Ethyl carbamate in foods and beverages: a review

Food and beverages contain many toxic chemicals that raise health concerns. Ethyl carbamate (EC) or urethane is the ethyl ester of carbamic acid. It occurs at low level, from ng/L to mg/L, in many fermented foods and beverages. Ethyl carbamate is genotoxic and carcinogenic for a number of species such as mice, rats, hamsters and monkeys. It has been classified as a group 2A carcinogen, “probably carcinogenic to humans”, by the World Health Organization’s International Agency for Research on Cancer (IARC) in 2007. The benchmark dose lower limit of ethyl carbamate is 0.3 mg/kg bw per day and the mean intake of ethyl carbamate from food is approximately 15 ng/kg bw per day. Those levels were calculated for relevant foods including bread, fermented milk products and soy sauce. Alcoholic beverages were not included in this calculation. However, high levels of ethyl carbamate can be found in distillated spirits at concentrations ranging from 0.01 to 12 mg/L depending on to the origin of spirit. Alcoholic drinks should thus be considered as a source of ethyl carbamate. Ethyl carbamate is produced by several chemical mechanisms: first, from urea and various proteins like citrulline produced during the fermentation step and second from cyanide, and hydrocyanic acid, via ethyl carbamate precursors such as cyanate. A large panel of ethyl carbamate formation mechanisms is described from simple ethanolysis of urea in homogeneous liquid phase to photochemical oxidation of cyanide ion or complex heterogeneous gas/solid catalytic reactions. Determination of ethyl carbamate in foods and beverages involves various strategies according to the material, food or beverage, solid or liquid, and according to the concentration, from ng/L to mg/L. Usually, adapted extractive techniques and pre-concentration step are followed by analysis by gas chromatography coupled to mass spectrometry (GC–MS of GC–MS–MS). High performance liquid chromatography (HPLC) and semi-quantitative spectroscopic methods (infra-red) are also proposed as valuable alternatives to the classical but time-consuming GC–MS. Various preventing methods are developed and used in some cases at industrial scale to lower ethyl carbamate levels in food. Two types of preventing methods are described. First, adapted and optimised practices in all step of the chain of foods’ (or beverages) production lead in general to low ethyl carbamate level. Second, the abatement of ethyl carbamate precursors can be done by adapted enzymatic, physical chemical or chemical methods according to the natures of raw materials and conditions of their production processes.     

Efficiency of mercapto flavor compounds in removing acrylamide under high temperature and low humidity conditions

Acrylamide (AA) is a potential human carcinogen, genotoxicant, and neurotoxicant. Thus, the aim of this study was to examine the ability of mercapto flavor compounds to remove AA released from consumer packaging into food products. Four mercapto flavor compounds including 1,2-ethanedithiol, 1-butanethiol, 2-methyl-3-furanthiol, and 2-furanmethanethiol were employed to extract AA in model system using high temperature and low humidity. Our study showed that mercaptans were effective in eliminating AA in our model system. In order to remove 0.2 μmol AA, the optimal conditions in the reaction system were mercaptan flavor chemicals at 5 μmol, temperature 180 °C, and reaction time 25 min. In the presence of a higher pH, the greater was the amount of AA eliminated. Evidence indicates that employment of mercapto flavor chemicals under certain temperature and pH conditions is a reliable method to remove any unwanted AA from food products.     

Variability in host plant chemistry: behavioural responses and life-history parameters of the Colorado potato beetle (Leptinotarsa decemlineata)

Summary. Many studies investigating effects of plant chemicals on herbivore performance have reported contradictory results, perhaps because of possible interaction between different chemicals. Also, a herbivore’s performance is not necessarily consistent with its food or oviposition preference. Our aim was to investigate simultaneously antibiosis (larval growth and survival) and antixenosis (oviposition and feeding preferences) responses in herbivore to three plant chemicals, of which one is expected to have positive and two are expected to have negative effects. Antibiosis was measured by correlating the nitrogen and glycoalkaloid levels in host plants to the survival and adult size of Leptinotarsa decemlineata, by rearing larvae on whole plants of three potato varieties. Although host plants differed in their glycoalkaloid levels, survival rate and adult body size did not differ among beetles reared on different potato varieties. This suggests that beetles are quite robust for differences in both foliar α-chaconine and foliar α-solanine content. However, differences in antixenosis were found although they could not be directly predicted from the leaf chemistry. Females preferred to lay their eggs on the variety with high α-solanine content (Nevsky) towards which males showed a tendency to feeding preference. Overall, our results confirm that beetles are well adapted to the chemical defences of potato plants as potato varieties did not significantly affect beetle performance, but differences in oviposition preference may still result in major differences in the amount of damage inflicted on plants in the fields.     

Sodium and potassium in the edible portions of thirty fish species

The 30 species of limnic and marine fishes analyzed in the present study represent excellent foods for inclusion in diets that require a low sodium content. In none of these species, not even in the marine ones, did the content of sodium exceed the maximum amount (100 mg/100 g fish meat) specified by food authorities for low sodium diets.     

Diet-induced chemical phytomimesis by twig-like caterpillars of Biston robustum Butler (Lepidoptera: Geometridae)

Summary. Polyphagous caterpillars of the giant geometer Biston robustum resemble the twigs of their respective food sources in color and shape. Common predatory ants, including Lasius and Formica, were often observed to freely prowl directly on caterpillars bodies, even after antennal contact. This suggests that the cuticular chemicals of the caterpillars resemble those of the twigs of the foodplants, so we analyzed both by GC and GC-MS. The chemical compositions differed among caterpillars fed on a cherry, Prunus yedoensis, a chinquapin Castanopsis cuspidata, and a camellia Camellia japonica. The cuticular chemicals of the caterpillars resembled those of their corresponding food sources. When the caterpillar diets were switched from the cherry to camellia or chinquapin at the 4^th instars, the caterpillars cuticular chemicals changed after molting to resemble those of their respective foods. Caterpillars also changed their cuticular chemicals when they perched on cherry twigs and fed on camellia or chinquapin leaves, but not when they perched on camellia or chinquapin twigs and fed on cherry leaves. The chemical similarities between the caterpillars and the twigs were due to the digestion of host leaves, which indicates that this is a diet-induced adaptation.     

太原地区食物中的林丹残留与人群摄食暴露(Oral Intake of Lindane by Population in Taiyuan)

尽管我国有机氯农药已禁用多年,但环境和食物中仍有有机氯农药残留.以太原市为研究区域,采集了代表性的6类24种食物,测定了林丹残留量,分析了太原人群对林丹的口摄暴露风险.研究结果表明,24种食物中林丹残留量在未检出到1.5ng·g-(1湿重)范围内.残留量较高的为鱼、水果、蔬菜和肉类.多数食物残留浓度高于2005～2007年北京和沈阳类似调查的结果.与历史数据(1992、2000年)相比,食物中林丹残留浓度大幅度下降,动物类食物下降1～2个量级,蔬菜和水果降幅较小.目前各类食物中林丹残留量均低于国家和欧盟的相应标准.平均而言,各年龄段人群日均口摄暴露量也低于美国环保局的标准,但由于食物残留浓度、个体体重及膳食结构变异较大,导致个体暴露水平差别很大,各年龄段,特别是成年人中有少数人日均口摄暴露浓度超过美国环保局制定的0.3g·kg-1·d-1的允许标准.     

Does optimal foraging theory explain why suburban Florida scrub-jays (Aphelocoma coerulescens) feed their young human-provided food?

Optimal foraging theory assumes that a forager can adequately assess the quality of its prey and predicts that parents feed their young low-quality foods only when suffering unpredicted reductions in their ability to provision. Wildland Florida scrub-jays feed their young exclusively arthropods, but suburban parents include human-provided foods in the nestling diet, with possible costs in terms of reduced growth and survival. We tested experimentally whether parents feed human-provided foods, given the apparent costs, because: 1) they do not discriminate between food types, 2) they switch to low-quality, abundant foods when natural food availability in the environment is low, or 3) they switch when the time needed to obtain natural food is high. Parents discriminated between natural and human-provided foods by showing a preference for natural foods when rearing young. When the handling time of natural foods was increased experimentally, parents in the suburban and wildland habitats switched to human-provided foods. Supplementation with natural foods increased preference for this food in both habitats. Suburban parents chose more natural foods than wildland parents, suggesting that they have a greater preference for natural foods. Regardless of preferences demonstrated at feeders, parents in both the suburbs and wildlands delivered mostly natural foods to nestlings, independent of natural food availability. Nonetheless, natural foods are likely to be scarcer in the environment than in our experimental tests. Because natural food availability is lower in the suburbs than in the wildland habitat, parents in the suburbs may be forced to switch to human-provided foods when feeding nestlings.     

Giving-updensity and dietary shifts in the white-footed mouse, Peromyscus leucopus

Dietary shifts are commonly exhibited by omnivorous consumers when foraging from variable food resources. One advantage of dietary shifts for a consumer is the ability to gain complementary resources from different foods. In addition, dietary shifts often affect food-web dynamics. Despite the importance of dietary shifts to organismal, community, and ecosystem ecology, empirical studies of the ecological mechanisms that control dietary shifts are limited in scope. In this study, we tested the effects of complementary resources on dietary shifts of an omnivorous mammal, the white-footed mouse Peromyscus leucopus, in the context of depletable food patches in the natural environment. We used two complementary resources: seeds that provide a higher energy gain per unit handling time and mealworms that provide a higher protein gain per unit handling time. Stable isotopes of carbon and nitrogen (delta13C, delta15N) in mouse plasma were used to quantify dietary shifts, and we determined giving-up density (GUD), the food density at which a forager leaves a food patch (for an optimal forager, it should correspond to the quitting harvest rate that balances net fitness gain with various costs of foraging). The results showed that GUD increased most significantly when a mixture of seeds and mealworms was added, compared to when only seeds or mealworms were added. This suggests that, given a similar level of food availability, a patch with a mixture of complementary foods is of higher quality than a patch with only one type of food. Moreover, GUD measured with seeds (GUDs) correlated positively with seed availability, and GUD measured with mealworms (GUDmw) correlated positively with mealworm availability, indicating that the marginal value of seeds or mealworms decreases with their relatively availability in the environment. As GUDs increased, P. leucopus shifted their diets toward higher trophic levels, and as GUDmw increased, P. leucopus shifted their diets toward lower trophic levels, suggesting dietary shifts driven by food complementarity. This study demonstrated that the combination of giving-up density and stable-isotope analysis holds great potential for testing ecological mechanisms underlying dietary shifts.     

Proximate control of siblicide in cattle egrets: a test of the food-amount hypothesis

Avian sibling aggression plays an important role in controlling food distribution among nest mates. The food-amount hypothesis predicts that the amount of food obtained by siblings acts as a proximate cue controlling their level of aggression. The importance of this cue to cattle egrets (Bubulcus ibis) in Oklahoma was evaluated by studying parental feeding rates, food distribution among nestlings, and nestling aggression in three-chick broods [A-(oldest), B-, and C-chicks]. We compared nests in which siblicide occurred to nests where all three chicks survived (nonsiblicide nests). Relative to nonsiblicide nests, siblicide nests received decreasing amounts of food as the day of siblicide approached. Similarly, aggression levels of all three chicks in siblicide nests increased significantly compared with nonsiblicide nests, with most of the aggressive behavior involving B- and C-chicks. As a result, on a per-day basis, food amount and aggression exhibited a strong, negative correlation, thus providing support for the food-amount hypothesis. Though the total amount of food delivered to siblicide nests declined on the days prior to siblicide, the amount of food received by A-chicks in these nests did not. Relative to nonsiblicide nests, A-chicks in siblicide nests received an increased share (percent of volume) of the food delivered at the expense of C-chicks, with the percent remaining the same for B-chicks. The percentage of food B-chicks received the day after siblicide increased significantly from that received the day before siblicide, with no change occurring in either the amount or percentage of food received by A-chicks; clearly, B-chicks were the beneficiary of their aggressive actions that resulted in the death of C-chicks. We provide evidence supporting the hypothesis that aggression is proximately linked to food amount, possibly by a relatively simple cue such as hunger. Received: 25 November 1994/Accepted after revision: 10 February 1996     

多溴联苯醚的生物富集效应研究进展

研究污染物的生物富集效应对于预测污染物在生物体内的含量、建立环境标准以及评估污染物的生态风险具有重要的意义.论文结合近年来国内外有关多溴联苯醚(PBDEs)的生物富集及其沿食物链(网)生物放大效应的研究文献,对PBDEs的生物富集效应进行了综述.文献计算的生物富集因子(BAFs)、生物-沉积物/土壤生物富集因子(BSAFs)和生物放大因子(BMFs)表明,生物对大多数PBDEs具有生物富集作用,且生物对PBDEs的富集能力与其生物进化等级及其营养级有关.文献计算的营养级放大因子(TMFs)表明,大多数PBDE单体可以在食物网上产生生物放大效应,但只有较少单体具有统计上的显著性.生物的生理生化参数、化合物本身的特性以及环境条件等因素影响了PBDEs在生物体内及食物链(网)上的富集与放大.     

Aluminium and calcium in soil and food from Guam,Palau and Jamaica: Implications for amyotrophic lateral sclerosis and parkinsonism-dementia syndromes of Guam

Low calcium and high aluminium concentrations in the soils, waters and native foods have been hypothesised as environmental factors contributing to the unusually high incidence of amyotrophic lateral sclerosis and parkinsonism with dementia (ALS-PD) found on the island of Guam. The amounts of elemental aluminium and calcium were measured in foods of the native diet of the Chamorro people of Guam. The amount of aluminium eluted from topsoil by water at pH 7 at 22 °C was also measured. For comparison, food, water and soil samples were collected from two islands which have not reported a high incidence of ALS-PD syndromes: Palau and Jamaica.Compared with agricultural soils of Jamaica or Palau, the agricultural soils of Guam averaged 42-fold higher yield of elutable aluminium. The food data, however, do not indicate a differentially high exposure to elemental aluminium or low calcium intake in the diet of any one population. While this study did not detect an unusually high dietary aluminium or low dietary calcium content, the soils and possibly the dusts of Guam may be a major source of aluminium entering the body of the native people, particularly through the respiratory epithelium. Since iipid soluble organic ligands of aluminium more readily penetrate epithelial membranes, further study of soil aluminium ligands is required.     

Correlations of food distribution and patch size with agonistic interactions in female vervets (Chlorocebus aethiops) and patas monkeys (Erythrocebus patas) living in simple habitats

Food distribution is hypothesized to be important in determining the nature of female relationships within social groups of primates. When food limits female reproductive success, spatially clumped foods are expected to produce strong, linear dominance hierarchies within groups, whereas more spatially dispersed foods are expected to produce weaker or non-existent dominance hierarchies. The association between food distribution and competitive relationships presumably occurs because clumped foods are usurpable but dispersed foods are not. We examined the spatial distribution of food patches (trees) and patch size relative to feeding behavior and agonistic interactions in vervets and patas monkeys, two closely related and sympatric species that nonetheless differ in the strength of the female dominance hierarchy. Food patches of both patas monkeys and vervets were small in size and randomly distributed in Acacia drepanolobium habitat. In contrast, in A. xanthophloea woodland, the habitat type that was exclusively used by vervets, food patches were larger and more spatially clumped. These similarities and differences between and within species were correlated with similarities and differences in the strength and linearity of their dominance hierarchies. Patas monkeys and vervets in A. drepanolobium habitat had dominance hierarchies that were weakly defined because there were relatively few agonistic interactions between females. By contrast, in A. xanthophloea habitat, vervets had a stronger, linear dominance hierarchy characterized by a higher rate of agonistic interactions over food. The covariation of agonistic interactions with patch size is discussed in relation to depletion time, another characteristic that may covary with food distribution, and resource renewal rate, an important determinant of agonistic interactions in insectivorous birds, fishes, insects, and mammals. Received: 18 February 2000 / Revised: 5 September 2000 / Accepted: 26 September 2000     

Movements of vervets (Cercopithecus aethiops) and patas monkeys (Erythrocebus patas) as estimators of food resource size, density, and distribution

The effect of food resources on behavior has been difficult to measure. Here we use animals themselves to describe “effective” food abundance and distribution by comparing, relative to where individuals stopped to eat, movements of (1) adult females living in a small group of vervet monkeys (Cercopithecus aethiops) with those living in a large group and (2) vervets and patas monkeys (Erythrocebus patas). Although females in the large vervet group travelled farther and stopped to eat more often than females in the small vervet group, these differences resulted from foraging in Acacia drepanolobium habitat. In A. xanthophloea habitat, females in the large group travelled less far, travelled shorter distances between foods, and stopped as often as females in the small group. Greater foraging costs of females in larger vervet groups may be offset by access to home ranges of better quality. Compared to patas, vervets travelled shorter distances, moved shorter distances between food sites, stopped less often, and had longer feeding bouts, suggesting that foods of vervets are denser and larger, overall, than foods of patas. When vervets foraged in A. drepanolobium habitat, also the habitat of patas, their foraging behavior became more like that of patas. Vervets travelled farther, stopped more often, and spent less time at food sites in A. drepanolobium habitat than in A. xanthophloea habitat, suggesting that foods are smaller and less usurpable in A. drepanolobium habitat. Distance between foods, a component of food distribution, did not increase, however. The critical variable underlying usurpability of foods may be food site depletion time, a temporal measure. Received: 14 March 1997 / Accepted after revision: 19 October 1997     

Chemically mediated competition between microbes and animals: microbes as consumers in food webs

Microbes are known to affect ecosystems and communities as decomposers, pathogens, and mutualists. However, they also may function as classic consumers and competitors with animals if they chemically deter larger consumers from using rich food-falls such as carrion, fruits, and seeds that can represent critical windfalls to both microbes and animals. Microbes often use chemicals (i.e., antibiotics) to compete against other microbes. Thus using chemicals against larger competitors might be expected and could redirect significant energy subsidies from upper trophic levels to the detrital pathway. When we baited traps in a coastal marine ecosystem with fresh vs. microbe-laden fish carrion, fresh carrion attracted 2.6 times as many animals per trap as microbe-laden carrion. This resulted from fresh carrion being found more frequently and from attracting more animals when found. Microbe-laden carrion was four times more likely to be uncolonized by large consumers than was fresh carrion. In the lab, the most common animal found in our traps (the stone crab Menippe mercenaria) ate fresh carrion 2.4 times more frequently than microbe-laden carrion. Bacteria-removal experiments and feeding bioassays using organic extracts of microbe-laden carrion showed that bacteria produced noxious chemicals that deterred animal consumers. Thus bacteria compete with large animal scavengers by rendering carcasses chemically repugnant. Because food-fall resources such as carrion are major food subsidies in many ecosystems, chemically mediated competition between microbes and animals could be an important, common, but underappreciated interaction within many communities.     

Chemical defense and evolution in the Sacoglossa (Mollusca: Gastropoda: Opisthobranchia)

Summary. Recent advances in both the systematics and the natural products chemistry of the order Sacoglossa (=Ascoglossa) in the gastropod subclass Opisthobranchia suggest a revised and improved historical account of the evolution of the group. Although the algal genus Caulerpa makes a suitable model for the ancestral food of the order, other siphonaceous algae are consistent with both morphological and chemical data. At an early evolutionary stage terpenoids are sequestered from the food, and used defensively, often with modification. With an evolutionary switch to different kinds of algal food, there is often a shift to other, related defensive chemicals. A switch to new food source sometimes leads to the abandonment of chemical defense, but in other cases there is de-novo synthesis of defensive metabolites. The synthesis of polypropionates, which are used defensively, occurs in some other gastropods, but otherwise is known only in fungi. The systematic distribution of the defensive polypropionates suggests that their defensive use has evolved several times among gastropods. Failure to detect them may mean that synthetic capacity has evolved more than once, or it may mean that they exist at low levels, perhaps having a non-defensive function. Received 9 February 1998; accepted 20 March 1998.     

Live algae as a vector candidate for hydrophobic polychlorinated biphenyls translocation to bivalve filter feeders for laboratory toxicity test

Live algae carrying hydrophobic xenobiotics can be an effective vector candidate for the chemical translocation to filter feeders in the laboratory toxicity test, but information on their application is lacking. Time-course uptake and elimination of polychlorinated biphenyls (PCBs) (0, 50, 100, and 500 ng g(-1) by two key algal foods, Isochrysis galbana and Tetraselmis suecica, were measured. Both of the algae achieved maximum concentration in an hourafter PCBs exposure regardless the chemical concentrations in our time-course measurements (0, 1, 5, 10, 24, 48 and 72 hrs). Once achieved the maximum concentration, the algae shortly exhibited elimination or eliminating tendency depending on the chemical concentrations. Algae exposed to the chemical for 1 and 24 hrs (hereafter 1 and 24 hr vectors, respectively) were then evaluated as a chemical translocation vector by feeding test to larval and spat Crassostrea gigas. In the feeding test the 24 hr vector, which contained lower chemicals than the 1-hr vector, appeared to be more damaging the early lives of the oyster. This was particularly significant for vectors of higher PCBs (p<0.05), probably due to algal reduction in food value by the prolonged chemical stress. These findings imply that 1 hr exposure is long enough for a generation of algal vector for laboratory toxicity test, minimizing data error resulted from reduction in food value by longer chemical stress.     

The use of simulation modeling to evaluate the mechanisms responsible for the nutritional benefits of food-for-protection mutualisms

In some mutualisms, a plant or insect provides a food resource in exchange for protection from herbivores, competitors or predators. This food resource can benefit the consumer, but the relative importance of different mechanisms responsible for this benefit is unclear. We used a colony-level simulation model to test the relative importance of increased larval production, increased worker foraging and increased worker survival for colony growth of fire ants, Solenopsis invicta, that consume plant-based foods. Increased food for larvae had the largest effect on colony growth of S. invicta followed by decreased worker mortality. Increased foraging rate had a small effect in the simulation model but data from a small laboratory experiment and another published study suggest that plant-based foods have little or no effect on foraging rates of S. invicta. Colony growth steadily increased the longer plant-based food was available and colonies were most responsive to plant-based food in the early summer (i.e., June). Our results demonstrate that population level simulation modeling can be a useful tool for examining the ecology of mutualistic interactions and the mechanisms through which species interact.     

Utility of check dams in dilution of fluoride concentration in ground water and the resultant analysis of blood serum and urine of villagers,Anantapur District,Andhra Pradesh,India

High levels of fluoride (beyond 1.5 ppm) in ground water as source of drinking water are common in many parts of Andhra Pradesh, India, causing fluorosis. The study carried out in endemic Nalgonda District, Andhra Pradesh, has indicated that the fluoride-rich ground water present in the wells located down stream and close to the surface water bodies is getting diluted by the low-fluoride surface water. Encouraged by this result, check dams were constructed upstream of the identified marginally high fluoride bearing ground water zones in Anantapur District to reduce fluoride levels as an alternate solution for safe drinking water.In this paper, an attempt is made to study the utility and effect of these check dams in dilution of fluoride concentration in drinking water and its resultant impact on the health aspects of certain villagers of Anantapur District through the analysis of their blood serum and urine. Ground water samples from three fluoride-affected villages, blood and urine of males and females from the same villages were collected and analyzed for fluoride using ion selective electrode method. The results indicated that the fluoride levels in blood serum and urine of males in the age group of 5–11 years are found to be the highest. The concentration of fluoride in ground water is directly proportional to the concentration of fluoride in blood serum and urine. The concentration of fluoride in ground water with depth of the aquifer is a function of lithology, amount and duration of rainfall, rate of infiltration, level of ground water exploitation in the area etc. The construction of check dams upstream of the identified marginally high fluoride waters will not only cause additional recharge of ground water but also reduces the fluoride concentration eventually improving the health of the villagers.     

Female sensory bias may allow honest chemical signaling by male Iberian rock lizards

Some mate choice theories propose that only male signals that are honest and condition-dependent can be stable, while another hypothesis states that males evolve signals that exploit the sensory system of females. However, sensory traps might evolve into honest signals if they are differentially costly for males. We tested whether a pre-existing sensory bias for food chemicals explained chemosensory preferences of female Iberian rock lizards for male scents. We manipulated hunger levels of females and found that food-deprived females had increased chemosensory responses to chemical stimuli from both invertebrate prey and femoral secretions of males, but not to control water. Further tests suggested that cholesta-5,7-dien-3-ol (provitamin D₃), a lipid found in both prey and males’ scent, may be one of the chemicals eliciting these responses. Moreover, hungry females spent more time on scent marks of males that had experimentally increased cholesta-5,7-dien-3-ol than on scent marks of males alone, whereas for control females this effect was not significant. We suggest that preexisting sensory bias for essential nutrients (i.e., provitamin D) may be the origin of similar female responses to male chemicals. However, previous studies have suggested that the allocation of these chemicals to ornaments is costly and only high quality males can afford it. Therefore, preexisting sensory bias for essential nutrients may further allow the evolution and maintenance of honest sexual displays.     

Lingual and biting responses to prey chemicals by ingestively naive scincid lizards: discrimination from control chemicals,time course,and effect of method of stimulus presentation

Summary. We tested responses to prey chemicals by lizard hatchlings of an oviparous species and neonates of a viviparous species, neither of which had never eaten. Both species responded more strongly to prey chemicals than to odorous and odorless control stimuli presented on cotton swabs. Although only a few species have been examined, all that have been tested have an innate capacity for prey chemical discrimination, suggesting that this innate response to prey chemicals is widespread among lizards that use the lingual-vomeronasal system to locate and identify prey. Innate prey chemical discrimination has the great advantage of permitting lizards lacking prior experience with food to respond appropriately to chemical cues associated with food. Both species discriminated prey chemicals from control substances at age three days, earlier than previously known. Our data hint that Mabuya macularia may be capable of discrimination on its day of birth, but further study is needed to determine the exact onset. A stronger tendency to attack swabs bearing prey chemicals by Scincella lateralis than by M. macularia may be explained by differences in defensiveness near an experimenter or by differences in the importance of visual prey cues for confirmation of chemical cues in the natural habitats of these species. In M. macularia responses to the control stimuli declined over days of testing, suggesting habituation, but responses to prey chemicals did not habituate by the third day of testing, which is interpreted as a possible adaptive response to permit location of food. In the standard method of stimulus presentation, a cotton swab bearing a chemical stimulus is placed anterior to a lizard's snout. We tested a new method in which the swab was placed in continuous contact with the lizard's anterior labial scales. The new method elicited significantly stronger responses from M. macularia. We discuss reasons for this finding and applications for the new method. Received 2 September 1999; accepted 15 December 1999