Summary
Environmental pollutants can disrupt chemical communication between aquatic organisms by interfering with the production, transmission, and/or detection of, as well as responses to, chemical cues. Here, we test the hypothesis that early-life exposure to naphthenic acid fraction compounds (NAFCs) from oil sands tailings disrupts antipredator-associated chemical communication in larval amphibians. Wild adult wood frogs (Rana sylvatica) captured during their natural breeding period were combined (1 female:2 males) in six replicate mesocosms filled with either uncontaminated lakewater or with NAFCs isolated from an active tailings pond in Alberta, Canada, at nominal 5 mg/L concentrations. Egg clutches were incubated and tadpoles maintained in their respective mesocosms for ∼40 days post-hatch. Tadpoles (Gosner stage 25-31) were then transferred individually to trial arenas filled with uncontaminated water and exposed to one of six chemical alarm cue (AC) stimuli solutions following a 3 × 2 × 2 design (3 AC types × 2 stimulus carriers × 2 rearing exposure groups). Relative to control tadpoles, NAFC-exposed tadpoles demonstrated higher baseline activity levels (line crosses and direction changes) when introduced to uncontaminated water. Antipredator responses differed in graded fashion with AC type, with control ACs eliciting the greatest latency to resume activity, water the least, and NAFC-exposed ACs intermediate. Pre- to post-stimulus difference scores were non-significant in control tadpoles, while NAFC-exposed tadpoles demonstrated significantly greater variation. While this suggests that exposure to NAFCs from fertilization through hatching may have interfered with AC production, it is unclear whether the quality or quantity of cues was affected. There was also no clear evidence that NAFC carrier water interfered with ACs or the alarm response in unexposed control tadpoles. These results emphasize the importance of understanding how behavioral and physiological effects of early-life NAFC exposure on critical antipredator responses may persist across life history stages.
Methodology
This experiment took place from 30 March to 9 June 2021 at the QE3 Living Lab at the Queen's University Biological Station (QUBS), Elgin, ON, Canada (concurrent with Robinson et al., 2023). Adult wood frogs (N = 6 female and N = 12 male) were captured overnight on 30 March as they migrated towards breeding wetlands on QUBS property and held separately by sex in coolers with snow and moss. Nine days later, six 20-L buckets were each filled with 3 L of filtered (52-μm sieve) water from the nearby reference Warner Lake (44° 31′ 43" N, 76° 22′ 54" W). Six 450-L cylindrical breeding mesocosms were filled with 50 L of filtered lakewater and provided with leaf litter and rocks for the frogs to rest and deposit eggs. Mesocosms were covered with bird netting to exclude predators and housed in an above-ground insulated tank of lakewater to provide a thermal buffer. Half (N = 3) of each container type (bucket or mesocosm) were assigned to either the Control (uncontaminated lakewater) or NAFC (nominal 5 mg/L concentration) exposure groups.