The causative agent of the evolution of social aggregation continues to baffle biologists.
Though many hypotheses exist, we continue to overlook species that exhibit sociality in nonvisual and non-auditory ways. These “cryptically” social animals can give us greater insight into how sociality evolved as they present social behavior in ways that have been previously
unexplored. Most reptiles are solitary for much of their lives and are traditionally viewed as nonsocial, aggregating mainly for reproductive needs (e.g., courtship and mating). However, some temperate snakes, rattlesnakes in particular, are well known for their massive denning
aggregations during winter, yet very few studies have investigated the possibility of “cryptic”
(i.e., chemically mediated) social interactions at these communal dens. This study aims to gain
insight into the details of Prairie rattlesnake population structure in the wild. We strive to
understand whether this species aggregates in a non-random fashion. This work was focused on aggregations of pregnant snakes at collective birthing sites called rookeries. We examined
rattlesnakes from five rookery sites and compared these with individuals from the general
population on Rattlesnake Butte in Steamboat Springs, Colorado. By genotyping microsatellite
loci, we determined patterns of relatedness by calculating FST and genetic differentiation with
GenePop R package. Our results showed 4 examples of high to moderate FST values across the
gravid female group comparison, which was supported by significant p-values in the gravid
female genetic differentiation analysis. Based on our current data, we see patterns of relatedness
in gravid female aggregations, supporting the possibility for the aggregations being kin
neighborhoods. Further studies need to be conducted to definitively identify the groupings as kin. These data have allowed us to further investigate population structure in cryptically social species to explore the evolution of sociality in broader contexts than have previously been
documented.