Know thy enemy: Behavioural response of a native mammal (Rattus lutreolus velutinus) to predators of different coexistence histories

Abstract Predation is recognized as a major selective pressure influencing population dynamics and evolutionary processes. Prey species have developed a variety of predator avoidance strategies, not least of which is olfactory recognition. However, within Australia, European settlement has brought with it a number of introduced predators, perhaps most notably the red fox (Vulpes vulpes) and domestic cat (Felis catus), which native prey species may be unable to recognize and thus avoid due to a lack of coexistence history. This study examined the response of native Tasmanian swamp rats (Rattus lutreolus velutinus) to predators of different coexistence history (native predator‐ spotted‐tail quoll (Dasyurus maculatus), domestic cats and the recently introduced red fox). We used an aggregate behavioural response of R. l. velutinus to predator integumental odour in order to assess an overall behavioural response to predation risk. Rattus lutreolus velutinus recognized the integumental odour of the native quoll (compared with control odours) but did not respond to either cat or fox scent (compared with control odur). In contrast, analyses of singular behaviours resulted in the conclusion that rats did not respond differentially to either native or introduced predators, as other studies have concluded. Therefore, measuring risk assessment behaviours at the level of overall aggregate response may be more beneficial in understanding and analysing complex behavioural patterns such as predator detection and recognition. These results suggest that fox and cat introductions (and their interactive effects) may have detrimental impacts upon small native Tasmanian mammals due to lack of recognition and thus appropriate responses.     

Ornithine Decarboxylase in Trypanosoma brucei brucei: Evidence for Selective Toxicity of Difluoromethylornithine1

ABSTRACT. Activity of ornithine decarboxylase, the major rate limiting enzyme of polyamine biosynthesis, was determined in bloodstream trypomastigotes of Trypanosoma brucei brucei. The enzyme required pyridoxal-5′-phosphate, dithiothreitol and EDTA for optimal activity. Several properties of the enzyme were investigated and compared to the mammalian enzyme. Most notably, the parasite enzyme was >60-fold more sensitive to the inhibitor DL-α-difluoromethylornithine than its mammalian counterpart, thus making it an attractive target for chemotherapy.     

Synthesis and Content of Polyamines in Bloodstream Trypanosoma brucei*

SYNOPSIS. The sensitive dansyl procedure was used to detect putrescine and spermidine, but not spermine and cadaverine, in pleomorphic Trypanosoma brucei. The polyamines were synthesized in vitro from [³H]ornithine, [¹⁴C]arginine and [¹⁴C]methionine. Proline, agmatine, and citrulline, but not glutamine, glutamic or pyroglutamic acids, stimulated spermidine formation from [¹⁴C]methionine. Putrescine and spermidine synthesis occurred rapidly from ornithine: putrescine synthesis peaked in 0.5 h, spermidine in 1 h. Trypanosoma brucei assimilated exogenous ¹⁴C-labeled putrescine, spermidine, and spermine; spermidine and spermine were taken up 5 times as rapidly as putrescine. Polyamine syntheses may therefore be a practical target for novel trypanocies.     

Acid Phosphatase in the Digestive Vacuoles and Lysosomes of Paramecium caudatum: A Timed Study1

Enzyme cytochemistry was used to determine when acid phosphatase (AcPase) becomes associated with the digestive vacuoles (DVs) of axenically grown Paramecium caudatum that were pulsed with latex beads for 2–3 min. When cells were incubated in the Gomori medium, AcPase was not observed in the discoidal vesicles, the acidosomes, and the newly released DVs up to 3 min old or in most DVs 3–6 min old. The number of AcPase-positive DVs increased to 56% when DVs were 12–18 min old. Similar results were obtained using the napthol AS-TR phosphate-hexaotized rosanilin method at the light microscopic level where hundreds of DVs were scored though the maximal level of positive DVs obtained by this method was lower. In addition to DVs of specific ages, AcPase was found in ER, in some Golgi vesicles, and small vesicles similar in diameter to Golgi vesicles which may represent primary lysosomes in this ciliate. Larger vesicles abundant near the DV-II were only partially filled with reaction product. These vesicles, which could be identified by their paracrystalline sheets and a prominent glycocalyx lining the luminal surface of their membranes, fit the definition for secondary lysosomes. These results, which indicate that lysosomes fuse with DVs only after they have attained a certain age, suggest the existence of specific recognition factors on the membranes of secondary lysosomes as well as DV-II.     

APPLIED ISSUES: Exploring the response of functional indicators of stream health to land‐use gradients

1. Broad‐scale assessment of stream health is often based on correlative relationships between catchment land‐use categories and measurements of stream biota or water chemistry. Few studies have attempted to characterise the response curves that describe how measures of ecosystem function change along gradients of catchment land use, or explored how these responses vary at broad spatial scales. 2. In autumn 2008, we conducted a survey of 84 streams in three bioregions of New Zealand to assess the sensitivity of functional indicators to three land‐use gradients: percentage of native vegetation cover, percentage of impervious cover (IC) and predicted nitrogen (N) concentration. We examined these relationships using general linear models and boosted regression trees to explore monotonic, non‐monotonic and potential threshold components of the response curves. 3. When viewing the responses to individual land‐use gradients, four of five functional indicators were positively correlated with the removal of native vegetation cover and N. In general, weaker and less responsive models were observed for the IC gradient. An analysis of the response to multiple stressors showed δ¹⁵N of primary consumers and gross primary productivity (GPP) to be the most responsive functional indicators to land‐use gradients. The multivariate models identified thresholds for change in the relationship between the functional indicators and all three land‐use gradients. Apparent thresholds were <10%IC, between 40 and 80% loss of native vegetation cover and at 0.5 and 3.2 mg L^?1 N. 4. The strength of regression models and the nature of the response curves suggest that measures of ecosystem function exhibit predictable relationships with land use. Furthermore, the responses of functional indicators varied little among three bioregions. This information provides a strong argument for the inclusion of functional indicators in a holistic assessment of stream health.     

Attempting to Manage Complex Predator-Prey Interactions Fails to Avert Imminent Extinction of a Threatened New Zealand Skink Population

Abstract: The current primary threats to biodiversity on a global scale are species invasions and habitat modification. Management of vulnerable populations often involves a lengthy sequence of 1) research to identify threats and recommend management strategies, 2) active management, and 3) results monitoring to assess effectiveness of management. The last mainland population of the large, endemic New Zealand skink (Whitaker's skink [Cyclodina whitakeri]) provides an opportunity to test this process in a system where the synergistic effects between invasive species (introduced rodents and grasses) have predicted outcomes. A low abundance of Whitaker's skink at the Pukerua Bay Scientific Reserve in the 1980s prompted management recommendations to remove grazing stock and revegetate the site to simultaneously restore habitat and provide protection against introduced mammalian predators. Since Whitaker's skink have low detectability, it was recommended that sympatric copper skink (C. aenea) be used an indicator species of management effectiveness. Grazing stock were removed in 1987, but efforts to revegetate the site were ineffective. Long-term monitoring (1984-2006) of the Whitaker's skink population and 4 other sympatric lizard species within a 336-m² area at the site resulted in 1,693 lizard captures over 7,597 trap days. Whitaker's skink represented 2.8% of all captures in 1984-1988, but declined relative to other species to represent only 0.2% of captures in 2000-2006 (representing 2 individuals). Congeneric copper skink showed a similar decline with capture rates also approaching zero by 2006. Removing grazing stock did not result in an increased abundance of Whitaker's skink or copper skink through improved habitat quality, as was intended by the management recommendation. Instead, reduced grazing has allowed introduced seeding grasses to proliferate, which may have led to periodic rodent irruptions, supporting a guild of introduced mammalian predators and depleting populations of Whitaker's skink and copper skink. In this instance, attempted protection may have driven a vulnerable population towards extinction. We recommend investigating the feasibility of constructing a mammal-proof fence around the core Whitaker's skink habitat, as the last remaining management option to salvage the population.     

OLFACTORY RESPONSIVENESS TO DIACETYL

Odor thresholds in the headspace over aqueous solutions of diacetyl (butane-2,3-dione) were measured in quadruplicate by a forced-choice procedure in 53 individuals. Mean individual thresholds varied over a factor of 256, with the group average at .005 μg/ml. Thresholds showed a modest negative correlation with suprathreshold intensity ratings. Intensity ratings were distributed bimodally, consistent with the existence of insensitive and sensitive groups and suggesting the possibility of a specific anosmia for this compound.     

The Diplomonad Fish Parasite Spironucleus vortens Produces Hydrogen

ABSTRACT. The diplomonad fish parasite Spironucleus vortens causes major problems in aquaculture of ornamental fish, resulting in severe economic losses in the fish farming industry. The strain of S. vortens studied here was isolated from an angelfish and grown in Keister's modified TY‐I‐S33 medium. A membrane‐inlet mass spectrometer was employed to monitor, in a closed system, O₂, CO₂, and H₂. When introduced into air‐saturated buffer, S. vortens rapidly consumed O₂ at the average rate of 62±4 nmol/min/10⁷ cells and CO₂ was produced at 75±11 nmol/min/10⁷ cells. Hydrogen production began under microaerophilic conditions ([O₂]=33.±15 μM) at a rate of 77±7 nmol/min/10⁷ cells. Hydrogen production was inhibited by 62% immediately after adding 150 μM KCN to the reaction vessel, and by 50% at 0.24 μM CO, suggesting that an Fe‐only hydrogenase is responsible for H₂ production. Metronidazole (1 mM) inhibited H₂ production by 50%, while CO₂ production was not affected. This suggests that metronidazole may be reduced by an enzyme of the H₂ pathway, thus competing for electrons with H⁺.