RELATEDNESS AND POPULATION DIFFERENTIATION IN A COLONIAL BUTTERFLY, EUCHEIRA-SOCIALIS (LEPIDOPTERA, PIERIDAE)

Eucheira socialis (Westwood) occurs above 1,800 m in mountains through out Mexico and has a remarkable suite of autapomorphies, including com munal larval nests and a mean primary sex ratio of 70% males. We gathe red allozyme data for 31 loci from individuals within nests within pop ulations and used hierarchical F statistics to assess population struc ture and relatedness at these levels. Allozyme variation was far lower than reported in most Lepidoptera, and was absent from the population s sampled from southern Mexico. Among 5 sample sites distributed throu ghout Mexico, differentiation was high (F-ST = 0.54), which is consist ent with a history of interrupted gene flow. At lower hierarchical lev els in the variable populations, we found significant excess heterozyg otes within nests (F-IN = -0.15) and evidence for structuring within s ubpopulations (F-IS = 0.015, significantly greater than F-IN) Average relatedness among nestmates was r(NS) = 0.28, which is significantly l ess than r = 0.5. This is probably caused largely by interchange among nests on multinest trees.