Nutrient limitation of phytoplankton growth in Waquoit Bay, Massachusetts, USA: a nutrient enrichment study

We conducted nutrient enrichment experiments and field sampling to address three questions: (1) is there nutrient limitation of phytoplankton accumulation within an estuary whose waters are exposed to relatively high nitrogen loading rates, (2) where in the salinity gradient from fresh to seawater (0 to 32‰) is there a shift from phosphorus to nitrogen limitation of phytoplankton accumulation, and (3) is there a seasonal shift in limiting function of phosphorus and nitrogen anywhere in the estuarine gradient. Nitrogen and phosphorus enrichment experiments in the Childs River, an estuary of Waquoit Bay, Massachusetts, USA, showed that the accumulation of phytoplankton biomass in brackish and saline water was limited by supply of nitrate during warm months. The effects of enrichment were less evident in fresh water, with short-lived responses to phosphate enrichment. There was no specific point along the salinity gradient where there was a shift from phosphorus- to nitrogen-limited phytoplankton accumulation; rather, the relative importance of nitrogen and phosphorus changed along the salinity gradient in the estuary and with season of the year. There was no response to nutrient additions during the colder months, suggesting that some seasonally-varying factor, such as light, temperature or a physiological mechanism, restricted phytoplankton accumulation during months other than May-Aug. There was only slight evidence of a seasonal shift between nitrogen- and phosphorus-limitation of chlorophyll accumulation. Phytoplankton populations in nutrient-rich estuaries with short flushing times grow fast, but at the same time the cells may be advected out of the estuaries while still rapidly dividing, thereby providing an important subsidy to production in nearby deeper waters. This revised version was published online in August 2006 with corrections to the Cover Date.     

ZUR MORPHOLOGIE DER HAUPTSPEICHELDRÜSE VON MYZUS PERSICAE

Zusammenfassung Die Hauptspeicheldrüse von Myzus persicae (Sulz.) erwies sich als ein differenziert aufgebautes Organ. An herauspräparierten ganzen Drüsen, die nach Feulgen gefärbt waren, wurden Größe und Form der einzelnen Zellkerne verglichen und auf diese Weise neun verschiedene Drüsenzellen unterschieden.

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Summary Principal salivary glands were separated under a stereo-microscope from adult wingless Myzus persicae which had been totally immersed in Feulgen stain. The nuclei were compared in size and shape and then assigned to different gland cells. In this way at least nine different cell types could be differentiated in the principal salivary gland. They have been labelled with letters A to I (see Fig. 1). In the main region there are four A-cells in two pairs, one pair of B-cells with larger nuclei, and the odd C-cell, which has a nucleus about double the size of those in B-cells. On the other side of each gland lobe are one pair of D-cells and one pair of F-cells. Nuclei of E-cells are very small compared with those of G-cells, which are extremely large and show a loose structure. The region of cover cells is composed of five cells (H) with irregularly shaped and weakly staining nuclei, and one odd cell (I) with a circular, intensely stained nucleus. In further studies the different cell types will be determined by specific histochemical reactions with a view to distinguishing different kinds of transmission of plant viruses by aphids.

     

Invertebrates in small shallow lakes and ponds: a new sampling method to study the influence of environmental factors on their communities

Aquatic Ecology - Small shallow lakes (SSL) are reservoirs of biodiversity and provide numerous ecosystem services. Therefore, tools to easily and rapidly assess the biological integrity and...     

Negative frequency-dependent selection and asymmetrical transformation stabilise multi-strain bacterial population structures

Streptococcus pneumoniae can be divided into many strains, each a distinct set of isolates sharing similar core and accessory genomes, which co-circulate within the same hosts. Previous analyses suggested the short-term vaccine-associated dynamics of S. pneumoniae strains may be mediated through multi-locus negative frequency-dependent selection (NFDS), which maintains accessory loci at equilibrium frequencies. Long-term simulations demonstrated NFDS stabilised clonally-evolving multi-strain populations through preventing the loss of variation through drift, based on polymorphism frequencies, pairwise genetic distances and phylogenies. However, allowing symmetrical recombination between isolates evolving under multi-locus NFDS generated unstructured populations of diverse genotypes. Replication of the observed data improved when multi-locus NFDS was combined with recombination that was instead asymmetrical, favouring deletion of accessory loci over insertion. This combination separated populations into strains through outbreeding depression, resulting from recombinants with reduced accessory genomes having lower fitness than their parental genotypes. Although simplistic modelling of recombination likely limited these simulations’ ability to maintain some properties of genomic data as accurately as those lacking recombination, the combination of asymmetrical recombination and multi-locus NFDS could restore multi-strain population structures from randomised initial populations. As many bacteria inhibit insertions into their chromosomes, this combination may commonly underlie the co-existence of strains within a niche.Subject terms: Population genetics, Microbial ecology, Microbial genetics, Bacterial genetics, Phylogenetics     

Polymorphisms in the TOLLIP Gene Influence Susceptibility to Cutaneous Leishmaniasis Caused by Leishmania guyanensis in the Amazonas State of Brazil

IntroductionThe clinical outcome to Leishmania-infection is determined by the individual adaptive immune T helper cell responses and their interactions with parasitized host cells. An early development of a proinflammatory immune response (Th1 response) is necessary for Leishmania-infection resolution. The Toll-interacting protein (TOLLIP) regulates human Toll-like receptors signaling pathways by down regulating the proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) and inducing the ant-inflammatory cytokine interleukin-10 (IL-10). Polymorphisms in the TOLLIP gene are associated with infectious diseases.ResultsThe G and T alleles of the rs5743899 and rs3750920 were more common in patients with CL than in healthy individuals (P = 2.6 x10^-8 ; odds ratio [OR], 1.7 [ 95% confidence interval (CI) 1.4–2.0] and P = 1.9 x10^-8 ; OR, 1.6 [95% CI 1.4–1.9] respectively). The r² and D’ linkage disequilibrium between the two polymorphisms are 0.05 and 0.473 with a confidence bounds of 0.37 to 0.57 respectively.ConclusionThe two polymorphisms are independently associated with an increased risk of developing CL.     

The influence of parent body colouration and nesting habitat on bird nest predation

ABSTRACT

Capsule: Parent body colouration and nesting habitat may influence nest predation risk and, therefore, influence parental decisions on offspring care.

Aims: To investigate the adaptiveness of bird colouration under two different habitat and light conditions.

Methods: We used painted polyurethane dummies to simulate parental presence near nests, where some dummies were red, and others were cryptic brown. We placed artificial nests on trees in open and forested areas, along with two quail eggs and parental dummies.

Results: The results showed major predation on nests of the open area, however, we found no significant effect of parent colour on nest predation.

Conclusion: We suggest that the costs involved with nest site selection may overcome the costs of colouration in species that occur in these environments.