Physiological and organism-level endpoints in the beetle Pterostichus oblongopunctatus (Coleoptera: Carabidae), inhabiting a gradient of heavy metal pollution.

摘要

Pollutant body burdens, ability to tolerate supplementary stressors, and biomarkers of physiological stress were investigated in the ground beetle, Pterostichus oblongopunctatus (Coleoptera: Carabidae), inhabiting a gradient of heavy metal contamination in Poland. The central question was to determine if beetles inhabiting polluted habitats incurred costs compared with beetles in less contaminated habitats. Metal body burdens in beetles ranged from 79 to 201 μg/g zinc, 0.174 to 8.66 μg/g lead, and 1.14 to 10.8 μg/g cadmium. Copper was efficiently regulated along the pollution gradient. Beetles from different sites were subjected to supplementary stressors (food deprivation and exposure to the organophosphorous insecticide, dimethoate). Beetles originating from the most contaminated sites (OLK2 and OLK3) were significantly less tolerant of food deprivation (measured as time to death) compared with beetles from the reference site (OLK7). Beetles from OLK2 and OLK3 were significantly more susceptible to dimethoate exposure (median survival times of 12 and 123 hours, respectively) compared with beetles from the reference site (359 hours). There was a negative correlation between chronic pollution burden and ability to survive additional stress. Trends in the enzyme activity of carboxylesterase and glutathione S-transferase (GST) in response to metal exposure were determined for beetles along the gradient. Significantly higher levels of GST were found in female beetles from OLK2 and OLK3 (p = 0.049 and p 0.001, respectively) compared with the reference site. Male beetles did not differ in enzyme activity along the gradient. There was no direct correlation between enzyme activity and exposure to metals. Respiration rate, recorded as CO₂ expiration, was also measured in beetles along the gradient. Beetles collected from OLK2 exhibited significantly lower respiration rates compared with other sites. Changes in respiration rate after challenge with dimethoate were measured to determine physiological responses following exposure to stress. After dosing, respiration rates increased significantly at all sites (p 0.0001), suggesting that chronic metal exposure did not impair the ability of beetles to increase respiration rate after dimethoate challenge. While clear costs of metal exposure were found at the organism level, there was no strong correlation that these costs placed beetles at their physiological limits to respond to additional stressors.