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Christopher Blair - One of the best experts on this subject based on the ideXlab platform.
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the effects of climate and demographic history in shaping genomic variation across populations of the desert horned lizard Phrynosoma platyrhinos
Molecular Ecology, 2021Co-Authors: Keaka Farleigh, Sarah A Vladimirova, Christopher Blair, Jason T Bracken, Nazila Koochekian, Drew R Schield, Daren C CardAbstract:Species often experience spatial environmental heterogeneity across their range, and populations may exhibit signatures of adaptation to local environmental characteristics. Other population genetic processes, such as migration and genetic drift, can impede the effects of local adaptation. Genetic drift in particular can have a pronounced effect on population genetic structure during large-scale geographic expansions, where a series of founder effects leads to decreases in genetic variation in the direction of the expansion. Here, we explore the genetic diversity of a desert lizard that occupies a wide range of environmental conditions and that has experienced post-glacial expansion northwards along two colonization routes. Based on our analyses of a large SNP data set, we find evidence that both climate and demographic history have shaped the genetic structure of populations. Pronounced genetic differentiation was evident between populations occupying cold versus hot deserts, and we detected numerous loci with significant associations with climate. The genetic signal of founder effects, however, is still present in the genomes of the recently expanded populations, which comprise subsets of genetic variation found in the southern populations.
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cryptic diversity and discordance in single locus species delimitation methods within horned lizards Phrynosomatidae Phrynosoma
Molecular Ecology Resources, 2017Co-Authors: Christopher Blair, Robert W BrysonAbstract:Biodiversity reduction and loss continues to progress at an alarming rate, and thus, there is widespread interest in utilizing rapid and efficient methods for quantifying and delimiting taxonomic diversity. Single-locus species delimitation methods have become popular, in part due to the adoption of the DNA barcoding paradigm. These techniques can be broadly classified into tree-based and distance-based methods depending on whether species are delimited based on a constructed genealogy. Although the relative performance of these methods has been tested repeatedly with simulations, additional studies are needed to assess congruence with empirical data. We compiled a large data set of mitochondrial ND4 sequences from horned lizards (Phrynosoma) to elucidate congruence using four tree-based (single-threshold GMYC, multiple-threshold GMYC, bPTP, mPTP) and one distance-based (ABGD) species delimitation models. We were particularly interested in cases with highly uneven sampling and/or large differences in intraspecific diversity. Results showed a high degree of discordance among methods, with multiple-threshold GMYC and bPTP suggesting an unrealistically high number of species (29 and 26 species within the P. douglasii complex alone). The single-threshold GMYC model was the most conservative, likely a result of difficulty in locating the inflection point in the genealogies. mPTP and ABGD appeared to be the most stable across sampling regimes and suggested the presence of additional cryptic species that warrant further investigation. These results suggest that the mPTP model may be preferable in empirical data sets with highly uneven sampling or large differences in effective population sizes of species.
Wade C Sherbrooke - One of the best experts on this subject based on the ideXlab platform.
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Choosing between a rock and a hard place: Camouflage in the round-tailed horned lizard Phrynosoma modestum
Oxford University Press, 2012Co-Authors: William E. Cooper, Wade C SherbrookeAbstract:The round-tailed horned lizard Phrynosoma modestum is cryptically colored and resembles a small stone when it draws legs close to its body and elevates its back. We investigated effectiveness of camouflage in P. modestum and its dependence on stones by placing a lizard in one of two microhabitats (uniform sand or sand with surface rocks approximately the same size as lizards). An observer who knew which microhabitat contained the lizard was asked to locate the lizard visually. Latency to detection was longer and probability of no detection within 60 s was higher for lizards on rock background than on bare sand. In arenas where lizards could choose to occupy rock or bare sand, much higher proportions selected rocky backgrounds throughout the day; at night all lizards slept among stones. A unique posture gives P. modestum a rounded appearance similar to many natural stones. Lizards occasionally adopted the posture, but none did so in response to a nearby experimenter. Stimuli that elicit the posture are unknown. That P. modestum is better camouflaged among rocks than on bare sand and prefers to occupy rocky areas suggests that special resemblance to rocks (masquerade) enhances camouflage attributable to coloration and immobility [Current Zoology 58 (4): 541–548, 2012]
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crypsis influences escape decisions in the round tailed horned lizard Phrynosoma modestum
Canadian Journal of Zoology, 2010Co-Authors: Wade C Sherbrooke, William E. CooperAbstract:Flight initiation distance (predator–prey distance when escape begins) increases as predation risk increases. Prey should have longer flight initiation distance when their background, movement, or current posture reduces crypsis. Flight initiation distance of ectotherms may increase at lower body temperature to compensate for slower running speed. However, for cryptic prey, fleeing might increase the probability of being detected. The Round-tailed Horned Lizard (Phrynosoma modestum Girard, 1852) is eucryptic and resembles small stones. We predicted that flight initiation distance by P. modestum is shorter among stones than on uniform sand. Because movement and upright posture disrupt crypsis, we predicted that flight initiation distance is greater after movement and when standing than when still and lying on the ground. As predicted, flight initiation distances were shorter on a rocky than sandy area, when lying flat than standing, and while immobile than after moving. We measured running speed and flight...
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Functional morphology of scale hinges used to transport water: convergent drinking adaptations in desert lizards (Moloch horridus and Phrynosoma cornutum)
Zoomorphology, 2007Co-Authors: Wade C Sherbrooke, Andrew J. Scardino, Rocky Nys, Lin SchwarzkopfAbstract:The Australian thorny devil, Moloch horridus Gray, 1841, and the Texas horned lizard, Phrynosoma cornutum Harlan, 1825, have the remarkable ability to rapidly move water through interscalar spaces on their skin’s surface to their mouth for drinking. The morphology of these scale hinges has not been studied. We used histological and SEM techniques to examine and compare the scale hinges of both species. Additional taxa in their respective lineages were examined in order to evaluate the potential that convergent evolution has occurred. In the two species that transport water, each scale hinge has a basally expanded and semi-enclosed channel formed by the hinge joint that is interconnected with all scale hinges on the body. We hypothesize that it is within this semi-tubular channel system of hinge joints, where the β-layer keratin of the integument is very thin, that water is transported. Hinge joint walls are covered by a complex topography of fractured surfaces that greatly expand the channel’s surface area and probably enhance capillary transport of water. In addition, we note differing morphology of scale surfaces at the rear of the jaws of both species. We hypothesize that capillary forces fill the scale-hinge system and additional forces, generated within the mouth by observed motions during drinking, depress local water-pressure to pull water through the channels of the hinge-joint system. We conclude that the combined features in the two species, semi-tubular hinge-joint channels with convoluted walls and a jaw-buccal cavity pumping-mechanism, have convergently evolved for capture, transport, and drinking of water from sporadic rainfall.
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Responses of Kit Foxes (Vulpes macrotis) to Antipredator Blood-Squirting and Blood of Texas Horned Lizards (Phrynosoma cornutum)
Copeia, 2004Co-Authors: Wade C Sherbrooke, George MiddendorfAbstract:Abstract Six related studies were conducted with four captive juvenile Kit Foxes (Vulpes macrotis) to test the hypothesis that blood-squirting from eye-socket tissues by Texas Horned Lizards (Phrynosoma cornutum) is a canid antipredator defense. In 16 trials, naive “hungry” foxes killed and ate adult Yarrow's Spiny Lizards (Sceloporus jarrovii; eight of eight trials) slightly more frequently than adult P. cornutum (six of eight trials). Adverse responses by foxes (head shaking) were seen in five of six trials in which Phrynosoma squirted blood. Later these experienced foxes, fed ad libitum, killed and ate mice (eight of eight trials) while largely ignoring P. cornutum (one killed and eaten in eight trials), suggesting a learned aversion to horned lizards as prey. During attacks on mice smeared with horned-lizard blood, foxes displayed behaviors typical of predatory encounters with horned lizard prey (head shaking and prey tearing). These prey-handling behaviors were in striking contrast to those elicited ...
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integumental water movement and rate of water ingestion during rain harvesting in the texas horned lizard Phrynosoma cornutum
Amphibia-reptilia, 2004Co-Authors: Wade C SherbrookeAbstract:Capture of rainfall on skin surfaces and its transport via capillary channels between scales to the mouth for drinking has been documented in a few agamid ( Moloch and Phrynocephalus ) and iguanid ( Phrynosoma spp.) lizards. Associated behaviors include a postural stance and jaw motions. This experimental study documents that rate of jaw opening and closing cycles is positively correlated with rate of water delivery to lizards' backs and to gain in mass of lizards attributable to drinking. The mean mass of water that can be held by the interscalar, capillary-flow system is correlated with body size, smaller lizards holding a larger percentage of their body mass in the rain-harvesting system. Ingestion mechanisms for water flow from the integumental channels to the mouth surfaces for drinking are discussed, with note being made of the possible roles of a fold of skin at the jaw angle (at the postlabial scales) and tongue actions. Recent hatchlings exhibit rain-harvesting behavior, suggesting its innate nature.
Robert W Bryson - One of the best experts on this subject based on the ideXlab platform.
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cryptic diversity and discordance in single locus species delimitation methods within horned lizards Phrynosomatidae Phrynosoma
Molecular Ecology Resources, 2017Co-Authors: Christopher Blair, Robert W BrysonAbstract:Biodiversity reduction and loss continues to progress at an alarming rate, and thus, there is widespread interest in utilizing rapid and efficient methods for quantifying and delimiting taxonomic diversity. Single-locus species delimitation methods have become popular, in part due to the adoption of the DNA barcoding paradigm. These techniques can be broadly classified into tree-based and distance-based methods depending on whether species are delimited based on a constructed genealogy. Although the relative performance of these methods has been tested repeatedly with simulations, additional studies are needed to assess congruence with empirical data. We compiled a large data set of mitochondrial ND4 sequences from horned lizards (Phrynosoma) to elucidate congruence using four tree-based (single-threshold GMYC, multiple-threshold GMYC, bPTP, mPTP) and one distance-based (ABGD) species delimitation models. We were particularly interested in cases with highly uneven sampling and/or large differences in intraspecific diversity. Results showed a high degree of discordance among methods, with multiple-threshold GMYC and bPTP suggesting an unrealistically high number of species (29 and 26 species within the P. douglasii complex alone). The single-threshold GMYC model was the most conservative, likely a result of difficulty in locating the inflection point in the genealogies. mPTP and ABGD appeared to be the most stable across sampling regimes and suggested the presence of additional cryptic species that warrant further investigation. These results suggest that the mPTP model may be preferable in empirical data sets with highly uneven sampling or large differences in effective population sizes of species.
Kevin V Young - One of the best experts on this subject based on the ideXlab platform.
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a hierarchical model for spatial capture recapture data
Ecology, 2008Co-Authors: Andrew J Royle, Kevin V YoungAbstract:Estimating density is a fundamental objective of many animal population studies. Application of methods for estimating population size from ostensibly closed populations is widespread, but ineffective for estimating absolute density because most populations are subject to short-term movements or so-called temporary emigration. This phenomenon invalidates the resulting estimates because the effective sample area is unknown. A number of methods involving the adjustment of estimates based on heuristic considerations are in widespread use. In this paper, a hierarchical model of spatially indexed capture–recapture data is proposed for sampling based on area searches of spatial sample units subject to uniform sampling intensity. The hierarchical model contains explicit models for the distribution of individuals and their movements, in addition to an observation model that is conditional on the location of individuals during sampling. Bayesian analysis of the hierarchical model is achieved by the use of data augmentation, which allows for a straightforward implementation in the freely available software WinBUGS. We present results of a simulation study that was carried out to evaluate the operating characteristics of the Bayesian estimator under variable densities and movement patterns of individuals. An application of the model is presented for survey data on the flat-tailed horned lizard (Phrynosoma mcallii) in Arizona, USA.
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How the horned lizard got its horns
2004Co-Authors: Kevin V Young, Edmund D. BrodieAbstract:Many descriptions of evolutionary adapta-tions are criticized as “just-so stories ” (1) that are based more on intuition than on direct tests of adaptive hypotheses. The elaborate crowns of horns possessed by many species of horned lizards (genus Phrynosoma) are classic examples of intuitively adaptive fea-tures that lack direct tests of function. The bony horns that give horned lizards their name are presumed to function as a defense against predators (Fig. 1B). Here we present data from the wild showing that natural se-lection by loggerhead shrikes favors longer horns (fig. S1) in the flat-tailed horned lizard (Phrynosoma mcalli)
Daren C Card - One of the best experts on this subject based on the ideXlab platform.
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the effects of climate and demographic history in shaping genomic variation across populations of the desert horned lizard Phrynosoma platyrhinos
Molecular Ecology, 2021Co-Authors: Keaka Farleigh, Sarah A Vladimirova, Christopher Blair, Jason T Bracken, Nazila Koochekian, Drew R Schield, Daren C CardAbstract:Species often experience spatial environmental heterogeneity across their range, and populations may exhibit signatures of adaptation to local environmental characteristics. Other population genetic processes, such as migration and genetic drift, can impede the effects of local adaptation. Genetic drift in particular can have a pronounced effect on population genetic structure during large-scale geographic expansions, where a series of founder effects leads to decreases in genetic variation in the direction of the expansion. Here, we explore the genetic diversity of a desert lizard that occupies a wide range of environmental conditions and that has experienced post-glacial expansion northwards along two colonization routes. Based on our analyses of a large SNP data set, we find evidence that both climate and demographic history have shaped the genetic structure of populations. Pronounced genetic differentiation was evident between populations occupying cold versus hot deserts, and we detected numerous loci with significant associations with climate. The genetic signal of founder effects, however, is still present in the genomes of the recently expanded populations, which comprise subsets of genetic variation found in the southern populations.