Predator And Environmental Effects On The Polymorphic Egg Masses Of Spotted Salamanders (Ambystoma maculatum)

Polymorphisms may be maintained if selection intensity and gene flow vary across a species’geographic range. Jelly coats of amphibian eggs are under many different selective forces,such as predators and external environment interactions. Spotted salamanders (Ambystomamaculatum) have polymorphic egg masses that are either clear or opaque depending on the presence or absence of hydrophobic protein crystals in the outer egg layer. This study investigated how different predator communities and environmental parameters influence the distribution of the polymorphic egg masses in high and low elevations of North Carolina. I conducted surveys of A. maculatum clutches in breeding ponds and recorded numbers of clear and opaque egg masses, as well as the presence of predator and water chemistry in seven North Carolina counties. I found that egg masses at high elevation sites were predominately opaque (~82%), whereas egg masses at low elevation sites were predominately clear (~98%). Although water chemistry (pH, conductance) varied greatly between high and low elevation locations, water chemistry was correlated with egg polymorphism only in the mountains. At both elevations, locations with greater predator occupancy tended to have higher proportions of opaque egg masses. These results suggest the selective forces shaping the distribution of A. maculatum egg masses include both predator and physiochemical forces, but the additive effects of both stressors may drive the high ratios of opaque egg masses.