Spiders are notoriously solitary and cannibalistic, with instances of colonial or social lifestyles in only about 50-60, or ~0.1% of 50,000 described species. Population analyses indicate that most colonies consist of multiple cohorts formed by close relatives. Territorial social spiders facultatively form colonies by interlinking individual webs, but further cooperation is infrequent, and only among juveniles or (rarely) females. In spiders, therefore, aggregations of males outside of the male-male competition context have been unknown. Here, we report on a discovery of a kite spider from Madagascar that exhibits unique colonies. We found colonies of the newly described araneid Isoxya manangona n. sp. formed by up to 41 interconnected, single-cohort adult female webs with up to 38 adult males aggregating on a central, single, non-sticky line. With males resting tightly together, we found no evidence of male-male aggression. Genetic analyses from RAD sequencing suggest that most colonies consist of unrelated individuals. Furthermore, the genetic variability of males was somewhat less than that of females. Single cohort colonies made up purely of adults, and peaceful male aggregations, have not previously been observed in spiders. Although direct behavioral observations are preliminary, we speculate based on the available evidence that these colonies may represent a novel and first case of lekking in spiders.

Genomic DNA was isolated from 80 individuals representing nine web colonies using the Qiagen DNeasy Blood and Tissue kit (Qiagen). SNP data was generated using the 3RAD technique detailed in Bayona-Vásquez et al. (2019). We used enzymes EcoRI, MspI, and ClaI following Petersen et al. (2012) and Burns et al. (2017), and adapters provided by the University of Georgia (BadDNA@UGA). Paired-end 150 base pair reads were generated for the 3RAD library with Nextseq at the University of California, Davis DNA Technologies Core. Further detail regarding our 3RAD procedure is given in Newton et al. (2020). Read demultiplexing, filtering, and clustering were performed with ipyrad (Eaton and Overcast, 2020). For each end of each locus, maxima of six uncalled bases, ten heterozygous sites, 25 SNPs, and ten indels were allowed. The clustering threshold was set to 0.9, and locus occupancy was set to a minimum of 50%.