On the occurrence, causes and potential consequences of low zooplankton to phytoplankton ratios in New Zealand lakes

SUMMARY. 1. New Zealand lakes are shown to have lower average zooplankton biomasses than north-temperate lakes of similar average phytoplankton biomass, expressed as cell volume or chlorophyll a , or similar average total phosphorus concentration, typically by a factor of 5 or more.
2. Evidence suggests that the relatively low zooplankton biomasses of New Zealand lakes may be related to a tendency for them to be dominated by large algae that are not directly available as food for zooplankton, with oligotrophy lakes in particular differing from north-temperate lakes in this respect.
3. This difference in turn may be related largely to their mixing regimes. All of the New Zealand lakes are polymietic or monomietic, whereas the northern lakes used for comparison are mostly dimietic. Also, hetero-cystous cyanobacteria are favoured by the low inorganic nitrogen concentrations that are typical of New Zealand lakes.
4. Poor nutritional quality of the phytoplankton, relating to nitrogen limitation in many New Zealand lakes, might supplement the effects of cell size.
5. Low exploitation of phytoplankton by zooplankton can be expected to produce a shift in the metabolism of New Zealand lakes towards the sediments. Among the potential consequences of this effect are increased hypolimnetic oxygen demand with increased susceptibility to development of large internal loads of nutrients, and consequently, increased sensitivity to accelerated eutrophication from any increase in external nutrient loads.     

A new rhizomatous Oryza species (Poaceae) from Sri Lanka

VAUGHAN, D. A., 1990. A new rhizomatous Oryza species (Poaceae) from Sri Lanka. The confusing taxonomy of the Sri Lankan Oryza officinalis complex is clarified with the recognition of a new rhizomatous species, Oryza rhizomatis Vaughan. This species has been found across the dry zone. The other species of the complex in Sri Lanka, O. eichingeri , occurs in moist habitats and is smaller and less common than 0. rhizomatis. The new species is described.     

Are smaller subspecies of common brushtail possums more omnivorous than larger ones?

Body size is often associated with a dietary divergence within taxonomically related groups so that large animals are often folivorous, while smaller species shift progressively towards omnivory or carnivory. This trend may be influenced by allometric constrains which result in relatively high energetic requirements, but low gut capacities in small animals, compared to their large counterparts. The common brushtail possum (Trichosurus vulpecula, Phalangeridae) has six subspecies ranging widely in weight (1–4 kg). They are not strictly folivorous, but supplement their diet with more nutritious, non‐foliar foods. We predicted that T. vulpecula subspecies diverged in diet in association with body size, with smaller subspecies consuming higher proportions of non‐foliar foods. We assessed this with a review and a meta‐analysis of previous Australian studies. We also investigated the previously unquantified diet of T. v. hypoleucus at three sites in the northern jarrah forest of Western Australia. Results from the meta‐analysis and the review supported our prediction. However, the large variability in the data highlighted their limitations and those of the techniques commonly used to quantify the diet of T. vulpecula. Nonetheless, small subspecies of T. vulpecula appear to consume higher proportions of non‐foliar foods. These results should encourage further research into the body size/diet relationship within T. vulpecula and other possum species. Results from the dietary study of T. v. hypoleucus emphasized their omnivorous diet, which was dominated by foliage and flowers and smaller proportions of invertebrates, seeds and fruits. The common brushtail possum is seldom an exclusive arboreal folivore, but rather ranges from folivory to omnivory.     

Demographic effects of temperature‐dependent sex determination: will tuatara survive global warming?

Global climate change is of particular concern for small and isolated populations of reptiles with temperature-dependent sex determination because low genetic variation can limit adaptive response in pivotal temperatures, leading to skewed sex ratios. We explore the demographic consequences of skewed sex ratios on the viability of a tuatara population characterized by low genetic diversity. We studied the rare species of tuatara ( Sphenodon guntheri ) on the 4 ha North Brother Island in New Zealand over two nesting seasons and captured 477 individuals, with a 60% male bias in the adult population. Females first breed at 15 years and have extremely low rates of gravidity, producing clutches of three to eight eggs every 9 years. Simulations of the population using population viability analysis showed that the current population is expected to persist for at least 2000 years at hatchling sex ratios of up to 75% male, but populations with 85% male hatchlings are expected to become extinct within approximately 300 years (some eight generations). Incorporation of inbreeding depression increased the probability of extinction under male biased sex ratios, with no simulated populations surviving at hatchling sex ratios >75% male. Because recent models have predicted that climate change could lead to the production of all male S. guntheri hatchlings by 2085, we examined whether periodic intervention to produce mixed or female biased sex ratios would allow the population to survive if only males were produced in natural nests. We show that intervention every 2–3 years could buffer the effects of climate change on population sex ratios, but translocation to cooler environs might be more cost-effective. Climate change threatens tuatara populations because neither modified nesting behaviour nor adaptive response of the pivotal temperature can modify hatchling sex ratios fast enough in species with long generation intervals.     

Initiation, Growth and Nuclear Characteristics of Tissue Cultures of Paeonia suffruticosa

Tissue cultures of the garden paeony, Paeonia suffruticosa have been established using explants of etiolated stems. Callus formation was induced on agar-solidified media containing ammonium ions or amino acids together with the hormones 2,4-dichlorophenoxyacetic acid and kinetin, but not on media lacking the reduced nitrogen component. Attempts to induce callus from explants from green plants were completely unsuccessful and were characterized by the production of intense brown colorations, both of the explant and the medium. Subcultured tissue without the added hormones produced roots, both on solid and liquid media. Growth was tested on a range of liquid media, SH/2, SH, SH × 2 and SH—M, containing 1250, 2500, 5000 and 2500 mg/l potassium nitrate. The SH—M medium also contained 1650 mg/l ammonium nitrate. Growth measured as increased fresh weight was best in the SH/2, SH and SH—M media and was curtailed in the SH × 2 medium. Soluble protein content was highest at the lowest nitrogen concentration. A histochemical comparison of tissue grown on the SH/2, SH—M and SH—M lacking hormones showed that the cells in all the cultures remained diploid while differences were established in total nuclear protein, measured using the ninhydrin-Schiff procedure. Nuclei from SH—M grown cells have a higher protein content than those from the SH/2 medium while cells from the SH—M medium lacking hormones show a further increase in nuclear protein. This raises the question whether this change in nuclear protein is related to the morphogenesis of roots which occurs in this medium.     

Seismic Stress Responses of Soybean to Different Photosynthetic Photon Flux

Physical agitation applied as periodic seismic stress (shaking)reduced stem clongation, leaf expansion, and biomass accumulationby vegetative soybeans. Level of photon flux (PPF) influencedthe type and extent of plant response to mechanical stress.Plant parts responded differently as PPF varied between 135and 592 µmol m^–2 S^–1. Stem length was significantlyreduced by seismic stress at 135 µmol m^–2 s^–1but this effect was insignificant at higher PPFs. Reduced stemlength resulted from an inhibition of internode elongation.Stem diameter was unaffected by stress at the PPFs tested. Incontrast to effects on stem elongation, leaf area was insensitiveto stress treatments at 135 µmol m^–2 S^–1 butwas progressively inhibited by stress as PPF increased. Statisticallysignificant reductions in shoot f. wt and d. wt by seismic stressoccurred only at 295 µmol m^–2 S^–1. Root biomassaccumulation was not affected by seismic stress at any PPF usedin this study. Glycine max (L.) Merr. cv. Century 84, mechanical stress, photosynthetic photon flux, seismic stress, soybean     

Immunological Detection of Cytoskeletal Proteins In the Exoerythrocytic Stages of Malaria By Fluorescence and Confocal Laser Scanning Microscopy

ABSTRACT. Using monospecific antibodies, the presence and distribution of tubulin, actin, myosin, intermediate filaments, and lamins were examined in the exoerythrocytic liver schizont of Plasmodium berghei by conventional indirect fluorescent antibody methods and confocal laser scanning microscopy. the binding reactivity of the antibodies to parasite proteins was determined by Western blot analysis. the localisation of all antibodies in control host hepatocytes followed expected distributions in both uninfected and infected hepatocytes; by contrast, reactivity to the exoerythrocytic schizont was variable. the parasite reacted positively with selected anti-tubulin, -actin, and -myosin antibodies in both fluorescence and Western blot analysis. Anti-lamin antibodies were positive by confocal indirect fluorescent antibody labelling, but no labelling was detected with anti-intermediate filament antibody. Within the technical limits of resolution of the methods as applied to asynchronous parasite infections, not one of the antibodies reacting positively with the parasite by the indirect fluorescent antibody technique could be shown to identify unequivocally the classic architectural features associated with their respective target organelles, i.e. microtubules, stress-fibres or the nuclear envelope.     

Effects of substrate structure on speed and acceleration capacity in climbing geckos

We studied the effects of substrate structure on locomotor performance in a climbing gecko, Hemidactylus garnoti . We quantified three performance traits (acceleration capacity, instantaneous speed, and final speed) on three substrates: (i) smooth wood, (ii) a cloth surface, and (iii) a wire mesh. While acceleration capacity and instantaneous speed were highest on the wooden surface, final speed did not differ significantly among substrates. Using scanning electron microscopy (SEM) pictures, we estimated that 98% of the wooden surface is available for adhesion by the setae on the toepads, while this percentage is much lower for the mesh and cloth (41 and 37%, respectively). We suggest that when a gecko climbs up a gap-filled substrate, such as the wire mesh or cloth, adhesion will only happen between part of the toepad and the substrate, resulting in a diminished acceleration capacity. The higher acceleration capacity on the wooden substrate and the fact that the geckos tend to slip less often on this particular surface, may explain the difference in instantaneous speed. As for final speed, geckos might achieve similar final speeds on all three substrates by employing different locomotor strategies. Our results suggest that microhabitat use in nature might have a profound effect on locomotor performance and survival for climbing lizards such as geckos.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 385–393.