Typically not long after learning about the incredible amphibian migrations to vernal pools in early spring, budding naturalists observe the egg masses of spotted salamanders and wood frogs taking on a dark green color. This is due to the growth of an alga, Oophila amblystomatis, we are told, which has colonized egg membranes and provides oxygen to the amphibian embryos while taking advantage of nitrogenous wastes. This tale of symbiosis adds another level of complexity to the saga of life in a vernal pool.
But it turns out the complexity might be profoundly greater. Dr. Ryan Kerney at Dalhousie University has reported algae within the embryonic cells of spotted salamanders; this discovery, if substantiated, would constitute the first known instance of an endosymbiotic relationship between a photosynthetic organism and a vertebrate. I eagerly await Dr. Kerney's formal publication, but in the meantime the news article spurred James Gibbs and me to consider what we might observe in any egg masses oviposited in the Heiberg pools this spring. Will algae "colonize" egg masses in the new pools, or would they require the assistance of dispersal vectors over varying periods of time? Digging through the literature on O. amblystomatis proved to be an unsatisfying experience, and an example of how conjecture can transform into widespread beliefs...
Although H. Orr is credited as the first to observe algae in spotted salamander egg membranes in an 1888 publication (widely cited but difficult to locate), it turns out that the alga species in question has never been formally described! Perry Gilbert in a 1942 paper describes how the name Oophila amblystomatis was informally adopted by F. D. Lambert ~30 years prior when distributing specimens to other researchers. Gilbert, at least, helps identification matters by providing extensive verbal descriptions, photographs, and illustrations of various forms of the alga, including non-motile and quadriflagellated forms. Gilbert also described experiments that strongly suggested that the pond water, not the parent, was the source provisioning algae to newly oviposited spotted salamander eggs. These results were corroborated by John Gatz with eggs of spotted salamanders, wood frogs, and Jefferson salamanders in a 1958 Journal of Herpetology note (7:137-138). Oddly, he cites an abstract from the 1969 Internation Botanical Congress by P. Biebel when offering the genus Chlamydomonas as a synonym for Oophila, but I cannot discern from the vague abstract how this is justified.
Additional key observations made by both Gilbert and Gatz are that among "several hundred" and "over a thousand" (respectively) spotted salamander egg masses observed in nature, each researcher recalled only a single instance of an egg mass lacking algae late in its development; the symbiosis appears to be nearly, but not completely, ubiquitous. Gilbert speculated that the egg mass lacking algae was located in an old stream bed, and so perhaps algae had been flushed from the system.
The failure of both Gilbert and Gatz to find algae within the reproductive tracts of female salamanders is in contrast to Kerney who supposedly found algae within adult salamander oviducts. This raises the possibility of vertical transmission of the symbiont, and that the salamanders themselves could be the vector bringing O. amblystomatis to novel habitats.
I wrote an email to Dr. Kerney last week to ask how he was dealing with the taxonomic impediments, and if he had any ecological insights regarding the colonization of O. ablystomatis in novel aquatic habitats such as the newly constructed pools at Heiberg. He replied that he has phylogenetic data that places "[their] local Oophila amblystomatis" in the Order Chlamydomonadales. Unfortunately, his research team lacks the resources to undertake more comprehensive phylogeographic analysis, but he speculated that a diversity of algal symbiont types could be associated with different salamanders. He added that it did not appear similar to any especially common northeastern species. In addition, Dr. Kerney confirmed that despite the strong evidence that O. amblystomatis is present in pond water and quickly colonizes newly deposited amphibian eggs, it has never been observed in a free-living state. He expressed a hunch that both vertical and horizontal algal acquisition might be at work, but resolving this experimentally has not been, nor will be, an easy task.
So, given some degree of cooperation by (or manipulation of!) reproductive spotted salamanders and wood frogs, we are poised to make some potentially interesting observations in our experimental system regarding the ecology of O. amblystomatis, with implications for the restoration of populations of amphibian species that enjoy the benefits of association with this ill-known alga(e?). James, Kim and I are in the initial phases of brainstorming experimental approaches to discerning vectors or reservoirs of O. amblystomatis. I wonder if any of the USC folks in the field have observed the tell-tale green egg masses in newly constructed pools down south, and within what kind of timeframes following construction?
This is to say nothing of the recently reported radical endosymbiosis, or what physiological titans spotted salamanders might become if they did not whisk themselves underground the first chance they get after metamorphosing....
Jim Arrigoni, SUNY-ESF
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