Oophilia amblystomatis Colonization of Embryonic Ambystoma maculatum: Maintaining Polymorphism

Chelsea Brown


Genetically based polymorphisms are difficult to explain because differential fitness should lead to the extinction of one morph, but selection on alternative morphs may be maintained if relative fitness varies spatially or temporally. In Ambystoma maculatum, egg mass morph is genetically determined and both morphs co-occur throughout much of the species’ range. White masses have been shown to have an advantage over the clear masses with regards to decreased predation, there is no known condition that favors the clear masses. The focus of this study is to better understand advantages of the clear morph. Association with Oophilia amblystomatis has been shown to provide fitness benefits such as faster growth and development and increased survivorship. If the opacity of the white masses does not allow for sufficient penetration of light, photosynthetic activity of the algae may be hindered. This would mean that the quality of the symbiosis would depend on the morph. We hypothesize that clear morphs may better facilitate the colonization of O. amblystomatis. Egg masses of both morphs were contained in mesh and anchored at water surface and at the pond bottom. Temperature and dissolved oxygen were measured weekly and masses were inspected regularly for hatchlings. Masses with hatchlings were returned to the lab to collect staging and survivorship data. Egg membranes were harvested from each mass to measure algal cell density. We found that clear masses anchored at the water surface had higher survivorship than white morph counterparts, but this advantage was not present at the pond bottom. We determined that egg masses at the pond bottom took a longer time to hatch and hatched at an earlier stage, regardless of morph. These results support our hypothesis that clear masses have a selective advantage in terms of the ability of O. amblystomatis to positively affect embryonic development.


Ambystoma maculatum; polymorphism; Oophilia amblystomatis; symbiosis

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