mating frequently occurred within each type, but not between types. Furthermore, no embryonic development was observed in the few cases of intertype mating. These results indicate that the A and B types had experienced cladogenic separation with pre- or postmating isolation, whereafter the A type, under geographic isolation, underwent genetic and phenotypic differentiation, while the B type, under extensive gene flow, did not undergo differentiation.     

Identification and physical characterization of yeast glucoamylase structural genes

Summary Each one of at least three unlinked STA loci (STA1, STA2 and STA3), in the genome of Saccharomyces diastaticus controls starch hydrolysis by coding for an extracellular glucoamylase. Cloned STA2 sequences were used as hybridization probes to investigate the physical structure of the family of STA genes in the genomes of different Saccharomyces strains. Sta⁺ strains, each carrying a single genetically defined STA locus, were crossed with a Sta^– strain and the segregation behavior of the functional locus (i.e. Sta⁺) and sequences homologous to a cloned STA2 glucoamylase structural gene at that locus were analyzed. The results indicate that in all strains examined there is a multiplicity of sequences that are homologous to STA2 DNA but that only the functional STA loci contain extensive 5 and 3 homology to each other and can be identified as residing on unique fragments of DNA; that all laboratory yeast strains examined contain extensive regions of the glucoamylase gene sequences at or closely linked to the STA1 chromosomal position; that the STA1 locus contains two distinct glucoamylase gene sequences that are closely linked to each other; and that all laboratory strains examined also contain another ubiquitous sequence that is not allelic to STA1 and is nonfunctional (Sta^–), but has retained extensive sequence homology to the 5 end of the cloned STA2 gene. It was also determined that the DEX genes (which control dextrin hydrolysis in S. diastaticus), MAL5 (a gene once thought to control maltose metabolism in yeast) and the STA genes are allelic to each other in the following manner: STA1 and DEX2, STA1 and MAL5, and STA2 and DEX1 and STA3 and DEX3.     

Temporal dynamics of estuarine phytoplankton: A case study of San Francisco Bay

Detailed surveys throughout San Francisco Bay over an annual cycle (1980) show that seasonal variations of phytoplankton biomass, community composition, and productivity can differ markedly among estuarine habitat types. For example, in the river-dominated northern reach (Suisun Bay) phytoplankton seasonality is characterized by a prolonged summer bloom of netplanktonic diatoms that results from the accumulation of suspended particulates at the convergence of nontidal currents (i.e. where residence time is long). Here turbidity is persistently high such that phytoplankton growth and productivity are severely limited by light availability, the phytoplankton population turns over slowly, and biological processes appear to be less important mechanisms of temporal change than physical processes associated with freshwater inflow and turbulent mixing. The South Bay, in contrast, is a lagoon-type estuary less directly coupled to the influence of river discharge. Residence time is long (months) in this estuary, turbidity is lower and estimated rates of population growth are high (up to 1–2 doublings d^–1), but the rapid production of phytoplankton biomass is presumably balanced by grazing losses to benthic herbivores. Exceptions occur for brief intervals (days to weeks) during spring when the water column stratifies so that algae retained in the surface layer are uncoupled from benthic grazing, and phytoplankton blooms develop. The degree of stratification varies over the neap-spring tidal cycle, so the South Bay represents an estuary where (1) biological processes (growth, grazing) and a physical process (vertical mixing) interact to cause temporal variability of phytoplankton biomass, and (2) temporal variability is highly dynamic because of the short-term variability of tides. Other mechanisms of temporal variability in estuarine phytoplankton include: zooplankton grazing, exchanges of microalgae between the sediment and water column, and horizontal dispersion which transports phytoplankton from regions of high productivity (shallows) to regions of low productivity (deep channels).Multi-year records of phytoplankton biomass show that large deviations from the typical annual cycles observed in 1980 can occur, and that interannual variability is driven by variability of annual precipitation and river discharge. Here, too, the nature of this variability differs among estuary types. Blooms occur only in the northern reach when river discharge falls within a narrow range, and the summer biomass increase was absent during years of extreme drought (1977) or years of exceptionally high discharge (1982). In South Bay, however, there is a direct relationship between phytoplankton biomass and river discharge. As discharge increases so does the buoyancy input required for density stratification, and wet years are characterized by persistent and intense spring blooms.     

Expression of monoclonal antibody-defined cell surface antigens during rat brain development

Using single-cell suspensions of mechanically dissociated, prenatal BDIX-rat brain cells (13th, 15th, and 21st days after fertilization) for immunization, we have established a collection of 37 monoclonal antibodies (Mabs) directed against neural cell surface determinants. The developmental-stage-dependent expression of cell-surface antigens recognized by these Mabs was analyzed both on plasma membranes isolated from whole brains of BDIX rats (prenatal days 13-22 and adults) using an indirect 125I solid-phase radioimmunoassay, and on intact BDIX-rat brain cells (prenatal days 13-22) using a fluorescence-activated cell sorter. Different types of developmental stage-dependent profiles of Mab binding were found, these being indicative of the presence of neural cell surface determinants whose expression increases, decreases, or does not change with brain development. Some of the Mab-binding profiles showed transient changes as a function of developmental stage. These Mabs are currently being used for the characterization, reproducible identification, and isolation of neural cell subpopulations of the developing rat brain, with the aim of investigating the cell type dependence and developmental (differentiation) stage dependence of malignant transformation following pulse exposure to the carcinogen N-ethyl-N-nitrosourea at defined stages of brain development.     

A syndromic approach to common parasitic diseases

Standard textbooks discuss parasitic disease according to specific organisms. In contrast, patients with parasitic infections present to physicians with a variety of clinical manifestations that may involve any of several organ systems and that often mimic nonparasitic diseases. A syndromic approach to the clinical situation may help the physician in considering the most important parasitic agents. Many parasitic infections can be acquired in temperate climates. While often considered tropical or exotic, other parasitic diseases are now seen more frequently in developed countries because of immigration and increased world travel. In this review the clinical syndromes associated with common parasitic diseases in North America are discussed, with an emphasis on risk factors and diagnosis of specific infections.     

Frequency selectivity of hearing in the green treefrog,Hyla cinerea

Frequency selectivity of hearing was measured in the green treefrog, Hyla cinerea. A psychophysical technique based on reflex modification was used to obtain masked threshold estimates for pure tones (300-5,400 Hz) presented against two levels of broadband masking noise. A pure tone (S-1) presented 200 ms prior to a reflex-eliciting stimulus (S-2) inhibited the motor reflex response to S-2. The magnitude of this reflex modification effect varied systematically with the sound pressure level (SPL) of S-1, and threshold was defined as the SPL of S-1 at which the reflex modification effect disappeared. Masked thresholds were used to calculate critical ratios, an index of the auditory system's frequency selectivity. The frequency selectivity of the treefrog's hearing is greatest and critical ratios are lowest (22-24 dB) at about 900 and 3,000 Hz, the two spectral regions dominant in the male treefrog's species-specific advertisement call. These results suggest that the treefrog's auditory system may be specialized to reject noise at biologically-relevant frequencies. As in other vertebrates, critical ratios remain constant when background noise level is varied; however, the shape of the treefrog's critical ratio function across frequencies differs from the typical vertebrate function that increases with increasing frequency at a slope of about 3 dB/octave. Instead, the treefrog's critical ratio function resembles its pure tone audiogram. Although the shape of the treefrog's critical ratio function is atypical, the critical ratio values themselves are comparable to those of many other vertebrates in the same frequency range. Critical ratio values here measured behaviorally do not match critical ratio values previously measured physiologically in single eighth nerve fibers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification and physical characterization of yeast maltase structural genes

Summary Each of at least five unlinked MAL loci (MAL1 through MAL4 and MAL6) on the yeast genome controls the ability to synthesize an inducible -D-glucosidase (maltase). A subcloned fragment of the coding sequence of the MAL6 maltase structural gene was used as a hybridization probe to investigate the physical structure of the family of MAL structural genes in the genomes of different Saccharomyces strains. Mal⁺ strains, each carrying a genetically defined MAL locus, were crossed with a Mal^- strain and the segregation behavior of the functional locus and of sequences complementary to the maltase structural gene at that locus analyzed. The maltase structural gene sequences of each MAL locus were detected by Southern blot hybridization using BamH1 digests of genomic DNA of the meiotic products. This restriction enzyme was previously shown to cleave outside the confines of the MAL6 locus.The results of such experiments indicate that each MAL locus encompasses at least one maltase structural gene sequence homologous to that of MAL6, that yeast strains that lack functional MAL loci may or may not contain the corresponding maltase structural gene sequence, that the MAL1 maltase structural gene sequence or one of its alleles can be detected in all laboratory yeast strains examined and that each MAL locus can be identified as a characteristic BamH1 fragment of genomic DNA which includes a maltase structural gene.Yeast strains vary in the number of maltase structural gene sequences that they carry. By using the approach described in this report, the ones corresponding to the different functional MAL loci and residing within a BamH1 generated restriction fragment can be identified.     

Larval development of Diploptera punctata reared alone and in groups

Larvae of the cockroach Diploptera punctata were reared in isolation, in pairs, or in groups of 8–10. Duration of larval development, age at each ecdysis, weights at birth and ecdyses, and adult head-capsule width were measured. Duration of larval development was longer and adult size was larger in isolated animals than in animals reared in pairs and groups. The effect of isolation on development was more pronounced in males. All females had 4 larval instars, whereas males had 3 or 4 instars. The proportion of males with 4 larval instars was higher among animals reared in isolation. There was no difference in the duration of larval development or adult size between pair- and group-reared animals. The sex of animals in the group did not affect adult size or the duration of larval development. Males which underwent 3 or 4 larval instars had different schedules of moulting. Rates of growth of males of both instar types reared in isolation and pairs were similar. Greater adult weight of isolated animals and 4-instar-type males was a result of their longer duration of larval development. Both a higher rate of growth and longer duration of larval development contribute to the larger adult size of females than males.     

Mitotic chromosomes of species in the subgenusDrosophila (Diptera:Drosophilidae)

The karyotypes of 17 species in the subgenusDrosophila are compared according to their taxonomical relationships. Although closely related species often possess similar karyotypes, the karyotypes diverge considerably within the subgenus. Thus extensive chromosome rearrangements did occur during the speciation. Species with higher chromosome numbers do not necessarily have higher average of total chromosome length per cell.