1. Communal Winter Denning in Western Diamond-backed Rattlesnakes
(Crotalus atrox): Molecular Evidence for Kin-related Social Structure
Schuett GW1,2,3, Clark RW4, Repp RA5, Smith CF2,3,6, Amarello M7, Douglas MR8,9, Douglas ME8,9, Herrmann H-W10
Introduction
The ubiquitous phenomenon of aggregation in all life forms has promoted the investigation of the formation, pattern, and persistence of this behavior. In vertebrates, aggregations of conspecifics can vary greatly in size from several individuals in primates to literally tens of thousands or greater in fishes and bats. It is not uncommon for these aggregations to be kin-based.
Western Diamond-backed Rattlesnakes (Crotalus atrox) aggregate in shelters (communal dens) during winter. This behavior is an important component of the spatial ecology and social structure of populations in southern Arizona .
Radio-telemetric analyses of 46 subjects (20 ♂, 26 ♀) at a single field site (Suizo Mountains) for 10 consecutive years ( ) revealed that selection and use of dens varied according to size (age) and sex. Aggregation of two or more individuals at a den was restricted to adults. The use of communal-type dens was significantly greater in adult males than in females. All males showed 100% fidelity to particular dens. Adult females showed den fidelity but many alternated between using communal-type dens and denning solitarily from year-to-year. The composition of communal dens was exclusively metamorphic rock associated with hillsides and mountains, whereas solitary individuals, particularly females, used burrows or nests of mammals associated with bajada or desert flats.
Conclusions
Based on the presence of many suitable den sites in the Suizo Mountains and results of our DNA-based analysis, selection of particular dens appears to be kin-based or by social choice. Accordingly, we propose that the function of communal-type dens in C. atrox, and perhaps other rattlesnakes of southern latitudes, is fundamentally different from species that occur in higher latitudes, where survival appears to be the primary
purpose of aggregation. Mating at or near dens in C. atrox
takes place during egress in spring, but other social behaviors
beyond courtship and coitus are possible and include,
eavesdropping, copying, kin-recognition and pair-bonding. The
role of family and culture is essentially unexplored in snakes.
Example results from Den-1 [AD-1]. U = unrelated. HS = half-sibs (above)
Methods and Results
We genotyped 191 adults (145 with no radio-telemetry) at 27 microsatellite loci (see Pozarowski et al., 2012; Clark et al., 2014). Of these, 50 were known to occupy 7 different dens. A test for mean genetic relatedness (R) across all dens was significant (mean R = 0.03, p < 0.001); however, 4 dens had several to many relatives (half-sibs) and the remaining 3 dens had no detectable relatives (U = unrelated).
1Department of Biology and Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA; 2The Copperhead Institute, Spartanburg, SC, USA; 3The Chiricahua Desert Museum, Rodeo, NM, USA; 4Department of Biology, San Diego State University, San Diego, CA, USA; 5National Optical Astronomy Observatory, Tucson, AZ, USA; 6Department of Biology, Wofford College, Spartanburg, SC, USA; 7Social Snakes, Tucson, AZ, USA; 9Illinois Natural History Survey, Prairie Research Institute, University of Illinois, Champaign, IL, USA; 10University of Arizona, Tucson, AZ, USA