Variation of Basal EROD Activities in Ten Passerine Bird Species – Relationships with Diet and Migration Status

Abstract

Inter-specific differences in animal defence mechanisms against toxic substances are currently poorly understood. The ethoxyresorufin-O-deethylase (EROD) enzyme plays an important role in defence against toxic chemicals in a wide variety of animals, and it is an important biomarker for environmental contamination. We compared basal hepatic EROD activity levels among ten passerine species to see if there is inter-specific variation in enzyme activity, especially in relation to their diet and migration status. Migratory insectivores showed higher EROD activity compared to granivores. We hypothesize that the variable invertebrate diet of migratory insectivores contains a wider range of natural toxins than the narrower diet of granivores. This may have affected the evolution of mixed function oxidases (MFO) system and enzyme activities. We further tested whether metabolic rates or relative liver size were associated with the variation in detoxification capacity. We found no association between EROD activity and relative (per mass unit) basal metabolic rate (BMR). Instead, EROD activity and relative liver mass (% of body mass) correlated positively, suggesting that a proportionally large liver also functions efficiently. Our results suggest that granivores and non-migratory birds may be more vulnerable to environmental contaminants than insectivores and migratory birds. The diet and migration status, however, are phylogenetically strongly connected to each other, and their roles cannot be fully separated in our analysis with only ten passerine species.

Expression of aryl hydrocarbon receptor 1 (AHR1), AHR1 nuclear translocator 1 (ARNT1) and CYP1 family monooxygenase mRNAs and their activity in chicken ovarian follicles following in vitro exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

“…Under control conditions, EROD and MROD activities in the chicken liver were assessed to be 1.17 and 0.93 nmol resorufin/mg protein/ min, respectively. A previous report of Rainio et al (2012) presented hepatic EROD activities among 10 avian species that varied between 0.35 to 1.1 nmol resorufin/mg protein/min. Our result confirmed high EROD activity in the chicken liver.…”

Anthropogenic Nest Materials May Increase Breeding Costs for Urban Birds

“…If confirmed, this pattern could be the consequence of male and female sparrows sharing, and thus diluting, the effect of exposure to cigarette butts, yet in both species the extent of damage is similar during early breeding, but lower in house sparrows than in finches (compare Figures 2C, 4C). Another possibility is that this interspecific difference indicates that P. domesticus, with a long urban history that should have brought it into contact with anthropogenic pollutants, may have developed adaptations such as enhanced enzymatic activity (e.g., Rainio et al, 2012), that increase its ability to detoxify itself (Schwagmeyer and Mock, 2003). This tantalizing possibility would constitute one of very few cases of phenotypic adjustments to cities that may not be explained just a consequence of plasticity, but as genuine adaptation to urban life (see Suárez-Rodríguez et al in press).…”

Stress response, biotransformation effort, and immunotoxicity in captive birds exposed to inhaled benzene, toluene, nitrogen dioxide, and sulfur dioxide

“…Avian defense mechanisms against toxic substances vary among species, and are poorly understood although birds are able to modulate their detoxification systems in response to pollution levels (Rainio et al, 2012). We know from many other species, that biotransformation capacity is very species-specific.…”