Variation of hind-wing colour and length in Sympetrum internum (Odonata: Libellulidae) from the Canadian prairie provinces

Abstract

AbstractAmber coloration, called saffroning, extends from 1 to 15 mm across the hind-wing base in females of Sympetrum internum Montgomery from the prairie provinces but extends only from 2 to 3 mm in males. There are no substantial differences in hind-wing length between the sexes. A significant correlation was found between hind-wing length and the extent of saffroning for both males and females. Regressions of these characters against latitude and longitude revealed that (1) there is a significant decrease in hind-wing length northward for both sexes; (2) there is a significant decrease in saffroning northward that is more significant for females; (3) there is no significant effect of longitude on hind-wing length; and (4) saffroning in females significantly increases westward but there is no similar effect in males, and the trend in females is much less significant than the latitudinal trend. Within the prairie provinces, extensive saffroning is confined to the Prairie Ecozone and moderate saffroning occurs around the edges of this ecozone. The surrounding Boreal Plains Ecozone is characterized by females with very limited saffroning. There is generally extensive variation in the extent of saffroning within some Prairie Ecozone locations, ranging from limited to moderate or extensive, but limited and moderate saffroning were more frequent at most locations in the Prairie Ecozone. Various explanations for saffroning are considered. Since limited, moderate, and extensive saffroning occur together throughout an extensive area, and occur within many populations and within a group emerging at the same time, formal taxonomic recognition of individuals with moderate or extensive saffroning seems unwarranted.