Meeting Abstract
All descriptions of symbioses require explanations about the acquisition of symbionts by the host. The discovery that unicellular green algal symbionts of egg masses of the northeastern yellow spotted salamander Ambystoma maculatum invade embryonic tissues and cells raised the possibility of vertical transmission as a mode of symbiont acquisition. Previous work also identified the free-living alga Oophila amblystomatis in A. maculatum breeding habitat, but no definitive tests have distinguished among modes of symbiont acquisition. We tested the mode of acquisition of O. amblystomatis in A. maculatum egg masses by collecting adult female salamanders from the wild during annual spring reproduction. Animals were held in pond water that was either untreated, treated with UV filters or autoclaved. The growth of algal cells in treated and control egg masses was monitored microscopically and quantified. Lower rates of algal growth were observed in egg masses treated with either UV filtered or autoclaved water, indicating that algae invade egg masses horizontally from pond water. However, in some cases of egg masses incubated in autoclaved water, algal growth was observed, raising the possibility that both horizontal and vertical modes of transmission are present. There remains an additional possible mode of acquisition: female salamanders fertilize themselves by collecting spermatophores. Therefore, evidence of “vertical transmission” may be from the spermatophore proper, or from algae accumulating on the surface of spermatophores during their period of exposure to pond water. Future tests will be designed to distinguish among these various modes of acquisition, and how they might vary among ponds and years.
