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We report the first field data on the seasonality of natural history events in the viviparous horned lizard species Phrynosoma ditmarsi. Our radiotelemetry tracking of seven adults (six females, one male) and other encounters allowed us to identify seasonal changes in movement patterns, brumation inactivity, some growth patterns of adults and juveniles, seasonal body temperatures, predation events, feeding patterns, diurnal and nocturnal site selections, mating, and parturition of young. During winter we noted females exhibit inactive brumation in poorly concealed and mildly protective retreats. They were often in physically exposed sites and two experienced winter predations. Our video recording of a natural mating in mid-November, together with three dramatic female weight losses (mean 42% of total weight) signaling parturition events in July, established fall mating and early summer parturition as the species' reproductive cycle, with a gestational period of 7–8 months. This clarifies our understanding of their reproductive cycle, one that facilitates rapid newborn growth and maternal resource replenishment during summer monsoonal rains, prior to fall mating by adults before the arrival of low winter activity, reduced growth, and brumation. The following summer, the previous year's juveniles experience a second monsoonal summer growth period, probably leading to their fall maturation as 15- to 16-month-old reproductive adults. [ABSTRACT FROM AUTHOR]

North American horned lizards of the genus Phrynosoma are largely myrmecophagous and squirt systemic blood from circumocular sinuses during encounters with certain mammalian predators. The predators react with distinct revulsion. Using bioassay-guided fractionation of blood plasma, we endeavored to identify the source and characteristics of the active chemical compound(s) responsible for this negative oral response. Our results of coyote bioassays and a series of novel mouse bioassay experiments were largely concordant. The active compound(s) was likely plasma-borne with a molecular weight (mw) of between 800 and 1,600. To identify the source of the active compound(s), we noted bioassay responses of different species of horned lizards. The active compound(s) was present in plasma fractions of species known to eat Pogonomyrmex and squirt blood, and it was absent in the plasma fractions of species that do not squirt blood and eat other ants or arthropods. Plasma fractions from individuals of P. cornutum, a blood-squirting species, fed Pogonomyrmex had more aversive levels of the active compound(s) compared to those given a cricket diet. In addition, extracts from Pogonomyrmex indicate that the active compound(s) in lizard plasma is associated with the abdomen of these ants, where venom is stored. The toxic enzymes of ant venom may be metabolized by horned lizards resulting in one or more small peptides that act as the active ingredient(s) in the lizard's circulating blood. We suggest that utilization of this widely dispersed, venomous, and abundant diet only became available to stem horned lizards with the evolution of unique prey capture techniques. This broadened diet then led to incorporation of the compound(s) from Pogonomyrmex spp. into their blood plasma, facilitating the evolution of antipredator blood-squirting. These transformative events apparently established an evolutionarily stable configuration that led to or expanded the unique "Phrynosoma suite" of characteristics from which subsequent diverse clades have evolved across arid North America. [ABSTRACT FROM AUTHOR]

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 initiation distance to determine relationships among body temperature, speed, and escape decisions. Running speed and flight initiation distance were reduced at lower body temperature, suggesting that crypsis reinforced by immobility is more advantageous than longer flight initiation distance for cool, slow lizards. The lizards adjusted escape decisions to current effectiveness of crypsis and escape ability. La distance d'initiation de la fuite (la distance entre le predateur et la proie an depart de la fuite) croit en fonction de l'augmentation du risque de predation. Les proies devraient avoir des distances d'initiation de la fuite plus grandes lorsque leur arriere-plan, leurs mouvements ou leur posture actuelle reduisent leur etat cryptique. La distance d'initiation de la fuite chez les ectolhermes peul augmenter aux temperatures corporelles infcricurcs pour compenser la vitesse de course reduite. Cependanl, chez les proies cryptiques, la fuite peut aceroitre la probability de decouverte. Le phrynosome a queue ronde (Phrynosoma modestum Girard, 1852) est eucryptique el ressetnble a de petites pierres. Nous avons predil que la dislance de l'initiation de la faite chez P. modestum serail plus courte sur les pierres que sur du sable uniforme. Parce que le mouvement et la position dressee diminuent l'effet cryptique, nous avons predit que la distance d'initiation de la fuite serait plus grande apres un mouvement ou en position dressee qu'en po77sition immobile et couchee au sol. Camine predit, les distances d'initiation de la fuite sont plus courtes sur les substrats rocheux que sur les sablonneux, en position couchee au sol qu'en position dressee et en etat d'immobilite qu'apres un mouvement. Nous avons mesure la vitesse de la course et la distance d'initiation de la fuite afin de determiner les relations entre la temperature corporelle, la vitesse. et les decisions de fuite. La vitesse de course et la distance d'initiation de la fuite sont reduites aux temperatures du corps plus basses, ce qui laisse croire qu'un etat cryptique renforce par l'immobilite est plus avantageux qu'une distance d'initiation de la fuite plus longue chez les lezards lents, a temperature fraiche. Les lezards ajustent leurs decisions de fuite a l'efficacite courante de leur etat cryptique et a leur capacite de s'enfuir. [Traduit par la Redaction], Introduction Crypsis is employed by diverse prey to reduce the probability of being detected by predators (Cott 1940; Edmunds 1974; Ruxton et al. 2004). Two major forms of crypsis are [...]

Our study adds an additional species of horned lizard, Phrynosoma ditmarsi, to seven other species (in three clades) found to have horns-raised and back-arched responses to cranial tactile pressures exerted by human fingers simulating a snake ingestion grasp. In contrast to these members of the subfamily Phrynosomatiae, we also tested a species in a different tribe (Callisaurini), Callisaurus draconoides, and a species of a different subfamily (Sceloporinae), Sceloporus magister, of nonhorned phrynosomatid lizards for similar responses. We conclude that horned members of the subfamily Phrynosomatinae (Phrynosoma) exhibit these probable antipredator responses but that these behavioral responses are lacking in the nonhorned members of the family. The horns-raised and back-arched behavioral responses are exhibited throughout the genus, even in species with the smallest horns. Like horns, they are plesiomorphic for the genus. Horn development is positively allometric but horns may have undergone developmental reversal in size in two clades. In addition, we note perhaps convergent aspects of head-positioning antipredator defense behaviors, coupled with distinctly different morphological features, within the genus Phrynosoma and Moloch horridus. Nuestro estudio agrega una especie adicional de lagarto cornudo, Phrynosoma ditmarsi, a otras siete especies (en tres clados) que tienen respuestas de cuernos levantados y espalda arqueada a las presiones táctiles craneales ejercidas por los dedos humanos que simulan un agarre de ingestión de serpiente. En contraste con estos miembros de la subfamilia Phrynosomatiae, también probamos una especie en una tribu diferente (Callisaurini), Callisaurus draconoides, y una especie de una subfamilia diferente (Sceloporinae), Sceloporus magister, de lagartos frinosomátidos sin cuernos para respuestas similares. Llegamos a la conclusión de que los miembros con cuernos de la subfamilia Phrynosomatinae (Phrynosoma) exhiben estas probables respuestas antipredadoras, pero que estas respuestas conductuales faltan en los miembros sin cuernos de la familia. Las respuestas de comportamiento de cuernos levantados y espalda arqueada se exhiben en todo el género, incluso en especies con los cuernos más pequeños. Al igual que los cuernos, son plesiomorfos para el género. El desarrollo de los cuernos es positivamente alométrico, pero los cuernos pueden haber sufrido una reversión del desarrollo en tamaño en dos clados. Además, notamos aspectos quizás convergentes de los comportamientos de defensa contra depredadores de posicionamiento de la cabeza, junto con características morfológicas claramente diferentes, dentro del género Phrynosoma y Moloch horridus. [ABSTRACT FROM AUTHOR]

In deserts, the capture of rain for drinking by lizards is difficult. Unusual behavioral and morphological features for capturing raindrops on skin surfaces have been documented in a few lizards, including three horned lizard species (Phrynosoma). We document rain-harvesting behavior for drinking by an adult female of an additional species, Phrynosoma ditmarsi, a species little studied since its discovery in 1890–1891. Emerging biomimicry applications of discovered unique directional features for capillary transport of water by scale hinges in P. cornutum suggest the value of further detailed research of this rain capture and transport system with additional Phrynosoma species. La recolección de lluvia en el desierto resulta una actividad complicada para las lagartijas. Se han documentado características morfológicas y de comportamiento inusuales para captar gotas de lluvia en la superficie de la piel en algunas lagartijas, entre ellas tres especies de camaleones (Phrynosoma). Se documento la conducta para captación de agua de lluvia para beber de una hembra adulta de una especie adicional, Phrynosoma ditmarsi, una especie poco estudiada desde su descubrimiento en 1890–1891. El descubrimiento de las aplicaciones del biomimetismo emergentes sobre las características direccionales únicas para el transporte de agua a través de los capilares de las escamas con articulaciones flexibles en P. cornutum sugieren el valor de una investigación más detallada de este sistema de recolección y transporte de lluvia con especies adicionales de Phrynosoma. [ABSTRACT FROM AUTHOR]