What Is Ambystoma Barbour?

When faced with the two distinct species of salamander, one must ask what their common ancestor looked like and whether it primarily lived in ponds or streams. Previous studies have presumed that Ambystoma barbouri, the stream dwelling species, is divergent from Ambystoma texanum, the pond dwelling species (Kraus and Petranka, 1989). This assumption is based on knowledge of environmental changes and the geographic spread of each species. Since the end of the last Ice Age, the availability of pond habitats has decreased, likely driving pond dwelling organisms to seek new habitats, meaning it is more probable that the salamanders migrated from ponds to streams, rather than from streams to ponds (Kraus and Petranka, 1989). A. texanum is also more widespread than A. barbouri, suggesting that they diverged less recently (Kraus and Petranka, 1989). If A. barbouri diverged from A. texanum, the changes in phenotype could be due to either selection for small gills and large tail or selection for increased plasticity. If the different phenotypes correlate with genetic differences that directly determine tail and gill size, the phenotypes are genetically determined and the divergence is a
result of selection for the stream phenotype. In this case, on a molecular level, the different phenotypes would be a result of differences in DNA sequences that control gene expression in the gills and tail. If the different phenotypes were due to selection for plasticity, however, genetic changes would control the response to the environment and genes would be differentially expressed in different environments in A. barbouri, but not A. texanum. Though the first case may seem more likely, previous research has shown that A. barbouri has a more plastic response to factors such as the amount of yolk present in eggs than A. texanum (Landberg, 2014). If A. barbouri has evolved a more plastic response in regard to yolk size, it may also have evolved plasticity in other areas. To learn whether the traits characteristic of A.
barbouri are genetically or environmentally determined, A. barbouri juveniles should be raised in a low-oxygen and predator free environment. If these individuals develop the gills and tail characteristic of A. texanum, we may conclude that the A. barbouri phenotype is a result of environmental influence on development. If these individuals retain the small gills and large tail seen in other A. barbouri, we may conclude that the populations have diverged due to selection for these traits. Additionally, A. texanum juveniles could be raised in a high-oxygen and predator rich environment. Transferring A. texanum individuals into this environment could potentially expose a hidden reaction norm and show how A. barbouri initially
diverged.