Basis Of Chemical Cues Research Articles

Reproductive isolation between sister species of Iberian pine voles, Microtus duodecimcostatus and M. lusitanicus

Contact zones of recently diverged species provide the ideal opportunity to study the nature of reproductive barriers. The Mediterranean (Microtus duodecimcostatus) and Lusitanian pine voles (M. lusitanicus) are a pair of recently diverged sister species endemic to Western Europe. Recent microsatellite data raised the possibility that hybridisation events, although rare, may still occur in the area of sympatry of both species. Here we evaluated the nature and extent of reproductive isolation between M. duodecimcostatus and M. lusitanicus through a laboratory crossbreeding experiment and two-way mate preference tests on the basis of chemical cues. Crossbreeding of sympatric individuals from the two species was successful and followed Haldane’s rule, revealing hybrid male sterility and reduced fertility of hybrid females. Results from mate preference tests showed males of both pine vole species could discriminate and preferred female conspecifics to heterospecifics or hybrid females on the basis of chemical cues alone. On the contrary, females of both pine vole species did not show a clear preference for conspecific over heterospecific male chemical cues, suggesting females may need additional cues to discriminate between males of the two species. As a whole our results indicate both prezygotic (i.e. species-specific mate recognition systems) and postzygotic barriers (i.e. male hybrid sterility, female reduced fertility and behavioural sterility ― decreased ability to find or attract mates) have evolved, and should make hybridisation of the Iberian pine voles under natural conditions an unlikely event. The role of both species mating preferences and interspecific behavioural interactions in the asymmetric mitochondrial introgression pattern of the Iberian pine voles is discussed.

Assessing the potential for egg chemoattractants to mediate sexual selection in a broadcast spawning marine invertebrate

In numerous species, egg chemoattractants play a critical role in guiding sperm towards unfertilized eggs (sperm chemotaxis). Until now, the known functions of sperm chemotaxis include increasing the effective target size of eggs, thereby promoting sperm-egg encounters, and facilitating species recognition. Here, we report that in the broadcast spawning mussel, Mytilus galloprovincialis, egg chemoattractants may play an unforeseen role in sexual selection by enabling sperm to effectively 'choose' between the eggs of different conspecific females. In an initial experiment, we confirmed that sperm chemotaxis occurs in M. galloprovincialis by showing that sperm are attracted towards unfertilized eggs when given the choice of eggs or no eggs in a dichotomous chamber. We then conducted two cross-classified mating experiments, each comprising the same individual males and females crossed in identical male × female combinations, but under experimental conditions that offered sperm 'no-choice' (each fertilization trial took place in a Petri dish and involved a single male and female) or a 'choice' of a female's eggs (sperm were placed in the centre of a dichotomous choice chamber and allowed to choose eggs from different females). We show that male-by-female interactions characterized fertilization rates in both experiments, and that there was remarkable consistency between patterns of sperm migration in the egg-choice experiment and fertilization rates in the no-choice experiment. Thus, sperm appear to exploit chemical cues to preferentially swim towards eggs with which they are most compatible during direct sperm-to-egg encounters. These results reveal that sperm differentially select eggs on the basis of chemical cues, thus exposing the potential for egg chemoattractants to mediate mate choice for genetically compatible partners. Given the prevalence of sperm chemotaxis across diverse taxa, our findings may have broad implications for sexual selection in other mating systems.

Sex Recognition via Chemical Cues in the Sex‐Role‐Reversed Gulf Pipefish (Syngnathus scovelli)

AbstractSexual selection theory predicts that members of the choosy sex, usually females, should employ multiple sensory systems to obtain information about potential mates. Such predictions should also apply to systems in which sexual selection acts most strongly on females (i.e. sex‐role‐reversed species), and males of these taxa should be the individuals employing multiple cues to assess female attractiveness. Very little work has been directed toward mate choice involving multiple sensory systems in sex‐role‐reversed taxa, but fishes of the family Syngnathidae (pipefishes, seahorses, and sea dragons) provide an excellent opportunity to contribute to this research enterprise. While much is known about visual communication in pipefish, the role of chemical communication has not been investigated. Using dichotomous choice tests, we found that male, but not female, Gulf pipefish attended to chemical cues of opposite sex conspecifics. Given that males distinguished sex on the basis of chemical cues, we also tested whether males could assess female body size, an important trait with respect to mate choice in pipefish, on the basis of chemical cues alone. When given the choice between chemical cues produced by large vs. small females, males exhibited no preference. Our results suggest that male pipefish can use chemical cues to distinguish between males and females but not to differentiate females of different body size.

Chemosensory cues allow male Tenebrio molitor beetles to assess the reproductive status of potential mates

Males of many insect species, including beetles, choose their mates according to their reproductive status. However, the ways in which male beetles evaluate female reproductive status have received little attention. We tested the existence of male mate choice in the mealworm beetle, Tenebrio molitor, by observing mating and courtship behaviour of males given simultaneous access to pairs of females differing in their reproductive status: (1) mature versus immature; (2) virgin versus previously mated; (3) familiar (mated with the experimental male) versus unfamiliar (mated with a different male). Males courted and mated preferentially with mature and virgin females. To determine whether chemical cues played a role in these discriminations, we exposed males to filter paper squares bearing chemical cues from different types of females: (1) virgin versus mated; (2) mature versus immature. Males were significantly more attracted to those squares bearing chemical cues from virgin and mature females, suggesting that males can assess female reproductive status on the basis of chemical cues alone.

Chemosensory cues allow male Tenebrio molitor beetles to assess the reproductive status of potential mates

Males of many insect species, including beetles, choose their mates according to their reproductive status. However, the ways in which male beetles evaluate female reproductive status have received little attention. We tested the existence of male mate choice in the mealworm beetle, Tenebrio molitor , by observing mating and courtship behaviour of males given simultaneous access to pairs of females differing in their reproductive status: (1) mature versus immature; (2) virgin versus previously mated; (3) familiar (mated with the experimental male) versus unfamiliar (mated with a different male). Males courted and mated preferentially with mature and virgin females. To determine whether chemical cues played a role in these discriminations, we exposed males to filter paper squares bearing chemical cues from different types of females: (1) virgin versus mated; (2) mature versus immature. Males were significantly more attracted to those squares bearing chemical cues from virgin and mature females, suggesting that males can assess female reproductive status on the basis of chemical cues alone.

Discrimination of oestrous status in giant pandas (Ailuropoda melanoleuca) via chemical cues in urine

AbstractGiant pandas Ailuropoda melanoleuca are a solitary, seasonally mono‐oestrous species, and as such are likely to rely heavily on chemical signals to co‐ordinate mating efforts. Perhaps the most crucial chemosensory task facing male pandas is the assessment of female reproductive condition on the basis of chemical cues. To test for this ability, eight male and 10 female giant pandas were presented with urine from oestrous and non‐oestrous females. Males but not females displayed a significant investigatory preference for oestrous over non‐oestrous female urine, as indicated by sniffing and flehmen. Males also investigated, displayed flehmen, and licked female urine more than did females. These findings indicate that female urine contains chemical cues permitting discrimination of oestrous status, and probably serves a reproductive advertisement function. The prevalence of flehmen and licking by males suggests that males may rely on the vomeronasal organ to assess female reproductive condition. Female odours may play an important role in the reproductive behaviour of male giant pandas and, therefore, may have implications for captive‐breeding programmes.

Host recognition in a desert mistletoe: early stages of development are influenced by substrate and host origin

Summary In many root parasites, chemical substances from the host are necessary for the successful initiation of germination and holdfast formation, and are the basis for host recognition and localization within the rhizosphere. In contrast, bird‐dispersed mistletoe seeds have no need for the chemical localization of a host, and possible mechanisms of host recognition are poorly understood. Many studies claim that mistletoes germinate readily in the absence of a host and independent of the substrate. In this study, the possible occurrence of substrate dependence and host recognition in mistletoes during the establishment of Plicosepalus acaciae Zucc. seeds on Acacia raddiana Savi was tested experimentally. In a laboratory experiment, no influence of substrate on germination could be found, but a significantly higher proportion of the germinated seeds developed a holdfast on natural (bark) substrate than on artificial (plastic) substrate. Moreover, the origin of the bark had a significant influence on holdfast formation frequency. Host influence was additionally tested in a reciprocal transplant experiment in two field sites with genetically different populations of the same host species. Those mistletoes of local origin germinated significantly more often than their non‐local counterparts. These results suggest the existence of interactions between mistletoe seed and host branch on the basis of chemical cues that are active at an early stage of seedling development and are host‐specific at the level of populations.

Behavioural responses of naive Arctic charr young to chemical cues from salmonid and non‐salmonid fish

The ability to distinguish among chemical cues from multiple predators is of key adaptive value for many prey fish. We examined the attractiveness and repulsiveness of chemical stimuli from different coexisting fish species fed on different diets on the behaviour of hatchery reared Arctic charr young in a Y‐maze fluviarum, where the charr could choose between two sides either with control water or stimulus water with fish odour. We used stimuli from (1) matching sized conspecifics, large (2) Arctic charr, (3) salmon, (4) brown trout and (5) brown trout fed on Arctic charr fry. Other salmonids were given pellet food. Additional fish odour treatments included piscivorous (6) pike and (7) burbot. In the control trials both sides received control water. Arctic charr young were expected to respond adaptively to the stimuli from coexisting piscivorous fish. The charr most strongly preferred water with the odour of their matching sized conspecifics, which was the only fish odour they were familiar with before the experiments. They also showed significant preference for other salmonid odours, even though these fish are potential predators on small charr. Chemical stimuli from pike and burbot, on the contrary, were strongly avoided, and burbot odour even prevented the charr to swim and enter the lateral halves of the fluviarum. Moreover, odour from brown trout fed on Arctic charr fry was avoided when compared to stimuli from trout fed on pellets. Although the Arctic charr young were completely naive regarding piscivores, the fact that they could distinguish between different predator taxa and diets on the basis of chemical cues only reflects the long coevolutionary history of these fish populations.

Who dares, learns: chemical inspection behaviour and acquired predator recognition in a characin fish

Individuals that dare approach predators (predator inspection behaviour) may benefit by acquiring information regarding the potential threat of predation. Although information acquisition based on visual cues has been demonstrated for fish, it is unknown whether fish will inspect predators on the basis of chemical cues or whether such inspection behaviour results in information acquisition. Here, we first ascertained whether predator inspection behaviour can be mediated by chemical cues from predators by exposing groups of predator-naive glowlight tetras (Hemigrammus erythrozonus) to the chemical cues of a potential fish predator (convict cichlidCichlasoma nigrofasciatum) that had been fed either tetras (which possess an alarm pheromone) or swordtails (Xiphophorus helleri, which lack Ostariophysan alarm pheromones). Tetras showed a significant increase in antipredator behaviour when exposed to the tetra-diet cue, but not when exposed to the swordtail-diet cue. Chemically mediated predator inspection behaviour was also affected. Both the latency to inspect and the minimum approach distance to the predator significantly increased, and the mean number of inspectors per predator inspection visit significantly decreased when tetras were exposed to the tetra-diet versus the swordtail-diet chemical cues. We then examined a potential benefit associated with chemically mediated predator inspection behaviour. Only tetras that were initially exposed to the tetra-diet cue and that had inspected the predator acquired the visual recognition of a convict cichlid as a predation threat. Our results thus demonstrate that (1) predator inspection behaviour in the glowlight tetra can be initiated by chemical cues, (2) chemically mediated inspection behaviour is affected by the presence of alarm pheromone, and (3) inspectors benefit by acquiring the recognition of novel predators.

Social recognition using chemical cues in cuttlefish ( Sepia officinalis Linnaeus, 1758)

Forty-five full-sized, virgin cuttlefish ( Sepia officinalis Linnaeus) were tested for social discriminations on the basis of chemical cues alone. Subjects were tested by placing them in the base of a Y-maze and permitting them to choose between the two arms of the maze, each arm with a different water supply. Each subject was tested three times: once with water from a male versus a female conspecific, once with water from a mated versus a virgin conspecific of the opposite sex, and once using plain seawater in both arms of the Y-maze as a control for any bias towards one of the arms of the maze. Results fail to support hypotheses for chemical communication in cephalopods; difficulties in using approach behavior to measure chemical communication in cephalopod and other mollusks are discussed.

Female bank vole ( Clethrionomys glareolus) recognition: preference for the stud male

Pregnant and nursing bank vole ( Clethrionomys glareolus) females were investigated for their ability to recognize their mated male on the basis of chemical cues. In a two-choice test pregnant females showed a strong preference, manifested by higher frequency of sniffs and time spent sniffing, to the odour of a stud male over that of unfamiliar male, but only during the days after insemination and around implantation. As gestation proceeds females exhibited no affinity for either of these two kinds of males. Olfactory bulbectomy abolished a pregnant females preference for her stud male. A lactating female chose the odour of her sexual partner untill the time of weaning of her young. Separation of the female from her pups during the early post partum period shortens the time of memory for the scent of the stud male. The results indicate that bank vole females form olfactory memory to the odour of stud males and its duration depends on physiological state of the females.

Learned Recognition of Predation Risk by Enallagma Damselfly Larvae (Odonata, Zygoptera) on the Basis of Chemical Cues

We studied two populations of damselfly larvae (Enallagma boreale): one population cooccurred with a predatory fish (northern pike, Esox lucius); the other did not. Damselflies that cooccurred with pike adopted antipredator behavior (reduced activity) in response to chemical stimuli from injured conspecifics, and to chemical stimuli from pike, relative to a distilled water control. Damselflies from an area where pike do not occur responded only to chemical stimuli from injured conspecifics. In a second set of experiments, we conditioned pike-naive damselflies to recognize and respond to chemical stimuli from pike with antipredator behavior. Damselfly larvae that were previously unresponsive to pike stimuli learned to recognize pike stimuli after a single exposure to stimuli from pike and injured damselflies or pike and injured fathead minnows (Pimephales promelas). The response to injured fathead minnows was not a general response to injured fish because damselfly larvae did not respond to chemical stimuli from injured swordtails (Xiphophorus helleri), an allopatric fish. Taken together, these data suggest a flexible learning program that allows damselfly larvae to rapidly acquire the ability to recognize local predation risk based on chemical stimuli from predators, conspecifics, and heterospecific members of their prey guild.

Toxic prey discrimination in a highly specialized predator Chaetodon melannotus (Block et Schneider): visual vs. chemical cues

The specialized predator Chaetodon melannotus (Bloch et Schneider) (Vertebrata, Pisces), which feeds on highly toxic and sometimes allelopathic octocorals, initially locates its prey using visual rather than chemical cues. A novel controlled experiment was carried out to further understand the basis of food preference and selection. Organic extracts were interchanged between colonies of three species of octocoral: Alcyonium molle (Dean), Clavularia inflata (Schenck) and Sinularia flexibilis (Quoy et Gaimard0 (Coelenterata, Octocorallia). Extracts were prepared by stepwise solvent extraction of the octocoral; first with ethanol, then with mixtures containing dichloromethane in ethanol, and finally with dichloromethane. All extractable organic material was removed. Concentrated extracts (in ether) were then reintroduced into the extracted colonies in the six possible permutations. In three smorgasbord-type experiments using two octocoral species at a time, C. melannotus were offered the six types of modified colonies, including controls without any extract, yielding a balanced matrix of visual and chemical cue combinations. Responses of the fish to prey choices were nonrandom in all cases. Alcyonium colonies with original extracts reintroduced were strongly preferred over Clavularia. Clavularia colonies and any colony containing their extracts received low preference. When offered with Sinularia, Clavularia colonies devoid of organic components received high preference. Chemical cues were determined to be important in this selection process. The Sinularia colonies in this situation received moderate acceptance. Sinularia colonies with their own extract reintroduced, received high preference when offered with Alcyonium. This indicated that there might be a subtle change in appearance or texture of Alcyonium (the preferred choice in an earlier study) as a result of the extraction. Responses were significantly different from that expected if the fish were cueing solely on the basis of either visual or chemical cues. A combination of visual and chemical cueing, possibly in sequence, appears to have produced the observed results. These results suggest that C. melannotus use visual cues to locate their prey and probably further select on the basis of chemical cues. We believe that the technique used here is valuable for use in the separation of visual and chemical cues for feeding.

The role of pheromones in the sexual behaviour of the goldfish

Male goldfish ( Carassius auratus) discriminate between ovulated and unovulated females on the basis of chemical cues. Goldfish males made temporarily anosmic by occlusion of the nares, or permanently anosmic by section of the olfactory nerves showed a marked decrease in sexual behaviour. Preference tests in a Y-maze indicate that the pheromone is present in the ovarian fluid of an ovulated female. It is concluded that shortly after ovulation the female goldfish releases a pheromone from the ovary which attracts the male and elicits the persistent courtship that accompanies spawning.

Aspects of the aggressive and sexual behaviour ofalpheus heterochaelissay

Alpheus heterochaelis were collected near Beaufort, N.C. Males have a greater ratio of claw length/total body length than females. In field‐caught pairs, females tend to have longer bodies and males tend to have larger claws. In Y‐maze tests, males tend to seek females on the basis of chemical cues. The intensity of the sound produced by the large claw is positively correlated with claw size. Thus, stimulus intensity offers potential cues to the size of an opponent. Cine studies reveal that the large claw closes within 1.67–5.00 msec during snap production. An ensuing water jet travels at ca. 1.5–4.0 mm/sec and is directed toward an opponent. Size restrictions found in paired shrimp are hypothesized to result from an agonistic “balance”; established during initial contacts made prior to sex determination and pairing. The male's larger claw size/body size is explained by selection pressure favouring his mating with larger females who can produce more offspring.

Responses of ecologically dissimilar populations of the water snakeNatrix s. sipedon to chemical cues from prey

Three populations of the water snake,Natrix s. sipedon, were tested for their responses to surface water extracts prepared from various prey species. It was clearly shown that these snakes can distinguish between different prey genera on the basis of chemical cues alone. Adult snakes caught at a fish hatchery where goldfish (Carassius auratus) were abundant responded most to goldfish extract, as did laboratory-born snakes reared on goldfish for one year. However, snakes caught in a relatively undisturbed mountain stream environment and naive young born to a mountain female responded more to the extracts of various sympatric-mountain fish and amphibians. The evidence indicates that newborn snakes have genetic predispositions for sympatric species of the classes of prey normally eaten. These preferences can be enhanced or inhibited during ontogeny.

Responses to chemical stimuli of prey in newly hatched snakes of the genus Elaphe

Naive, isolated, newly hatched Elaphe vulpina vulpina, tested on a variety of animal surface extracts, demonstrated a tongue-flick response rate significantly higher only to newborn mouse extract (representing a common prey class) than to a distilled water control. A second experiment with Elaphe guttata guttata concentrating on the comparison of mouse extract and distilled water accounted for the effect of novel stimulation and revealed a significant, stable difference between extract and control. A preliminary experiment with air-borne odours resulted in a clear instance of predatory behaviour, including constriction, in the presence of mouse odour. The results indicate that newborn Elaphe can differentiate potential prey on the basis of chemical cues alone.