Response of the green alga Oophila sp., a salamander endosymbiont, to a PSII‐inhibitor under laboratory conditions

Abstract

In a rare example of autotroph-vertebrate endosymbiosis, eggs of the yellow-spotted salamander (Ambystoma maculatum) are colonized by a green alga (Oophila sp.) that significantly enhances salamander development. Previous studies have demonstrated the potential for impacts to the salamander embryo when growth of the algae is impaired by exposure to herbicides. To further investigate this relationship, the authors characterized the response of the symbiotic algae (Oophila sp.) alone to the photosystem II (PSII) inhibitor atrazine under controlled laboratory conditions. After extraction of the alga from A. maculatum eggs and optimization of culturing conditions, 4 toxicity assays (96 h each) were conducted. Recovery of the algal population was also assessed after a further 96 h in untreated media. Average median effective concentration (EC50) values of 123 µg L(-1) (PSII yield), 169 µg L(-1) (optical density), and 299 µg L(-1) (growth rate) were obtained after the 96-h exposure. Full recovery of exposed algal populations after 96 h in untreated media was observed for all endpoints, except for optical density at the greatest concentration tested (300 µg L(-1) ). Our results show that, under laboratory conditions, Oophila sp. is generally less sensitive to atrazine than standard test species. Although conditions of growth in standard toxicity tests are not identical to those in the natural environment, these results provide an understanding of the tolerance of this alga to PSII inhibitors as compared with other species.

Effects of atrazine on egg masses of the yellow-spotted salamander (Ambystoma maculatum) and its endosymbiotic alga (Oophila amblystomatis)

“…Slight opposite effects were reported for cultured Oophila sp. in Baxter et al, 2014, where yield of PSII was significantly (6%) greater than controls in units previously treated at 300 mg/L after 96 h in untreated media.…”

“…Therefore, the Oophila population in the egg masses examined in this study may have nearly ceased reproducing prior to exposure, since the study was initiated at stage 23 or greater, which also may have affected observed differences in sensitivity. Despite these possibilities, the lowest effect concentration observed for motile algae in laboratory culture (EC10 for 96-h optical density ¼ 35 mg/L; Baxter et al, 2014) was still nearly 10-fold greater than the maximum concentration measured in Ontario surface waters (3.91 mg/L; Byer et al, 2011). Additionally, exposures in Ontario are more likely to occur during the later stages of embryonic development, when algae has ceased reproducing, since concentrations of atrazine in surface waters tend to peak in midJune (Byer et al, 2011), while egg masses are typically deposited in April to early May.…”

“…Exposure and recovery tests were conducted using sterile modified Bristol's media in 250 mL Erlenmeyer flasks on a shaker table (90 rpm) in an environmental chamber (retrofitted Controlled Environments Ltd. Model E15) set at 18 C and a 12:12 L:D cycle (PAR fluence of approximately 200 mmol/m 2 /s) as in Baxter et al (2014).…”

Optimization of culturing conditions for toxicity testing with the algaOophilasp. (Chlorophyceae), an amphibian endosymbiont

“…Reductions in PSII yield appeared to be similar between these species, with a 96‐h EC25 range of 34 µg/L to 57 µg/L in Oophila sp. and 43 µg/L in P. subcapitata (72‐h value) .…”

Growth Recovery of Lemna gibba and Lemna minor Following a 7-Day Exposure to the Herbicide Diuron

“…No previous studies have been found that characterize recovery of duckweed from a catchment-specific exposure event simulated in the laboratory to diuron. However, this hypothesis has been explored extensively with atrazine by introducing variability in exposure duration and a recovery phase into testing with a variety of aquatic primary producers [green algae (Baxter et al 2013(Baxter et al , 2014, periphyton , and duckweed (Brain et al 2012)]. Haynes et al (2000) reported some recovery of photosynthesis in a seagrass species after significant inhibition of photosynthesis following diuron exposure (0.1-80 lg L -1 ) to diuron for 5 days.…”