New chromosome reports in the subtribes Diocleinae and Glycininae (Phaseoleae: Papilionoideae: Fabaceae)

The base chromosome number of x = 11 is the most probable in all the subtribes included in tribe Phaseoleae, although some aneuploid reduction is evident in Collaea and Galactia (Diocleinae) and chromosome duplications are seen in Amphicarpaea, Cologania and Glycine (Glycininae). The aims of this study were to improve the cytological knowledge of some species of Collaea and Galactia and to examine the anomalous counts reported for Calopogonium (Glycininae) and verify its taxonomic position. In addition, a molecular phylogeny was constructed using nuclear ribosomal DNA sequences (internal transcribed spacer region), and the chromosome number was optimized on the topology. In this work, the chromosome counts for Galactia lindenii, Galactia decumbens and Collaea cipoensis (all 2n = 20), and Calopogonium sericeum (2n = 22) are reported for the first time. The new reports for Galactia and Collaea species are in agreement with the chromosome number proposed for subtribe Diocleinae. The study rejects the concept of a cytologically anomalous Calopogonium and, based on the phylogenetic analysis, corroborates the position of this genus within subtribe Glycininae. The ancestral basic chromosome number of x = 11 proposed for Phaseoleae is in agreement with the evolutionary pathway of chromosome numbers analysed in this work. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 336–341.     

Variation in the trophic basis of production and energy flow associated with emergence of larval salamander assemblages from forest ponds

1. Larval amphibians are a dominant consumer in many freshwater systems, yet limited data on energy transfers between aquatic food resources and larvae and between metamorphosed larvae and adjacent habitats preclude an accurate assessment of their roles as links between aquatic and terrestrial food webs.
2. During 2003–04, we derived prey-specific assimilation efficiencies, analysed stomach contents, and intensively sampled ambystomatid salamander assemblages in four ponds to quantify the trophic basis of larval production. Using estimates of the contribution of each prey taxon to larval production, we constructed quantitative food webs and assessed variation in pathways of energy flow associated with emergences.
3. Overall, metamorphosed salamanders exported 3–8% of total prey production, required to account for total salamander production, to adjacent forest. Aquatic insects, zooplankton and amphibian prey were most important to energy flow associated with emergence; amounts of larval production attributed to each of these prey types shifted during development and varied among salamander taxa.
4. The majority of variation in the trophic basis of production among species was attributed to copepods (Cyclopidae) and three families of aquatic insects (Chironomidae, Chaoboridae and Culicidae). Dominant prey types contributing to the production of metamorphosed salamanders varied among ponds, representing different pathways for energy transfers between aquatic resources and forest habitats. These findings further our understanding of the ecological roles of amphibians and thus the consequences of amphibian declines and extinctions.     

Effects of hatching age on development and hatchling morphology in the red-eyed tree frog, Agalychnis callidryas

The red-eyed treefrog, Agalychnis callidryas , lays eggs on leaves overhanging ponds. Tadpoles hatch and enter the water at different ages, and late-hatched tadpoles survive aquatic predators better than do early-hatched tadpoles. Here I assess developmental consequences of hatching age through: (1) a morphological study of embryos and tadpoles through the plastic hatching period; (2) a behavioural assay for an effect of hatching age on feeding; and (3) a field experiment testing the effect of hatching age on growth to metamorphosis. Substantial development of feeding, digestive, respiratory and locomotor structures occurs in embryos over the plastic hatching period. Hatchling morphology thus varies with age, with consequences for behaviour and predation risk. Hatched tadpoles develop faster than embryos, and early-hatched tadpoles feed before late-hatched tadpoles. After all tadpoles have hatched, the effect of hatching age on size decreases. I found no evidence for an effect of hatching age on size at metamorphosis and only weak evidence for an effect on larval period. Hatching age affects the sequence of developmental change: early-hatched tadpoles lose external gills while otherwise more developed embryos maintain them. Plasticity in external gill resorption may be adaptive given differences in the respiratory environments of embryos and tadpoles. Early-hatched tadpoles also diverge from embryos in shape, growing relatively smaller tails. The study of functional morphology and developmental plasticity will contribute to understanding hatching as an ontogenetic niche shift.     

Population Responses to Environmental Change: Life History Variation, Individual-based Models, and the Population Dynamics of Short-lived Organisms

SYNOPSIS. We review two potentially important approaches topredicting the consequences of environmental change for populationsof short-lived organisms. First, we examine the concepts of"feasible life histories" and "feasible demographies" and presentthe results of a set of simulations in which the effects onpopulation growth rate of varying one of the demographic variables(average nest survival, average juvenile survival rates, averageannual adult survival rates, or age-specific fecundity) overa broad range of values while the others are maintained at long-termpopulation average values for the Grapevine Hills, Texas populationof the short-lived lizard Sceloporus merriami. The results ofthese simulations are compared to an analogous set of simulationsfor a Michigan population of the relatively long-lived snappingturtle (Chelydra serpentina, Congdon et al., 1994). The implicationsof differences in feasible demographies and life histories suchas described for these two species are discussed. We also discuss the approach of using individual-based, physiologicallystructured models to predict population response to environmentalvariation and present the results of simulations using a modeldeveloped for predicting population-level effects of operativeenvironmental variation in the lizard S. merriami under twodifferent climate change scenarios. This individual-based, physiologicallystructured model incorporates population-specific data on ecologicalenergetics, thermal and size dependence of digestive physiologyand metabolic rates, energetics of individual growth, allometricrelationships, social structure and mating system, and the dependenceof mortality rates on age, size, and social status of individuals.The data necessary to such models of population response toenvironmental variation can come only from detailed long-termstudies of individual populations.     

The role of nitrogen in promoting the toxic cyanophyte Cylindrospermopsis raciborskii in a subtropical water reservoir

1. The relative contribution of dissolved and atmospheric nitrogen to promoting dominance of the toxic nitrogen‐fixing cyanobacterium, Cylindrospermopsis raciborskii was examined in a subtropical water reservoir, North Pine Reservoir. 2. A combination of process studies in situ and analysis of historical water quality data suggests that nitrogen fixation was not the principal mechanism for acquiring nitrogen and unlikely to be the mechanism whereby C. raciborskii gains a competitive advantage. Ammonium was the preferred nitrogen source, followed by nitrate then nitrogen fixation. 3. Ammonium uptake rates in the euphotic zone were higher in the summer and autumn months compared with winter and spring coinciding with lower ammonium concentrations. Nitrate uptake rates did not appear to vary seasonally and were lower than those for ammonium in the summer, but similar in winter. Nitrate concentrations were higher in winter than summer and generally higher than ammonium concentrations. 4. Ammonium and nitrate uptake rates were similar at light intensities between 10% and 100% of surface light, contrasting with primary productivity which peaked between about 10 to 20% of surface light. Thus the phytoplankton population was adapted to low light conditions but remained able to utilise dissolved inorganic nitrogen over a wide range of light conditions. 5. The ammonium pool in the surface waters was relatively small compared with the phytoplankton uptake rates, and ammonium must therefore be rapidly recycled through the food web over periods of less than 1 h. Short‐term depletion may result, during which time the higher concentrations of nitrate are likely to provide a supplementary supply of nitrogen. 6. The dominance of C. raciborskii in this reservoir is more likely to be due to a superior ability to scavenge and store the low concentrations of phosphate, and a superior adaptation to the low light conditions exacerbated by artificial mixing.     

FLAVOR THRESHOLD AS AFFECTED BY INTERACTION AMONG THREE DAIRY‐RELATED FLAVOR COMPOUNDS*

The hypothesis of the present study was that the presence of one or more flavor compounds in a matrix would alter the perception (either enhance or suppress) of individual compounds as compared to a single flavor compound in a matrix. Thresholds were established for the flavor compounds (diacetyl, hexanal and δ‐decalactone) within each matrix; for each compound in the presence of a second compound; and for each compound in the presence of the remaining two compounds. An ascending order 2‐alternative forced choice test with 12 panelists was used for the evaluations. Results showed that diacetyl in water was suppressed by the presence of hexanal, but the presence of δ‐decalactone with hexanal reversed the trend. In the binary skim milk solutions diacetyl perception was enhanced, while being suppressed in the ternary solution. The perception of hexanal was enhanced in water (binary and ternary solutions). Hexanal and δ‐decalactone were suppressed in skim milk (binary and ternary solutions). δ‐Decalactone showed similar trends as hexanal in water, except that it was suppressed in the presence of diacetyl.     

Interaction of vesicular-arbuscular mycorrhizal fungi and root knot nematode on cultivars of tomato and white clover susceptible to Meloidogyne hapla

The interactive effects of vesicular-arbuscular mycorrhizal (VAM) fungi and root-knot nematode (Meloidogyne hapla) were studied on nematode-susceptible cultivars of tomato (cv. Scoresby) and white clover (cv. Huia) at four levels of applied phosphate. The relative merits of simultaneous inoculation with mycorrhizal fungi and nematodes and of inoculation with mycorrhizal fungi prior to nematode inoculation were evaluated. Mycorrhizal plants were more resistant than non-mycorrhizal plants to root-knot nematode at all phosphate levels and growth benefits were generally greater in plants preinfected with mycorrhizal fungi. Nematode numbers increased with increasing levels of applied phosphate. In mycorrhizal root systems, nematode numbers increased in the lower phosphate soils; at higher phosphate levels nematode numbers were either unaffected or reduced. The numbers of juveniles and adults per gram of root were always lower in mycorrhizal treatments. Mycorrhizal root length remained unaffected by nematode inoculation. Mycorrhizal inoculation thus increased the plants' resistance to infection by M. hapla. This was probably due to some alteration in the physiology of the root system but was not entirely a result of better host nutrition and improved phosphorus uptake by mycorrhizal plants.     

Demonstration of Various Acid Hydrolases and Preliminary Characterization of Acid Phosphatase in Naegleria fowleri1

ABSTRACT. Extracts of the pathogenic ameba Naegleria fowleri, prepared by freeze-thawing and sonication, were analyzed for their content of various hydrolytic enzymes that have acid pH optima. The organism is rich in acid phosphatase activity as well as a variety of glycosidases which include β-glucosidase, β-galactosidase, β-fucosidase, α-mannosidase, hexosaminidase, arylsulfatase A, and β-glucuronidase. The crude extract contained only negligible levels of sphingomyelinase, neuraminidase, or arylsulfatase B. All of the hydrolases exhibited higher activity at pH 5.5 than at 7.0, indicating that they are truly “acid” hydrolases. In general, after centrifugation (100,000 g, 1 h), except for arylsulfatase B, more than half of the activity of each of the various hydrolases was recovered in the supernatant fraction. The acid phosphatase in the high-speed supernatant was purified 45-fold (32% yield) by chromatography on QAE-Sephadex and Sephadex G-200 and shown to have the following properties: 1) pH optima, 5.5; 2) K_m (4-methylumbelliferyl phosphate), 0.60 mM; 3) molecular weight (estimated by gel filtration chromatography), 92,000; 4) inhibited by heteropolymolybdate complexes but not by L(+) sodium tartrate (0.5 mM) or sodium fluoride (0.5 mM). In addition, unlike the tartrate-resistant acid phosphatase of Leishmania donovani, the major acid phosphatase of N. fowleri is less than 5% as effective in inhibiting superoxide anion production by f-Met-Leu-Phe-stimulated human neutrophils. The finding of high levels of a number of acid hydrolases in Naegleria fowleri raises several questions that merit further study: Do the hydrolases perform a housekeeping function in this single cell eukaryote or do they play some role in the pathogenic process that ensues when the organism infects a suitable host?