Journal Abstracts: Anolis and Other Iguanids Visual and Chemical Reception
See also Abstracts for Iguana iguana
Compiled by Melissa Kaplan, 2002
Anoles, like other reptiles and most (if not all) other animals, have many ways in which they receive input from their environment. The ones we tend to think of are the ones that we humans consciously make the most use of: sight, sound, smell, touch and taste. What we remain largely unconscious of is something that many researchers - and perfume designers - are well aware of: we also receive chemical input that is processed through different pathways than our more obvious senses.
What does this have to do with anoles and other animals? Humans tend to forget that animals rely more heavily on chemical input than we do As a result, how well they do - or don't do - in captivity may be affected by not only what they see and hear, but by the chemicals they are picking up with their tongue and vomeronasal (Jacobson's) organ. Anoles, bearded dragons, leopard geckos and other lizards who live in dynamic social groups can become highly stressed by being forced to live with dominant conspecifics in the close quarters imposed by captivity. This leads to abnormal behavior and, eventually, illness, even death, if the lizard isn't moved out of the enclosure; some may even require being moved into another room so as to be out of smell range as well as out of sight of the dominant lizard. (For more information, please see Alison Albert's article, Lizard Tough Guys.)
and behavioral studies of femoral gland secretions in iguanid lizards.
Comparative studies on the chemistry and behavioral significance of femoral gland secretions in desert iguanas (Dipsosaurus dorsalis) and green iguanas (Iguana iguana) are reviewed. Field and laboratory studies suggest that femoral gland secretions function in conspecific recognition and range marking. In desert iguanas, secretions are of low volatility and may be detected initially using long-range ultraviolet visual cues. In contrast, green iguana secretions contain a diversity of volatile lipids and appear to be localized by chemoreception. Interspecific differences in femoral gland chemistry may reflect adaptations to the diverse climatic conditions of arid desert and tropical forest environments.
and anaerobic metabolism of paired male lizards (Anolis carolinensis).
The associations of physical activity, skin color, body mass difference and conspecific olfactory cues with short-term aerobic and anaerobic metabolism in paired male Anolis carolinesis were examined. Control measurements for mild laboratory manipulation (such as the movement of a metabolic chamber) yielded significant increases in the rate of oxygen consumption, but not in the lactate concentration of these animals; stronger manipulation increased both. A possible influence of conspecific olfactory cues on the metabolism of lizards introduced into empty chambers was undetected. Anolis that turned from green to brown with handling showed an increase in oxygen uptake, but an association between this color shift and total body lactate level was not detected. Elevated rates of oxygen use and glycolysis were found in pairs of males in the absence of physical activity. Lactate levels of the individuals of a pair were positively correlated with one another; the lactate concentrations of lizards placed into occupied metabolic chambers were correlated with the difference in body mass of the pair.
and endocrine aspects of tongue-flicking and exploratory behavior in Anolis
Tongue-flicking in reptiles is frequently seen to increase in novel habitats and is presumed to involve the acquisition of chemical information. Like most behavioral patterns, however, tongue-flicking has both multiple causes and multiple functions, only some of which involve chemosensation. This paper describes units of exploratory behavior, including use of the tongue, in a microsmatic lizard, the green anole, Anolis carolinensis. This species employs its tongue in a manner suggestive of chemosensory exploration, but it possesses modest peripheral chemosensory organs and reduced central representation of chemosensory target cell groups. Further, specific elements of exploratory behavior are affected differently by treatments that involve altering levels of stress-sensitive hormones, androgen, and central catecholamines. Such differential responses suggest that exploratory behavior is an ensemble of individual units, some of which are selectively sensitive to specific physiological elements of the stress response and of elevated arousal.
delivery to the vomeronasal organs and functional domain of squamate chemoreception.
While evidence exists that many squamate behaviors are released by chemical stimuli, the specific sensory system that detects such stimuli and mediates subsequent behavior has been determined infrequently. Techniques and experimental approaches that have been used to determine the roles that the main olfactory and vomeronasal systems play in mediation of specific behaviors are discussed.
evolution of chemoreception in squamate reptiles: a phylogenetic approach.
Recent advances in the field of squamate reptile chemoreception have been paralleled by the growth and preeminence of cladistics in the field of systematics, but for the most part, workers in the former have failed to incorporate the conceptual and informational advances of the latter. In this paper, I attempt a preliminary rapprochement by combining the methods of phylogenetic systematics and current hypotheses of squamate relationships with an overview of squamate chemosensory biology. This purely phylogenetic approach leads to a number of falsifiable generalizations about the evolution of chemoreception in squamates: 1) Evolution of this system is conservative rather than plastic, reflecting to a large extent suprafamilial attributes rather than adaptation to local conditions; 2) Anguimorphs are highly chemosensory and teiids show convergence with this group; 3) Tongue-flicking, a bifurcated tongue tip, a vomeronasal (VNO) mushroom body, and a complete circular muscle system in the tongue are a correlated character complex associated with the attainment, in squamates, of a direct VNO-oral connection and the loss of a VNO-nasal connection; 4) There is little support for a visual-chemosensory dichotomy within Squamata; 5) Gekkotans are allied with Autarchoglossa, both phylogenetically and in terms of chemosensory biology; 6) Iguania are highly variable in chemosensory development; iguanids represent the primitive iguanian condition, while agamids and chamaeleonids have secondarily reduced or lost their chemosensory abilities; 7) Apparent contradictions in chemosensory behavior among iguanids probably represent intrafamilial divergence; 8) Ecological correlates within Iguanidae and other taxa might be spurious, resulting from historical factors unrelated to the adaptations in question; 9) The mechanical demands of lingual food prehension have constrained chemosensory evolution in Iguania; chemosensory evolution within Scleroglossa was permitted by the liberation of the tongue from this ancestral role.
Discrimination by Chemoreception in the Desert Iguana, Dipsosaurus
The ability of the desert iguana, Dipsosaurus dorsalis, to discriminate conspecific chemical deposits by lingual sampling was examined during their breeding season. We individually tested 12 males and 12 females in a series of cages in which we presented the following stimuli in a randomized order: male and female conspecific odor, male and female heterospecific odor, cologne odor, and distilled water. The number of tongue extrusions and the latency to the first extrusion were recorded and used as a measure of the lizard's responsiveness to each of the chemical stimuli.
Because males and females did not differ in their responses to the six chemical stimuli, their data were combined for analyses. Conspecific odors elicited more tongue extrusions than did other stimuli, and no differences were found in tongue extrusion frequency to male versus female conspecific odor. These results suggest that the desert iguana is capable of discriminating conspecifics from heterospecifics based on chemical cues alone. No difference in latency to first extrusion was observed with any of the chemical stimuli presented.
status, gonadal state, and the adrenal stress response in the lizard,
Adult males of the small arboreal iguanid lizard, Anolis carolinensis, form social dominance hierarchies when placed in habitats with limited resources. Skin color changes occur during hierarchy formation, most conspicuously in subordinates, who appear darker (more brown) than dominants (more green). Because skin color in this species is under the control of hormones frequently associated with physiological stress, radioimmunoassay of plasma levels of the principal reptilian adrenal steroid, corticosterone, was performed. To examine the influence of gonadal androgen, known to influence the aggression that attends hierarchy formation, lizard pairs were constituted in which one or both members were castrated. Corticosterone levels of intact subordinates were significantly elevated, whereas those of castrated subordinates or dominants showed levels comparable to those of isolates. No significant differences in spermatogenic stage could be detected between intact dominants or subordinates.
and behavioral responses to aggression and social dominance in the green
anole lizard, Anolis carolinensis.
Adult males of the small arboreal iguanid lizard, Anolis carolinensis, will fight and form social dominance hierarchies when placed in habitats with limited resources. The relationships between time since initial aggressive interaction, relative social dominance, reproductive activity, and corticosterone and androgen levels were determined for 34 pairs of lizards. A discriminant analysis established a "dominance index" which indicated that over 90% of the difference between individuals who had won or lost aggressive interactions (putative social dominants and subordinates) was attributable to a single discriminant function reflecting altered body color, perch site selection, and circulating androgen. Animals that had darker body color also selected lower perch sites and had depressed rates of courtship relative to winners of fights and were thus designated as social subordinates. These animals also had levels of circulating androgen significantly lower than that of dominants, but circulating corticosterone was not significantly affected. Winners of fights showed a dramatic surge in circulating androgen at 1 hr but returned to near control values by 1 week; losers, however, showed depressed circulating androgen levels at 1 week.
correlates of adrenergic activity during aggression in the lizard, Anolis
Aggressive interactions in Anolis carolinensis result in increased circulating levels of epinephrine (Epi) and norepinephrine (NE) and conspicuous color changes. This activation of the adrenergic component of an acute stress response is externally represented by the darkening of the postorbital eyespot of A. carolinensis. In adult males, this site darkens in response to stressful physical stimulation (trauma, passive restraint) or psychological stimuli, most notably the sight of an aggressively intruding conspecific. Aggressive male A. carolinensis exhibit postorbital eyespot darkening; animals that have a longer latency to expression of this eyespot and those that never show this response were defeated in agonistic interactions. Also, during agonistic interactions, subjects that subsequently win are the first to display eyespot darkening. Plasma catecholamine levels are significantly elevated within 30 sec in both combatants. At 30 sec following the determination of the outcome, winning male lizards have plasma NE levels which are higher than those of losers. Castration, however, significantly increases the latency to eyespot darkening and extends its duration. Testosterone levels may therefore enhance the onset of Epi-mediated eyespot darkening as well as other aspects of the endocrine stress response. Elevated androgen levels and more rapid activation of acute catecholamine response increases the likelihood of becoming socially dominant.
responses to aggression vary in different types of agonistic encounters
in male tree lizards, Urosaurus ornatus.
Hormonal responses to male-male interactions have been detected in some studies of vertebrates but not others. One hypothesis that may partially explain these discrepancies is that differences in the duration of male-male interactions cause different hormonal responses. In social systems based on dominance-subordinance hierarchies interactions often last longer than if exclusive territories are maintained. Tests of the hypothesis that encounter duration explains discrepancies in hormonal responses would be facilitated by a species that shows elements of both types of social systems, such as species in which males practice alternative reproductive tactics. We compared plasma levels of corticosterone and testosterone in males of the territorial morph of the tree lizard (Urosaurus ornatus) subjected either to short (15 min) male-male encounters or to long (7 days) dominance interactions. In the long interactions, dominant males had lower levels of corticosterone than did subordinate males over the first day, but this difference subsequently disappeared. In sharp contrast, winners of short-term encounters had elevated plasma corticosterone levels which peaked the day after the encounter. Thus, males isolated after a short encounter experienced an increase in corticosterone that was apparently inhibited in males who continued interacting with other males. The delayed increase in corticosterone after a short encounter may facilitate metabolic recovery from the encounter, mobilize metabolic substrates useful in subsequent encounters, or may alter subsequent behavior. The response does not appear to be simply recovery from exercise because in a second experiment males exercised for 15 min did not show a similar delayed increase in corticosterone the following day. Testosterone levels were also monitored and did not change in any of these treatments. These results demonstrate that the duration and the outcome of male-male interactions may each independently influence hormone levels.
in Anolis carolinensis during agonistic encounters.
We examined the influences of territorial status, encounter outcome, body mass difference, activity, and display on lactate accumulation in adult male Anolis carolinensis during agonistic interactions. Of the pairs of lizards frozen at the onset of an encounter, intruders had significantly higher lactate concentrations than residents. Lactate levels at the onset of an interaction were not significantly different from those at the conclusion, suggesting a limited role for glycolysis during such events. The outcome of an agonistic encounter was not based on fatigue. Individuals that were larger or changed sites had a lower relative lactate concentration at the conclusion of an interaction than smaller or sedentary animals. We consider the influence of autonomic arousal on glycolysis.
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