Effects of Habitat on Competition Between Kit Foxes and Coyotes

Abstract: San Joaquin kit foxes (Vulpes macrotis mutica) are an endangered species with a narrow geographic range whose natural populations are limited by predation by coyotes (Canis latrans). In the warm, arid grassland and shrubland habitats where kit foxes occur, coyotes are more cover dependent than kit foxes, creating the possibility of habitat segregation. Effects of habitat variation on coyote and kit fox competition are unknown. We assessed exploitation and interference competition between coyotes and kit foxes in grassland and shrubland habitats to determine if such competition varies among habitats. With respect to exploitation competition, we evaluated habitat and spatial partitioning, diet, prey abundance, and survival for kit foxes and coyotes at the Lokern Natural Area in central California, USA, from January 2003 through June 2004. Kit foxes partitioned habitat, space, and diet with coyotes. Coyotes primarily used shrubland habitats whereas kit foxes selectively used burned grasslands. Kit foxes and coyotes had high dietary overlap with regards to items used, but proportional use of items differed between the 2 species. Kit foxes selected for Heermann's kangaroo rats (Dipodomys heermanni), which were closely tied to shrub habitats. With respect to interference competition, predation was the primary source of mortality for kit foxes, and survival of individual kit foxes was inversely related to proportion of shrub habitat within their home ranges. Our results suggest that a heterogeneous landscape may benefit kit foxes by providing habitat patches where predation risk may be lower.     

Functional characterization and evolution of PTH/PTHrP receptors: insights from the chicken

ABSTRACT: BACKGROUND: The parathyroid hormone (PTH)-family consists of a group of structurally related factors that regulate calcium and bone homeostasis and are also involved in development of organs such as the heart, mammary gland and immune system. They interact with specific members of family 2 B1 G-protein coupled receptors (GPCRs), which have been characterised in teleosts and mammals. Two PTH/PTHrP receptors, PTH1R and PTH2R exist in mammals and in teleost fish a further receptor PTH3R has also been identified. Recently in chicken, PTHfamily members involved in calcium transport were characterized and specific PTHRs are suggested to exist although they have not yet been isolated or functionally characterized. The aim of this study is to further explore the evolution and function of the vertebrate PTH/PTHrP system through the isolation, phylogenetic analysis and functional characterization of the chicken receptors. RESULTS: Two PTHRs were isolated in chicken and sequence comparison and phylogenetic analysis indicate that the chicken receptors correspond to PTH1R and PTH3R, which emerged prior to the teleost/tetrapod divergence since they are present in cartilaginous fish. The vertebrate PTH2R receptor and its ligand TIP39 have been lost from bird genomes. Chicken PTH1R and PTH3R have a divergent and widespread tissue expression and are also evident in very early embryonic stages of development. Receptor stimulation studies using HEK293 cells stably expressing the chicken PTH1R and PTH3R and monitoring cAMP production revealed they are activated by chicken 1-34 N-terminal PTH-family peptides in a dose dependent manner. PTH-L and PTHrP were the most effective peptides in activating PTH1R (EC50 = 7.7 nM and EC50 = 22.7 nM, respectively). In contrast, PTH-L (100 nM) produced a small cAMP accumulation on activation of PTH3R but PTHrP and PTH (EC50 = 2.5 nM and EC50 = 22.1 nM, respectively) readily activated the receptor. PTHrP also stimulated intracellular Ca2+ accumulation on activation of PTH1R but not PTH3R. CONCLUSION: Two PTHR homologues of the vertebrate PTH1R and PTH3R were isolated and functionally characterized in chicken. Their distinct pattern of expression during embryo development and in adult tissues, together with their ligand preference, suggests that they have acquired specific functions, which have contributed to their maintenance in the genome. PTH2R and its activating ligand, TIP39, are absent from bird genomes. Nonetheless identification of putative PTH2R and TIP39 in the genome of an ancient agnathan, lamprey, suggests the PTH/PTHrP ligand and receptor family was already present in an early basal paraphyletic group of vertebrates and during the vertebrate radiation diverged via gene/genome duplication and deletion events. Knowledge of the role PTH/PTHrP system in early vertebrates will help to establish evolution of function.     

Competition with Egyptian Geese Alopochen aegyptiaca overrides environmental factors in determining productivity of Black Sparrowhawks Accipiter melanoleucus

We studied a population of Black Sparrowhawks Accipiter melanoleucus that has recently colonized the Cape Peninsula, South Africa. Black Sparrowhawks are winter breeders: over most of their range winters are dry, but the Cape Peninsula has a Mediterranean climate, with most rain falling in winter. The birds bred at an average density of 38 pairs/100 km². Monitoring of 70 breeding attempts by 26 pairs showed that the birds favoured large stands of trees for breeding. Birds breeding in smaller stands were more randomly spaced, dispersion being determined by habitat availability. Parameters related to climate, habitat and aspects of nest-site selection failed to predict the birds' productivity despite the fact that they had recently colonized a novel climatic window. Rather, productivity was best explained by the probability of nest usurpation by highly aggressive Egyptian Geese Alopochen aegyptiaca . Pairs encountering Goose usurpation problems raised an average of 0.76 chicks per breeding attempt, compared with 1.58 chicks for pairs without Geese. The only defence against nest usurpation by Geese appears to be the construction of multiple nests, an option most available to and most exploited by birds breeding in large stands of trees.     

The Effects of the Methylating Agent 1,2-Bis(methylsulfonyl)-1-methylhydrazine on Morphology, DNA Content and Mitochondrial Function of Trypanosoma brucei Subspecies

Repeated exposure of trypanosomes in vitro or in vivo to low concentrations of the methylating agent 1,2-bis(methylsulfonyl)-1-methylhydrazine induces a series of moderately synchronous morphological and biochemical changes. Cell division halts and the long-slender bloodstream forms transform to short-stumpy forms via larger intermediate-stage cells which contain approximately double the normal G₂ content of DNA. In common with naturally occurring short-stumpy trypanosomes, drug-induced short-stumpy forms do not infect rodents and when transferred to Cunningham's medium, transform to and replicate as procylics. Furthermore, these short-stumpy forms exhibit α-ketoglutarate supported motility and oxygen consumption, acquire the ability to reduce nitroblue tetrazolium (NADH diaphorase positivity) and appear to be in the G₁ or G₀ stage of the cell cycle based upon DNA content.     

The relative efficacy of repellents against mosquito vectors of disease

Laboratory tests of insect repellents by various different methods showed that An.stephensi Liston was consistently more susceptible than An.gambiae Giles, An.albimanus Wiedemann or An.pulcherrimus Theobald. The six repellents tested were di-ethyl toluamide (deet), di-methyl phthalate (DMP), ethyl-hexanediol, permethrin, citronella and cedarwood oil. Testing systems in which the mosquitoes were presented with a choice gave consistently lower ED50 values than when there was no choice, i.e. the standards of tolerance are not absolute but depend on the options available. In field tests in an experimental hut a curtain with a high dose of di-ethyl toluamide (deet) reduced biting in the hut but had to be re-impregnated frequently. Deet-impregnated anklets gave about 84% protection against Culex quinquefasciatus Say for 80 days after one impregnation, in a trial in which the anklets were brought out of sealed storage and tested for 2 h nightly. Similar protection was found against An.funestus Giles but the protection against An.gambiae s.l., An. coustani Laveran and Mansonia spp. was not as good. There were highly significant differences between the four collectors' mosquito attractiveness but this varied highly significantly between the mosquito species.     

4-Aminotetrolic Acid : New Conformational-restricted Analogue of γ-Aminobutyric Acid

RECENT studies strongly support a role for γ-aminobutyric acid (GABA) as an inhibitory transmitter at certain synapses in the mammalian central nervous system. Structure activity correlations of many GABA analogues implicate both the intramolecular distance between the zwitterionic centres and the rotational freedom of the molecule as important factors governing the synaptic activity of these substances¹. The following observations provide pertinent information about the active conformation(s) of GABA recognized by the receptor. (1) Muscimol, an isoxazole isolated from Amanita muscaria, seems to function as a GABA analogue as its inhibitory action on central neurones is comparable with that of GABA both in potency² and with respect to antagonism by bicuculline³. Molecular orbital calculations suggest that GABA and muscimol can assume similar conformations as zwitterions with the charged centres (N⁺ and 0^?) at least 5 and, more likely, 6 Å apart⁴. (2) The selective GABA antagonist bicuculline exhibits some degree of structural similarity with particular conformations of GABA and muscimol³. (3) X-ray crystallography indicates that GABA exists in a partially folded conformation in the solid state^5,6. (4) A model of the GABA receptor proposes that GABA adopts a folded conformation with a distance of less than 4.4 Å between the charged centres⁷. Observations (1) and (2) suggest extended conformations for GABA, while (3) and (4) suggest folded conformations.     

Effects of community-wide use of lambdacyhalothrin-impregnated bednets on malaria vectors in rural Sierra Leone

Abstract. The effect of community-wide use of bednets treated with lambdacyhalothrin 10mg/m² on the malaria vector Anopheles gambiae (forest form) was evaluated in Sierra Leone. Sixteen similar villages near the town of Bo were randomly allocated either to remain without nets or to receive treated bednets for all inhabitants, with effect from June 1992. Mosquitoes were sampled using human biting catches on verandas, light-trap catch (beside an occupied untreated bednet), window exit-trap catch and pyrethrum spray collections. During the first year of intervention (June 1992 to July 1993) the treated bednets provided personal protection for people sleeping under them, but had very little impact on densities of An. gambiae collected on human bait. The human blood index (HBI) of An.gambiae was not affected (HBI = 99% in villages with and without nets). An.gambiae parous rates were significantly reduced in all intervention villages, but malaria sporozoite rates fell in only some of the villages. These results are intermediate between those obtained from other projects in Tanzania and Burkina Faso, where treated bednets reduced man-biting, parity and sporozoite rates, versus The Gambia where treated bednets had no significant impact on any of these factors. Possible reasons for these contrasted findings are discussed.     

Variation in rates of nitrogen fixation in termites: response to dietary nitrogen in the field and laboratory

Abstract. Termites contribute nitrogen to their habitat through the nitrogenase activity of their bacterial symbionts. Previous studies indicate that high levels of dietary nitrogen suppress nitrogen fixation in termites. We examined the effects of dietary nitrogen on fixation rates in termites in both field and laboratory experiments. Ten field cplonies of Reticulitermes were collected and assayed for nitrogenase activity in July 1993, October 1993, January 1994, and April 1994. The nitrogen content of the wood collected with each colony was determined. There was no correlation between termite nitrogen fixation rates and the amount of nitrogen in their food for any of the four collection periods. In laboratory experiments, nitrogen fixation rates decreased when termites were fed filter paper treated with 2% and 5% ammonium nitrate or a 5% mixture of the amino acids proline, tryptophan and leucine, compared to water-treated controls. By contrast, the nitrogenase activity of termites fed filter paper treated with 2% and 5% ammonium phosphate, a mixture of the amino acids histidine, serine and aspartic acid, or 2% and 5% urea did not differ from the controls. However, nitrogenase activity increased when termites were fed with 2% uric acid. No clear association exists between termite nitrogen fixation and the nitrogen content of their food.     

HANDS-FREE, "POP-UP," ADHESIVE TAPE METHOD FOR MICROBIAL SAMPLING OF MEAT SURFACES

Microbial contamination of food is a concern to both food producers and consumers. For the food production industry surface sampling of foods is one of the simplest ways to monitor the microbial load. The objective of this experiment was to investigate the feasibility of using the less expensive and quicker "Pop-up" tape method instead of the conventional swab/rinse method for the microbial sampling of meat surfaces. An analyst can place the unit on the wrist and then use both hands to lay out all the necessary materials and take the sample with one hand. The "Pop-up" tape method was able to measure microbial loads up to 2.2 log CFU/cm² on meat surfaces. The conventional swab/rinse method was able to measure up to 8.3 log CFU/cm² on meat surfaces. The correlation coefficient (R) between the two methods was 0.91 (n=42). These data show that the "Pop-up" tape method is a viable alternative to other methods for estimating microbial surface contamination.