Here we review research over the past quarter century regarding the systematics and taxonomy of a... more Here we review research over the past quarter century regarding the systematics and taxonomy of an ancient, popular and economically valuable group of snakes referred to as pythons (Serpentes, Pythonidae). All recent phylogenetic studies recognize the pythons as monophyletic; however, the phylogenetic relationships at supraspecific levels are conflicting, and many of the relationships recovered are paraphyletic. We identify several taxonomic changes as necessary to clarify supraspecific relationships and which resolve the issue of paraphyly recovered in several studies. Overall, our review of the phylogenetic systematics of pythons points to considerable incongruence among recovered relationships. Instances of paraphyly emerge, low node support is detected, and terminal taxa are unstable across phylogenetic hypotheses. We thus recognize that pythonid gene trees have been unable, for various reasons, to reveal the true species tree. This occurrence is not unexpected and can arise from incomplete taxon sampling, long-branch attraction and repulsion, homoplasy, ancestral polymorphism, and, more notably, the anomaly zone. These phenomena ultimately yield incomplete lineage sorting, or the failure of lineages to coalesce over evolutionary time. We discuss future directions to resolve these troubling issues. Without resolution, adaptive hypotheses about pythons will be limited, including hypotheses of geographic origin. Analyses that recover the clade Python as sister to the Indo-Australian clade are interpreted to support a Laurasian origin of Pythonidae. In contrast, a Gondwanan origin is supported when the Indo-Australian clade is recovered as basal to the Python clade. We describe the morphology of two recently proposed genera. Finally, we designate and describe the neotype for Morelia azurea and offer a list of the currently accepted python species and their taxonomy.
Ecosystems transition quickly in the Anthropocene, whereas biodiversity adapts more slowly. Here ... more Ecosystems transition quickly in the Anthropocene, whereas biodiversity adapts more slowly. Here we simulated a shifting woodland ecosystem on the Colorado Plateau of western North America by using as its proxy over space and time the fundamental niche of the Arizona black rattlesnake (Crotalus cerberus). We found an expansive (= end-of-Pleistocene) range that contracted sharply (= present), but is blocked topographically by Grand Canyon/Colorado River as it shifts predictably northwestward under moderate climate change (= 2080). Vulnerability to contemporary wildfire was quantified from available records, with forested area reduced more than 27% over 13 years. Both 'ecosystem metrics' underscore how climate and wildfire are rapidly converting the Plateau ecosystem into novel habitat. To gauge potential effects on C. cerberus, we derived a series of relevant 'conservation metrics' (i.e. genetic variability, dispersal capacity, effective population size) by sequencing 118 individuals across 846 bp of mitochondrial (mt)DNA-ATPase8/6. We identified five significantly different clades (net sequence divergence = 2.2%) isolated by drainage/topography, with low dispersal (F ST = 0.82) and small sizes (2N ef = 5.2). Our compiled metrics (i.e. dispersal barriers) underscore the susceptibility of this woodland specialist to a climate and wildfire tandem. We offer adaptive management scenarios that may counterbalance these metrics and avoid the extirpation of this and other highly specialized, relictual woodland clades.
Aim We derived phylogenies, phylogeographies, and population demographies for two North American ... more Aim We derived phylogenies, phylogeographies, and population demographies for two North American pitvipers, Agkistrodon contortrix (Linnaeus, 1766) and A. piscivorus (Lacepede, 1789) (Viperidae: Crotalinae), as a mechanism to evaluate the impact of rapid climatic change on these taxa.
We analyzed both mitochondrial (MT-) and nuclear (N) DNAs in a conservation phylogenetic framewor... more We analyzed both mitochondrial (MT-) and nuclear (N) DNAs in a conservation phylogenetic framework to examine deep and shallow histories of the Beaded Lizard (Heloderma horridum) and Gila Monster (H. suspectum) throughout their geographic ranges in North and Central America. Both MTDNA and intron markers clearly partitioned each species. One intron and MTDNA further subdivided H. horridum into its four recognized subspecies (H. n. alvarezi, charlesbogerti, exasperatum, and horridum). However, the two subspecies of H. suspectum (H. s. suspectum and H. s. cinctum) were undefined. A supertree approach sustained these relationships. Overall, the Helodermatidae is reaffirmed as an ancient and conserved group. Its most recent common ancestor (MRCA) was Lower Eocene [35.4 million years ago (mya)], with a $25 my period of stasis before the MRCA of H. horridum diversified in Lower Miocene. Another $5 my passed before H. h. exasperatum and H. h. horridum diverged, followed by $1.5 my before H. h. alvarezi and H. h. charlesbogerti separated. Heloderma suspectum reflects an even longer period of stasis ($30 my) before diversifying from its MRCA. Both H. suspectum (México) and H. h. alvarezi also revealed evidence of historic range expansion following a recent bottleneck. Our conservation phylogenetic approach emphasizes the origin and diversification of this group, yields information on the manner by which past environmental variance may have impacted its populations and, in turn, allows us to disentangle historic from contemporary impacts that might threaten its long-term persistence. The value of helodermatid conservation resides in natural services and medicinal products, particularly venom constituents, and these are only now being realized.
—The beaded lizard (Heloderma horridum) and Gila monster (H. suspectum) are large, highly venomou... more —The beaded lizard (Heloderma horridum) and Gila monster (H. suspectum) are large, highly venomous, anguimorph lizards threatened by human persecution, habitat loss and degradation , and climate change. A recent DNA-based phylogenetic analysis of helodermatids (Douglas et al. 2010. Molecular Phylogenetics and Evolution 55: 153–167) suggests that the current infraspecific taxonomy (subspecies) of beaded lizards underestimates their biodiversity, and that species status for the various subspecies is warranted. Those authors discussed " conservation phylogenetics, " which incorporates historical genetics in conservation decisions. Here, we reassess the taxonomy of beaded lizards utilizing the abovementioned molecular analysis, and incorporate morphology by performing a character mapping analysis. Furthermore, utilizing fossil-calibrated sequence divergence results, we explore beaded lizard diversification against a backdrop of the origin, diversification , and expansion of seasonally dry tropical forests (SDTFs) in Mexico and Guatemala. These forests are the primary biomes occupied by beaded lizards, and in Mesoamerica most are considered threatened, endangered, or extirpated. Pair-wise net sequence divergence (%) values were greatest between H. h. charlesbogerti and H. h. exasperatum (9.8%), and least between H. h. alvarezi and H. h. charlesbogerti (1%). The former clade represents populations that are widely separated in distribution (eastern Guatemala vs. southern Sonora, Mexico), whereas in the latter clade the populations are much closer (eastern Guatemala vs. Chiapas, Mexico). The nominate subspecies (Heloderma h. horridum) differed from the other subspecies of H. horridum at 5.4% to 7.1%. After diverging from a most-recent common ancestor ~35 mya in the Late Eocene, subsequent diversification (cladogen-esis) of beaded lizards occurred during the late Miocene (9.71 mya), followed by a lengthy stasis of up to 5 my, and further cladogenesis extended into the Pliocene and Pleistocene. In both beaded lizards and SDTFs, the tempo of evolution and diversification was uneven, and their current distributions are fragmented. Based on multiple lines of evidence, including a review of the use of trinomi-als in taxonomy, we elevate the four subspecies of beaded lizards to full species: Heloderma alvarezi (Chiapan beaded lizard), H. charlesbogerti (Guatemalan beaded lizard), H. exasperatum Río Fuerte beaded lizard), and H. horridum (Mexican beaded lizard), with no changes in their vernacular names. Finally, we propose a series of research programs and conservation recommendations. Resumen.—El escorpión (Heloderma horridum) y el monstruo de Gila (H. suspectum) son lagartijas grandes, anguimorfas, y muy venenosas que están sufriendo diversas amenazas como resultado de la persecución humana, degradación y pérdida del hábitat y el cambio climático global. Un análisis filogenético reciente basado en ADN de este grupo (Douglas et al. 2010. Molecular Phylogenetics and Evolution 55: 153–167) sugiere que la actual taxonomía intraespecífica (subespecies) del es-corpión está subestimando la diversidad biológica, y el reconocimiento de especies es justificable. Estos autores discuten la utilidad del enfoque denominado " conservación filogenética " , que hace hincapié en la incorporación de la genética histórica en las decisiones de conservación. En este estudio, reevaluamos la taxonomía del escorpión utilizando el análisis molecular antes mencionado e incorporamos la morfología en un análisis de mapeo de caracteres. Así mismo, con los resultados de la secuencia de divergencia calibrada con fósiles, se explora la diversificación del escorpión en forma yuxtapuesta al origen, la diversificación y la expansión de los bosques tropicales estacional-mente secos (SDTFs) en México y Guatemala. Estos bosques son los principales biomas ocupados por los escorpiones, y en Mesoamérica la mayoria son considerados amenazados, en peligro o
During the past quarter century, quantifying and understanding diversification of mating systems ... more During the past quarter century, quantifying and understanding diversification of mating systems in vertebrates has undergone a renaissance with the advent of DNA-based methods to ascertain parentage. In snakes, accurate parentage assignments are complicated by secretive lifestyles, sperm storage, cryptic female choice, multiple paternity, and facultative parthenogenesis. However, parentage analysis using genotypic (microsatellite) methods can resolve most of these difficulties. We employed 22 microsatellite loci to determine parentage and quantify the mating system of a population of copperhead snakes (Agkistrodon contortrix) in Connecticut, USA. From 2001 to 2003, we sampled 114 adults (56 males, 58 female) and 137 neonates (sex not determined) from known mothers. Our primary goal was to estimate opportunities for fecundity (I) selection, sexual selection (Is) and Bateman gradients (βss) for adult males and females. We also tested for association between multiple paternity and mal...
During the mating seasons (late summer and spring), male copperheads (Agkistrodon contortrix; Ser... more During the mating seasons (late summer and spring), male copperheads (Agkistrodon contortrix; Serpentes, Viperidae) engage in aggressive physical interactions for priority of access to females. These fights generally involve two individuals and are characterized by prominent vertical displays, a high degree of physical contact, and the absence of biting. Ritualized aggression does not occur in females. Although intrasexual aggression in conspecifics has obvious energetic costs (e.g., lactate accumulation) that can affect subsequent behavior, few studies have addressed these costs in reptiles, and no studies have examined snakes. Moreover, recent studies suggest psychoneuroendocrine (catecholamines, glucocorticoids) regulation of metabolism during and following aggressive episodes. There were three main questions addressed in this study. Do winners and losers of staged, pair-wise encounters show differences in post-fight (60-min) levels of plasma lactate and corticosterone (CORT)? Ar...
ABSTRACT Intentional provisioning of food and water at specific locations, commonly bird feeders ... more ABSTRACT Intentional provisioning of food and water at specific locations, commonly bird feeders and bird baths, may alter bird and mammal abundance, distribution, and recruitment; yet no studies have examined the indirect effects of resource supplementation on terrestrial reptilian mesopredators such as rattlesnakes. In the southwestern deserts of North America, anecdotal evidence suggests provisioning birds with food and water attracts rattlesnakes to exurban yards, either indirectly by increasing prey availability or directly through attraction to water. We conducted the first experimental test of this hypothesis by providing bird seed, water, or bird seed and water at 2 national monuments in Arizona, USA, and followed the responses of adult western diamond-backed rattlesnakes (Crotalus atrox) equipped with radiotransmitters, and endothermic prey species, primarily rodents, birds, and lagomorphs. We found differing responses among prey taxa to supplemental food and water provisioning: rodents showed no response to any treatment, birds responded to food treatments, and lagomorphs responded to water treatments. Overall, spatial responses by adult rattlesnakes were weak, but several subjects appeared to respond to individual treatment grids. We did not find evidence of a direct response by rattlesnakes to supplemental water. Overall, we found little support for the prevalent belief that food and water sources at provisioning stations increase local concentrations of rattlesnakes; we provide several explanations for this counter-intuitive result. 2015 The Wildlife Society.
KEY WORDS Arizona, artificial waters, birds, Crotalus atrox, lagomorph, nuisance wildlife, small mammal, resource supplementation.
Differences in resource availability and quality along environmental gradients are important infl... more Differences in resource availability and quality along environmental gradients are important influences contributing to intraspecific variation in body size, which influences numerous life-history traits. Here, we examined variation in body size and sexual size dimorphism (SSD) in relation to temperature, seasonality, and precipitation among 10 populations located throughout Arizona of the western diamondbacked rattlesnake (Crotalus atrox). Specifically, in our analyses we addressed the following questions: (i) Are adult males larger in cooler, wetter areas? (ii) Does female body size respond differently to environmental variation? (iii) Is seasonality a better predictor of body size variation? (iv) Is SSD positively correlated with increased resources? We demonstrate that male and female C. atrox are larger in body size in cooler (i.e., lower average annual maximum, minimum, and mean temperature) and wetter areas (i.e., higher average annual precipitation, more variable precipitation, and available surface water). Although SSD in C. atrox appeared to be more pronounced in cooler, wetter areas, this relationship did not achieve statistical significance.
Long-term studies of individual animals in nature contribute disproportionately to our understand... more Long-term studies of individual animals in nature contribute disproportionately to our understanding of the principles of ecology and evolution. Such field studies can benefit greatly from integrating the methods of molecular genetics with traditional approaches. Even though molecular genetic tools are particularly valuable for species that are difficult to observe directly, they have not been widely adopted. Here, we used molecular genetic techniques in a 10-year radio-telemetric investigation of the western diamond-backed rattlesnake (Crotalus atrox) for an analysis of its mating system and to measure sexual selection. Specifically, we used microsatellite markers to genotype 299 individuals, including neonates from litters of focal females to ascertain parentage using full-pedigree likelihood methods. We detected high levels of multiple paternity within litters, yet found little concordance between paternity and observations of courtship and mating behavior. Larger males did not father significantly more offspring, but we found evidence for size-specific male-mating strategies, with larger males guarding females for longer periods in the mating seasons. Moreover, the spatial proximity of males to mothers was significantly associated with reproductive success. Overall, our field observations alone would have been insufficient to quantitatively measure the mating system of this population of C. atrox, and we thus urge more widespread adoption of molecular tools by field researchers studying the mating systems and sexual selection of snakes and other secretive taxa.
Here we review research over the past quarter century regarding the systematics and taxonomy of a... more Here we review research over the past quarter century regarding the systematics and taxonomy of an ancient, popular and economically valuable group of snakes referred to as pythons (Serpentes, Pythonidae). All recent phylogenetic studies recognize the pythons as monophyletic; however, the phylogenetic relationships at supraspecific levels are conflicting, and many of the relationships recovered are paraphyletic. We identify several taxonomic changes as necessary to clarify supraspecific relationships and which resolve the issue of paraphyly recovered in several studies. Overall, our review of the phylogenetic systematics of pythons points to considerable incongruence among recovered relationships. Instances of paraphyly emerge, low node support is detected, and terminal taxa are unstable across phylogenetic hypotheses. We thus recognize that pythonid gene trees have been unable, for various reasons, to reveal the true species tree. This occurrence is not unexpected and can arise from incomplete taxon sampling, long-branch attraction and repulsion, homoplasy, ancestral polymorphism, and, more notably, the anomaly zone. These phenomena ultimately yield incomplete lineage sorting, or the failure of lineages to coalesce over evolutionary time. We discuss future directions to resolve these troubling issues. Without resolution, adaptive hypotheses about pythons will be limited, including hypotheses of geographic origin. Analyses that recover the clade Python as sister to the Indo-Australian clade are interpreted to support a Laurasian origin of Pythonidae. In contrast, a Gondwanan origin is supported when the Indo-Australian clade is recovered as basal to the Python clade. We describe the morphology of two recently proposed genera. Finally, we designate and describe the neotype for Morelia azurea and offer a list of the currently accepted python species and their taxonomy.
Ecosystems transition quickly in the Anthropocene, whereas biodiversity adapts more slowly. Here ... more Ecosystems transition quickly in the Anthropocene, whereas biodiversity adapts more slowly. Here we simulated a shifting woodland ecosystem on the Colorado Plateau of western North America by using as its proxy over space and time the fundamental niche of the Arizona black rattlesnake (Crotalus cerberus). We found an expansive (= end-of-Pleistocene) range that contracted sharply (= present), but is blocked topographically by Grand Canyon/Colorado River as it shifts predictably northwestward under moderate climate change (= 2080). Vulnerability to contemporary wildfire was quantified from available records, with forested area reduced more than 27% over 13 years. Both 'ecosystem metrics' underscore how climate and wildfire are rapidly converting the Plateau ecosystem into novel habitat. To gauge potential effects on C. cerberus, we derived a series of relevant 'conservation metrics' (i.e. genetic variability, dispersal capacity, effective population size) by sequencing 118 individuals across 846 bp of mitochondrial (mt)DNA-ATPase8/6. We identified five significantly different clades (net sequence divergence = 2.2%) isolated by drainage/topography, with low dispersal (F ST = 0.82) and small sizes (2N ef = 5.2). Our compiled metrics (i.e. dispersal barriers) underscore the susceptibility of this woodland specialist to a climate and wildfire tandem. We offer adaptive management scenarios that may counterbalance these metrics and avoid the extirpation of this and other highly specialized, relictual woodland clades.
Aim We derived phylogenies, phylogeographies, and population demographies for two North American ... more Aim We derived phylogenies, phylogeographies, and population demographies for two North American pitvipers, Agkistrodon contortrix (Linnaeus, 1766) and A. piscivorus (Lacepede, 1789) (Viperidae: Crotalinae), as a mechanism to evaluate the impact of rapid climatic change on these taxa.
We analyzed both mitochondrial (MT-) and nuclear (N) DNAs in a conservation phylogenetic framewor... more We analyzed both mitochondrial (MT-) and nuclear (N) DNAs in a conservation phylogenetic framework to examine deep and shallow histories of the Beaded Lizard (Heloderma horridum) and Gila Monster (H. suspectum) throughout their geographic ranges in North and Central America. Both MTDNA and intron markers clearly partitioned each species. One intron and MTDNA further subdivided H. horridum into its four recognized subspecies (H. n. alvarezi, charlesbogerti, exasperatum, and horridum). However, the two subspecies of H. suspectum (H. s. suspectum and H. s. cinctum) were undefined. A supertree approach sustained these relationships. Overall, the Helodermatidae is reaffirmed as an ancient and conserved group. Its most recent common ancestor (MRCA) was Lower Eocene [35.4 million years ago (mya)], with a $25 my period of stasis before the MRCA of H. horridum diversified in Lower Miocene. Another $5 my passed before H. h. exasperatum and H. h. horridum diverged, followed by $1.5 my before H. h. alvarezi and H. h. charlesbogerti separated. Heloderma suspectum reflects an even longer period of stasis ($30 my) before diversifying from its MRCA. Both H. suspectum (México) and H. h. alvarezi also revealed evidence of historic range expansion following a recent bottleneck. Our conservation phylogenetic approach emphasizes the origin and diversification of this group, yields information on the manner by which past environmental variance may have impacted its populations and, in turn, allows us to disentangle historic from contemporary impacts that might threaten its long-term persistence. The value of helodermatid conservation resides in natural services and medicinal products, particularly venom constituents, and these are only now being realized.
—The beaded lizard (Heloderma horridum) and Gila monster (H. suspectum) are large, highly venomou... more —The beaded lizard (Heloderma horridum) and Gila monster (H. suspectum) are large, highly venomous, anguimorph lizards threatened by human persecution, habitat loss and degradation , and climate change. A recent DNA-based phylogenetic analysis of helodermatids (Douglas et al. 2010. Molecular Phylogenetics and Evolution 55: 153–167) suggests that the current infraspecific taxonomy (subspecies) of beaded lizards underestimates their biodiversity, and that species status for the various subspecies is warranted. Those authors discussed " conservation phylogenetics, " which incorporates historical genetics in conservation decisions. Here, we reassess the taxonomy of beaded lizards utilizing the abovementioned molecular analysis, and incorporate morphology by performing a character mapping analysis. Furthermore, utilizing fossil-calibrated sequence divergence results, we explore beaded lizard diversification against a backdrop of the origin, diversification , and expansion of seasonally dry tropical forests (SDTFs) in Mexico and Guatemala. These forests are the primary biomes occupied by beaded lizards, and in Mesoamerica most are considered threatened, endangered, or extirpated. Pair-wise net sequence divergence (%) values were greatest between H. h. charlesbogerti and H. h. exasperatum (9.8%), and least between H. h. alvarezi and H. h. charlesbogerti (1%). The former clade represents populations that are widely separated in distribution (eastern Guatemala vs. southern Sonora, Mexico), whereas in the latter clade the populations are much closer (eastern Guatemala vs. Chiapas, Mexico). The nominate subspecies (Heloderma h. horridum) differed from the other subspecies of H. horridum at 5.4% to 7.1%. After diverging from a most-recent common ancestor ~35 mya in the Late Eocene, subsequent diversification (cladogen-esis) of beaded lizards occurred during the late Miocene (9.71 mya), followed by a lengthy stasis of up to 5 my, and further cladogenesis extended into the Pliocene and Pleistocene. In both beaded lizards and SDTFs, the tempo of evolution and diversification was uneven, and their current distributions are fragmented. Based on multiple lines of evidence, including a review of the use of trinomi-als in taxonomy, we elevate the four subspecies of beaded lizards to full species: Heloderma alvarezi (Chiapan beaded lizard), H. charlesbogerti (Guatemalan beaded lizard), H. exasperatum Río Fuerte beaded lizard), and H. horridum (Mexican beaded lizard), with no changes in their vernacular names. Finally, we propose a series of research programs and conservation recommendations. Resumen.—El escorpión (Heloderma horridum) y el monstruo de Gila (H. suspectum) son lagartijas grandes, anguimorfas, y muy venenosas que están sufriendo diversas amenazas como resultado de la persecución humana, degradación y pérdida del hábitat y el cambio climático global. Un análisis filogenético reciente basado en ADN de este grupo (Douglas et al. 2010. Molecular Phylogenetics and Evolution 55: 153–167) sugiere que la actual taxonomía intraespecífica (subespecies) del es-corpión está subestimando la diversidad biológica, y el reconocimiento de especies es justificable. Estos autores discuten la utilidad del enfoque denominado " conservación filogenética " , que hace hincapié en la incorporación de la genética histórica en las decisiones de conservación. En este estudio, reevaluamos la taxonomía del escorpión utilizando el análisis molecular antes mencionado e incorporamos la morfología en un análisis de mapeo de caracteres. Así mismo, con los resultados de la secuencia de divergencia calibrada con fósiles, se explora la diversificación del escorpión en forma yuxtapuesta al origen, la diversificación y la expansión de los bosques tropicales estacional-mente secos (SDTFs) en México y Guatemala. Estos bosques son los principales biomas ocupados por los escorpiones, y en Mesoamérica la mayoria son considerados amenazados, en peligro o
During the past quarter century, quantifying and understanding diversification of mating systems ... more During the past quarter century, quantifying and understanding diversification of mating systems in vertebrates has undergone a renaissance with the advent of DNA-based methods to ascertain parentage. In snakes, accurate parentage assignments are complicated by secretive lifestyles, sperm storage, cryptic female choice, multiple paternity, and facultative parthenogenesis. However, parentage analysis using genotypic (microsatellite) methods can resolve most of these difficulties. We employed 22 microsatellite loci to determine parentage and quantify the mating system of a population of copperhead snakes (Agkistrodon contortrix) in Connecticut, USA. From 2001 to 2003, we sampled 114 adults (56 males, 58 female) and 137 neonates (sex not determined) from known mothers. Our primary goal was to estimate opportunities for fecundity (I) selection, sexual selection (Is) and Bateman gradients (βss) for adult males and females. We also tested for association between multiple paternity and mal...
During the mating seasons (late summer and spring), male copperheads (Agkistrodon contortrix; Ser... more During the mating seasons (late summer and spring), male copperheads (Agkistrodon contortrix; Serpentes, Viperidae) engage in aggressive physical interactions for priority of access to females. These fights generally involve two individuals and are characterized by prominent vertical displays, a high degree of physical contact, and the absence of biting. Ritualized aggression does not occur in females. Although intrasexual aggression in conspecifics has obvious energetic costs (e.g., lactate accumulation) that can affect subsequent behavior, few studies have addressed these costs in reptiles, and no studies have examined snakes. Moreover, recent studies suggest psychoneuroendocrine (catecholamines, glucocorticoids) regulation of metabolism during and following aggressive episodes. There were three main questions addressed in this study. Do winners and losers of staged, pair-wise encounters show differences in post-fight (60-min) levels of plasma lactate and corticosterone (CORT)? Ar...
ABSTRACT Intentional provisioning of food and water at specific locations, commonly bird feeders ... more ABSTRACT Intentional provisioning of food and water at specific locations, commonly bird feeders and bird baths, may alter bird and mammal abundance, distribution, and recruitment; yet no studies have examined the indirect effects of resource supplementation on terrestrial reptilian mesopredators such as rattlesnakes. In the southwestern deserts of North America, anecdotal evidence suggests provisioning birds with food and water attracts rattlesnakes to exurban yards, either indirectly by increasing prey availability or directly through attraction to water. We conducted the first experimental test of this hypothesis by providing bird seed, water, or bird seed and water at 2 national monuments in Arizona, USA, and followed the responses of adult western diamond-backed rattlesnakes (Crotalus atrox) equipped with radiotransmitters, and endothermic prey species, primarily rodents, birds, and lagomorphs. We found differing responses among prey taxa to supplemental food and water provisioning: rodents showed no response to any treatment, birds responded to food treatments, and lagomorphs responded to water treatments. Overall, spatial responses by adult rattlesnakes were weak, but several subjects appeared to respond to individual treatment grids. We did not find evidence of a direct response by rattlesnakes to supplemental water. Overall, we found little support for the prevalent belief that food and water sources at provisioning stations increase local concentrations of rattlesnakes; we provide several explanations for this counter-intuitive result. 2015 The Wildlife Society.
KEY WORDS Arizona, artificial waters, birds, Crotalus atrox, lagomorph, nuisance wildlife, small mammal, resource supplementation.
Differences in resource availability and quality along environmental gradients are important infl... more Differences in resource availability and quality along environmental gradients are important influences contributing to intraspecific variation in body size, which influences numerous life-history traits. Here, we examined variation in body size and sexual size dimorphism (SSD) in relation to temperature, seasonality, and precipitation among 10 populations located throughout Arizona of the western diamondbacked rattlesnake (Crotalus atrox). Specifically, in our analyses we addressed the following questions: (i) Are adult males larger in cooler, wetter areas? (ii) Does female body size respond differently to environmental variation? (iii) Is seasonality a better predictor of body size variation? (iv) Is SSD positively correlated with increased resources? We demonstrate that male and female C. atrox are larger in body size in cooler (i.e., lower average annual maximum, minimum, and mean temperature) and wetter areas (i.e., higher average annual precipitation, more variable precipitation, and available surface water). Although SSD in C. atrox appeared to be more pronounced in cooler, wetter areas, this relationship did not achieve statistical significance.
Long-term studies of individual animals in nature contribute disproportionately to our understand... more Long-term studies of individual animals in nature contribute disproportionately to our understanding of the principles of ecology and evolution. Such field studies can benefit greatly from integrating the methods of molecular genetics with traditional approaches. Even though molecular genetic tools are particularly valuable for species that are difficult to observe directly, they have not been widely adopted. Here, we used molecular genetic techniques in a 10-year radio-telemetric investigation of the western diamond-backed rattlesnake (Crotalus atrox) for an analysis of its mating system and to measure sexual selection. Specifically, we used microsatellite markers to genotype 299 individuals, including neonates from litters of focal females to ascertain parentage using full-pedigree likelihood methods. We detected high levels of multiple paternity within litters, yet found little concordance between paternity and observations of courtship and mating behavior. Larger males did not father significantly more offspring, but we found evidence for size-specific male-mating strategies, with larger males guarding females for longer periods in the mating seasons. Moreover, the spatial proximity of males to mothers was significantly associated with reproductive success. Overall, our field observations alone would have been insufficient to quantitatively measure the mating system of this population of C. atrox, and we thus urge more widespread adoption of molecular tools by field researchers studying the mating systems and sexual selection of snakes and other secretive taxa.
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bird baths, may alter bird and mammal abundance, distribution, and recruitment; yet no studies have
examined the indirect effects of resource supplementation on terrestrial reptilian mesopredators such as
rattlesnakes. In the southwestern deserts of North America, anecdotal evidence suggests provisioning birds
with food and water attracts rattlesnakes to exurban yards, either indirectly by increasing prey availability or
directly through attraction to water. We conducted the first experimental test of this hypothesis by
providing bird seed, water, or bird seed and water at 2 national monuments in Arizona, USA, and followed
the responses of adult western diamond-backed rattlesnakes (Crotalus atrox) equipped with radiotransmitters,
and endothermic prey species, primarily rodents, birds, and lagomorphs. We found differing
responses among prey taxa to supplemental food and water provisioning: rodents showed no response to any
treatment, birds responded to food treatments, and lagomorphs responded to water treatments. Overall,
spatial responses by adult rattlesnakes were weak, but several subjects appeared to respond to individual
treatment grids. We did not find evidence of a direct response by rattlesnakes to supplemental water.
Overall, we found little support for the prevalent belief that food and water sources at provisioning stations
increase local concentrations of rattlesnakes; we provide several explanations for this counter-intuitive
result. 2015 The Wildlife Society.
KEY WORDS Arizona, artificial waters, birds, Crotalus atrox, lagomorph, nuisance wildlife, small mammal, resource
supplementation.
contributing to intraspecific variation in body size, which influences numerous life-history traits. Here,
we examined variation in body size and sexual size dimorphism (SSD) in relation to temperature, seasonality,
and precipitation among 10 populations located throughout Arizona of the western diamondbacked
rattlesnake (Crotalus atrox). Specifically, in our analyses we addressed the following questions:
(i) Are adult males larger in cooler, wetter areas? (ii) Does female body size respond differently to
environmental variation? (iii) Is seasonality a better predictor of body size variation? (iv) Is SSD positively
correlated with increased resources? We demonstrate that male and female C. atrox are larger in body
size in cooler (i.e., lower average annual maximum, minimum, and mean temperature) and wetter areas
(i.e., higher average annual precipitation, more variable precipitation, and available surface water).
Although SSD in C. atrox appeared to be more pronounced in cooler, wetter areas, this relationship did
not achieve statistical significance.
factors (temperature, precipitation, humidity), which in turn influence the timing of birth or hatching. In the
present study, we provide evidence that parturition in a large-bodied North American pitviper, the western
diamond-backed rattlesnake (Crotalus atrox), is environmentally cued. Specifically, we tested the hypothesis of
births coinciding with rainfall events during the second-half of the monsoon season (late July to mid September)
using randomization modelling. Twenty-one adult females surgically implanted with radio-transmitters were
tracked for extended periods from 2001–2010. From 2003 to 2007, the 21 females gave birth to 38 litters,
generating sufficient data to test our hypothesis. In all years, births were restricted to a 4-week period from 5
August to 7 September, which spanned between 6 and 19 days (mean ± SD, 15 ± 5.2 days). Most births (92.1%)
occurred in August. Births were significantly associated with rainfall events in 2007, although births in 2003 and
2005 occurred closer to rain events than randomly generated births for respective years. However, when birth
events across all 5 years were pooled, the model indicated a significance difference in mean rain-days versus
random rain-days. Hence, births occurred more closely to rain events than random days. Other variables associated
with monsoon events (increases in cloud cover and humidity; changes in barometric pressure) were not measured
but constitute potential cues. The present research is the first long-term, individual-based radio-telemetric study
of a snake species to investigate environmental cues related to parturition using procedures of randomization
modelling. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 866–877.
ADDITIONAL KEYWORDS: climate change – drought – ecdysis – hormones – life-history – North American
Monsoon – phenotypic plasticity – reptile – Sonoran Desert.
ecology and evolution. Such field studies can benefit greatly from integrating the methods of molecular genetics with
traditional approaches. Even though molecular genetic tools are particularly valuable for species that are difficult to observe
directly, they have not been widely adopted. Here, we used molecular genetic techniques in a 10-year radio-telemetric
investigation of the western diamond-backed rattlesnake (Crotalus atrox) for an analysis of its mating system and to
measure sexual selection. Specifically, we used microsatellite markers to genotype 299 individuals, including neonates from
litters of focal females to ascertain parentage using full-pedigree likelihood methods. We detected high levels of multiple
paternity within litters, yet found little concordance between paternity and observations of courtship and mating behavior.
Larger males did not father significantly more offspring, but we found evidence for size-specific male-mating strategies,
with larger males guarding females for longer periods in the mating seasons. Moreover, the spatial proximity of males to
mothers was significantly associated with reproductive success. Overall, our field observations alone would have been
insufficient to quantitatively measure the mating system of this population of C. atrox, and we thus urge more widespread
adoption of molecular tools by field researchers studying the mating systems and sexual selection of snakes and other
secretive taxa.
bird baths, may alter bird and mammal abundance, distribution, and recruitment; yet no studies have
examined the indirect effects of resource supplementation on terrestrial reptilian mesopredators such as
rattlesnakes. In the southwestern deserts of North America, anecdotal evidence suggests provisioning birds
with food and water attracts rattlesnakes to exurban yards, either indirectly by increasing prey availability or
directly through attraction to water. We conducted the first experimental test of this hypothesis by
providing bird seed, water, or bird seed and water at 2 national monuments in Arizona, USA, and followed
the responses of adult western diamond-backed rattlesnakes (Crotalus atrox) equipped with radiotransmitters,
and endothermic prey species, primarily rodents, birds, and lagomorphs. We found differing
responses among prey taxa to supplemental food and water provisioning: rodents showed no response to any
treatment, birds responded to food treatments, and lagomorphs responded to water treatments. Overall,
spatial responses by adult rattlesnakes were weak, but several subjects appeared to respond to individual
treatment grids. We did not find evidence of a direct response by rattlesnakes to supplemental water.
Overall, we found little support for the prevalent belief that food and water sources at provisioning stations
increase local concentrations of rattlesnakes; we provide several explanations for this counter-intuitive
result. 2015 The Wildlife Society.
KEY WORDS Arizona, artificial waters, birds, Crotalus atrox, lagomorph, nuisance wildlife, small mammal, resource
supplementation.
contributing to intraspecific variation in body size, which influences numerous life-history traits. Here,
we examined variation in body size and sexual size dimorphism (SSD) in relation to temperature, seasonality,
and precipitation among 10 populations located throughout Arizona of the western diamondbacked
rattlesnake (Crotalus atrox). Specifically, in our analyses we addressed the following questions:
(i) Are adult males larger in cooler, wetter areas? (ii) Does female body size respond differently to
environmental variation? (iii) Is seasonality a better predictor of body size variation? (iv) Is SSD positively
correlated with increased resources? We demonstrate that male and female C. atrox are larger in body
size in cooler (i.e., lower average annual maximum, minimum, and mean temperature) and wetter areas
(i.e., higher average annual precipitation, more variable precipitation, and available surface water).
Although SSD in C. atrox appeared to be more pronounced in cooler, wetter areas, this relationship did
not achieve statistical significance.
factors (temperature, precipitation, humidity), which in turn influence the timing of birth or hatching. In the
present study, we provide evidence that parturition in a large-bodied North American pitviper, the western
diamond-backed rattlesnake (Crotalus atrox), is environmentally cued. Specifically, we tested the hypothesis of
births coinciding with rainfall events during the second-half of the monsoon season (late July to mid September)
using randomization modelling. Twenty-one adult females surgically implanted with radio-transmitters were
tracked for extended periods from 2001–2010. From 2003 to 2007, the 21 females gave birth to 38 litters,
generating sufficient data to test our hypothesis. In all years, births were restricted to a 4-week period from 5
August to 7 September, which spanned between 6 and 19 days (mean ± SD, 15 ± 5.2 days). Most births (92.1%)
occurred in August. Births were significantly associated with rainfall events in 2007, although births in 2003 and
2005 occurred closer to rain events than randomly generated births for respective years. However, when birth
events across all 5 years were pooled, the model indicated a significance difference in mean rain-days versus
random rain-days. Hence, births occurred more closely to rain events than random days. Other variables associated
with monsoon events (increases in cloud cover and humidity; changes in barometric pressure) were not measured
but constitute potential cues. The present research is the first long-term, individual-based radio-telemetric study
of a snake species to investigate environmental cues related to parturition using procedures of randomization
modelling. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 866–877.
ADDITIONAL KEYWORDS: climate change – drought – ecdysis – hormones – life-history – North American
Monsoon – phenotypic plasticity – reptile – Sonoran Desert.
ecology and evolution. Such field studies can benefit greatly from integrating the methods of molecular genetics with
traditional approaches. Even though molecular genetic tools are particularly valuable for species that are difficult to observe
directly, they have not been widely adopted. Here, we used molecular genetic techniques in a 10-year radio-telemetric
investigation of the western diamond-backed rattlesnake (Crotalus atrox) for an analysis of its mating system and to
measure sexual selection. Specifically, we used microsatellite markers to genotype 299 individuals, including neonates from
litters of focal females to ascertain parentage using full-pedigree likelihood methods. We detected high levels of multiple
paternity within litters, yet found little concordance between paternity and observations of courtship and mating behavior.
Larger males did not father significantly more offspring, but we found evidence for size-specific male-mating strategies,
with larger males guarding females for longer periods in the mating seasons. Moreover, the spatial proximity of males to
mothers was significantly associated with reproductive success. Overall, our field observations alone would have been
insufficient to quantitatively measure the mating system of this population of C. atrox, and we thus urge more widespread
adoption of molecular tools by field researchers studying the mating systems and sexual selection of snakes and other
secretive taxa.