Papers by Michael Cardwell
Wilderness & Environmental Medicine, Jun 1, 2022
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Herpetological Review, 2006
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Journal of Zoology, 2007
The reproductive ecology of Mohave rattlesnakes Crotalus scutulatus was investigated in the weste... more The reproductive ecology of Mohave rattlesnakes Crotalus scutulatus was investigated in the western Mohave Desert using radiotelemetry from August 2001 to November 2004. This paper documents reproductive behavior across successive seasons in the context of seasonal timing, mean daily movement, home range, body temperature and relationship with abiotic factors such as time of day, temperature, precipitation, photoperiod and microhabitat. This population of C. scutulatus used a bimodal mating system, with reproductive behavior occurring in late summer/fall (21 August to 7 October), interrupted by 4 months of cold weather, and concluding in the spring (16 March to 16 May). Drought apparently curtailed courtship and copulation during the 2002 activity season, but the pregnancy rates in 2002 and 2003 were not significantly affected. Communal denning was not detected and there was no indication of seasonal migration. Autumnal and vernal movements appeared to be driven by reproductive effort, predominantly males engaged in prolonged mate searching. Sexual maturity was achieved at 2.0 years/600 mm snout-vent length (SVL) for females, and 1.5 years/400 mm SVL for males.
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Understanding the origin and maintenance of phenotypic variation, particularly across a continuou... more Understanding the origin and maintenance of phenotypic variation, particularly across a continuous spatial distribution, represents a key challenge in evolutionary biology. For this, animal venoms represent ideal study systems: they are complex, variable, yet easily quantifiable molecular phenotypes with a clear function. Rattlesnakes display tremendous variation in their venom composition, mostly through strongly dichotomous venom strategies, which may even coexist within a single species. Here, through dense, widespread population-level sampling of the Mojave rattlesnake, <i>Crotalus scutulatus</i>, we show that genomic structural variation at multiple loci underlies extreme geographical variation in venom composition, which is maintained despite extensive gene flow. Unexpectedly, neither diet composition nor neutral population structure explain venom variation. Instead, venom divergence is strongly correlated with environmental conditions. Individual toxin genes corre...
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Toxicon
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Wilderness & Environmental Medicine, 2022
Crotalus scutulatus (Mohave rattlesnake) is a clinically significant pit viper broadly distribute... more Crotalus scutulatus (Mohave rattlesnake) is a clinically significant pit viper broadly distributed across much of the arid southwestern United States and mainland Mexico. Identification of C scutulatus is a concern among emergency medical service and emergency department personnel owing to its reputation for severe envenomations and difficulty in visually differentiating between C scutulatus and other species, primarily Crotalus atrox (western diamond-backed rattlesnake). We contrast distinctive characteristics of C scutulatus, C atrox, and 3 other sympatric species: Crotalus molossus, Crotalus ornatus, and Crotalus viridis (western and eastern black-tailed rattlesnakes and prairie rattlesnake, respectively). Greenish coloration eliminates C atrox but does not confirm C scutulatus. Obvious coarse and fine speckling of the dorsal pattern and a pale postocular stripe intersecting the mouth characterize C atrox. Dorsal speckling is insignificant or absent in the other species, whereas the pale postocular stripe passes above the mouth in C scutulatus and C viridis and is absent in C molossus and C ornatus. Tails boldly ringed with alternating black and white or contrasting shades of gray are shared by C atrox and C scutulatus, respectively, but a lack of boldly ringed tails characterizes the other species. The proximal rattle segment is yellow and black, or entirely yellow, in C scutulatus but black in the others. The most reliable visual identifications are based on evaluations of multiple traits, all of which are variable to some extent. Traits such as tail ring width and the size and number of crown scales have frequently been overemphasized in the past.
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Proceedings of the Royal Society B: Biological Sciences, 2019
Understanding the origin and maintenance of phenotypic variation, particularly across a continuou... more Understanding the origin and maintenance of phenotypic variation, particularly across a continuous spatial distribution, represents a key challenge in evolutionary biology. For this, animal venoms represent ideal study systems: they are complex, variable, yet easily quantifiable molecular phenotypes with a clear function. Rattlesnakes display tremendous variation in their venom composition, mostly through strongly dichotomous venom strategies, which may even coexist within a single species. Here, through dense, widespread population-level sampling of the Mojave rattlesnake, Crotalus scutulatus , we show that genomic structural variation at multiple loci underlies extreme geographical variation in venom composition, which is maintained despite extensive gene flow. Unexpectedly, neither diet composition nor neutral population structure explain venom variation. Instead, venom divergence is strongly correlated with environmental conditions. Individual toxin genes correlate with distinct...
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Wilderness and Environmental Medicine, 2022
Crotalus scutulatus (Mohave rattlesnake) is a clinically significant pit viper broadly distribute... more Crotalus scutulatus (Mohave rattlesnake) is a clinically significant pit viper broadly distributed across much of the arid southwestern United States and mainland Mexico. Identification of C scutulatus is a concern among emergency medical service and emergency department personnel owing to its reputation for severe envenomations and difficulty in visually differentiating between C scutulatus and other species, primarily Crotalus atrox (western diamond-backed rattlesnake). We contrast distinctive characteristics of C scutulatus, C atrox, and 3 other sympatric species: Crotalus molossus, Crotalus ornatus, and Crotalus viridis (western and eastern black-tailed rattlesnakes and prairie rattlesnake, respectively). Greenish coloration eliminates C atrox but does not confirm C scutulatus. Obvious coarse and fine speckling of the dorsal pattern and a pale postocular stripe intersecting the mouth characterize C atrox. Dorsal speckling is insignificant or absent in the other species, whereas the pale postocular stripe passes above the mouth in C scutulatus and C viridis and is absent in C molossus and C ornatus. Tails boldly ringed with alternating black and white or contrasting shades of gray are shared by C atrox and C scutulatus, respectively, but a lack of boldly ringed tails characterizes the other species. The proximal rattle segment is yellow and black, or entirely yellow, in C scutulatus but black in the others. The most reliable visual identifications are based on evaluations of multiple traits, all of which are variable to some extent. Traits such as tail ring width and the size and number of crown scales have frequently been overemphasized in the past.
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From the Department of Surgery, Division of Emergency Medicine, University of Utah, Salt Lake Cit... more From the Department of Surgery, Division of Emergency Medicine, University of Utah, Salt Lake City, UT (Drs Caravati, Fuller, Kanaan, Ray, and Stewart); Department of Surgery, Division of General Surgery, University of Utah, Salt Lake City, UT (Dr Russell); Department of Surgery, Division of Emergency Medicine, Stanford University School of Medicine, Stanford, CA (Dr Norris); Department of Biological Sciences, California State University, Sacramento, CA (Mr Cardwell); Department of Toxinology, Women’s and Children’s Hospital, North Adelaide, South Australia, Australia (Dr Weinstein); and the East Carolina University Brody School of Medicine, Greenville, NC (Dr Bush).
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Wilderness & Environmental Medicine
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Herpetological Review, 2006
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Wilderness & environmental medicine, Jun 11, 2016
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James Biardi is a contributing author, &amp;amp;amp;amp;amp;amp;quot;The ecological and evolu... more James Biardi is a contributing author, &amp;amp;amp;amp;amp;amp;quot;The ecological and evolutionary context of mammalian resistance to pitviper venoms&amp;amp;amp;amp;amp;amp;quot;, pp. 557-568. Book description: Eliciting so many emotions of persons coming into contact with rattlesnakes, including fascination, curiosity, awe, and fear, this book showcases the finest research to date by investigators encompassing an enormous breadth of expertise. With 50 original contributions from 98
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Herpetological Review
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Herpetological Review
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Papers by Michael Cardwell