Chemical Prey Luring in Jackson's Chameleons.

Lizards in the family Chamaeleonidae have been described as wiping a viscous substance from a pouch (the temporal pouch) at the angle of the jaw on branches and then capturing flies that land near the area where the wiping occurs. We confirmed the presence of this pouch in Jackson's chameleons. Histological work suggested that the material contained within is a result of decomposition of food and sloughed skin that has been trapped in the pouch rather than a glandular secretion. Gas chromatography-mass spectrometry indicated the presence of compounds that are both volatile and odiferous and similar to insect pheromones. Choice tests with houseflies revealed attraction to the temporal pouch material. Some authors have speculated that the temporal pouch material serves a function in territory marking and/or predator deterrence. While it may play these roles, our results suggest that it also plays a role in chemical luring of prey.

Corticosterone treatment has subtle effects on thermoregulatory behavior and raises metabolic rate in the New Zealand common gecko, Hoplodactylus maculatus.

Baseline concentrations of adrenal glucocorticoids often vary substantially in wild vertebrates in the field. In at least one ectotherm, females of the New Zealand common gecko, Hoplodactylus maculatus, this variation in baseline (not stress-induced) corticosterone appears to be correlated with variation in body temperature (T(b)). We tested the hypothesis that elevated corticosterone affects thermoregulatory behavior so as to raise T(b) and that, independently of an increase in T(b), corticosterone increases metabolic rate. Compared with geckos receiving placebo implants, those that received implants containing corticosterone displayed heat-seeking behaviors, had a higher mean T(b) in their home cages, and, at one time of day, selected a higher mean T(b) in a thermal gradient. At a constant T(b), corticosterone-treated geckos consumed oxygen at a rate approximately 50% higher than placebo geckos. This work has far-reaching implications for a variety of physiological and ecological processes in ectotherms and suggests that corticosterone should be considered as a variable influencing T(b) and metabolism in future studies.

ACTH-induced stress response during pregnancy in a viviparous gecko: no observed effect on offspring quality.

The typical stress response in reptiles involves the release of corticosterone from the adrenal glands. Elevated maternal concentrations of corticosterone in mammals during pregnancy may have deleterious effects on offspring fitness, and recent work has shown a suppression of the hormonal response to stress during pregnancy in rats. Little is known about the influence of reproductive state on the secretion of corticosterone in viviparous reptiles or on the effects of high levels of corticosterone during reproduction on the developing embryos. We examined whether New Zealand common geckos (Hoplodactylus maculatus), pregnant with embryos at stages 34-35 of development, secrete corticosterone in response to adrenocorticotrophic hormone (ACTH) and whether an ACTH-induced increase in maternal corticosterone affects the outcome of pregnancy. Corticosterone concentrations in pregnant lizards increased more than seven-fold over basal levels following injection of ACTH. However, there were no significant effects of elevated corticosterone on the duration or success of pregnancy, or on various morphological measures, growth, or sprint speed of the offspring. This may reflect a lack of sensitivity of relevant embryonic tissues to corticosterone under the conditions of the present experiment or an ability of the embryos to bind, degrade, or restrict placental transport of corticosterone. Future studies should investigate the possibility of corticosteroid effects on other offspring tissues, including effects in adult life.

A pharmacological examination of Na+ and Cl- transport in two species of freshwater fish.

We examined branchial Na(+) and Cl(-) uptake in two species of stenohaline, freshwater fish (goldfish and the Amazonian neon tetra). Kinetic analysis revealed that the two species had similar uptake capacities and affinities for Na(+) and Cl(-). However, while uptakes of Na(+) and Cl(-) (JNain and JClin, respectively) by goldfish were completely inhibited at pH 4.5 and below, uptake in tetras was unaffected by pH down to 3.25. Examination of Cl(-) transport with blockers indicated that goldfish and neon tetras utilize Cl(-)/HCO-3 exchange; SITS and SCN(-) inhibited Cl(-) uptake in both species. In contrast, large differences in Na(+) transport were indicated between the species. In goldfish, exposure to four Na(+)/H(+) exchange blockers, as well as the Na(+) channel blocker phenamil, strongly inhibited JNain. Further, Na(+) and Cl(-) uptake were strongly inhibited by the Na(+)/K(+)/Cl(-) cotransport inhibitor furosemide, as was JNain in "Cl(-)-free" water and JClin in "Na(+)-free" water. This suggests the presence of multiple transporters and possibly even a direct linkage between the transport of Na(+) and Cl(-) in goldfish. In contrast, none of these drugs strongly reduced Na(+) transport in neon tetras, which raises the possibility of a significantly different Na(+) transport mechanism in this acid-tolerant species.

Protecting embryos from stress: corticosterone effects and the corticosterone response to capture and confinement during pregnancy in a live-bearing lizard (Hoplodactylus maculatus).

Hormones in the embryonic environment, including those of the hypothalamo-pituitary-adrenal (HPA) axis, have profound effects on development in eutherian mammals. However, little is known about their effects in reptiles that have independently evolved viviparity. We investigated whether exogenous corticosterone affected embryonic development in the viviparous gecko Hoplodactylus maculatus, and whether pregnant geckos have a corticosterone response to capture and confinement that is suppressed relative to that in non-pregnant (vitellogenic) females and males. Corticosterone implants (5 mg, slow-release) administered to females in mid-pregnancy caused a large elevation of corticosterone in maternal plasma (P<0.001), probable reductions in embryonic growth and development (P=0.069-0.073), developmental abnormalities and eventual abortions. Cool temperature produced similar reductions in embryonic growth and development (P< or =0.036 cf. warm controls), but pregnancies were eventually successful. Despite the potentially harmful effects of elevated plasma corticosterone, pregnant females did not suppress their corticosterone response to capture and confinement relative to vitellogenic females, and both groups of females had higher responses than males. Future research should address whether lower maternal doses of corticosterone produce non-lethal effects on development that could contribute to phenotypic plasticity. Corticosterone implants also led to increased basking in pregnant females (P<0.001), and basal corticosterone in wild geckos (independent of reproductive condition) was positively correlated with body temperature (P<0.001). Interactions between temperature and corticosterone may have broad significance to other terrestrial ectotherms, and body temperature should be considered as a variable influencing plasma corticosterone concentrations in all future studies on reptiles.

Effects of body temperature and hydration state on organismal performance of toads, Bufo americanus.

Temperature and humidity are dominant environmental variables affecting performance of nocturnal, terrestrial amphibians. Toads are frequently active at body temperatures (T(b)) and hydration states (HS) that yield suboptimal performance. We investigated the combined effects of T(b) and HS on feeding, locomotion, and metabolism of Bufo americanus. More toads responded to the presence of prey when fully hydrated than when dehydrated, and times to orient to prey, maneuver around a barrier, and reach prey were less in hydrated than in dehydrated animals. Time to capture prey decreased with increasing T(b) in fully hydrated, but not dehydrated, toads, and hydrated animals caught prey more rapidly than did dehydrated animals. Distance traveled in 5 min and aerobic scope were affected by T(b). Generally, individuals that performed well in the feeding experiments at a particular T(b) and HS also performed well at a different T(b) and HS. The same was true for distance traveled and aerobic scope. However, within combinations of T(b) and HS, correlations between performance variables were minimal. Specialization of a particular variable resulting in high performance at a certain T(b) and HS does not appear to exact a cost in terms of performance at a different T(b) and HS.

Glomerular and medullary architecture in the kidney of Anna's Hummingbird.

Hummingbirds have rates of water turnover that are among the highest of any bird, consuming up to five times their body mass in nectar each day. To determine if the processing of these extraordinary volumes of water is associated with structural specializations in the kidney, we examined the renal morphology of Anna's hummingbird (Calypte anna) using scanning electron microscopy of vascular and tubular casts. The glomerular tufts are simple, containing a single, unbranched capillary that is spiraled or folded back on itself only one or two times. There is no evidence that nectarivory in this species is associated with a relative increase in the size of the glomeruli. The medullary cones are small, containing only a few loops of Henle and collecting ducts. The vasa recta form a complex network of branching and anastomosing capillaries. In this nectarivore, the structures necessary to produce urine that is hyperosmotic to plasma are poorly developed or absent, which is consistent with urine osmolalities that are uniformly low. J. Morphol. 240:95-100, 1999. © 1999 Wiley-Liss, Inc.

Prey-handling and the evolutionary ecology of sand-swimming lizards (Lerista : Scincidae).

Fossorial lizards differ in morphology from their surface-dwelling relatives. The Australian sphenomorphine skink genus Ctenotus consists of surface-dwelling species, and is closely related to the genus Lerista, which includes both surface-dwelling and fossorial species. Sand-swimming represents the derived condition and has evolved independently in several lineages of Lerista. The heads of lizards in the two genera differ in shape (blunt snout for Ctenotus versus wedge-shaped for Lerista) and in length relative to the body (approximately 20% of snout-vent length for Ctenotus versus 12% for sand-swimming Lerista). Do these specializations affect the sizes or types of prey that can be consumed by Lerista? We compared prey-handling by Ctenotus and Lerista to correlate morphological differences with differences in prey-handling ability, and to distinguish the effects of snout shape and head length. Feeding trials included three categories of insect prey that the lizards normally eat: soft-bodied larvae (Lepidoptera), hard-bodied larvae (Coleoptera), and roaches (Blatoidea). In comparisons based on the mass of a prey item relative to the mass of a lizard, Lerista had longer handling times for all prey categories and were limited to smaller prey than were Ctenotus. However, when comparisons were based on the length of prey relative to the length of a lizard's head, Lerista ate some elongate prey as fast or faster than did Ctenotus, and both genera successfully swallowed prey more than twice the length of their own head. Thus, the differences in prey-handling performance of Ctenotus and Lerista probably result from the fact that Lerista have a relatively shorter head than Ctenotus. All Lerista species, surface-dwelling and fossorial, have short heads compared to primitive sphenomorphine lizards. Fossorial species of Lerista have elongate trunks, and consequently their heads are shorter in proportion to trunk length than those of surface-dwelling Lerista. However, most fossorial species of Lerista are longer and heavier than any of their surface-dwelling congeners, and the heads of these fossorial species are large relative to the prey they encounter. As a consequence, the diets of large fossorial species of Lerista do not appear to be limited by their morphological specialization for sand-swimming.