Multiple Stressors and Salamanders: Effects of an Herbicide, Food Limitation, and Hydroperiod

Abstract

Amphibian populations can be affected adversely by multiple biotic and abiotic stressors that together can contribute to their local and global decline. We focused on the combined effects of food limitation, drying conditions, and exposure to possibly the most abundant and widely used herbicide in the world, atrazine. We used a factorial design to evaluate the effects of exposure to four ecologically relevant doses of atrazine (approximate measured doses: 0, 4, 40, and 400 g/L), two food levels (limited and unlimited food), and two hydroperiods (presence or absence of a dry down) on the survival, life history, and behavior of the streamside salamander, Ambystoma barbouri, from the embryo stage through metamorphosis. In general, food and atrazine levels did not interact statistically, and atrazine affected dependent variables in a standard, dose-dependent manner. Exposure to 400 g/L of atrazine decreased embryo survival and increased time to hatching. Drying conditions and food limitation decreased larval survival, while 400 g/L of atrazine only reduced larval survival in one of the two years tested, suggesting that the lethality of atrazine may be condition dependent. Sublethal effects included elevated activity and reduced shelter use associated with increasing concentrations of atrazine and food limitation. The larval period was lengthened by food limitation and shortened by 400 g/L of atrazine. Drying conditions accelerated metamorphosis for larvae exposed to 0 and 4 g/L of atrazine but did not affect timing of metamorphosis for larvae exposed to 40 or 400 g/L of atrazine. Food limitation, drying conditions, and 400 g/L of atrazine reduced size at metamorphosis without affecting body condition (relationship between mass and length), even though feeding rates did not differ significantly among atrazine concentrations at any time during development. This suggests that high atrazine levels may have increased larval energy expenditures. Because smaller size at metamorphosis can lower terrestrial survival and lifetime reproduction, resource limitations, drying conditions, and environmentally realistic concentrations of atrazine have the potential to contribute to amphibian declines in impacted systems.

Early-life exposure to a herbicide has enduring effects on pathogen-induced mortality

“…To quantify actual atrazine concentrations, water samples were taken from every tank 1 h after dosing and atrazine was quantified using the Abraxis (Abraxis LLC, Warminster, PA) ELISA microtiter plate kit, with each sample processed in duplicate (measured concentrations were 65.9 + 3.48 mg l 21 , mean + s.e.). Atrazine has a long half-life [21] and was shown to have negligible breakdown over a 7-day period [41].…”

The toxicology of climate change: Environmental contaminants in a warming world

“…While species have historically acclimated or adapted to changes in climate, the rapid rate of current climate change coupled with increasingly fragmented and impaired habitats present unprecedented challenges for modern species (Boone et al, 2007;Fisk et al, 2005;OcchipintiAmbrogi, 2007;Rohr et al, 2004;Schiedek et al, 2007).…”

The cause of global amphibian declines: a developmental endocrinologist's perspective

“…A number of pesticides can inhibit or delay anuran metamorphosis as well (Distel and Boone, 2009;Howe et al, 2004;Mackey and Boone, 2009;Sparling and Fellers, 2009), including atrazine (Carr et al, 2003;Sullivan and Spence, 2003). Some pesticides accelerate metamorphosis -for example, atrazine accelerated metamorphosis in at least two species of salamanders (Forson and Storfer, 2006b;Rohr et al, 2004) -and some can even have biphasic effects (Brodeur et al, 1997). Finally, pesticide mixtures can also delay metamorphosis, probably via an increase in corticosterone (Hayes et al, 2006a).…”