Color and Morphological Differences in Two Populations of Progomphus obscurus
Robert D. Barber
In 1995, I found a population of Progomphus obscurus on the Schroon River, Essex County, New York, in the Adirondack Mountains. This removed the species from the state "historic" list. There are no recent records of a former population on the coastal plain. This is probably the northernmost population of the species in the U. S.. In subsequent years, we found that P. obscurus is found on lower sections of the Schroon River to its confluence with the upper Hudson river and is fairly common on the sandier portions of the Hudson River through Warren County.
In comparison to more southerly populations, the New York specimens are slightly larger. There is a slight difference in the male appendages, as seen in the graphic above. Besides being longer and thinner, the most significant difference is in the tip of the inferior appendage, which appears smooth and spoon shaped on the New York specimens, and lacking the "toothed" rim as is typical of the species elsewhere. In color, the yellow on the New York specimens is greatly reduced, but is somewhat variable. I have seen none with as much yellow as more southerly populations, or other populations from the coastal plain, at least as far north as Massachusetts.
The size and color differences could be adaptations for a much harsher environment, and since the New York population has probably been isolated for a very long time it could be a fledgling subspecies.