Salamander embryos were selected from an acidic body of water called Bat Lake.  Though salamanders typically breed in temporary bodies of water, this lake is abundant in this species because the acidity prevents the establishment of predatory fish. The protective egg capsule and jelly mass found surrounding Yellow Spotted Salamander (Ambystoma maculatum) embryos act as a barrier, limiting the movement of oxygen into the egg (Mills et al., 2001). Coupled with low environmental oxygen levels of salamander breeding ponds which tend to have a high biological oxygen demand (Mills et al., 2001), embryonic salamanders face a potential developmental period beset with low oxygen. To cope with this hypoxia, embryos take advantage of the establishment of unicellular Oophila ambystomatis within the capsule which acts as a local oxygen provider during photosynthesis (Gilbert, 1944).  In return, the algae receives protection, nitrogenous wastes and carbon dioxide. Additionally, convective currents created by surface cilia are known to enhance oxygen transport into the egg (Hunter and Vogel, 1986), emphasizing the importance of embryonic motion in successful development.
    Thus, we are interested in better understanding this symbiosis, from an ecological to a physiological perspective.  For example, does the algae assist the embryos in accelerated development by provisioning oxygen?  Is there a cost to the embryo of living within an environment with too much oxygen?  Does embryonic motion (ciliary and muscular) change depending on whether algae are allowed to co-exist with the embryos?

Experiment:
The egg masses were divided and reared in three different light conditions: 24 hours of dark (0L:24D), 12 hours of light (12L:12D) and 24 hours of light (24L:0D), yielding no algal growth in the first group and similar algal concentrations in the light groups. Similar to previous studies (Mills et al., 2001), lower hatching success, more deformities and higher mortality was observed in the hypoxic (0:24) group which completely lacked algae. Embryos associated with algae had greater success in these areas, with the 24 hour light group showing slightly greater overall success. Seemingly random rotational movements via surface cilia were observed in early stage embryos. This spinning occurred more frequently in algae-free embryos than in the algae-inhabited groups and more frequently in algae-inhabited subjected to periods of light than those subjected to periods of dark; movement was likely a response to lack of photosynthesis-derived oxygen supplies. At later developmental periods when cilia movements were replaced with spontaneous muscular movements, described as twitching, movement was much more predominant in algae-associated masses observed under light;  thus groups with more oxygen contracted more often. It would seem, then, that muscular twitches do not play the same role as ciliary movements (ie. convective mixing) and that the higher oxygen demands that accompany progressive developmental complexity may exceed the oxygen available to algae-free embryos and inhibit muscular contractions during hypoxia.

Publications

Tattersall, GJ, and Spiegelaar, N. 2008. Embryonic motility and hatching of Ambystoma maculatum are influenced by the symbiotic algae. Canadian Journal of Zoology 86: 1289-1298.