Does maternal condition or predation risk influence small mammal population dynamics?

There is strong debate over whether the intrinsic traits of individuals or the extrinsic environment exert the greater influence on small mammal population dynamics. We test the roles of maternal effects (an intrinsic factor) and predation risk (an extrinsic factor) in the population dynamics of wild strain house mice using a 2-factor enclosure experiment. Pre-release supplemental feeding with a high-fat diet created female treatment founders that were 6–10% heavier than controls, a condition that we predicted would be passed on as a maternal effect. Predation risk was enhanced using regular application of predator (red fox Vulpes vulpes ) scats. Founder populations of six females and six males released into eight, 15×15 m enclosures showed near exponential population growth over 17 weeks (maximum 3 generations). But there were no responses to either treatment in terms of survival, inherited body weights, fecundity or population size. We suggest that elevated maternal condition may have only minor and transient intergenerational effects with little long-term consequence. We also suggest that the general significance of predator scats as a cue to predation risk to alter prey behaviour may have been overestimated. Hence our results question the role of either factor in causing long-term responses that influence condition to affect population processes.     

Diversity of Anopheles species and trophic behavior of putative malaria vectors in two malaria endemic areas of northwestern Thailand

We determined the species diversity, blood‐feeding behavior, and host preference of Anopheles mosquitoes in two malaria endemic areas of Tak (Mae Sot District) and Mae Hong Son (Sop Moei District) Provinces, located along the Thai border with Myanmar, during a consecutive two‐year period. Anopheline mosquitoes were collected using indoor and outdoor human‐landing captures and outdoor cow‐baited collections. Mosquitoes were initially identified using morphological characters, followed by the appropriate multiplex AS‐PCR assay for the identification of sibling species within Anopheles (Cellia) complexes and groups present. Real‐time PCR was performed for parasite‐specific detection in mosquitoes (Plasmodium spp. and Wuchereria bancrofti). A total of 7,129 Anopheles females were captured, 3,939 from Mae Sot and 3,190 from Sop Moei, with 58.6% and 37% of all anophelines identified as An. minimus, respectively. All three malaria vector complexes were detected in both areas. One species within the Minimus Complex (An. minimus) was present along with two related species in the Funestus Group, (An. aconitus, An. varuna), two species within the Dirus Complex (An. dirus, An. baimaii), and four species within the Maculatus Group (An. maculatus, An. sawadwongporni, An. pseudowillmori, and An. dravidicus). The trophic behavior of An. minimus, An. dirus, An. baimaii, An. maculatus, and An. sawadwongporni are described herein. The highest An. minimus densities were detected from February through April of both years. One specimen of An. minimus from Mae Sot was found positive for Plasmodium vivax.     

Metabolism of Caffeine and Related Purine Alkaloids in Leaves of Tea (Camellia sinensis L.)

Purine alkaloid catabolism pathways in young, mature and agedleaves of tea (Camellia sinensis L.) were investigated by incubatingleaf sections with ¹⁴C-labelled theobromine, caffeine, theophyllineand xanthine. Incorporation of label into CO₂ was determinedand methanol-soluble metabolites were analysed by high-performanceliquid chromatography-radiocounting and thin layer chro-matography.The data obtained demonstrate that theobromine is the immediateprecursor of caffeine, which accumulates in tea leaves becauseits conversion to theophylline is the rate limiting step inthe purine alkaloid catabolism pathway. The main fate of [8-¹⁴C]theophyllineincubated with mature and aged leaves, and to a lesser extentyoung leaves, is conversion to 3-methylxanthine and onto xanthinewhich is degraded to ¹⁴CO₂ via the purine catabolism pathway.However, with young leaves, sizable amounts of [8-¹⁴C]-theophyllinewere salvaged for the synthesis of caffeine via a 3-methylxanthine     

Ecosystem function and species loss – a microcosm study

There are too many kinds of organisms to be able to study and manage each, yet the loss of a single species can sometimes unravel an ecosystem. Such `fusewire species'– critical in the same sense that an electrical fuse can cut out a whole circuit – would be a rewarding focus for research and management effort. However, this approach can only be effective if these `fusewires' represent but a small proportion of the number of species in the system.  

Aim

To demonstrate methods for measuring what proportion of the species in a system are critical to ecosystem function.  

Methods

The prevalence of fusewire species was measured in manipulative experiments on an aquatic microcosm.  

Results

No single genus deletion caused changes in key characteristics of the system.  

Main conclusions

Comparison of these results with other published studies shows that the proportion of critical fusewire species varies amongst different ecosystems. The oxidation pond microcosms were shown to contain no single species indispensable to system function. They appear to be ill-suited to a management strategy which focuses on priority eukaryote species. However, a single study provides no evidence that this result is general or even typical of other kinds of ecosystems; it is presented here as an empirical model. Other methods of investigation are available; they are less experimentally rigorous but more practical. These could provide important guidance in planning an approach to management in a particular ecosystem.     

Patterns of junctional communication in skin: Studies on cultured keratinocytes

Junctional communication has long been suggested to play a role in coordinating the development of multicellular tissues. A better understanding of the patterns of communication between cells in such tissues is important for the identification of areas where this process may have a role. We have investigated the patterns of communication in cultures of human epidermal keratinocytes by iontophoretic injection of Lucifer Yellow CH, using involucrin expression as a marker of cells undergoing terminal differentiation. Cells that lack involucrin (i.e., the basal, proliferating cells) transfer dye preferentially to other involucrin-negative cells, whereas involucrin-positive cells either are not coupled or transfer dye with similar frequency to involucrin-positive and involucrin-negative neighbors. This decrease in communication associated with terminal differentiation was observed in both the presence and the absence of assembled desmosomes. Our observations lead us to speculate that loss of junctional communication may influence the commitment of basal keratinocytes to terminal differentiation.     

Evidence of abortive recombination in ruv mutants of Escherichia coli K12

Summary Genetic recombination in Escherichia coli was investigated by measuring the effect of mutations in ruv and rec genes on F-prime transfer and mobilization of nonconjugative plasmids. Mutation of ruv was found to reduce the recovery of F-prime transconjugants in crosses with recB recC sbcA strains by about 30-fold and with recB recC sbcB sbcC strains by more than 300-fold. Conjugative plasmids lacking any significant homology with the chromosome were transferred normally to these ruv mutants. Mobilization of the plasmid cloning vectors pHSG415, pBR322, pACYC184 and pUC18 were reduced by 20- to 100-fold in crosses with ruv rec ⁺ sbc ⁺ strains, depending on the plasmid used. Recombinant plasmids carrying ruv ⁺ were transferred efficiently. With both F-prime transfer and F-prime cointegrate mobilization, the effect of ruv was suppressed by inactivating recA. It is proposed that the failure to recover transconjugants in ruv recA ⁺strains is due to abortive recombination and that the ruv genes define activities which function late in recombination to help convert recombination intermediates into viable products.     

Posttranslational modification and intracellular transport of a trypanosome variant surface glycoprotein

After synthesis on membrane-bound ribosomes, the variant surface glycoprotein (VSG) of Trypanosoma brucei is modified by: (a) removal of an N-terminal signal sequence, (b) addition of N-linked oligosaccharides, and (c) replacement of a C-terminal hydrophobic peptide with a complex glycolipid that serves as a membrane anchor. Based on pulse-chase experiments with the variant ILTat-1.3, we now report the kinetics of three subsequent processing reactions. These are: (a) conversion of newly synthesized 56/58-kD polypeptides to mature 59-kD VSG, (b) transport to the cell surface, and (c) transport to a site where VSG is susceptible to endogenous membrane-bound phospholipase C. We found that the t 1/2 of all three of these processes is approximately 15 min. The comparable kinetics of these processes is compatible with the hypotheses that transport of VSG from the site of maturation to the cell surface is rapid and that VSG may not reach a phospholipase C-containing membrane until it arrives on the cell surface. Neither tunicamycin nor monensin blocks transport of VSG, but monensin completely inhibits conversion of 58-kD VSG to the mature 59-kD form. In the presence of tunicamycin, VSG is synthesized as a 54-kD polypeptide that is subsequently processed to a form with a slightly higher Mr. This tunicamycin-resistant processing suggests that modifications unrelated to N-linked oligosaccharides occur. Surprisingly, the rate of VSG transport is reduced, but not abolished, by dropping the chase temperature to as low as 10 degrees C.