Isopropyl (Z9)-hexadecenoate as a male attractant pheromone from the sternal gland of the rove beetle Aleochara curtala (Coleoptera: Staphylinidae)

Summary. In the rove beetle Aleochara curtula, a male specific sternal gland is described. Isopropyl (Z9)-hexadecenoate has been identified by GC/MS of surface and sternal gland extracts as a male specific compound. Its emission in the air was demonstrated by closed-loopstripping-analyses. In field experiments, conspecific males and females were attracted by the odor of carrion, caged males from laboratory cultures, and by the synthetic ester. Isopropyl (Z9)-hexadecenoate or live males, combined with fresh carrion attract more beetles than a fresh carcass alone. Isopropyl hexadecanoate as a minor compound was not attractive. The term “aggregation” pheromone and the ecological significance of attracting females to a fresh carcass allowing early copulation and egg-deposition are discussed. Received 20 August 1998; accepted 15 January 1999.     

The lexicon of love: what cues cause size-assortative courtship by male garter snakes?

Cues that females use to select potential mates have attracted substantial research effort, but the criteria for male mate choice remain very poorly known. Red-sided garter snakes ( Thamnophis sirtalis parietalis) court and mate in large aggregations around overwintering dens in southern Manitoba, Canada. Both courtship and mating are size-assortative: small male snakes court small as well as large females, whereas larger males court only large females. This system provides a unique opportunity to assess the cues that males use in selecting mates, and in particular the mechanisms that generate a size-related shift in mate preference. Experiments in which we manipulated body sizes and scents showed that both vision and scent (sex pheromones) were important. Large males directed intense courtship only when the stimulus provided both visual and chemical (skin lipid) evidence of large body size. Small males were much less discriminating in both respects. Thus, size-assortative mating in this system is generated not by larger males excluding their smaller rivals from the largest females (as has been reported in other reptile species), but by a size-related shift in the visual and pheromonal cues that elicit courtship. Males of some species may thus show complex patterns of mate choice, with the cues that stimulate courtship differing even among males within a single population based on traits such as age or body size.     

Surface glycoproteins are not the contact pheromones in the Lysmata shrimp

Behavioral evidence suggests that some male caridean shrimp, such as those of Lysmata species, identify conspecific females via contact pheromones that coat the cuticle surface of the females. In this study, we attempted to determine whether the contact pheromones in three Lysmata species, Lysmata ankeri, Lysmata boggessi, and Lysmata wurdemanni, are glycoproteins as hypothesized previously in a diverse group of aquatic invertebrates. Twenty lectins were screened and lectin-binding experiments indicated that lectin treatment did not affect mate recognition in the shrimps. The behavior of the male-phase (MP) shrimp in the three treatments (non-lectin-treated MP and lectin-treated euhermaphrodite-phase (EP) shrimp, lectin-treated MP and lectin-treated EP shrimp, and lectin-treated MP and non-lectin-treated EP shrimp) and in the control was not different in responding to lectin-treated and control EP shrimp. All the MP shrimp copulated with lectin-treated and control EP shrimp successfully. All the MP shrimp copulated with ethylenediamine tetraacetate-treated EP shrimp (with glycoproteins removed from their cuticle surface) immediately after they detected the EP shrimp. The results suggest that glycoproteins are not likely to be the contact sex pheromones in the three Lysmata shrimp species.     

Courting male garter snakes (Thamnophis sirtalis parietalis) use multiple cues to identify potential mates

Mating aggregations of red-sided garter snakes (Thamnophis sirtalis parietalis) in Manitoba provide a unique opportunity to identify the cues that attract a male snake and induce him to court. The snakes are abundant, tolerate human presence, and males direct courtship to a subset of other males ("she-males") as well as to females. Previous work has emphasised the role of pheromonal cues (skin lipid profiles) as sexual attractants in snakes. However, pheromones are so widely distributed throughout the den area that these chemical cues may be difficult for males to use to localise females. Our field studies show that males and females differ in several other attributes such as size (females are larger than males), body temperature (very cold snakes are often females), muddiness (females are often covered in mud) and whether or not they are solitary (most females are surrounded by courting males). Experiments show that males use all of these cues to identify possible sexual partners. Visual and thermal cues are particularly important for solitary mate-searching males; but after a mating ball forms around a female, pheromones may be most important. Our study also reveals substantial variation among individuals: females vary in attractiveness, and males vary in their intensity of courtship as well as in the magnitude of their preference for one potential partner versus another. Thus, a male snake's "decision" whom to court depends not only on visual and thermal as well as chemical cues, but also on the male's own preferences and on subtle differences among potential sexual "targets".     

Chemical communication in green and golden bell frogs: do tadpoles respond to chemical cues from dead conspecifics?

Captive bred animals often lack the ability of predator recognition and predation is one of the strongest causes of failure of breed and release projects. Several tadpole and fish species respond defensively to chemical cues from injured or dead conspecifics, often referred to as alarm pheromones. In natural conditions and in species that school, the association of chemical cues from predators to alarm pheromones released by attacked conspecifics may lead to the learning of the predator-related danger without experiencing an attack. In the laboratory, this chemical communication can also be used in associative learning techniques to teach naïve tadpoles to avoid specific predators and improve survivorship of released animals. In our experimental trials, tadpoles of the threatened green and golden bell frog (Litoria aurea) did not avoid or decrease their activity when exposed to solutions of conspecific macerate, suggesting that the chemicals released into the water by dead/injured conspecifics do not function as an alarm pheromone. This non-avoidance of dead conspecific chemicals may explain why green and golden bell frog tadpoles have seemingly not developed any avoidance behaviour to the presence of introduced mosquito fish, and may render attempts to teach naïve tadpoles to avoid this novel predator more difficult.     

Volatile attractant phytochemicals for a population of white-spotted longicorn beetles Anoplophora malasiaca (Thomson) (Coleoptera: Cerambycidae) fed on willow differ from attractants for a population fed on citrus

Male white-spotted longicorn beetles Anoplophora malasiaca raised on willow Salix schwerinii were preferentially attracted to the odour of wounded S. schwerinii branches when released near a female model in the laboratory. This attractiveness rapidly decreased within 2 h after wounding. Solid phase microextraction and subsequent gas chromatography analyses of volatiles from the wounded branches detected three highly volatile monoterpenes: 1,8-cineole, nerol and geraniol. Among the monoterpene compounds, nerol showed a significant attractiveness to the male beetles raised on Salix. Sesquiterpene hydrocarbons, which have been identified as attractants for a beetle population raised on citrus, were detected only in trace amounts in S. schwerinii branches. These results suggest that beetles raised on these two hosts use different odour cues for mate location.     

Population differences in male responses to chemical mating cues in the white-spotted longicorn beetle, Anoplophora malasiaca

Adult Anoplophora malasiaca beetles were collected from field populations inhabiting three different host plants: Citrus, Salix and Vaccinium. Male orientation responses towards odours of wounded branches of each host plant were examined. Males of all three populations were attracted most frequently to odours of their original hosts, indicating that male orientation behaviour was induced by the odours of the plants from which they were originally collected. We also observed the mating responses of the males to elytra extracts from young and mature females of the three populations and chemically analysed those extracts. Citrus males were highly responsive to female extracts, regardless of origin. Salix males were less reactive than Citrus males, but responded moderately to female extracts of all populations. Vaccinium males were never attracted to Citrus female extracts and responded more to extracts from mature Vaccinium and Salix females, indicating that males might distinguish female origin and maturity. All eight hydrocarbons, four ketones, and three lactones that were previously identified as female contact sex pheromones were found in the extracts of three populations and both ages. Higher amounts of lactones on mature females likely caused greater male responses. These results suggested that males would be more likely to approach a female feeding on the same host plant and subsequently recognise her sexual maturity based on the profile of contact sex pheromones on her elytra.     

Predation risk assessment by green frog (<Emphasis Type="Italic">Rana clamitans</Emphasis>) tadpoles through chemical cues produced by multiple prey

Many prey assess predation risk through predator chemical cues. Numerous studies have shown that (1) prey sometimes respond to chemical cues produced by heterospecifics and (2) that many species are capable of associative learning. This study extends this research by focusing on predation risk assessment and antipredator behavior in environments containing chemical cues produced by multiple prey species. The results show that green frog (Rana clamitans) tadpoles (1) assess risk from the chemical cue produced during predation by a heterospecific (gray tree frog, Hyla versicolor, tadpoles) and (2) can exhibit similarly strong behavioral responses to a mix of conspecific and heterospecific cues compared to conspecific cue alone, depending on their conditioning environment. I then discuss how the prey choice of the predators and the relative abundances of the prey species should influence the informational value of heterospecific cues.     

Conspecifics as cues: A mechanism for habitat selection in the Panamanian grass anole (Anolis auratus)

Summary In an experimental choice situation, individuals of both sexes of the lizard Anolis auratus choose to associate with a conspecific individual regardless of its sex. Further, individuals of both sexes associate with an individual of A. tropidogaster, a related species. Given the choice between the two species, they choose their own. Given the choice between a conspecific and a small patch of natural habitat, they do not choose one or the other consistently. These experiments indicate that conspecific association does not function just as a mate selection mechanism as has been previously proposed. The initial association may, in addition, serve a habitat selection function. Conspecifics can thus be seen as cues indicating the presence of suitable habitat as well as being important biological factors in themselves.     

Male and female developmental differences in chemosensory investigations by African elephants (Loxodonta africana) approaching waterholes

Although communication is vital for members of a social species, the sexes may differ in the type and degree of information sought. In many polygynous societies, males search for reproductively active females and compete intrasexually for access to females with older males often being most successful. In social mammals, females may mature sooner than males and thus at an earlier age behave more like adults. This maturation may include the assessment of potential mates directly or via indicative signals. In this study, we observed the behavior of African elephants (Loxodonta africana) during their approach to waterholes. Waterholes provide an opportunity for elephants to investigate conspecific chemical signals from feces and urine, and each other. We examined the presence of sexual dimorphism in behaviors of the trunk that are indicative of olfactory investigation. We predicted that upon approach to a waterhole, adult males would show greater interest than females in conspecific chemical signals. Females were predicted and observed to exhibit adult-like rates of investigatory behavior at a younger age than males because females mature sooner. Adult males took the longest to reach the waterhole in the last 100 m of approach; they also demonstrated greater investigatory rates to conspecific feces. Each sex showed adult-type investigative behaviors with the trunk before the age of reproduction. Rather than showing a common chronological developmental pattern across sex, the exhibition of investigatory, chemosensory behaviors reflected sex-specific changes in reproductive development, perhaps reflective of the relative strength of intra- and intersexual selection on communication patterns.     

Role of sex and breeding status in grooming and total tick load of impala

The lesser mouse lemur (Microcebus murinus) is a prosimian primate which presents evidence of sex ratio bias of offspring that agrees with the direction of bias predicted by the local resource competition model for facultative sex ratio adjustment. That is, females overproduced sons when grouped prior to mating, whereas isolated females exhibited the opposite tendency. In this solitary species, social communication relies heavily on urinary chemical signals. To test the hypothesis that sex biases induced by social factors may be linked to urinary cues, isolated females were exposed (n = 76) or not (control group, n = 16) to urinary cues from other reproductively active females from the beginning of the breeding season (induced by long photoperiod) until oestrus. During that period, females were either continuously (n = 17) or partially (n = 59) exposed to chemosignal stimulation. Females in oestrus were placed in contact with a breeding male and subsequently isolated until they gave birth. All females entered oestrus but the timing of oestrus was significantly delayed by 1 week in urine-exposed females. A general depressive effect of long-term urine exposure on fecundity was demonstrated, involving fewer impregnations, higher abortion frequency and smaller litter sizes. Among females giving birth (n = 55) to a total of 129 young, a significant positive correlation was found between sex ratio bias towards males and the duration of urine exposure. However, the shift in sex ratio at birth depended on the duration of urine stimulation during a sensitive period extending from the beginning of the long photoperiod until the beginning of the follicular phase. In the absence of urinary cues during the sensitive period, females significantly overproduced daughters (32% males of 53 newborn). As urine exposure increased during the sensitive phase, the proportion of males in litters increased from 54% males (n = 50) in partially urine-exposed females to a significant bias towards males (69.2% of 26 newborn) in totally exposed females. The biased sex ratio in response to chemical cues did not show consistent relationships with maternal body weight, parity or litter size. Although the intrinsic mechanisms involved in sex-biased conceptions are not known, chemical cues could interact with the photoperiodic control of gonadotropin secretions. Received: 14 January 1995/Accepted after revision: 26 November 1995     

Aggregation pheromone compounds of the black larder beetle Dermestes haemorrhoidalis Kuster (Coleoptera: Dermestidae)

Gas chromatography with simultaneous flame ionisation and electroantennographic detection (GC–EAD) and gas chromatography with mass spectrometry analysis (GC–MS) of abdominal extracts of adult male Dermestes haemorrhoidalis Kuster (Coleoptera: Dermestidae) revealed the presence of electrophysiologically and behaviourally active compounds to its conspecific males and females. Isopropyl dodecanoate (3), isopropyl (Z)-9-tetradecenoate (5), isopropyl tetradecanoate (6), isopropyl (Z)-9-hexadecenoate (7) and isopropyl hexadecanoate (8) were detected in male abdominal extracts only. Analysis of collected male headspace volatiles revealed the presence of six EAD-active compounds (3), (5), (6) and isopropyl tridecanoate (4) plus two unidentified compounds (1) and (9). Synthetic compounds (3), (4), (5), (6) and (7) showed EAD activity with antennae of both sexes in contrast to synthetic (8) which showed EAD activity with female antennae only. Male and female antennae of D. haemorrhoidalis reacted with high receptor potentials to isopropyl (Z)-9-dodecenoate (2), although this compound itself was detected in neither male nor female abdominal extracts or headspace volatiles. Petri dish bioassays indicated that male abdominal extracts and compounds (2), (3), (5) and (6) aroused and attracted conspecific male and female beetles significantly (P < 0.05) compared to female extracts. These results suggested the presence of a male-produced aggregation pheromone in D. haemorrhoidalis. Field assays with any of the described compounds, however, did not result in attraction of this beetle in significant numbers.     

Chemically mediated avoidance of a predatory odonate (Anaxjunius) by American toad (Bufoamericanus) and wood frog (Ranasylvatica) tadpoles

Predators can have significant nonlethal effects on prey by modifying prey behaviour through chemically mediated interactions. We examined behavioural responses of wood frog (Ranasylvatica) and American toad (Bufoamericanus) tadpoles to both direct and indirect chemical signals associated with a predatory odonate (Anaxjunius). In laboratory trials, tadpoles of both species responded strongly to water conditioned with Anax nymphs by decreasing foraging rates, becoming immobile, and moving away from the stimulus. The responses to water conditioned with starved Anax versus Anax that fed on conspecific tadpoles did not differ significantly; these results suggest that tadpoles rely primarily on direct signals to detect odonates. Rana did not respond to water conditioned with conspecific tissue extracts, while Bufo responded with behaviours that were indistinguishable from those of tadpoles exposed to Anax chemicals. In a field experiment, the responses of R. sylvatica tadpoles to Anax chemicals were similar to those of tadpoles observed in the laboratory. Collectively, our data indicate that tadpoles of both species use chemical cues to assess predation risk from other community members. Tadpoles can selectively distinguish members who pose a threat, and only evacuate food patches or reduce foraging rates when in danger. These behaviours appear to be adaptive and are consistent with the predictions of optimality theory. Received: 1 August 1997 / Accepted after revision: 22 November 1997     

Female preferences based on male nutritional chemical traits

Selection favors females that attend to reliable information about male genetic quality and fitness. Male nutritional condition can be a significant sign of mate quality since poor nutrition can be related to reduced sperm quality, low sperm quantity, sexually transmitted diseases, and parasites. We tested whether female Nile tilapia, Oreochromis niloticus, preferred the chemical cues of males that were well fed with high-protein diet over those fed with low-protein diet. Females do not only discriminate between males but also show a preference for well-fed males, discriminating between the odors with respect to nutritional state, suggesting that they were responding to a food-specific chemical cue. It is therefore likely that nutritional condition is related to the production of pheromones in males. Our results suggest that information about male nutritional state can be conveyed in chemical cues and that females attend to these cues during mate choice.     

Green leaf volatiles enhance sex attractant pheromone of the tobacco budworm,Heliothis virescens (Lep.: Noctuidae)

Summary Components of the green leaf volatile complex (Z-3-hexenyl acetate andE-2-hexenyl acetate) were shown to enhance responses of tobacco budworm,Heliothis virescens, males to the sex attractant pheromone of conspecific females in the field. The results are discussed with regard to green leaf volatiles which enhance the attractant pheromone of a cohabiting species, and serve as attractants of a parasitoid of conspecific larvae.     

Sex pheromones and attractants in the Eucosmini and Grapholitini (Lepidoptera,Tortricidae)

Summary The geometric isomers (E,E)-, (E,Z)-, (Z,E)-, and (Z,Z)-8,10-dodecadien-1-yl acetate were identified as sex pheromone components or sex attractants in the tribes Eucosmini and Grapholitini of the tortricid subfamily Olethreutinae. Species belonging to the more ancestral Tortricinae were not attracted. Each one isomer was behaviourally active in males ofCydia andGrapholita (Grapholitini), either as main pheromone compound, attraction synergist or attraction inhibitor. Their reciprocal attractive/antagonistic activity in a number of species enables specific communication with these four compounds.Pammene, as well as otherGrapholita andCydia responded to the monoenic 8- or 10-dodecen-1-yl acetates. Of the tribes Olethreutini and Eucosmini,Hedya, Epiblema, Eucosma, andNotocelia trimaculana were also attracted to 8,10-dodecadien-1-yl acetates, but several otherNotocelia to 10,12-tetradecadien-1-yl acetates. The female sex pheromones ofC. fagiglandana, C. pyrivora, C. splendana, Epiblema foenella andNotocelia roborana were identified. (E,E)- and (E,Z)-8,10-dodecadien-1-yl acetate are producedvia a commonE9 desaturation pathway inC. splendana. CallingC. nigricana andC. fagiglandana females are attracted to wingfanning males.     

Sesquiterpene Hydrocarbons: Kairomones with a releaser effect in the sexual communication of the white-spotted longicorn beetle, <Emphasis Type="Italic">Anoplophora malasiaca</Emphasis> (Thomson) (Coleoptera: Cerambycidae)

Summary.  We conducted a series of experiments with the white-spotted longicorn beetle Anoplophora malasiaca (Thomson), and its host plant, Citrus unshiu, to examine the origin of the sesquiterpene hydrocarbons (SHCs; including β-elemene, β-caryophyllene, α-humulene, α-farnesene, and several unidentified compounds) that are contained in the elytra of the beetles and act as an attractant. In the laboratory, mechanically wounded citrus branches, as well as those fed upon by A. malasiaca, attracted males more frequently than intact branches. Solid phase microextraction (SPME) and subsequent analyses by gas chromatography (GC) analyses detected measurable SHCs from the air around both mechanically wounded and beetle-infested branches, as well as trace amounts from intact branches. The SHCs were also detected for a certain time from beetles that had fed on the citrus branches, but the amounts decreased rapidly after they were removed from the host. This decrease generally corresponded with a reduction of attractiveness of the beetles in a behavioural assay. Isolated females acquired the SHCs after exposure to, but not upon contact with, other females that had fed on C. unshiu branches. We hypothesize that the citrus SHCs are adsorbed in, retained on, and released from the wax layer of the beetle elytra. Since these compounds are released from branches when beetles feed, they may indirectly signal the presence of beetles to others in the field. The high response rate to SHCs by males is likely representing mate searching behavior. The SHCs act as kairomones with a releaser effect in the communication system of A. malasiaca. Hiroe Yasui, Toshiharu Akino, Midori Fukaya: These authors contributed equally to this article.     

Profiles of cuticular hydrocarbons mediate male mate choice and sexual isolation between hybridising <Emphasis Type="Italic">Chrysochus</Emphasis> (Coleoptera: Chrysomelidae)

Summary. Chemical signals frequently underlie sexual isolation between insect species. Our understanding of the evolutionary forces influencing these signaling systems is known for very few systems, challenging both our efforts to understand insect speciation, and our ability to predict long-term changes in the chemical communication systems of insects. Thus, we are in need of more systems in which both the chemical signals causing sexual isolation and the evolutionary forces driving sexual isolation are understood. Sexual isolation in the hybrid zone between Chrysochus cobaltinus and C. auratus has apparently increased in response to natural selection against hybridisation (i.e. reinforcement). Previous experiments suggested that this isolation was due, at least in part, to male preferences for conspecific females. Here, we confirm this role of male choice, and document that male mate choice in this system is influenced by cuticular hydrocarbon (CHC) profiles. Specifically, male C. cobaltinus responses to control cadavers and conspecific female cadavers painted with different cuticular hexane extracts, together with analyses of the composition of those extracts, revealed that male mate choice is governed by CHC profiles. Multivariate analyses of GC profiles demonstrated that those profiles are indeed both sex- and species-specific. Although GC-MS enabled identification and quantification of the specific cuticular hydrocarbons, we have not yet determined which individual compounds govern mate choice. Having established that CHCs influence sexual isolation in this system, we can now assess the evolutionary lability of these cues, which will inform both our understanding of speciation, and of the conditions under which the chemical signaling systems that influence mate choice in insects can evolve.     

Nestmate recognition in three species of stenogastrine wasps (Hymenoptera,Vespidae)

The capacity to recognise a conspecific intruder was investigated in Parischnogaster jacobsoni, Liostenogaster flavolineata and L. vechti, three species of primitively social wasps of the subfamily Stenogastrinae. Results of behavioural experiments carried out in the field showed that females of all three species react pacifically if presented with female nestmates, but aggressively reject an intruder from a conspecific colony. As L. flavolineata and L. vechti both build large clusters of nests, often very close to each other, the recognition capacity among females from different nests, but in the same conspecific cluster, was also investigated. Females of both species were more aggressive towards females from a different colony in the same cluster than towards their female nestmates. Additional experiments on L. flavolineata showed that there was no difference in reaction towards females from colonies nearer or further from the tested colony but within the same cluster, nor towards females from a different cluster. The capacity to recognise an alien conspecific nest containing immature brood was investigated in P. jacobsoni. Adult females of this species, invited to land on an alien nest which had experimentally been exchanged for their own, accepted the new nest and partially destroyed the immature brood. The behaviour of the females when they land on an alien nest, however, suggests that they do recognise the nest as foreign. Acceptance of foreign nests coupled with low immature brood destruction is probably due to the high energetic costs of egg-deposition and larval rearing in stenogastrine wasps. These results suggest that nestmate recognition in these wasps is very efficient, even though they belong to the most primitive subfamily of social wasps. Received: 16 April 1996/Accepted after revision: 9 August 1996     

Effects of embryonic exposure to conspecific chemical cues on hatching and larval traits in the common frog <Emphasis Type="Italic">(Rana temporaria)</Emphasis>

Summary. Recent studies indicate that amphibian eggs are capable of hatching plasticity in response to chemical cues released by predators feeding on conspecific eggs or larvae. However, information is scarce on the relative importance of predator and conspecific cues in such a process. In particular, no attempt has been made to compare the effects of embryonic exposures to chemical cues indicative of a predation risk for eggs and larvae, although both life stages can co-occur in natural habitats. In this context, common frog embryos (Rana temporaria) were raised until hatching in the presence of crushed conspecific extracts from eggs and tadpoles to assess their respective influences on some hatching and larval traits. While a significant delay in hatching time was observed in embryos exposed to chemical cues from tadpole extract, this life-history shift appeared unaffected by embryonic exposure to egg extract. Hatchlings derived from eggs incubated in the presence of both conspecific extracts showed a significantly greater weight than unexposed controls. However, such an effect was no longer apparent 15, 30 and 50 days after hatching, suggesting that embryonic exposure to chemical cues from damaged conspecific eggs and tadpoles has no influence on larval growth. Lastly, morphological measurements performed on hatchlings and older tadpoles (15, 30 and 50 days old) revealed no significant effect of embryonic treatments on the shape of body and tail.