Geographic Variation in Scatella stagnalis (Diptera: Ephydridae)

A multiple discriminant functions analysis of Scatella stagnalis (Diptera: Ephydridae) from 40 localities in North America showed that only a small portion of the interlocality variation can be accounted for by the geographic positions of the localities. It was hypothesized that the observed variation was due to some combination of local selective pressures and non-selective factors. The data suggest that gene flow is of little importance in this species. Analysis of variance indicated significant interpopulational differences in all 12 characters measured for both males and females, except for the length of the 3rd antennal segment in males. Further analysis showed the females to be larger than the males with respect to all characters. The variational patterns found in males were only partially paralleled in females. This may be a reflection of the varying patterns of sexual dimorphism or it might indicate that males and females are being subjected to somewhat different selective pressures. The analysis indicated that the recognition of geographic races (subspecies) would be inappropriate.