Geographic patterns of colour variation in North AmericanNicrophorusburying beetles (Coleoptera; Silphidae)

Abstract

Adult individuals of the burying beetle species Nicrophorus defodiens Mannerheim, N. guttula Motschulsky, and N. investigator Zetterstedt show extensive geographic variation in elytral colour patterns, from an orange and black banded pattern to one where maculations are extremely reduced. Individuals with slightly to extensively reduced maculations are generally confined to Pacific coastal localities but, as variation is continuous and extremes are often sympatric, do not warrant separate specific or subspecific status. Examination of the geographic distribution of the colour of the basal article of the antennal club of N. guttula individuals shows the colour of the article to be associated with variation in elytral colour. This confirms that N. hecate Bland, previously characterized by a red basal article of the antennal club, is a junior synonym of N. guttula Motschulsky, previously characterized by a black basal article. The possible roles of thermoregulation and mimicry accounting for the variation in elytral colour are briefly discussed.