Southwestern Research Station

AZ, United States

Southwestern Research Station

AZ, United States
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Weiss S.L.,University of Puget Sound | Mulligan E.E.,University of Puget Sound | Wilson D.S.,Southwestern Research Station | Kabelik D.,Indiana University | Kabelik D.,Rhodes College
Journal of Experimental Biology | Year: 2013

Signal honesty is theorized to be maintained by condition-dependent trait expression. However, the mechanisms mediating the condition dependence of sexually selected traits are often unknown. New work suggests that elevated glucocorticoid levels during physiological stress may play a role in maintaining signal honesty. Here, we experimentally examine the effect of both chronic and acute stress on the expression of the condition-dependent ornamentation of female striped plateau lizards, Sceloporus virgatus. Females were stressed either chronically via corticosterone implants or relatively acutely via autotomy, were sham manipulated or were left unmanipulated. Both stressors resulted in elevations in corticosterone within physiologically relevant levels, though the implants resulted in significantly higher levels than did autotomy. Corticosterone-implanted females were less likely to produce a clutch of eggs, but those individuals that did reproduce had reproductive output similar to that of females from other treatment groups. Compared with females in other groups, the corticosterone-implanted females tended to develop smaller ornaments that had less UV and orange-to-red wavelength reflectance relative to medium wavelength reflectance. The sex steroid hormones testosterone and estradiol were correlated to corticosterone levels, but did not appear to underlie the effect on ornament expression; of the steroids measured, only corticosterone levels were negatively related to ornament size and coloration. Thus, the condition-dependent ornamentation of female lizards is sensitive to chronic elevations in stress hormones, supporting their importance in the maintenance of signal honesty. © 2013. Published by The Company of Biologists Ltd.


Cooper W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Ethology | Year: 2016

A prey's body orientation relative to a predator's approach path may affect risk of fleeing straight ahead. Consequently, prey often turn before fleeing. Relationships among orientation, turn, and escape angles and between these angles and predation risk have not been studied in terrestrial vertebrates and have rarely been studied in the field. Escape angles are expected to lead away from predators and be highly variable to avoid being predictable by predators. Using approach speed as a risk factor, we studied these issues in the zebra-tailed lizard, Callisaurus draconoides. Lizards fled away from human simulated predators, but most did not flee straight away. Escape angles were variable, as expected under the unpredictability hypothesis, and had modes at nearly straight away (i.e., 0°) and nearly perpendicular to the predator's approach path (90°). The straight away mode suggests maximal distancing from the predator; the other mode suggests maintaining ability to monitor the predator or possibly an influence of habitat features such as obstacles and refuges that differ among directions. Turn angles were larger when orientation was more toward the predator, and escape angles were closer to straight away when turn angles were larger. Turning serves to reach a favorable fleeing direction. When orientation angle was more toward the predator, escape angle was unaffected, suggesting that turn angle compensates completely for increased risk of orientation toward the predator. When approached more rapidly, lizards fled more nearly straight away, as expected under greater predation risk. Turn angles were unrelated to approach speed. © 2016 Blackwell Verlag GmbH.


Cooper W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Behaviour | Year: 2015

Flight initiation distance (FID = predator-prey distance when escape begins) increases as starting distance (predator-prey distance when approach begins) increases. The flush early and avoid the rush (FEAR) hypothesis proposes that this relationship exists because monitoring an approach is costly. Hypothesized causes are increase in assessed risk and decrease in obtainable benefits while monitoring as starting distance increases.We propose the delay risking emergence and avoid dying (DREAD) hypothesis: hiding time in refuge increases as starting distance increases because prey use risk assessed during approach to estimate risk upon emerging. In the lizard Callisaurus draconoides, FID increased as standardized starting distance increased at faster approach speeds, supporting the FEAR hypothesis. In its first test, the DREAD hypothesis was supported: hiding time in the lizard Sceloporus virgatus increased as standardized starting distance increased. No large benefits were attainable, suggesting that dynamic increase in assessed risk accounts for these findings. © 2015 Koninklijke Brill NV, Leiden.


Cooper W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Behavioral Ecology and Sociobiology | Year: 2015

Prey monitor predator movements to assess risk, as required to make escape decisions and avoid being captured unaware. For prey that exhibit behavioral signs that they have detected predators, alert distance is the predator-prey distance when the prey performs the behavior and then continuously monitors the predator’s approach. Many other prey do not usually give any indication of having detected a predator prior to fleeing. This is especially likely in prey having laterally placed eyes that are approached from one side, as in typical studies of lizards. We conducted field trials to detect overt signs of monitoring by zebra-tailed lizards, Callisaurus draconoides, which usually exhibit no signs of monitoring. When a researcher walked in an arc starting at some distance from a lizard’s side and continuing until he was directly in front of or behind it, the lizard cocked its head and/or reoriented its body or fled and then reoriented. These behaviors allowed lizards to keep the researcher in view as he passed out of a monocular visual field. The findings demonstrate that monitoring occurs in these lizards, suggest that monitoring is so important that lizards risk being detected by moving, and suggest a possible method for studying effects of alert distance in prey that do not perform alerting behaviors when approached in full view. Alerting responses have been observed infrequently in lizards because researchers are in one of the wide lateral visual fields when they start to approach. Unless the predator moves out of view, prey with limited or no binocular vision have no need for postural adjustment to focus on the predator. © 2015, Springer-Verlag Berlin Heidelberg.


Cooper Jr. W.E.,Indiana University - Purdue University Fort Wayne | Wilson D.S.,Southwestern Research Station
Herpetologica | Year: 2010

During encounters with predators, prey that flee into refuges decide how long to hide. Refuge use theory predicts that hiding time increases as the risk of emerging increases. Lizards that escape by autotomizing their tails incur costs, including temporary decrease in speed and loss of ability to use autotomy. Thus, risk of being captured upon emergence is greater after autotomy. Also, a predator that captures a prey may later be assessed as posing greater threat. We predicted that hiding time increases after a lizard has been captured or has undergone autotomy. A previous study of striped plateau lizards (Sceloporus virgatus) showed that the proportion of lizards that entered refuges increased after autotomy but not after earlier capture. To examine unstudied effects of autotomy and capture on hiding time, we conducted a 2 × 2 factorial field experiment with handling and autotomy as factors. The four groups were (1) unhandled intact controls; (2) unhandled autotomized; (3) captured (and handled) intact, but not autotomized; and (4) captured, handled and autotomized. Because entering cool refuges entails costly decrease in body temperature, hiding times are shorter in cooler refuges. We controlled this effect statistically by conducting analyses of covariance incorporating difference in air temperature inside and outside refuges as the covariate. As predicted, autotomy and handling led to longer hiding times. However, handling affected hiding time only in intact lizards. Our results add autotomy and capture to risk factors known to affect hiding time, augmenting a growing body of knowledge supporting the hypothesis that trade-offs between costs of emerging and remaining in a refuge guide decisions about hiding time. © 2010 by the Herpetologists' League, Inc.


Cooper Jr. W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Canadian Journal of Zoology | Year: 2010

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.


Cooper Jr W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Ethology | Year: 2010

Escape theory predicts that the probability of fleeing and flight initiation distance (predator-prey distance when escape begins) increase as predation risk increases and decrease as escape cost increases. These factors may apply even to highly cryptic species that sometimes must flee. Horned lizards (Phrynosoma) rely on crypsis because of coloration, flattened body form, and lateral fringe scales that reduce detectability. At close range they sometimes squirt blood-containing noxious substances and defend themselves with cranial spines. These antipredatory traits are highly derived, but little is known about the escape behavior of horned lizards. Of particular interest is whether their escape decisions bear the same relationships to predation risk and opportunity costs of escaping as in typical prey lacking such derived defenses. We investigated the effects of repeated attack and direction of predator turning on P. cornutum and of opportunity cost of fleeing during a social encounter in P. modestum. Flight initiation distance was greater for the second of two successive approaches and probability of fleeing decreased as distance between the turning predator and prey increased, but was greater when the predator turned toward than away from a lizard. Flight initiation distance was shorter during social encounters than when lizards were solitary. For all variables studied, risk assessment by horned lizards conforms to the predictions of escape theory and is similar to that in other prey despite their specialized defenses. Our findings show that these specialized, derived defenses coexist with a taxonomically widespread, plesiomorphic method of making escape decisions. They suggest that escape theory based on costs and benefits, as intended, applies very generally, even to highly cryptic prey that have specialized defense mechanisms. © 2010 Blackwell Verlag GmbH.


Cooper Jr. W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Behavioral Ecology and Sociobiology | Year: 2013

Escape latency theory models the tradeoff between maintaining crypsis by remaining immobile near an immobile predator versus moving to flee or engage in fitness-enhancing activities. The model predicts that latency to flee increases as cost of fleeing increases and decreases as cost of remaining immobile increases. As predation risk increases, cost of fleeing, primarily due to abandoning crypsis due to immobility, decreases. Predictions have been tested for few risks and a single cost of immobility factor in only two species of active foragers. To gauge the breadth of applicability of the model, we tested effects of four risk factors and two cost of immobility factors in ambush-foraging phrynosomatid lizards, which we selected for testing because foraging mode strongly affects many aspects of ecology and behavior of lizards. Latency to flee decreased as standing distance (predator-prey distance before fleeing) decreased, predator approach speed increased, directness of approach increased, and predator persistence increased. Latency to move was shorter in the presence of food and shorter for males in the presence of females. Lizards often moved toward food or females instead of fleeing. Latency was affected as predicted by all risk and by cost of remaining immobile factors. Our findings agree with previous results for the same four risk factors and the foraging cost of immobility. That social cost of immobility affects latency as predicted is a novel finding. The model is robust, applying to ecologically diverse prey and to a wide range of factors affecting costs of fleeing and of immobility. © 2013 Springer-Verlag Berlin Heidelberg.


Cooper Jr. W.E.,Indiana University - Purdue University Fort Wayne | Sherbrooke W.C.,Southwestern Research Station
Current Zoology | Year: 2012

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. © 2012 Current Zoology.


Cooper Jr. W.E.,Indiana University | Sherbrooke W.C.,Southwestern Research Station
Herpetologica | Year: 2010

Horned lizards are difficult to detect because of their cryptic coloration and behavior, but often flee from approaching predators and use specialized behavioral, morphological, and physiological defenses at close quarters. Escape theory predicts that flight initiation distance (predatorprey distance when escape begins) increases as predation risk increases. We predicted that, despite relying on crypsis, Texas horned lizards (Phrynosoma cornutum) would have greater flight initiation distances when approached rapidly than slowly and when approached directly than indirectly. Flight initiation distance was greater for rapid than slow and direct than indirect approach, verifying the predictions for prey that do not rely exclusively on crypsis, forgoing escape. Effect size was larger for approach speed than for directness of approach, in part because the difference between minimum bypass distances was small (0.0 m for direct and 0.6 m for indirect approaches). We also investigated responses to a shadow passing over a lizard, which might be a cue to imminent risk. When a model accipiter passed overhead, lizards were much more likely to move and jump if and when the model cast a shadow directly on them than if the shadow passed nearby without falling on them. Some lizards fled when the shadow fell on them. We interpret these novel findings as indicating that P. cornutum assess themselves as being in immediate peril when suddenly covered by a shadow. They reacted primarily by immediate flight or jumping, possibly reflecting preparation to use alternative defensive strategies at close quarters or to delay escape while further assessing risk. Thus, although Texas horned lizards rely strongly on crypsis, they make escape decisions based on degree of predation risk. © 2010 The Herpetologists' League, Inc.

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