Characteristics of cannibalistic morph barred tiger salamanders in a prairie pothole lake
Juvenile barred tiger salamanders (Ambystoma mavortium) can occur as two possible morphotypes. The ‘’typical’’ morph has a relatively small head size and very minute vomerine teeth, whereas the much rarer “cannibalistic” morph has a relatively broad head size and enlarged recurved vomerine teeth. The cannibal morph is thought to be a plastic response triggered by high conspecific competition. This morph typically accounts for 5-30% of local populations and has predominately been reported for very dense populations of barred tiger salamanders in the southwestern United States. Here we report the first cannibal morphs for the gray tiger salamander subspecies (Ambystoma mavortion diaboli). During the summer of 2012 we collected a total of 54 barred tiger salamanders with funnel traps from the lake in central North Dakota with a known cannibal morph population. Individuals were measured in the lab with a focus on body length, skull, and dentition measurements. From this we were able to clearly describe the morphotype of each individual. We used typical morph larval barred tiger salamanders from a nearby lake for measurement comparisons.
Using dentition measurements we classified all 54 individuals as cannibalistic morphs, which we compared to 7 typical morphs collected from another population in a nearby wetland. The snout vent lengths did not significantly differ between the cannibalistic morphs (97 + 1.5mm; mean + one standard error) compared to the typical morphs (98 + 2.3; U = 45, P > 0.05). However, as the cannibal morphs had both longer (U = 78, P < 0.05) and wider skulls (U = 84.5, P < 0.05) than the typical morphs. The cannibal morphs came from a habitat with a relatively low abundance of salamanders (2 individuals/trap), but a high abundance of fathead minnows (Pimephales promelas; 800 fish/trap). By contrast, the typical morphs came from a habitat with a low abundance of salamanders (3 individuals/trap) and no fathead minnows present. These intriguing preliminary results suggest that the cannibalistic morph may be induced when competing vertebrates are at high densities, challenging conventional interpretations and calling for more research.