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Endemic Australian mammal species are exposed to pesticides used for locust control as they occupy the same habitat as the target insect. The authors examined the impact of an ultra-low volume formulation of the organophosphorous insecticide fenitrothion (O,O-dimethyl-O-[3-methyl-4-nitrophenol]-phosphorothioate) on a suite of physiological measures that affect the ability of animals to survive in free-living conditions: locomotory and thermogenic functions, metabolic performance, body mass, and hematocrit and hemoglobin levels. Plasma and brain cholinesterase activity in relation to time since exposure to pesticide were also determined. An orally applied dose of 90 mg kg(-1) fenitrothion reduced running endurance in the stripe-faced dunnart, Sminthopsis macroura, by 80% the day after exposure concomitantly with a reduction of approximately 50% in plasma and 45% in brain acetylcholinesterase activity. These adverse effects disappeared by 10 d postexposure. Maximal metabolic rates reached during running were unaffected by pesticide, as were body mass and hemoglobin and hematocrit levels. Maximal cold-induced metabolic rate (measured as peak 2 min metabolic rate attained during cold exposure), time taken to reach peak metabolic rate on cold exposure, cumulative total oxygen consumed during shivering thermogenesis, and body temperature before and after cold exposure were unaffected by fenitrothion. Dunnart rectal temperatures showed a reduction of up to 5 °C after exposure to fenitrothion but returned to pre-exposure levels by 10 d postdose. Such physiological compromises in otherwise asymptomatic animals demonstrate the importance of considering performance-based measures in pesticide risk assessments., (© 2015 SETAC.)

The scarcity of information on the effects of pesticides on native Australian vertebrates constrains the development of biologically relevant risk assessments in Australia for the registration of pesticides. The concern that endemically old and unique Australian vertebrate fauna might display high sensitivity to pesticides used for locust control provoked examination of the acute oral toxicity of the organophosphorus pesticide fenitrothion for the fat-tailed dunnart, Sminthopsis crassicaudata (Gould 1844), and the stripe-faced dunnart, S. macroura (Gould 1845). By using the up-and-down method for determining acute oral toxicity, S. crassicaudata and S. macroura were found to have estimated median lethal doses (LD50s) of 129 mg/kg (95% confidence interval [CI] = 74.2-159.0) and 97 mg/kg (95% CI = 88.3-120.0), respectively. These values are 10 to 14 times lower than the reported LD50 values for a similar-sized eutherian mammal, Mus musculus (L. 1758; LD50 = 1,100-1,400 mg/kg) and lower than all other reported mammalian LD50 values. Such wide interspecific variation in sensitivity to fenitrothion may be a consequence of underlying differences in the metabolic pathway for fenitrothion detoxification in mammals and a possible explanation for the increased toxicity of fenitrothion to dunnarts, compared with other mammals, is proposed. The unexpectedly high sensitivity of these Australian marsupials to fenitrothion emphasises the importance of adequately evaluating the risks of pesticides to endemic Australian fauna., (Copyright © 2011 SETAC.)

We measured aerobic metabolism during cold exposure and exercise performance (run duration and oxygen consumption while running at 1 m s(-1)) in the fat-tailed dunnart Sminthopsis crassicaudata, a dasyurid marsupial, before and after ingestion of 30 mg kg(-1) of fenitrothion, an organophosphate (OP) pesticide. Running endurance of OP-exposed animals was less than half that of control animals over the first 3 days after dosing and 55% of control animal endurance on day 5 post-dose. Despite these declines, peak metabolic rate at this running speed (9.3 times basal metabolic rate; BMR) was unaffected by OP exposure. Peak metabolic rate (PMR) and cumulative oxygen consumption during a 1-h exposure to conditions equivalent to -20 degrees C did not differ between OP-treated and control dunnarts, with PMR averaging 11 times BMR. We conclude that fenitrothion-induced exercise fatigue is not due to limitations in oxygen or substrate delivery to muscle or in their uptake per se, but more likely relates to decreased ability to sustain high-frequency neuromuscular function. The persistence of locomotor impairment following OP exposure in otherwise asymptomatic animals emphasizes the importance of using performance-based measures when characterising sublethal effects of pesticide exposure in an ecological context.

Acetylcholinesterase (AChE) distribution in the dorsal lateral geniculate nucleus (LGd) of 3 polyprotodont and 3 diprotodont marsupials has been compared with the cytoarchitecture and, as appropriate, with retinal terminal bands (RTBs) as demonstrated by tracers injected into the vitreous body. In this series those polyprotodont marsupials showing only partial segregation of retinal input (Virginia opossum and Tasmanian devil), display the least cell laminar differentiation. In them AChE staining is mainly diffuse but stronger in areas of greatest retinal terminal overlap. Segregation of visual input increases progressively in the remaining polyprotodont (eastern quoll) and in the diprotodonts (Tasmanian bettong, Tasmanian potoroo and brush-tailed possum), culminating in the last-named, in which segregation is most complete. Related to this development varying numbers of cell laminae/sublaminae appear and retinal terminal laminae/sublaminae (bands) are revealed. AChE activity can be correlated with both specific cell laminae/sublaminae and retinal terminal laminae/sublaminae in these complex LGds. Greatest AChE staining in every case is related to laminae/RTBs located in the medial part of the lateral (alpha) segment of LGd. Cytoarchitecturally, the ventral lateral geniculate nucleus (LGv), unlike the heterogeneous LGd, is remarkably homogeneous in the series of animals studied and shows well-stained AChE patches relating to areas receiving significant retinal input.