Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes
Island tameness results largely from a lack of natural predators. Because some insular rattlesnake populations lack functional rattles, presumably the consequence of relaxed selection from reduced predation, we hypothesized that the Santa Catalina Island, California, USA, population of the southern...
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| Format: | Article |
| Language: | English |
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MDPI AG
2024-03-01
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| Series: | Toxins |
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| Online Access: | https://www.mdpi.com/2072-6651/16/3/157 |
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| author | William K. Hayes Carl E. Person Gerad A. Fox Julie L. King Erick Briggs Eric C. K. Gren |
| author_facet | William K. Hayes Carl E. Person Gerad A. Fox Julie L. King Erick Briggs Eric C. K. Gren |
| author_sort | William K. Hayes |
| collection | DOAJ |
| description | Island tameness results largely from a lack of natural predators. Because some insular rattlesnake populations lack functional rattles, presumably the consequence of relaxed selection from reduced predation, we hypothesized that the Santa Catalina Island, California, USA, population of the southern Pacific rattlesnake (<i>Crotalus helleri</i>, which possesses a functional rattle), would exhibit a decrement in defensive behavior relative to their mainland counterparts. Contrary to our prediction, rattlesnakes from the island not only lacked tameness compared to mainland snakes, but instead exhibited measurably greater levels of defensiveness. Island snakes attempted to bite 4.7 times more frequently as we endeavored to secure them by hand, and required 2.1-fold more time to be pinned and captured. When induced to bite a beaker after being grasped, the island snakes also delivered 2.1-fold greater quantities of venom when controlling for body size. The additional venom resulted from 2.1-fold larger pulses of venom ejected from the fangs. We found no effects of duration in captivity (2–36 months), which suggests an absence of long-term habituation of antipredator behaviors. Breeding bird surveys and Christmas bird counts indicated reduced population densities of avian predators on Catalina compared to the mainland. However, historical estimates confirmed that populations of foxes and introduced mammalian predators (cats and pigs) and antagonists (herbivorous ungulates) substantially exceeded those on the mainland in recent centuries, and therefore best explain the paradoxically exaggerated defensive behaviors exhibited by Catalina’s rattlesnakes. These findings augment our understanding of anthropogenic effects on the behaviors of island animals and underscore how these effects can negatively affect human safety. |
| first_indexed | 2024-04-24T17:46:47Z |
| format | Article |
| id | doaj.art-00bd7d5db37f41eeaa6e146d4c803a68 |
| institution | Directory Open Access Journal |
| issn | 2072-6651 |
| language | English |
| last_indexed | 2024-04-24T17:46:47Z |
| publishDate | 2024-03-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Toxins |
| spelling | doaj.art-00bd7d5db37f41eeaa6e146d4c803a682024-03-27T14:06:26ZengMDPI AGToxins2072-66512024-03-0116315710.3390/toxins16030157Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of RattlesnakesWilliam K. Hayes0Carl E. Person1Gerad A. Fox2Julie L. King3Erick Briggs4Eric C. K. Gren5Department of Earth and Biological Sciences, Loma Linda University, Loma Linda, CA 92350, USADepartment of Earth and Biological Sciences, Loma Linda University, Loma Linda, CA 92350, USADepartment of Earth and Biological Sciences, Loma Linda University, Loma Linda, CA 92350, USACatalina Island Conservancy, P.O. Box 2739, Avalon, CA 90704, USANatural Solutions Wildlife Enterprises, P.O. Box 418, Yucca Valley, CA 92286, USADepartment of Biological Sciences, Southwestern Adventist University, Keene, TX 76059, USAIsland tameness results largely from a lack of natural predators. Because some insular rattlesnake populations lack functional rattles, presumably the consequence of relaxed selection from reduced predation, we hypothesized that the Santa Catalina Island, California, USA, population of the southern Pacific rattlesnake (<i>Crotalus helleri</i>, which possesses a functional rattle), would exhibit a decrement in defensive behavior relative to their mainland counterparts. Contrary to our prediction, rattlesnakes from the island not only lacked tameness compared to mainland snakes, but instead exhibited measurably greater levels of defensiveness. Island snakes attempted to bite 4.7 times more frequently as we endeavored to secure them by hand, and required 2.1-fold more time to be pinned and captured. When induced to bite a beaker after being grasped, the island snakes also delivered 2.1-fold greater quantities of venom when controlling for body size. The additional venom resulted from 2.1-fold larger pulses of venom ejected from the fangs. We found no effects of duration in captivity (2–36 months), which suggests an absence of long-term habituation of antipredator behaviors. Breeding bird surveys and Christmas bird counts indicated reduced population densities of avian predators on Catalina compared to the mainland. However, historical estimates confirmed that populations of foxes and introduced mammalian predators (cats and pigs) and antagonists (herbivorous ungulates) substantially exceeded those on the mainland in recent centuries, and therefore best explain the paradoxically exaggerated defensive behaviors exhibited by Catalina’s rattlesnakes. These findings augment our understanding of anthropogenic effects on the behaviors of island animals and underscore how these effects can negatively affect human safety.https://www.mdpi.com/2072-6651/16/3/157cloacal gland dischargeisland syndromeraptorsrattlingvenom expenditureViperidae |
| spellingShingle | William K. Hayes Carl E. Person Gerad A. Fox Julie L. King Erick Briggs Eric C. K. Gren Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes Toxins cloacal gland discharge island syndrome raptors rattling venom expenditure Viperidae |
| title | Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes |
| title_full | Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes |
| title_fullStr | Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes |
| title_full_unstemmed | Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes |
| title_short | Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes |
| title_sort | paradoxical exception to island tameness increased defensiveness in an insular population of rattlesnakes |
| topic | cloacal gland discharge island syndrome raptors rattling venom expenditure Viperidae |
| url | https://www.mdpi.com/2072-6651/16/3/157 |
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