Species and Geographic Variability of Surface Pits in the Esocidae

Abstract

In the Esocidae, the lateral line sensory system on the body consists of shallow pits, each containing a group of neuromasts and partially bordered by a notched (cardioid) scale. In all species, the number of sensory pits shows little intraspecific geographic variability. A similar type of pit, but lacking neuromasts, is also present on the body of Esox a. americanus, E. a. vermiculatus and E. niger. The number of these nonsensory pits shows considerable intraspecific geographic variability. In E. a. americanus the variability is clinal, with numbers peaking in North Carolina and decreasing north and south of this region. In E. niger the geographic pattern may be more complex. At the population level, number of nonsensory pits is highly variable and in some cases population range approaches species range. No apparent correlation between number of nonsensory pits and latitude, distance from coastal plain, water quality or physiological function could be demonstrated. This variability would suggest that these pits are not under selective pressure and are nonfunctional. This is consistent with evidence supporting an hypothesis that the nonsensory pits are an aplasic condition of the lateral line system.