Using Morphological, Genetic, and Venom Analyses to Present Current and Historic Evidence of Crotalus horridus x adamanteus Hybridization on Jekyll Island, Georgia

Chad M. Harrison^1,*, Joseph Colbert^2,3, Collin J. Richter⁴, Preston J. McDonald⁵, Lauren M. Trumbull⁵, Schyler A. Ellsworth⁶, Michael P. Hogan⁶, Darin R. Rokyta⁶, and Mark J. Margres^5,*

¹Saint Charles County Government - Parks, Wentzville, MO 63385. ²Jekyll Island Authority Conservation Department, Jekyll Island, GA 31527. ³The Rattlesnake Conservancy, Jacksonville, FL 32211. ⁴Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602. ⁵Department of Integrative Biology, University of South Florida, Tampa, FL 33620. ⁶Department of Biological Sciences, Florida State University, Tallahassee, FL 33306. *Corresponding authors.

Southeastern Naturalist, Volume 21, Issue 2 (2022): 158–174

Abstract
On 17 June 2019, we collected a unique juvenile rattlesnake from a wildlife response call on Jekyll Island State Park, GA. The snake exhibited intermediate color patterns and gross anatomical features suggesting potential hybridization between Crotalus horridus (Canebrake/Timber Rattlesnake) and Crotalus adamanteus (Eastern Diamondback Rattlesnake). Using mitochondrial and nuclear genetic sequencing, venom analyses, and morphological characteristics to test that hypothesis, we were able to verify that this specimen represents only the second documented observation of natural hybridization between C. adamanteus and C. horridus and the first reported with multiple lines of evidence sufficient for confirmation. Surprisingly, genetic analyses found evidence of previous introgression between these species, suggesting hybridization may not be a rare occurrence in the area (and perhaps specifically on Jekyll Island). We will continue to monitor the hybrid individual via radio-telemetry to assess its survival and any subsequent F2 hybridization reproduction events.

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