Relatedness and population differentiation in a colonial butterfly, Eucheira socialis (Lepidoptera: Pieridae)

Abstract

Eucheira socialis (Westwood) occurs above 1,800 m in mountains throughout Mexico and has a remarkable suite of autapomorphies, including communal larval nests and a mean primary sex ratio of 70% males. We gathered allozyme data for 31 loci freom individuals within nests within populations and used hierarchical F statistics to assess population structure and relatedness at these levels. Allozyme variation was far lower than reported in most Lepidoptera, and was absent freom the populations sampled freom southern Mexico. Among 5 sample sites distributed throughout Mexico, differentiation was high (FST = 0.54), which is consistent with a history of interrupted gene flow. At lower hierarchical levels in the variable populations, we found significant excess heterozygotes within nests (FIN = 0.15) and evidence for structuring within subpopulations (FIS = 0.015, significantly greater than FIN) Average relatedness among nestmates was r(NS) = 0.28, which is significantly less than r = 0.5. This is probably caused largely by interchange among nests on multinest trees.