Phrynosoma Research Articles

Monitoring of the Flat‐Tailed Horned Lizard With Methods Incorporating Detection Probability

Abstract: Difficulty in monitoring the flat‐tailed horned lizard (Phrynosoma mcallii) has led to controversy over its conservation status. The difficulty in detecting this species has discouraged large‐scale estimates of abundance and led to uncertainty over whether the species exists in population sizes of sufficient size for long‐term persistence. We incorporated detection probability into monitoring of this species using closed mark—recapture and distance‐sampling methods. Density estimation from mark—recapture abundance estimates was improved using an estimate of the proportion of time lizards were on the plot. We estimated the probability of detection on the line for distance sampling and adjusted density estimates accordingly. We estimated the populations of the Yuha Basin Management Area in 2002 and the East Mesa Management Area, Imperial County, California, USA, in 2003 to be 25,514 (95% CI 14,444‐38,970) and 42,619 (95% CI 23,161‐67,639), respectively. Two estimates of detection probability on the line in distance sampling by different methods were 0.45 and 0.65. Density estimates derived from distance analyses for 3 East Mesa Management Area plots and the Yuha Basin Management Area were 1.55 per ha (95% CI 0.64‐3.76) and 0.41 per ha (95% CI 0.22‐0.7), respectively. These are the first large‐scale estimates of abundance and density for P. mcallii.

Morphological correlates of ant eating in horned lizards (Phrynosoma)

The North American horned lizards (Phrynosoma) represent a morphologically specialized group of ant-eating lizards. Although variation in dietary fidelity is observed among the species, all appear to possess morphological specializations thought to be related to their ant-eating diets. Previous studies have examined morphological specialization in Phrynosoma, but they have not taken into account the phylogenetic relationships of its member species. In the present study, the morphological characteristics of the head, jaws and teeth that are thought to be important in prey capture and prey processing were examined to test whether variation in cranial morphology is associated with diet in lizards of the genus Phrynosoma. It is suggested that lizards of the genus Phrynosoma are indeed morphologically specialized and that ant-eating is associated with reduced dentition and an overall reduction in the robustness of morphological structures important in prey processing. Although this trend holds for the highly myrmecophagous species of Phrynosoma, a robust cranial morphology is apparent in the short-horned lizard clade (Phrynosoma ditmarsi, Phrynosoma douglasii, Phrynosoma hernandesi, Phrynosoma orbiculare), implying the ability to process a variety of dietary items. The present study suggests that additional feeding specializations exist within an already specialized clade (i.e. the short-horned lizard clade) and highlights the need for more detailed dietary and behavioural studies of feeding behaviour in this uniquely specialized group of lizards.

How the Horned Lizard Got Its Horns

Many descriptions of evolutionary adaptations 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 features 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 selection by loggerhead shrikes favors longer horns (fig. S1) in the flat-tailed horned lizard (Phrynosoma mcalli).

Horned lizard ( Phrynosoma) phylogeny inferred from mitochondrial genes and morphological characters: understanding conflicts using multiple approaches

The genus Phrynosoma includes 13 species of North American lizards characterized by unique and highly derived morphologies and ecologies. Understanding interspecific relationships within this genus is essential for testing hypotheses about character evolution in this group. We analyzed mitochondrial ND4 and cytochrome b gene sequence data from all species of Phrynosoma in conjunction with a previously published dataset including 12S and 16S rRNA gene sequences and morphological characters. We used multiple phylogenetic methods and diagnostic tests for data combinability and taxonomic congruence to investigate the data in separate and combined analyses. Separate data partitions resulted in several well-supported lineages, but taxonomic congruence was lacking between topologies from separate and combined analyses. Partitioned Bremer support analyses also reveals conflict between data partitions in certain tree regions. When taxa associated with well-supported clades were removed from analyses, phylogenetic signal was lost. Combined, our results initially suggest conflict between data partitions, but further tests show the data are only appropriate for phylogenetic reconstruction of those parts of the topology that were well resolved. Nonetheless, our data analyses reveal five well-supported clades: (1) Phrynosoma ditmarsi and Phrynosoma hernandesi, (2) P. ditmarsi, P. hernandesi, and Phrynosoma douglasii, (3) P. ditmarsi, P. hernandesi, P. douglasii, and Phrynosoma orbiculare, (4) Phrynosoma mcallii and Phrynosoma platyrhinos, and (5) Phrynosoma braconnieri and Phrynosoma taurus.

Movement, Home Range, and Activity Patterns of the Horned Lizard, Phrynosoma mcallii

Abstract Sixty-nine telemetered Phrynosoma mcallii from the Colorado Desert in California were relocated for up to nine months to examine activity patterns, home-range sizes and overlap, distance traveled between relocations, and onset and duration of hibernation. Total area used by the lizards ranged from 651–59,237 m2. Males had significantly larger mean summer home ranges and traveled significantly further than females. The duration of winter dormancy for eight telemetered lizards was 85 ± 8 (mean ± SE) days. Nearly all telemetered lizards were underground by mid-November and emerged as early as late December. Telemetered P. mcallii were out in the open or underneath a shrub throughout the day during spring and fall. They retreated into burrows to escape the midday summer heat. When out in the open, males perched on an elevated surface 19.0% of the time, whereas females perched 4.3%. Telemetered lizards exhibited considerable overlap among their home ranges; males shared 11% of their home ranges with f...

Reproductive Characteristics of the Roundtail Horned Lizard, Phrynosoma modestum (Phrynosomatidae), from the Chihuahuan Desert of Mexico

Reproductive Characteristics of the Roundtail Horned Lizard, Phrynosoma modestum (Phrynosomatidae), from the Chihuahuan Desert of Mexico

Bottom-Up Effects on Persistence of a Specialist Predator: Ant Invasions and Horned Lizards

Maintaining biodiversity within fragmented landscapes has become a primary focus of ecology. Despite many theoretical and comparative studies on species persistence following fragmentation, experimental studies investigating the mechanisms behind population declines remain rare. In recent years, coastal horned lizards (Phrynosoma coronatum) have disappeared throughout much of their range in coastal southern California. In addition to the direct impact of habitat loss due to urbanization, horned lizard populations continue to decline in the remaining fragmented landscape. One factor that may contribute to their decline is the invasion of exotic species from the surrounding urban matrix. Horned lizards are ant specialists, and they may be particularly vulnerable to changes in the native ant community resulting from the invasion of Argentine ants (Linepithema humile). In this study we examined how Argentine ants influence horned lizard growth rates by raising hatchlings on prey typical of invaded and uninvaded sites. Hatchling horned lizards maintained positive growth rates on a diet of just one native ant species (Crematogaster californica). However, on a diet of Argentine ants or arthropods typical of an invaded community, horned lizard growth rates were either negative or averaged near zero. In addition, when lizards were switched from a diet of Argentine ants to native ants, growth rates increased. One factor contributing to growth was foraging rate; capture success appears partly responsible for why horned lizards specialize on ants vs. other, harder to capture, arthropods. Moreover, a comparison of diets among age classes of coastal horned lizards suggests a diversity of ants is necessary to support lizard populations. While stochastic demographic and environmental processes are often invoked to explain the decline of populations following fragmentation, it appears that horned lizards are disappearing from habitat remnants in southern California at least in part due to the deterministic effects of a biological invasion.

BOTTOM-UP EFFECTS ON PERSISTENCE OF A SPECIALIST PREDATOR: ANT INVASIONS AND HORNED LIZARDS

Maintaining biodiversity within fragmented landscapes has become a primary focus of ecology. Despite many theoretical and comparative studies on species persistence following fragmentation, experimental studies investigating the mechanisms behind population declines remain rare. In recent years, coastal horned lizards (Phrynosoma coronatum) have disappeared throughout much of their range in coastal southern California. In addition to the direct impact of habitat loss due to urbanization, horned lizard populations continue to decline in the remaining fragmented landscape. One factor that may contribute to their decline is the invasion of exotic species from the surrounding urban matrix. Horned lizards are ant specialists, and they may be particularly vulnerable to changes in the native ant community resulting from the invasion of Argentine ants (Linepithema humile). In this study we examined how Argentine ants influence horned lizard growth rates by raising hatchlings on prey typical of invaded and uninvaded sites. Hatchling horned lizards maintained positive growth rates on a diet of just one native ant species (Crematogaster californica). However, on a diet of Argentine ants or arthropods typical of an invaded community, horned lizard growth rates were either negative or averaged near zero. In addition, when lizards were switched from a diet of Argentine ants to native ants, growth rates increased. One factor contributing to growth was foraging rate; capture success appears partly responsible for why horned lizards specialize on ants vs. other, harder to capture, arthropods. Moreover, a comparison of diets among age classes of coastal horned lizards suggests a diversity of ants is necessary to support lizard populations. While stochastic demographic and environmental processes are often invoked to explain the decline of populations following fragmentation, it appears that horned lizards are disappearing from habitat remnants in southern California at least in part due to the deterministic effects of a biological invasion.

Spatial Patterns in the Abundance of the Coastal Horned Lizard

Coastal horned lizards ( Phrynosoma coronatum) have undergone severe declines in southern California and are a candidate species for state and federal listing under the Endangered Species Act. Quantitative data on their habitat use, abundance, and distribution are lacking, however. We investigated the determinants of abundance for coastal horned lizards at multiple spatial scales throughout southern California. Specifically, we estimated lizard distribution and abundance by establishing 256 pitfall trap arrays clustered within 21 sites across four counties. These arrays were sampled bimonthly for 2-3 years. At each array we measured 26 "local" site descriptors and averaged these values with other "regional" measures to determine site characteristics. Our analyses were successful at identifying factors within and among sites correlated with the presence and abundance of coastal horned lizards. These factors included the absence of the invasive Argentine ant ( Linepithema humile) (and presence of native ant species eaten by the lizards), the presence of chaparral community plants, and the presence of sandy substrates. At a regional scale the relative abundance of Argentine ants was correlated with the relative amount of developed edge around a site. There was no evidence for spatial autocorrelation, even at the scale of the arrays within sites, suggesting that the determinants of the presence or absence and abundance of horned lizard can vary over relatively small spatial scales ( hundreds of meters). Our results suggest that a gap-type approach may miss some of the fine-scale determinants of species abundance in fragmented habitats.

Do vertebral-line patterns in two horned lizards (Phrynosoma spp.) mimic plant-stem shadows and stem litter?

All species of the genus Phrynosoma are cryptically colored and patterned, but two species have bold black or white vertebral-line patterns on their dorsal surfaces. Phrynosoma mcallii lives on aeolian-sand substrates and often rests below shrubs. It has a black vertebral line which is hypothesized to mimic dark shadows of stems falling on the smooth, litter-free sand beneath shrubs. Phrynosoma cornutum inhabitats grasslands and arid shrub-habitats in which below-shrub sites are littered with bleached plant stems. The white middorsal stripe of this species is thought to mimic white stems of the under-shrub litter. Although crypticity in horned lizards has been extensively studied, the two examples of apparent object mimicry described herein have not been reported previously.

Blood-Squirting Variability in Horned Lizards (Phrynosoma)

Variability within the genus Phrynosoma in the occurrence of ocular-sinus blood-squirting, reportedly a defense used in canid encounters, is reviewed from the literature. Six species have been reported to squirt blood, and seven species remain unreported. Five of the latter species were tested in dog trials; one exhibited blood-squirting (Phrynosoma hernandesi), one exhibited precursor behaviors but failed to squirt blood (Phrynosoma ditmarsi), and three yielded negative results (Phrynosoma mcallii, Phrynosoma modestum, and Phrynosoma platyrhinos). Instances of blood-squirting in response to human encounters were collected and largely support the negative results for the three species P. mcallii, P. modestum, and P. platyrhinos. A phylogeny of blood-squirting and nonblood-squirting species is presented with blood-squirting being plesiomorphic in the genus and the synapomorphic condition of nonsquirting species being restricted to a single clade of P. mcallii-modestum-platyrhinos. The possibility of P. douglasii independently evolving an autapomorphic condition remains unresolved. Dog trials with 40 adult Phrynosoma cornutum were conducted to determine influences of body size and sex on squirt frequency and blood mass expelled, as well as to examine aspects of the potential physiological cost of the defense. In 153 trials, 85% of all lizards squirted in at least one trial, 82% squirted in more than one trial, and two lizards squirted daily over the seven-day trial period. Initial body mass positively correlated with the total number of squirts/individual (r2 = 0.28; P < 0.001) and the number of days a lizard continued squirting (r2 = 0.63; P < 0.01). Number of squirts/individual/day declined over the seven-day trial period (r2 = 0.20; P < 0.05). Cumulative mass loss for individual lizards attributable to blood-squirting averaged 0.7 ± 0.8 g (2.0 ± 2.0% body mass), with a high of 2.8 g (6.8% body mass). In addition, juvenile P. cornutum and P. hernandesi were shown to squirt blood in dog trials, illustrating the early developmental onset of the behavior.

Comparison of Blood Squirted from the Circumorbital Sinus and Systemic Blood in a Horned Lizard, Phrynosoma cornutum

sponse to attacks by greater roadrunners, Geococcyx californianus (Sherbrooke, 1990a) or southern grasshopper mice, Onychomys torridus (Sherbrooke, 1991). Although the specific effect of blood squirting by Phrynosoma remains undocumented, stimuli eliciting the behavior suggest an antipredator defense (Middendorf and Sherbrooke, 1992). Anecdotal observations reported in the literature (Holder, 1901; Reeve, 1952), along with our own observations (dog; kit fox, Vulpes macrotis), suggest that it is not the act of squirting, but some component in the blood itself that serves this deterrent

Prey Selection in Horned Lizards Following the Invasion of Argentine Ants in Southern California

Biological invasions can have severe direct and indirect impacts on natural communities and are one of the leading reasons behind the loss of biodiversity. We investigated the indirect effects of Argentine ant (Linepithema humile) invasions on coastal horned lizards (Phrynosoma coronatum) through an examination of prey selection in the field and laboratory. In non-invaded areas, coastal horned lizard diet consists predominately of ants (>94% by prey item in three reserves examined), particularly harvester ants in the genera Pogonomyrmex and Messor. In invaded areas, most native ants were displaced, and remaining horned lizards incorporated more non-ant arthropods and smaller ants into their diet. In addition, Argentine ants were never detected in horned lizard fecal pellets, suggesting that they are not a suitable replacement food source for the native species they are displacing. Analysis of prey selection in uninvaded areas reveals that ant species consumption by adult lizards is correlated with ant body size rather than ant abundance, foraging behavior, or defensive method. Differences in diet between adult and juvenile lizards suggest that a diversity of ant species is necessary to support both age classes. Laboratory experiments, consisting of paired presentations of four native ant species and the Argentine ant, confirmed patterns found in the field. Both adult and juvenile horned lizards preferred native ants to Argentine ants. Patterns of preference suggest that, in addition to L. humile's small size, other factors may contribute to the horned lizard's aversion to this species. Populations of coastal horned lizards have undergone severe declines in recent years. While habitat loss has been the primary concern, the invasion of Argentine ants into their remaining suitable habitat needs to be monitored. Reserves need to be managed to prevent the penetration of Argentine ants in order to minimize their direct and indirect effects on natural communities.

PREY SELECTION IN HORNED LIZARDS FOLLOWING THE INVASION OF ARGENTINE ANTS IN SOUTHERN CALIFORNIA

Biological invasions can have severe direct and indirect impacts on natural communities and are one of the leading reasons behind the loss of biodiversity. We inves- tigated the indirect effects of Argentine ant (Linepithema humile) invasions on coastal horned lizards (Phrynosoma coronatum) through an examination of prey selection in the field and laboratory. In non-invaded areas, coastal horned lizard diet consists predominately of ants (>94% by prey item in three reserves examined), particularly harvester ants in the genera Pogonomyrmex and Messor. In invaded areas, most native ants were displaced, and remaining horned lizards incorporated more non-ant arthropods and smaller ants into their diet. In addition, Argentine ants were never detected in horned lizard fecal pellets, sug- gesting that they are not a suitable replacement food source for the native species they are displacing. Analysis of prey selection in uninvaded areas reveals that ant species con- sumption by adult lizards is correlated with ant body size rather than ant abundance, foraging behavior, or defensive method. Differences in diet between adult and juvenile lizards suggest that a diversity of ant species is necessary to support both age classes. Laboratory exper- iments, consisting of paired presentations of four native ant species and the Argentine ant, confirmed patterns found in the field. Both adult and juvenile horned lizards preferred native ants to Argentine ants. Patterns of preference suggest that, in addition to L. humile's small size, other factors may contribute to the horned lizard's aversion to this species. Populations of coastal horned lizards have undergone severe declines in recent years. While habitat loss has been the primary concern, the invasion of Argentine ants into their remaining suitable habitat needs to be monitored. Reserves need to be managed to prevent the penetration of Argentine ants in order to minimize their direct and indirect effects on natural communities.

Reproductive Mode and Female Reproductive Cycles of Two Endemic Mexican Horned Lizards (Phrynosoma taurusandPhrynosoma braconnieri)

Two species of horned lizards, Phrynosoma braconnieri and P. taurus, are endemic to México and inhabit medium and high-elevation sites in the states of Oaxaca, Guerrero, and Puebla. We compiled information on distribution and reproductive cycle for these two species from the literature and from an examination of specimens in systematic collections. Our study confirms a viviparous mode of reproduction for both species and suggests that their reproductive cycles may be different from that observed in other viviparous Phrynosoma. Specifically, embryonic development occurs during the late fall and winter months, with a parturition date in early spring. In contrast, other viviparous horned lizards gestate during the spring and summer months and give birth to their young in the late summer. Examining the phylogenetic distribution of reproductive modes in this genus suggests that two high–elevation clades of horned lizards have independently evolved viviparity from an oviparous ancestor, yet each of these clades has evolved a distinct reproductive cycle.Las especies endémicas de México Phrynosoma braconnieri y P. taurus habitan elevaciones intermedias y altas en los estados de Oaxaca, Guerrero y Puebla. En este trabajo revisamos ejemplares de colecciones y recopilamos información bibliográfica sobre la distribución y ciclos reproductivos de estas dos especies. Este estudio confirma la existencia de un modo de reproducción vivíparo en ambas especies, y sugiere que su ciclo reproductivo difiere del observado en otras especies vivíparas de Phrynosoma. En particular, en P. braconnieri y P. taurus el desarrollo embrionario se lleva a cabo durante el final del otoño y principios de invierno dándose el parto al principio de la primavera. En contraste, en otras especies vivíparas de Phrynosoma la gestación se realiza durante la primavera y el verano mientras que el parto ocurre en el verano tardío. La revisión de la distribución filogenética de los modos reproductivos en éste género, sugiere que dos clados de Phrynosoma que viven en elevaciones altas han adquirido independientemente un modo vivíparo a partir de un ancestro ovíparo. Sin embargo, cada uno de estos clados ha evolucionado un ciclo reproductivo particular.

The Evolution of Female-Biased Sexual Size Dimorphism: A Population-Level Comparative Study in Horned Lizards (Phrynosoma)

The Evolution of Female-Biased Sexual Size Dimorphism: A Population-Level Comparative Study in Horned Lizards (Phrynosoma)

Horned lizards

Horned lizards

The Bedbugs' Night Dance and Other Hopi Sexual Tales: Mumuspi'yyungqa tuutuwutsi

The mysteries and complexities of sex--the wonder of sexual initiation, the discomfort of sexual desire, the penalties of indulgence, and the power of erotic love--have all found expression in Hopi tales. Sometimes cast in animal fables, sometimes presented in monstrous exaggeration to emphasize the power of sexual appetite, and sometimes as wildly bawdy as Shakespeare, the tales evoke the candor of Hopi imagination and the vitality of Hopi culture. This volume gives each tale in the original Hopi and in English translation on facing pages. The tales include Bedbug Boy and his constantly interrupted dinner, how the Hehey'as tricked the Itsivus and took advantage of their wives, and how the Horned Lizard girls found a new use for chili powder. Ekkehart Malotki's preface and glossary clarify terms and concepts and provide background for the stories and the storytelling. E. N. Genovese's introduction puts the collection in the broad context of classical Greek and Latin literature and describes how the Hopi stories are distinct in their own right.

Developers' devious digressions

In spite of the many laws and regulations regarding the development of property and the protection of open space and wildlife, developers often try to get around compliance with the law using subtle, or not–so–subtle, tactics. In some cases, they violate the law because they know that there is little or no enforcement, or, if caught, they pay the fine and charge it up as a cost of doing business which is of course tax-deductible. Over the last few years I have been involved in a status study on two species of lizards of special concern (the Orange-throated Whiptail, Cnemidophorus hyperythrus and the Coastal Horned Lizard, Phrynosoma coronatum) for the California Department of Fish and Game. During this study, I noticed several of what I call ‘developers' devious digressions’. As a biologist and environmental consultant, I have seen, over the last few decades, developers use these same ways of getting around environmental laws in Arizona, Montana, Mexico, and Australia. I have placed these digressions, detours and non-conformities, with the law in the following several categories.

Behavioral (Predator-Prey) Interactions of Captive Grasshopper Mice (Onychomys torridus) and Horned Lizards (Phrynosoma cornutum and P. modestum)

-In predatory attacks by Onychomys torridus 20% of the 30-min encounters involving Phrynosoma cornutum were fatal, whereas 43% of those with Phrynosoma modestum were fatal. When the trials of juvenile P. cornutum were combined with those of adult P. modestum, which are similar in size, large horned lizards (adult P. cornutum) suffered 0% mortality whereas small lizards (adult P. modestum plus juvenile P. cornutum) experienced significantly higher mortality, 55%. Horned lizard antipredator behaviors involved displays that increase apparent size, aggressive attacks that intimidate, and the absence of flight responses that might elicit Onychomys attack behavior. Lizard mortality was mainly attributable to attacks involving chewing of the cranium around the orbit. Adult Phrynosoma cornutum possess sufficient armament around the eyes and parietal region to successfully defend against such attacks. Also their tough dorsal skin hinders laceration by the mice. In contrast, P. modestum and juvenile P. cornutum were easy prey for 0. torridus.