Effects of chemical and visual exposure to adults on growth, hormones, and behavior of juvenile green iguanas.

For 1 year, groups of juvenile male green iguanas (Iguana iguana) were housed such that one group was visually exposed to an adult female, a second group was both visually and chemically exposed to an adult female, a third group was visually exposed to an adult male, and a fourth group was both visually and chemically exposed to an adult male. Juvenile males exposed to signals from adult males showed signs of chronic stress, including reduced growth rates, lower testosterone levels, higher corticosterone levels, and decreased frequencies of headbob display. Although visual exposure alone was sufficient to suppress growth, testosterone levels, and rates of display, the addition of chemical exposure strengthened some of these effects. Both chemical and visual exposure to an adult male were necessary to produce elevated corticosterone levels. In contrast, juvenile males exposed to visual and chemical signals from an adult female exhibited growth rates, hormone levels, and behavior patterns typical of juvenile males housed in the absence of adults of either sex. These results suggest that visual and chemical signals from dominants may serve to reinforce social relationships among males through their influence on the physiology and behavior of receivers.

Differential resource use, growth, and the ontogeny of social relationships in the green iguana.

Growth rates, resource use, and ontogeny of behavior patterns were examined in captive groups of juvenile green iguanas (Iguana iguana). Four groups were housed in large arenas where supplemental heat and perch sites were limited, whereas two control groups were housed in similar arenas without limited resources. Growth, frequency and types of displays, behavioral interactions, and the use of resources were monitored. By 35-70 days of age, male hatchlings in arenas with limited resources could be classified into two groups: rapid growing dominant individuals and slow growing subordinate individuals. Growth and dominance were not correlated with size of individuals at hatching. Digestive efficiency of males was related to dominance and access to limited resources, but all lizards exhibited a similar digestive efficiency when maintained at a constant ambient temperature. Dominant males used the resources, especially supplemental heat sources, twice as often as subordinate males. The dominant/subordinate relationships and accompanying skew in body size were not evident in the control groups, or in females of any group. At 105 days, control groups were introduced to conditions with limited resources, resulting in increased aggressive interactions and divergence in growth rates. Onset of adult behavioral patterns was related to body size, and the species-specific signature display was observed in dominant males up to several months before subordinate males. These results indicate that male green iguanas establish a dominance hierarchy immediately posthatching when resources are limited, and as a consequence, both physiological and behavioral maturation are delayed in subordinate individuals.

Chemical 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.

Postbite elevation in tongue-flicking rate by an iguanian lizard,Dipsosaurus dorsalis.

The herbivorous iguanid lizardDipsosaurus dorsalis exhibited PETF (postbite elevation in tongue-flicking rate), an increase in tongue-flicking rate after experimental removal from the mouth of food that had been bitten. This was demonstrated by a significantly higher tongue-flick rate after having bitten food than in three experimental conditions controlling for responses to the experimental setting, sight of food, and mechanical disturbance caused by the experimental removal of food from a lizard's mouth. As in most other families of lizards, PETF was brief, occurring only during the first minute. Lizards are divided into two major suprafamilial taxa, Iguania and Scleroglossa, consisting of carnivorous species characterized by two major foraging modes, ambush and active, and of herbivores and omnivores. PETF is absent in the two families of carnivorous iguanian lizards studied that are ambush foragers but present in three families of scleroglossan lizards that are active foragers. However, PETF is absent in the two species studied in a scleroglossan family, Gekkonidae, which forages by ambush, and present in an iguanian herbivore, as reported herein. We propose that the presence or absence of PETF, in addition to its phylogenetic determinants, is adaptively adjusted to foraging mode.

Seasonal productivity of lizard femoral glands: relationship to social dominance and androgen levels.

Social and hormonal correlates of femoral gland productivity were investigated in groups of adult and juvenile green iguanas (Iguana iguana) over 12 months. Femoral gland productivity, pore size, and the percentage of lipids in the secretions were correlated with plasma testosterone (T) levels in dominant, although not in subordinate, adult males. Secretory activity peaked during the breeding months, at which time dominants produced more secretion than subordinates. Pore size in juvenile males was positively correlated with plasma T levels and frequency of headbob displays in the months corresponding to the adult breeding season. After 18 months of age, individuals that performed visual displays had significantly larger pores than individuals that did not display. These results indicate that femoral gland secretions could function in the ontogeny and maintenance of dominance relationships.

Seasonal variation of lipids in femoral gland secretions of male green iguanas (Iguana iguana).

Femoral gland secretions were collected from 21 captive adult male green iguanas (Iguana iguana) in Orotina, Costa Rica, and San Diego, California, during the breeding (November) and nonbreeding (March) seasons. Lipids were extracted with methylene chloride, weighed, separated by thin-layer chromatography, and analyzed by gas chromatography-mass spectrometry. Free and esterified C14-C26 fatty acids, 5ß-cholestan-3α-ol (epico-prostanol), cholest-5-en-3ß-ol (cholesterol), cholest-5-en-24-methyl-3ß-ol (campesterol), cholesta-5,22-dien-24b-ethyl-3ß-ol (stigmasterol), cholesta-8,24(5α)-dien-4,4,14α-trimethyl-3ß-ol (lanosterol), cholest-5-en-24-ethyl-3ß-ol (ß-sitosterol), and two uncharacterized sterols were indicated. More lipids were recovered from femoral gland secretions obtained during the breeding than the nonbreeding months, indicating that secretion deposits may be more detectable during the mating season.

Naive ophiophagus lizards recognize and avoid venomous snakes using chemical cues.

Monitor lizards prey on snakes. Conversely, venomous snakes prey on juvenile monitor lizards. Immediately after hatching, monitor lizards are naive to all prey items, thus correct assessment of snake prey is paramount for survival. Experiments were conducted to determine how hatchling monitor lizards (Varanus albigularis) with no previous exposure to snakes reacted to sympatric venomous and nonvenomous snakes. Hatchling lizards attacked harmless snakes, but avoided venomous species. Lizards readily accepted meat from skinned snakes, regardless of species. When invertebrate prey covered with skin segments from venomous snakes were restrained from moving, they were usually investigated by tongue-flicking and rejected. Unrestrained skin-covered prey, however, were generally attacked and eaten without prior evaluation by tongue-flicking. Attack was inhibited in trials in which unrestrained prey were tongue-flicked, suggesting that chemical cues contained in snake skins mediate avoidance of venomous snakes. Selection for the ability to perceive snake integumental chemicals may be especially strong in species that both consume and are consumed by snakes.

Tongue-flicking and biting in response to chemical food stimuli by an iguanid lizard (Dipsosaurus dorsalis) having sealed vomeronasal ducts: Vomerolfaction may mediate these behavioral responses.

In the iguanid lizardDipsosaurus dorsalis, chemical food stimuli were discriminated from other odorants by vomerolfaction. This was demonstrated in a 2 × 3 experiment in which groups of lizards with sealed vomeronasal ducts or sham-sealed vomeronasal ducts responded to carrot chemical stimuli, cologne, and distilled water presented on cotton-tipped applicators. Abilities to detect and discriminate food chemicals were abolished in lizards having sealed vomeronasal ducts. For tongue-flick attack score and number of lizards biting, the sham-sealed group responded more strongly to carrot stimuli than to the control stimuli, but the group having sealed ducts did not. Lizards having sham-sealed ducts responded more strongly to carrot stimuli than did lizards having sealed ducts; responses by the two groups of lizards to control stimuli did not differ. Tongue-flicking occurred when the vomeronasal system detected a chemical stimulus from either carrot or cologne. Biting occurred only when the vomeronasal organ detected food stimuli (from carrot). Most duct-sealed lizards opened their mouths, some repeatedly. Mouth-opening thus occurs when the vomeronasal organ does not detect chemicals. It may be an attempt to stimulate or prime the vomeronasal organ or to dislodge the sealant.

Chemical properties of femoral gland secretions in the desert iguana,Dipsosaurus dorsalis.

This study investigates the chemistry of femoral gland secretions in the desert iguana,Dipsosaurus dorsalis (Lacertilia: Iguanidae), and discusses their possible functional significance. Electrophoretic and proton NMR studies indicated that the secretions are composed of approximately 80 % protein and 20% lipid material. Individual differences in polyacrylamide gel banding patterns of femoral gland proteins were found. Reflectance spectroscopy revealed that the secretions strongly absorb longwave ultraviolet light, a feature that may be important in the localization of secretion deposits in the environment.