The spotted salamander, Ambystoma maculatum, breeds and lays its eggs in seasonal freshwater ponds. Egg masses are surrounded with a protective jelly matrix and are found in sympatrically occurring clear and white varieties. The opacity of white masses is due to the presence of hydrophobic protein crystals. However, it is not understood how these two egg mass morphs persist over time, as natural selection is expected to favor one over the other. It is well established that a symbiosis exists between embryonic salamanders and a unicellular alga, Oophila ambystomatis, providing developing embryos with supplemental oxygen. Though the algae may consume yolk, as a previous study found that embryos reared with algae were smaller at hatching. A difference in interaction with this algal symbiont could explain persistence of this egg mass dimorphism in the highly variable environment of vernal ponds. To examine the interaction between egg mass morph and symbiotic algae under laboratory conditions, we compared embryonic development and hatching success of the two morphs in the presence of symbitoic algae. To control growth of O. ambystomatis, we allowed whole masses and individual eggs from white and clear masses to develop in both light and dark conditions. Individual eggs that had been removed from clear jelly masses were significantly heavier at hatching in both treatments. Survivorship of both morphs in the dark was high when embryos were separated from the jelly mass, but was very low when egg mass jelly was intact, supporting previous observations that the algae benefit embryos by increasing embryonic access to oxygen.
