Genetic basis of woven nest size in subsocial spider mites

The variation in nest size of social spider mites of the genus Stigmaeopsis is assumed to correspond to their anti-predator strategy and to be a key aspect of their social organization and speciation. It is known that the length of the dorsal setae (sc1, 2nd propodosomal setae) correlates with the nest size. We conducted interspecies cross experiments to determine the heredity of sc1 length and nest size using two closely related species that build different sized nests, Stigmaeopsis saharai Saito et Mori and Stigmaeopsis takahashii Saito et Mori. A cross between a S. saharai female and a S. takahashii male produced several viable F1 females. We measured sc1 length and the nest size of the F1 females and then compared these values with those of their parent species. The sc1 length of F1 females and the nest size constructed by these mites were intermediate with respect to the values of the two parent species. Therefore, the length of the sc1 and nest size are heritable. This result sheds light on the importance of considering the genetic basis for the variations in social organization.