Predator-induced physiological responses in tadpoles challenged with herbicide pollution

Abstract

Predators induce plastic responses in multiple prey taxa, ranging from morphological to behavioral or physiological changes. In amphibians, tadpoles activate plastic responses to reduce predation risk by reducing their activity rate and altering their morphology, specifically tail depth and pigmentation. Furthermore, there is now evidence that tadpoles’ defenses are modified when predators combine with other stressful factors such as pollutants or competitors, but our knowledge on the physiological responses underlying these responses is still scarce. Here we study physiological responses in Pelobates cultripes tadpoles exposed to a natural predator (larvae of the aquatic beetle Dytiscus circumflexus), non-lethal concentrations of herbicide (gly-phosate, 0.5 mg/L and 1.0 mg/L) or both factors combined. We measured corticosterone levels, standard metabolic rate, oxidative damage (TBARS) and activity of antioxidant enzymes, and immune response (via leukocyte count). Tadpoles reduced their corticosterone concentration by ca. 24% in the presence of predator cues, whereas corticosterone did not change in the presence of glyphosate. Two enzymes involved in antioxidant response also decreased in the presence of predators (14.7% and 13.2% respectively) but not to glyphosate. Herbicide, however, increased the number of neutrophils and reduced that of lymphocytes, and had an interaction effect with predator presence. Standard metabolic rate did not vary across treatments in our experiment. Thus we show a marked physiological response to the presence of predators but little evidence for interaction between predators and low levels of herbicide. Multiple assessment of the physiological state of animals is important to understand the basis and consequences of phenotypic plasticity.

Physiological Stress Responses in Amphibian Larvae to Multiple Stressors Reveal Marked Anthropogenic Effects even below Lethal Levels

“…Common stress-induced changes in the proportion of leukocytes include neutrophilia (abnormally high number of neutrophils) and lymphopenia (abnormally low number of neutrophils) and are often associated with increased GC levels (Davis et al 2008). Herbicide, however, had no apparent effects on the immune system in this experiment; glyphosate has been shown to affect the leukocyte proportion of tadpoles (Shutler and Marcogliese 2011;Burraco et al 2013).…”

“…Amphibians are also deeply affected by human disturbances and indeed constitute the most threatened group of vertebrates (Hoffman et al 2010). CORT regulation is a common stress response in anuran tadpoles to pond drying, pollutants, predators, acidification, or UV-B radiation (Glennemeier and Denver 2001;Chambers and Belden 2009;Burraco et al 2013;Chambers et al 2013;Maher et al 2013). However, CORT regulation has many potential cascading effects on other aspects of amphibian biology, and these are seldom studied.…”

Pigmentation plasticity enhances crypsis in larval newts: associated metabolic cost and background choice behaviour

“…This way we simultaneously obtained measures of oxygen consumption (mg/L) for five independent individuals. The respirometer was calibrated at least once daily using a saturated sodium sulphite solution and oxygen saturated water to achieve 0 and 100% oxygen concentrations96. Respirometry trials were conducted after two weeks of experiment, when changes in skin pigmentation were clearly observable.…”

Training for Translocation: Predator Conditioning Induces Behavioral Plasticity and Physiological Changes in Captive Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) (Cryptobranchidae, Amphibia)

“…The four chambers were connected to two pumps each via impermeable plastic tubing. The first pump moved fresh water into the chambers while the second pump recirculated water past the oxygen sensor that recorded readings every 30 s. All oxygen sensors were calibrated to 0% O 2 using sodium-sulfite-treated water and 100% O 2 using fully aerated water [41]. We submerged all chambers, tubing, and pumps in a large 180-gallon sump full of UV-sterilized water [42].…”

“…We also acclimated hellbenders in open circuit respirometers for five minutes then created a closed, recirculating circuit for each individual chamber [41]. Hellbenders are primarily nocturnal; therefore, we conducted all experiments during daylight hours and kept overhead lights on in the experimental room to reduce activity.…”