Examining the taxonomic identity of the green alga Oophila amblystomatis (Chlamydomonadales), the biogeography of its symbiont Ambystoma maculatum (Amphibia), and the response of the green alga to two herbicides

Abstract

The yellow spotted salamander (Ambystoma maculatum) shares a unique endosymbiotic relationship with the unicellular green alga Oophila amblystomatis. Though a number of studies have isolated and identified O. amblystomatis, the alga’s taxonomic identity is yet to be resolved. In this study the nuclear SSU rRNA gene was used to identify two well supported Oophila clades that included sequences from past studies in addition to isolates from the current study, and showed that O. amblystomatis does not group monophyletically with its own members, and groups paraphyletically with other species of green algae. Past studies have also assessed the potential for indirect effects on embryo development via herbicidal exposure to the endosymbiotic algae, but few have taken into account the possibility of correct species identification, strain, or locale sensitivity. In this study, the response of O. amblystomatis to the exposure of two herbicides, atrazine and 2,4-dichlorophenoxyacetic (96 h exposure acute toxicity tests), followed by recovery (96 h recovery in untreated media) acid were characterized. Lowest growth inhibition no-observed effect concentrations of 70 μg/L and 30 mg/L of atrazine and 2,4-D, respectively, followed by full recovery at these concentrations, indicate that these herbicides do not pose a risk of growth inhibition to egg-inhabiting algae. This study proposes a revision of the current taxonomy of O. amblystomatis, and demonstrates the need for species identification and thorough phylogenetic reconstruction in toxicity testing.