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146 results for “rattlesnake”
FIGURE 8 in Accessing cryptic diversity in Neotropical rattlesnakes (Serpentes: Viperidae: Crotalus) with the description of two new species
FIGURE 8. Crotalus ehecatl in life, (A) ECO-CH-H 3778, holotype from San José Tintonishac, Las Margaritas, Chiapas; (B) adult specimen from Tuxtla Gutiérrez, Chiapas; (C) UTA-R 51456, adult male from Santa Inés, Santa María Chimalapa, Oaxaca; (D) neonate specimen from Santa María Mixtequilla, Oaxaca; (E) neonate specimen from San Pedro Tapanatepec, Oaxaca; (F) adult specimen from San Pedro Totolápam, Oaxaca. Photos by J.A. Hidalgo García (A), E.B. Jiménez Díaz (B), E.N. Smith courtesy of J.A. Campbell (C), I.T. Ahumada Carrillo (D), HERP.MX (E), and F. Martínez Belmar (F).
FIGURE 5 in Accessing cryptic diversity in Neotropical rattlesnakes (Serpentes: Viperidae: Crotalus) with the description of two new species
FIGURE 5. Dorsal and lateral view of the head of the holotype of Crotalus mictlantecuhtli (SDNHM 22416).
FIGURE 3 in Accessing cryptic diversity in Neotropical rattlesnakes (Serpentes: Viperidae: Crotalus) with the description of two new species
FIGURE 3. (A), Results of the principal component analyses between the members of the Crotalus durissus species complex with 95% confidence regions. PC1 and PC2 together explain 33.4% of the total variance. (B), Reanalysis including only members of norhten clade (Crotalus culminatus); (C), members of southern clade (Crotalus durissus) with morphological data available. (D), Bivariate plots with 95% confidence regions for the first two axes derived from scores of discriminant analyses for members of Crotalus durissus species complex.
FIGURE 1 in Accessing cryptic diversity in Neotropical rattlesnakes (Serpentes: Viperidae: Crotalus) with the description of two new species
FIGURE 1. (A) Maximum-likelihood phylogram of the four genes (cyt b, ND4, ND2, c-mos, 2596 bp) analysis (-ln L=- 17,270.83). Tip labels are as follows: 3-letter subspecies code for the Crotalus durissus species complex, following Campbell & Lamar (2004), locality and haplotypes in parentheses, see Appendix 1. Numbers along branches indicate bootstrap support-ML and Bayesian posterior probability. For clarity, support is only shown for important nodes. (B) Maximum-likelihood phylogram of the four genes (cyt b, ND4, ND2, c-mos, 2596 bp) analysis (-ln L=-17,270.83). Tip labels are as follows: 3-letter subspecies code for the Crotalus molossus species complex and outgroups, following Campbell & Lamar (2004) and Anderson & Greenbaum (2012), locality and haplotypes in parentheses, see Appendix 1. Numbers along branches indicate bootstrap support-ML and Bayesian posterior probability. For clarity, support is only shown for important nodes.
Data from: The molecular basis of venom resistance in a rattlesnake-squirrel predator-prey system
Understanding how interspecific interactions mould the molecular basis of adaptations in coevolving species is a long-sought goal of evolutionary biology. Venom in predators and venom resistance proteins in prey are coevolving molecular phenotypes, and while venoms are highly complex mixtures it is unclear if prey respond with equally complex resistance traits. Here we use a novel molecular methodology based on protein affinity columns to capture and identify candidate blood serum resistance proteins ('Venom Interactive Proteins' – VIPs) in California Ground Squirrels (Otospermophilus beecheyi) that interact with venom proteins from their main predator, Northern Pacific Rattlesnakes (Crotalus o. oreganus). This assay showed that serum-based resistance is both population- and species-specific, with serum proteins from ground squirrels showing higher binding affinities for venom proteins of local snakes compared to allopatric individuals. Venom protein specificity assays identified numerous and diverse candidate prey resistance VIPs but also potential targets of venom in prey tissues. Many specific VIPs bind to multiple snake venom proteins and, conversely, single venom proteins bind multiple VIPs, demonstrating that a portion of the squirrel blood serum "resistome" involves broad-based inhibition of non-self proteins and suggests that resistance involves a toxin scavenging mechanism. Analyses of rates of evolution of VIP protein homologs in related mammals show that most of these proteins evolve under purifying selection possibly due to molecular constraints that limit the evolutionary responses of prey to rapidly evolving snake venom proteins. Our method represents a general approach to identify specific proteins involved in coevolutionary interactions between species at the molecular level.
Data from: Genotyping-in-Thousands by sequencing reveals marked population structure in Western Rattlesnakes to inform conservation status
<p>Delineation of units below the species level is critical for prioritizing conservation actions for species at-risk. Genetic studies play an important role in characterizing patterns of population connectivity and diversity to inform the designation of conservation units, especially for populations that are geographically isolated. The northernmost range margin of Western Rattlesnakes (<em>Crotalus oreganus</em>) occurs in British Columbia, Canada, where it is federally classified as threatened and restricted to five geographic regions. In these areas, Western Rattlesnakes hibernate (den) communally, raising questions about connectivity within and between den complexes. At present, Western Rattlesnake conservation efforts are hindered by a complete lack of information on genetic structure and degree of isolation at multiple scales, from the den to the regional level. To fill this knowledge gap, we used Genotyping-in-Thousands by sequencing (GT-seq) to genotype an optimized panel of 362 single nucleotide polymorphisms (SNPs) from individual samples (n = 461) collected across the snake's distribution in western Canada and neighboring Washington (USA). Hierarchical STRUCTURE analyses found evidence for population structure within and among the five geographic regions in BC, as well as in Washington. Within these regions, 11 genetically distinct complexes of dens were identified, with some regions having multiple complexes. No significant pattern of isolation-by-distance and generally low levels of migration were detected among den complexes across regions. Additionally, snakes within dens generally were more related than those among den complexes within a region, indicating limited movement. Overall, our results suggest that the single, recognized designatable unit for Western Rattlesnakes in Canada should be re-assessed to proactively focus conservation efforts on preserving total genetic variation detected range wide. More broadly, our study demonstrates a novel application of GT-seq for investigating patterns of diversity in wild populations at multiple scales to better inform conservation management.</p>
Data from: Limitations of climate data for inferring species boundaries: insights from speckled rattlesnakes
Phenotypes, DNA, and measures of ecological differences are widely used in species delimitation. Although rarely defined in such studies, ecological divergence is almost always approximated using multivariate climatic data associated with sets of specimens (i.e., the "climatic niche"); the justification for this approach is that species-specific climatic envelopes act as surrogates for physiological tolerances. Using identical statistical procedures, we evaluated the usefulness and validity of the climate-as-proxy assumption by comparing performance of genetic (nDNA SNPs and mitochondrial DNA), phenotypic, and climatic data for objective species delimitation in the speckled rattlesnake (Crotalus mitchellii) complex. Ordination and clustering patterns were largely congruent among intrinsic (heritable) traits (nDNA, mtDNA, phenotype), and discordance is explained by biological processes (e.g., ontogeny, hybridization). In contrast, climatic data did not produce biologically meaningful clusters that were congruent with any intrinsic dataset, but rather corresponded to regional differences in atmospheric circulation and climate, indicating an absence of inherent taxonomic signal in these data. Surrogating climate for physiological tolerances adds artificial weight to evidence of species boundaries, as these data are irrelevant for that purpose. Based on the evidence from congruent clustering of intrinsic datasets, we recommend that three subspecies of C. mitchellii be recognized as species: C. angelensis, C. mitchellii, and C. Pyrrhus.
Data from: Seed ingestion and germination in rattlesnakes: overlooked agents of rescue and secondary dispersal
Seed dispersal is a key evolutionary process and a central theme in the population ecology of terrestrial plants. The primary producers of most land-based ecosystems are propagated by and maintained through various mechanisms of seed dispersal that involve both abiotic and biotic modes of transportation. By far the most common biotic seed transport mechanism is zoochory, whereby seeds, or fruits containing them, are dispersed through the activities of animals. Rodents are one group of mammals that commonly prey on seeds (granivores) and play a critical, often destructive, role in primary dispersal and the dynamics of plant communities. In North America, geomyid, heteromyid and some sciurid rodents have specialized cheek pouches for transporting seeds from plant source to larder, where they are often eliminated from the pool of plant propagules by consumption. These seed-laden rodents are commonly consumed by snakes as they forage, but unlike raptors, coyotes, bobcats, and other endothermic predators which eat rodents and are known or implicated to be secondary seed dispersers, the role of snakes in seed dispersal remains unexplored. Here, using museum-preserved specimens, we show that in nature three desert-dwelling rattlesnake species consumed heteromyids with seeds in their cheek pouches. By examining the entire gut we discovered, furthermore, that secondarily ingested seeds can germinate in rattlesnake colons. In terms of secondary dispersal, rattlesnakes are best described as diplochorous. Because seed rescue and secondary dispersal in snakes has yet to be investigated, and because numerous other snake species consume granivorous and frugivorous birds and mammals, our observations offer direction for further empirical studies of this unusual but potentially important channel for seed dispersal.
Data from: When one phenotype is not enough - divergent evolutionary trajectories govern venom variation in a widespread rattlesnake species
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 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 geographic 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 environmental factors, suggesting that different selective pressures can act on individual loci independently of their co-expression patterns or genomic proximity. Our results challenge common assumptions about diet composition as the key selective driver of snake venom evolution and emphasise how the interplay between genomic architecture and local-scale spatial heterogeneity in selective pressures may facilitate the retention of adaptive functional polymorphisms across a continuous space.
Data from: Phenotypic integration in the feeding system of the eastern diamondback rattlesnake (Crotalus adamanteus)
Selection can vary geographically across environments and temporally over the lifetime of an individual. Unlike geographic contexts, where different selective regimes can act on different alleles, age-specific selection is constrained to act on the same genome by altering age-specific expression. Snake venoms are exceptional traits for studying ontogeny because toxin expression variation directly changes the phenotype; relative amounts of venom components determine, in part, venom efficacy. Phenotypic integration is the dependent relationship between different traits that collectively produce a complex phenotype and, in venomous snakes, may include traits as diverse as venom, head shape and fang length. We examined the feeding system of the eastern diamondback rattlesnake (Crotalus adamanteus) across environments and over the lifetime of individuals and used a genotype–phenotype map approach, protein expression data and morphological data to demonstrate that: (i) ontogenetic effects explained more of the variation in toxin expression variation than geographic effects, (ii) both juveniles and adults varied geographically, (iii) toxin expression variation was a result of directional selection and (iv) different venom phenotypes covaried with morphological traits also associated with feeding in temporal (ontogenetic) and geographic (functional) contexts. These data are the first to demonstrate, to our knowledge, phenotypic integration between multiple morphological characters and a biochemical phenotype across populations and age classes. We identified copy number variation as the mechanism driving the difference in the venom phenotype associated with these morphological differences, and the parallel mitochondrial, venom and morphological divergence between northern and southern clades suggests that each clade may warrant classification as a separate evolutionarily significant unit.
Microevolutionary change in mimicry? Erosion of rattling behaviour among nonvenomous snakes on islands lacking rattlesnakes
Batesian mimics––harmless species that converge on the warning signals of a dangerous species––are spectacular examples of adaptation, but few documented cases involve acoustic signals. Even fewer studies have documented microevolutionary change in mimicry of any kind. Here, we describe potential evolutionary change in acoustic mimicry. Many nonvenomous snakes vibrate their tail tip when threatened, making a sound resembling a venomous rattlesnake. When we compared this behaviour between gopher snakes from mainland California where rattlesnakes are present versus nearby derived island populations where rattlesnakes are absent, we found that island snakes vibrated their tail for a shorter duration. Thus, defensive tail vibration may be acoustic mimicry of rattlesnakes that is undergoing erosion in an area lacking rattlesnakes, providing evidence of possible microevolutionary change in mimicry.
Rattlesnake
[1923.06.0165](http://collections.smvk.se/carlotta-vkm/web/object/101305) figurefigure; sculpturesculpture; rattlesnake; snake, Azteker Source: Objaverse 1.0 / Sketchfab
Variation in behavior drives multiscale responses to habitat conditions in timber rattlesnakes (Crotalus horridus)
<p>Variations in both the behavior of wildlife and the scale at which the environment most influences the space use of wild animals (i.e., scale of effect) are critical, but often overlooked in habitat selection modeling. Ecologists have proposed that biological responses happening over longer time frames are influenced by environmental variables at larger spatial scales, but this has rarely been empirically tested. Here, we hypothesized that long-term patterns of behavior (i.e., lasting multiple weeks to months) would be associated with larger scales of effect than more sporadic behaviors. We predicted site use by 43 radio-telemetered timber rattlesnakes (<i>Crotalus horridus</i>) exhibiting four distinct, time-varying behaviors (foraging, digestion, ecdysis, and gestation) using remotely-sensed environmental variables related to forest structure and landscape topography. Among sites used by snakes, warmer temperatures and higher levels of forest disturbance were predictive of behaviors dependent on thermoregulation including gestation and ecdysis while more moderate temperatures and drier, more oak-dominated sites were predictive of foraging. Long-term behaviors were associated with larger spatial scales across most variables, supporting our hypothesis that the scale at which habitat selection occurs is linked to the temporal scale of relevant behaviors. Management recommendations based on single-scale models of habitat use that do not account for fine-scale variations in behavior may obscure the importance of potentially limiting habitat features needed for infrequent behaviors that are important for growth and reproduction of this and related species.</p>
Western Diamondback Rattlesnake interaction matrices for network analysis
<p>Social network ecology is a powerful framework to assess patterns of interconnectedness and identify group-level interactions. We investigated social network structure in a pitviper (<em>Crotalus atrox</em>) to determine if group-level interactions result in network structures for denning, pairing, and parentage. We tested if network centrality was influenced by body length, sex, home range size/location, or generic relatedness. We revealed that networks were structurally modular but not nested. Sex was the only significant predictor of centrality in the parentage network, likely due to high levels of multiple paternity. Genotypic data revealed interacting focal individuals were unlikely to be related in networks; however, analysis of a larger group of subjects suggests kin-association at communal dens. Den selection may be driven by a combination of social preference, experience, and/or genetic relatedness. We demonstrated strong fission-fusion dynamics connected to annual migrations to summer home ranges and use of communal winter dens. Furthermore, both sexes show high fidelity to home ranges and dens, but females occasionally alter den sites, indicating active manipulation of their social environment. Our study illustrates that comprehensive, long-term datasets incorporating social network analysis with spatial and genetic information provide robust and unique insights to understanding social structure of understudied, cryptic taxa.</p>
Evidence that genomic incompatibilities and other multilocus processes impact hybrid fitness in a rattlesnake hybrid zone
<p>Hybrid zones provide valuable opportunities to understand the genomic mechanisms that promote speciation by providing insight into factors involved in intermediate stages of speciation. Here we investigate introgression in a hybrid zone between two rattlesnake species (<em>Crotalus viridis</em> and <em>C. oreganus concolor</em>) that have undergone historical allopatric divergence and recent range expansion and secondary contact. We use Bayesian genomic cline models to characterize genomic patterns of introgression between these lineages and identify loci potentially subject to selection in hybrids. We find evidence for a large number of genomic regions with biased ancestry that deviate from the genomic background in hybrids (i.e., excess ancestry loci), which tend to be associated with genomic regions with higher recombination rates. We also identify suites of excess ancestry loci that show highly correlated allele frequencies (including conspecific and heterospecific combinations) across physically unlinked genomic regions in hybrids. Our findings provide evidence for multiple multilocus evolutionary processes impacting hybrid fitness in this system.</p>
Figure 8 in The Origin and Evolution of the Rattlesnake Rattle: Misdirection, Clarification, Theory, and Progress
Figure 8. Multi-modal aposematic threat display by an iconic rattlesnake species of the Southwest. An adult Crotalus atrox in a typical raised posture. In addition to postural signals, such displays incorporate sound (rattling and hissing), other visual signals (tongue arching, stark black and white tail banding), and overt intimidation (mock strikes). Together these signals comprise an integrated deterrent (warning) system. Photo by Martin J. Feldner.
Figure 7 in The Origin and Evolution of the Rattlesnake Rattle: Misdirection, Clarification, Theory, and Progress
Figure 7. Unbroken sequence of evolutionary stages in rattle development illustrating the caudal luring hypothesis (CLH) of the rattle's origin. We partitioned this evolutionary sequence into six conceptual stages to emphasize possible transitions of selective influences on the incipient rattle organ system. Mimicry dominated the incipient stages (stages 1–3), which first resulted in terminal scale enlargement, followed by constriction of the end scale. Mimetic selective forces (Box 1) increased the tail's resemblance to a cephalized, segmented invertebrate, which also brought about changes in the generative tissue (matrix) and its bony substratum at the apex of the tail. In our opinion, the major evolutionary transition occurred between stages 3 and 4, when a bi- or tri-lobed end-cap, which was formerly shed during molts, gained a clasping configuration and a position shifting developmental process by which a new proximal lobe was added anterior to the old proximal lobe from the previous ecdysis (see Meik and Schuett, this volume, Rattle Evo-Devo). This innovation would have opened the door for sound production. Subsequently, with the advent of specialized rapid tail movements and changes in behavior, the aposematic role of this organ system became the dominant selective influence (stage 5). Based on multiple lines of evidence, we suggest that early rattlesnakes had small, relatively quiet rattles which could be deployed for only short durations (e.g., Sistrurus miliarius). Once aposematic sound production was achieved, certain lineages evolved hyper-aposematic, multi-modal displays (stage 6) involving increased body size (formidability), large rattles and hissing (acoustic), bold defensive postures (behavioral), starkly banded tails (black and white), larger quantities of venom per bite, and perhaps in some cases increased toxicity (Figure 8). In reference to a purely aposematic hypothesis to account for the origin of the rattle, this model fills major theoretical gaps in selective regimes present and acting on the early proto-rattle and incipient rattle. Namely, it adds stages 2 and 3, which provide an explanation for early and important morphological changes that must have required evolutionary tinkering. The transition (gradient) in selection (mimetic to aposematic) advantage appears to be complete in derived rattlesnakes (e.g., C. atrox), but is incomplete in those species that still employ caudal luring (Figures 2–4), most of which are small as adults and have limited and less dramatic aposematic repertoires (see Eberhard, 2011).
Figure 6 in The Origin and Evolution of the Rattlesnake Rattle: Misdirection, Clarification, Theory, and Progress
Figure 6. Species of vertebrates that show prey-luring. a) Painted Frogfish (Antennarius pictus). b) Alligator Snapping Turtle (Macroclemmys sp.). c) Tasselled Wobbegong (Eucrossorhinus dasypogon). d) Cottonmouth (Agkistrodon piscivorus).
Figure 5 in The Origin and Evolution of the Rattlesnake Rattle: Misdirection, Clarification, Theory, and Progress
Figure 5. Differences between values for respiratory activity of midbody and tail muscle reported by Moon (2001). VO 2 = rate of oxygen consumption, sdh = succinic dehydrogenase, and co = cytochrome oxidase (change in optical density). Moon (2001) reported raw values that were perhaps not intuitive to reviewers, and asserted that Agkistrodon contortrix displayed muscle oxidative capacities intermediate between tail-rattling colubrids (Coluber constrictor) and rattlesnakes (Sistrurus miliarius and Crotalus horridus). Plotting differences between mid-body and tail muscle measurements leads to a revised conclusion. Error bars = SD calculated as the square root of the sum of variances. The crosshatched bar is reported here as a positive number, but would have been negative as reported by Moon (a possible transposition).
Figure 4 in The Origin and Evolution of the Rattlesnake Rattle: Misdirection, Clarification, Theory, and Progress
Figure 4. Species of rattlesnakes that hunt by caudal luring. a) Newborn Ridgenose Rattlesnakes (Crotalus willardi) with their putative mother, from Arizona. Note that the tail is off-white. See paper by Schuett et al. (1984). Photo by Brendan O'Connor. b) A newborn Rock Rattlesnake (Crotalus lepidus), from Arizona. Note the bright yellow tail. See paper by Kauffeld (1943). Photo by Martin J. Feldner.
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