Electrophysiological responses of four fungivorous coleoptera to volatiles of Trametes versicolor: implications for host selection

Fungi of the genus Trametes are known as important wood decomposers and are colonized by various species of Coleoptera and other arthropods. The aim of the present study was to investigate the importance of volatile chemical compounds as key attraction factors in recognition and host selection by species of Erotylidae (Dacne bipustulata, Tritoma bipustulata) as well as Cisidae (Sulcacis affinis) and Tenebrionidae (Diaperis boleti). Volatiles from freshly collected Trametes versicolor were collected by headspace sampling technique and identified by combined gas chromatography–mass spectrometry (GC–MS). To evaluate the biological significance of the volatiles we performed behavioural tests and recorded antennal responses of the fungus-inhabiting species by gas chromatography with electroantennographic detection (GC-EAD). The scent of T. versicolor was found to be dominated by sesquiterpenes; in GC-EAD 6 of these compounds elicited reproducible antennal signals in the tested species. Highly significant attraction effects to the fungus, the obtained odour samples and previously described fungal C₈-compounds were observed in behavioural tests. The possibility to detect these chemical compounds as a key cue for host selection implicate that beetles are able to discriminate between fungi of different age as well as different stages of colonization.     

Effects of testosterone supplementation on chemical signals of male Iberian wall lizards: consequences for female mate choice

In some lizards, female mate choice is influenced by chemicals secreted by males, e.g., via the femoral glands. Secretions of the femoral glands are under direct androgenic control and vary seasonally with androgen production. However, whether increased testosterone (T) levels affect the concentration and chemical composition of secretions or their attractiveness to females is unknown. We manipulated T levels of male Iberian wall lizards, Podarcis hispanica, with silastic implants. Differential tongue-flick rates indicated that females detected and discriminated between femoral secretions of control and T-implanted males based on chemical cues alone. Females showed greater responses to secretions of T-males, which might suggest that T increased the concentration of chemical signals. Further analyses by gas chromatography–mass spectrometry indicated that T supplementation induced qualitative changes in lipid composition of femoral secretions. T-males had decreased relative proportions of cholesta-5,7-dien-3-ol in secretions, which might be related to the negative effects of T on the immune system and on lipid metabolism. However, experiments of choice of males’ scent showed that females neither preferred nor avoided the scent marks of T-males but preferred males that maintained higher proportions of cholesta-5,7-dien-3-ol in secretions, independently of the experimental manipulation. Thus, because this steroid is negatively affected by T, there might be trade-offs among increasing T levels to increase the production of chemical secretions, maintain metabolism, and attract females.     

Interpopulational variation in chemosensory responses to selected steroids from femoral secretions of male lizards, Podarcis hispanica, mirrors population differences in chemical signals

Chemical signals are important for mate and species recognition. If variation in chemical signals occurs between populations of the same species, these differences could later preclude mating between populations and lead to speciation. In the Iberian wall lizard, Podarcis hispanica, the lipophilic fraction of femoral secretions of males is mainly a mix of steroids and fatty acids. Among steroids, the most abundant compounds are cholesterol and cholesta-5,7-dien-3-ol, which are implicated in intraspecific communication and sexual selection. Interpopulational differences in chemical signals of males, and in response to these chemicals, could contribute to reproductive isolation between populations, which would explain the known genetic differences between these populations. Chemical analyses indicated that five distinct populations of this lizard from Madrid (Central Spain) differed in the proportions of two steroids (cholesterol and cholesta-5,7-dien-3-ol) in femoral secretions. Moreover, lizards discriminated and had high chemosensory responses (i.e., high tongue-flick rates) to these steroids, but showed interpopulational differences. Lizards from populations with cold temperatures and high relative humidity (i.e., northern Madrid) elicited higher responses to these steroids, whereas the converse occurred for lizards from populations occupying dry and hot habitats (i.e., southern Madrid). Interestingly, the magnitude of the chemosensory responses to cholesta-5,7-dien-3-ol in each population mirrored the abundance of this compound in secretions of males of that population. These results suggest that the importance of cholesta-5,7-dien-3-ol in males’ secretions might be lower for lizards from the southern populations. These differences in the relative importance of chemical signals could explain reproductive isolation and cryptic speciation between populations of this lizard.     

Interpopulational differences in chemical composition and chemosensory recognition of femoral gland secretions of male lizards Podarcis hispanica: implications for sexual isolation in a species complex

Summary. Molecular studies suggest that the Iberian wall lizard, Podarcis hispanica, forms a species complex with several monophyletic types. In Central Spain two of these types are spatially not isolated and may interact. Sex pheromones are important for species recognition and, thus, differences between lizards’ types in chemicals used in intraspecific communication could lead to reproductive isolation. Analyses by GC-MS showed that the femoral gland secretions of adult males of different types were different. Males of one type had twelve exclusive compounds, and proportions of some shared compounds differed. This presumably would reflect selection for the persistency and efficiency of chemical signals in different environments; less volatile compounds and with a higher chemical stability being favoured in the type of lizards inhabiting more humid climatic conditions. Differential tongue-flick rates to scents from femoral secretions indicated that males were able to detect and discriminate between males of different types based on chemical cues alone. In contrast, females detected but did not seem able to discriminate between scents of the two types of males. Thus, multiple factors might be simultaneously acting either against or in favor of speciation, leading, on the one hand, to genetic differences between types, but, on the other hand, probably precluding an effective reproductive isolation in areas where both types of lizards may interact.     

The scent of sun worship: basking experience alters scent mark composition in male lizards

Signals used in female choice should honestly advertise the benefits that males can provide, with direct benefits often argued as being more important than indirect benefits. However, the nature of direct benefits in species without paternal care or nuptial gifts is poorly understood. Previous studies on lizards suggest that females decide where to settle and assumedly who to mate with based on information contained in scent marks from territorial males. Access to high-quality thermal resources is crucial for female reproductive success. Females may therefore be able to detect and exploit thermal-induced variation in the chemical composition of male scent marks when assessing the quality of his territory. We show that the amount of time male wall lizards (Podarcis muralis) are allowed to bask significantly alters the chemical composition of their femoral secretions used in scent marking. The direction of the change is consistent with adaptive plasticity to maintain signalling efficacy under warm conditions that increase evaporation of femoral secretions. The compounds affected by basking experience included those previously associated with male quality or shown to mediate male–male competition in lizards. However, whilst female lizards could discriminate between scent marks of males that had experienced different basking conditions, they did not preferentially associate with the scent from males from high-quality thermal conditions. These results highlight the potential importance of a previously neglected environmental effect on chemical signalling. We suggest thermal effects may have significant consequences for scent-mark composition in variable environments, with potential repercussions on olfactory communication in lizards.     

Experimental support for the cost–benefit model of lizard thermoregulation

According to Huey and Slatkin’s [Q Rev Biol 51:363–384, 1976] cost–benefit model of behavioural thermoregulation, lizards should adjust their thermoregulatory strategy between active thermoregulation and thermoconformity (no thermoregulation) according to the costs (time and energy spent thermoregulating, exposure to predators), benefits (optimised physiological performance) and thermal quality of environment associated with a given situation. However, Gilchrist’s [Am Nat 146:252–270, 1995] model of thermal specialisation suggests that apparently costly mechanisms of behavioural thermoregulation can greatly increase fitness if the optimal body temperature is achieved. Field studies of ectotherm thermoregulatory strategies under extreme cold conditions and experiments testing the effects of cool environments on thermoregulatory behaviour are surprisingly scarce. We conducted laboratory experiments to test if common lizards Zootoca vivipara (an active thermoregulator in the field) are able to switch between active thermoregulation and thermoconformity in response to different thermal environments. We found that lizards in treatments with an opportunity to reach their preferred body temperature thermoregulated accurately, maintained their level of daily activity and improved their body condition considerably. In contrast, lizards in the treatment where the preferred body temperature could not be reached became thermoconformers, decreased their daily activity (except for gravid females) and did not increase their body condition. Our results show that lizards can indeed change their thermoregulatory strategy but stress that maintaining the preferred body temperature and, thus, optimising the physiological performance have high priority in lizard behaviour.     

Size-based predation by kookaburras (Dacelo novaeguineae) on lizards (Eulamprus tympanum: Scincidae): what determines prey vulnerability?

Lizards and birds are both popular ”model organisms” in behavioural ecology, but the interactions between them have attracted little study. Given the putative importance of birds as predators of diurnal lizards, it is of considerable interest to know which traits (of lizards as well as birds) influence the outcome of a predatory attempt. We studied predation by giant terrestrial kingfishers (kookaburras, Dacelo novaeguineae: Alcedinidae) on heliothermic diurnal lizards (highland water skinks, Eulamprus tympanum: Scincidae), with particular reference to the role of prey (lizard) size. Our approach was twofold: to gather direct evidence (sizes of lizards consumed in the field, compared to those available) and indirect evidence (size-related shifts in lizard behaviour). We quantified the size structure of a natural population of skinks (determined by an extensive mark-recapture program), and compared it to the sizes of wild lizards taken by kookaburras (determined by analysis of prey remains left at the birds’ nests). Kookaburras showed size-based predation: they preyed mainly on small and medium-sized rather than large lizards in the field. However, the mechanism producing this bias remains elusive. It is not due to any distinctive behavioural attributes (locomotor ability, activity level, habitat usage) of the lizards of the size class disproportionately taken by the kookaburras. The greater vulnerability of subadult lizards may reflect subtle ontogenetic shifts in ecological and behavioural traits, but our data suggest that great caution is needed in inferring patterns of vulnerability to predation from indirect measures based on either the prey or the predator alone. Instead, we need direct observations on the interaction between the two. Received: 30 May 2000 / Revised: 29 July 2000 / Accepted: 26 August 2000     

Does responsiveness to predator scents affect lizard survivorship?

Many prey organisms respond to predator scent by shifting behaviour. These alterations to behaviour are often assumed to increase an animal's chances of evading predators. Responsiveness to predator scents is therefore believed to ultimately increase a prey's chances of surviving encounters with predators. This notion is widely accepted among behavioural ecologists but has rarely been empirically tested. I staged encounters between adult snakes (Demansia psammophis) and pairs of unrestrained adult lizards (Lampropholis guichenoti) that responded strongly to snake predator scent ("responsive") or weakly to snake predator scent ("non-responsive"). Responsive lizards decreased activity and mobility during the staged encounters with snake predators. In turn this shift in behaviour decreased the chances that snakes detected responsive lizards. Since snakes almost always captured lizards that were detected, responding strongly to predator scent decreased a lizard's chances of being captured by predators. This finding is the first experimental demonstration in any terrestrial animal that responsiveness to predator scents can function to increase survival probability.     

Chemical polymorphism in male femoral gland secretions matches polymorphic coloration in common wall lizards (Podarcis muralis)

Previous studies showed that common wall lizards (Podarcis muralis) are polymorphic in colour, both sexes showing three main ventral morphs (white, yellow and red) within the same population and that the three morphs correlate with many life-history traits, including a positive assortative mating according to colour. Chemical communication plays a key role in intra-specific recognition and in social organization of lizards; thus chemical cues might be involved in morph recognition and mate choice. We used gas chromatography–mass spectrometry (GC–MS) to investigate possible differences in the lipophilic fraction of femoral gland secretions between size/age classes and to explore whether chemical secretions match male colour morphs. As expected, most males shared the same compounds, but smaller males showed significantly higher proportions of aldehydes, alcohols and ketones and significantly lower proportions of tocopherols than larger males. Interestingly, inter-morph differences in the proportion of some compounds (especially tocopherols and furanones) matched ventral colour polymorphism. Pairwise comparisons showed that white lizards had significantly different chemical profiles than both the yellow and red ones, whereas differences between yellow and red males were only marginal. A further canonical analysis of principal coordinates correctly classified 67.2 % on average of the chemical profiles according to colour morph (white 85.0 %, red 60.9 %, yellow 57.1 %). We hypothesized that chemical differences associated with colour polymorphism may play a central role in intra-specific communication and even in sexual selection, allowing individuals to choose their partners according to their age, and more interestingly according to their colour morph, in a non-random mating population system.     

Prey chemical discrimination in ambush foragers: absence in representatives of two additional iguanian lizard families and probable olfactory mediation in a gekkonine gecko

Summary. Lingually mediated prey chemical discrimination in lizards has evolved in active foragers, been lost in taxa that have reverted to ambush foraging, and has not evolved in taxa that have retained the ancestral ambushing. Previous studies have shown that all families of insectivorous ambushers lack prey chemical discrimination, including most families of iguanian lizards and two gekkonid species. I conducted experimental studies of prey chemical discrimination in representatives of two additional iguanian families and a third gekkonid lizard. An oplurid species, Oplurus cuvieri and a corytophanid, Corytophanes cristatus, did not discriminate among prey chemicals and control substances. Prey chemical discrimination is now known to be absent in insectivorous ambush foragers in all but one of the families in Iguania, one of the two major lizard radiations. Hoplocercidae remains unstudied. Like other ambushing gekkonid lizards, Pachydactylus turneri did not exhibit elevated tongue-flick rates in response to prey chemicals. However, after tongue-flicking or being touched on the labial scales by cotton swabs, these lizards bit swabs bearing prey chemicals more frequently than control stimuli. They also exhibited buccal pulsing more frequently in response to prey chemicals than deionized water, suggesting olfactory sampling. The unusually highly developed olfactory organs of gekkonid lizards and their nocturnal habits suggest that olfaction may be more important to foraging than in other lizards. Further studies are needed to determine relative roles of olfaction and vomerolfaction in selective response to prey chemicals and to ascertain whether and to what extent the tongue may be used to locate and identify prey. Received 30 March 1999; accepted 26 July 1999     

Kin discriminators in the eusocial sweat bee <Emphasis Type="Italic">Lasioglossum malachurum</Emphasis>: the reliability of cuticular and Dufour’s gland odours

The ability to discriminate degrees of relatedness may be expected to evolve if it allows unreciprocated altruism to be preferentially directed towards kin (Hamilton in J Theor Biol 7:1–16, 1964). We explored the possibility of kin recognition in the primitively eusocial halictid bee Lasioglossum malachurum by investigating the reliability of worker odour cues that can be perceived by workers to act as indicators of either nest membership or kinship. Cuticular and Dufour’s gland compounds varied significantly among colonies of L. malachurum, providing the potential for nestmate discrimination. A significant, though weak, negative correlation between chemical distance and genetic relatedness (r = −0.055, p < 0.001) suggests a genetic component to variation in cuticular bouquet, but odour cues were not informative enough to discriminate between different degrees of relatedness within nests. This pattern of variation was similar for Dufour’s gland bouquets. The presence of unrelated individuals within nests that are not chemically different from their nestmates suggests that the discrimination system of L. malachurum is prone to acceptance errors. Compounds produced by colony members are likely combined to generate a gestalt colony chemical signature such that all nestmates have a similar smell. The correlation between odour cues and nest membership was greater for perceived compounds than for non-perceived compounds, suggesting that variability in perceived compounds is a result of positive selection for nestmate recognition despite potentially stabilising selection to reduce variability in odour differences and thereby to reduce costs derived from excessive intracolony nepotistic behaviour.     

Competitor assessment by scent matching: an experimental test

Summary If males assess potential opponents by comparing their odour with that of scent marks in the vicinity (the so called scent matching hypothesis) they should be more reluctant to fight when these odours are the same. Under these circumstances the potential opponent is thus identified as a resource holder (a male monopolising a territory or group of females) that would escalate encounters to defend its resources. We tested this prediction by comparing the fighting behaviour of male house mice, Mus domesticus, when on a scent-marked substrate that matched the odour of an opponent with their behaviour on a substrate that did not match. As predicted, the delay before the first fight was longer and the rate of subsequent fighting lower when the scents matched. This result is consistent with the interpretation that resource holders scent mark to provide opponents with a means of competitor assessment and that they thus reduce the costs of resource defence. Offprint requests to: L.M. Gosling     

The influence of refuge sharing on social behaviour in the lizard Tiliqua rugosa

Refuge sharing by otherwise solitary individuals during periods of inactivity is an integral part of social behaviour and has been suggested to be the precursor to more complex social behaviour. We compared social association patterns of active versus inactive sheltering individuals in the social Australian sleepy lizard, Tiliqua rugosa, to empirically test the hypothesis that refuge sharing facilitates social associations while individuals are active. We fitted 18 neighbouring lizards with Global Positioning System (GPS) recorders to continuously monitor social associations among all individuals, based on location records taken every 10 min for 3 months. Based on these spatial data, we constructed three weighted, undirected social networks. Two networks were based on empirical association data (one for active and one for inactive lizards in their refuges), and a third null model network was based on hypothetical random refuge sharing. We found patterns opposite to the predictions of our hypothesis. Most importantly, association strength was higher in active than in inactive sheltering lizards. That is, individual lizards were more likely to associate with other lizards while active than while inactive and in shelters. Thus, refuge sharing did not lead to increased frequencies of social associations while lizards were active, and we did not find any evidence that refuge sharing was a precursor to sleepy lizard social behaviour. Our study of an unusually social reptile provides both quantitative data on the relationship between refuge sharing and social associations during periods of activity and further insights into the evolution of social behaviour in vertebrates.     

Chemical ornaments of male lizards <Emphasis Type="Italic">Psammodromus algirus</Emphasis> may reveal their parasite load and health state to females

Evidence for parasite-mediated sexual selection has been found in many species that use visual ornaments to attract females. However, in many animals, variation in female responses to scents of parasitized males suggests that parasitic infections might also affect information conveyed by pheromones (i.e., chemical ornaments). Thus, pheromones might also function in parasite-mediated sexual selection. We show here that female lizards Psammodromus algirus responded differently to femoral gland secretions of males according to the parasite load and health of these males. Scents of healthier males elicited more tongue flicks (a chemosensory behavior) by females, suggesting that these scents were more attractive. Chemical analyses showed that parasite load and the T-cell-mediated immune response were related to the variability in the proportions of some lipids in secretions of males. Further trials testing the chemosensory responses of females to chemical standards indicated that females actually discriminated the chemicals related to males’ health from other chemicals found in secretions. We suggest that these chemical ornaments may provide reliable information on the health and degree of parasitic infection of a male.     

Odour profile congruity in two closely related desert tenebrionid beetles: Homology as the basis for a cleptoparasitic relationship?

Summary Parastizopus armaticeps andEremostibes opacus are two closely related desert tenebrionids which also live in close association, the former having biparental brood care and the latter cleptoparasitising the brood.E. opacus is unable to discriminate between the conspecific and host odour even in the absence of physical contact. Gas chromatographic analysis of headspace volatiles of resting animals showed almost complete qualitative and quantitative odour congruity between them. Comparison of these odour profiles with those of two other tenebrionids sharing the same ecological niche,Gonopus agrestis andHerpiscius sp. (damaralis?) showed that congruity was independent of common foodplant utilisation. It is also independent of common defensive gland secretions. Parallels between resting odour spectra, defensive secretion spectra and systematic status suggest that the origins of congruity lie in odour homology, by means of which the cleptoparasite was able to exploit its host.     

Population differentiation in female sex pheromone and male preferences in a solitary bee

Population differentiation in female mating signals and associated male preferences can drive reproductive isolation among segregated populations. We tested this assumption by investigating intraspecific variation in female sex pheromone and associated male odour preferences among distant populations in the solitary bee Colletes cunicularius (L.) by using quantitative gas chromatography and by performing field bioassays with synthetic blends of key sex pheromone compounds. We found significant differences in sex pheromone blends among the bee populations, and the divergence in odour blends correlated positively with geographic distance, suggesting that genetic divergence among distant populations can affect sex pheromone chemistry. Our behavioural experiments, however, demonstrate that synthetic copies of allopatric female sex pheromones were cross-attractive to patrolling males from distant populations, making reproductive isolation by non-recognition of mating signals among populations unlikely. Our data also show that patrolling male bees from different populations preferred odour types from allopatric populations at the two sites of bioassays. These male preferences are not expected to select for changes in the female sex pheromone, but may influence the evolution of floral odour in sexually deceptive orchids of the genus Ophrys that are pollinated by C. cunicularius males.     

Chemical ecology involved in invasion success of the cuckoo bumblebee <Emphasis Type="Italic">Psithyrus vestalis</Emphasis> and in survival of workers of its host <Emphasis Type="Italic">Bombus terrestris</Emphasis>

In bumblebees all species of the subgenus Psithyrus are social parasites in the nests of their Bombus hosts. In the bumblebee B. terrestris we investigated how colony size influences survival rates of nest entering females of the social parasite Psithyrus vestalis. Furthermore, we studied whether the host worker’s dominance status and age are reflected in its individual scent and whether Psithyrus females use volatiles to selectively kill host workers. The survival rate of Psithyrus vestalis females drops from 100%, when entering colonies with five workers, to 0% for colonies containing 50 host workers. Older host workers, born before the nest invasion, were selectively killed when Psithyrus females entered the nest. In contrast, all workers born after the nest invasion survived. The host workers’ dominance status and age are reflected by their individual odours: newly emerged workers produced a significantly lower total amount of secretions than 4-day-old workers. In chemical analyses of female groups we identified saturated and unsaturated hydrocarbons, aldehydes, and unsaturated wax-type esters of fatty acids. In a discriminant function analysis different worker groups were mainly separated by their bouquets of hydrocarbons. Killed workers release significantly more scent and of a different chemical composition, than survivors. Survivors alter scent production and increase it beyond the level of the killed workers within 1 day of the invasion. The Psithyrus female clearly maintains reproductive dominance utilizing these differences in the odour bouquets as criteria for killing workers that compete for reproduction.     

Chemosensory mate recognition may facilitate prolonged mate guarding by male snow skinks, Niveoscincus microlepidotus

We provide evidence that male lizards can use chemosensory cues to identify individual females and probably therefore maintain long-term associations with these females in the wild. In the laboratory, males preferentially followed the scent trail of their vitellogenic female “partner” rather than that of another vitellogenic female. Our 5-year field study of the small viviparous scincid lizard (Niveoscincus microlepidotus) in alpine Tasmania showed that sexually mature males and females commonly formed “pairs” for long periods (on average 29 days). These pairs occurred primarily during the mating season, always involved one adult male and one adult female, and usually involved vitellogenic rather than gravid females. Our laboratory experiments suggest that a significant factor in maintaining those prolonged partnerships is male scent trailing of partners. Received: 28 October 1997 / Accepted after revision: 28 May 1998     

Terminal double bonds in the alkenes and acetates of defensive secretion from the thrips Suocerathrips linguis Mound & Marullo, 1994 (Thysanoptera: Phlaeothripidae)

Defensive secretions of adult males and females of the subsocial thrips Suocerathrips linguis were examined using gas chromatography–mass spectrometry (GC–MS). The samples contained six long-chain acetates and five aliphatic alkanes and alkenes. Whole-body extracts yielded six methyl esters of fatty acids as well as hexadecyl acetate. Structures of the two main components, (11Z)-icosa-11,19-dienyl acetate and octadecyl acetate, were confirmed. The third most abundant substance was identified as octadec-17-enyl acetate, which is a new natural product. In addition, (9Z)-octadec-9-enyl acetate was identified along with other acetates. Pure icosadienyl acetate was found to remain liquid down to −15°C, and is the solvent for the solid components of the secretion cocktail. A tentative biosynthetic pathway for all of the 12 acetates, alkanes and alkenes is discussed, considering especially the components with terminal double bonds that are uncommon in Thysanoptera and other insects.     

Relative contribution of dietary carotenoids and vitamin E to visual and chemical sexual signals of male Iberian green lizards: an experimental test

Carotenoid-based sexual ornaments are widespread, but the role of carotenoids as honest signalers in the trade-off between coloration and antioxidant protection remains controversial. It has been suggested that the function of carotenoids might not be an antioxidant per se, but that colorful carotenoids may indirectly reflect the levels of nonpigmentary antioxidants, such as melatonin or vitamin E. We experimentally fed male Iberian green lizards (Lacerta schreiberi) additional carotenoids or vitamin E alone, or a combination of carotenoids and vitamin E dissolved in soybean oil, whereas a control group only received soybean oil. We examined the effects of the dietary supplementations on characteristics of lizard sexual coloration and of the chemical profile of femoral gland secretions. Results indicated that both carotenoids and vitamin E in the diet increased the expression of some visual signals (head and chest, but not dorsum) in comparison to controls. However, different traits were differentially affected, and in many cases, the addition of vitamin E, alone or in combination with carotenoids, had a greater effect on the expression of coloration than the addition of carotenoids alone, even for carotenoid-dependent ornaments. Our results support the idea that other nonpigmentary antioxidants, such as vitamin E, are needed in addition to carotenoids to increase the expression of coloration of L. schreiberi lizards. Therefore, coloration may only indirectly reflect the levels of nonpigmentary antioxidants. In contrast, an increase in dietary nonpigmentary antioxidant vitamin E was directly reflected in the chemical signals. Because of an observed concordance between visual and chemical signals, we suggest that both may be used in different contexts albeit conveying similar messages in different sensory channels.