Does the reproductive status of male round gobies (<Emphasis Type="Italic">Neogobius melanostomus</Emphasis>) influence their response to conspecific odours?

While pheromone communication has been well documented in the female round goby, male responses have not been examined. We determined if male round gobies responded to odours of their conspecifics, and whether that response varied with their reproductive status (reproductive and non-reproductive). No significant differences were observed for any treatment (dechlorinated water, or water conditioned by reproductive males (RM) and non-reproductive males (NRM) and females), although RM spent more time inside shelter than NRM (p < 0.05). Morphologically, length and weight did not vary, but gonadosomatic index, seminal vesicle somatic index and relative head width did differ between the two male groups (p = 0.000). Round goby males guard nests in cavities, and so a preference for shelter with increasing reproductive status is expected. Also, a lack of male responses to conspecific odours may be adaptive in this species, since males nest together in high densities, where increased aggression might prove detrimental for nesting males.     

Discrimination of conspecific faecal chemicals and spatial decisions in juvenile Iberian rock lizards (<Emphasis Type="Italic">Lacerta monticola</Emphasis>)

Faeces play a role in intraspecific chemical communication in many vertebrates, including lizards. Here, we hypothesised that juvenile Iberian rock lizards (Lacerta (=Iberolacerta) monticola) use substrate-borne conspecific faecal chemicals to assess the social environment and base their spatial decisions. To test this hypothesis, we prepared chemical stimuli by dissolving faeces in an organic solvent (dichloromethane, DCM) and conducted chemosensory trials where we quantified latency to the first tongue flick (TF) and TF rates when young captive-borne juveniles were placed in an arena compartment whose substrate was labelled by (1) a control (DCM), (2) their own faecal chemicals, (3) faecal chemicals of another juvenile, (4) faecal chemicals of an adult female or (5) faecal chemicals of an adult male. Following TF observations, we removed a partition that separated the labelled compartment from a chemically unlabelled one, and recorded for 5 min when juveniles first crossed to the unlabelled compartment and total time spent in the labelled compartment. Each juvenile was tested with all stimuli in a randomised order. In addition, juveniles belonged to different families and were unrelated to and unfamiliar with faeces donors. Taken together, TF and spatial responses toward stimuli indicate that juveniles discriminated between faecal chemicals of conspecific juveniles, adult females and males, and that they avoided remaining in substrates labelled by adult male faecal chemicals. We suggest that juveniles assess the social environment based on conspecific faecal chemicals thus avoiding aggression and cannibalistic risks undertaken from encounters with adult males.     

Responses of Snow Voles, Chionomys nivalis, Towards Conspecific Cues Reflect Social Organization during Overwintering Periods

Among microtine rodents, reaction to chemical cues from conspecifics is assumed to reflect social and spatial relationships. Generally, strong attraction of particular odours correlates with non‐aggressive behaviour and high spatial tolerance towards odour donors, whereas weak attraction correlates with greater levels of aggression and spatial segregation. In the present study, we examined whether winter odour preferences of the snow vole Chionomys nivalis, a rock‐dwelling microtine principally found at high‐mountainous regions, differ from that of other vole species, owing to their different social organization during overwintering periods. The social structure of C. nivalis over the winter period is relatively unusual among vole species in that they become nomadic and solitary. In odour choice trials under laboratory conditions, we found that both males and females avoided zones with conspecific odours of both sexes in comparison with unscented control zones or own odours. These results are consistent with the elevated levels of intraspecific aggression and spatial isolation of C. nivalis during overwintering periods. Furthermore, scent‐elicited self‐grooming increased when their own odour was offered against conspecific cues. This, in combination with an active avoidance of conspecific odours, might functionally contribute to minimize direct confrontations between solitary individuals, thereby reducing the risks of aggressive encounters during overwintering periods.     

Sex‐specific responses of Asian citrus psyllid to volatiles of conspecific and host‐plant origin

Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is the primary vector of Candidatus Liberibacter spp. bacteria that cause citrus greening, a disease of worldwide importance. Olfactometry was employed to test responses of D. citri to odours from intact citrus plants (Mexican lime, Citrus aurantifolia, sour orange, Citrus aurantium, Marsh grapefruit, Citrus paradisi and Valencia orange, Citrus sinensis), citrus plants previously infested with D. citri, and odours of conspecifics including nymphs, adult insects of same and opposite sex, and their products (honeydew), both alone and in combination. In contrast to other studies, psyllids of both sexes were attracted to volatiles of undamaged Mexican lime leaves, whereas undamaged grapefruit attracted only females, and leaves of Valencia and sour orange did not attract either sex. All four plant species attracted female psyllids when previously infested, but only Mexican lime and sour orange‐attracted males. Thus, Citrus species appear to vary in the production of both constituitive and induced volatiles that attract adult psyllids. Volatiles emitted by nymphs did not attract either sex, but psyllid honeydew was attractive to males, likely due to female pheromone residues. Males oriented to the odour of females, whereas the reverse was not true, and neither males nor females oriented to same‐sex volatiles. The addition of conspecific cues (adults, nymphs or honeydew) did not increase female attraction to previously infested leaves, but male response was increased by the presence of adults and honeydew, regardless of plant species. Thus, female psyllids appear to orient more strongly to volatiles of plant origin, whereas males respond more strongly to cues emanating from females and conspecific excretions. These results suggest that female psyllids drive the initial colonization of host plants, whereas males orient to females and infested plants. Identification of the specific volatiles involved may permit their use in monitoring and management of this pest.     

Amino acid cues emanating from Pacific salmon eggs and ovarian fluid

The eggs of salmonid fishes are an important food source for many aquatic predators that detect eggs using olfaction. Moreover, chemicals from eggs and ovarian fluid aid sperm cells in detecting and locating eggs for fertilization, and ovarian fluid is attractive to conspecific males. Thus chemicals from eggs and ovarian fluid may facilitate reproduction but may also attract egg predators. The authors sampled mature females of three Pacific salmon species – Chinook (Oncorhynchus tshawytscha), coho (Oncorhynchus kisutch) and sockeye (Oncorhynchus nerka) – and determined the proportional representation of amino acids, potent fish odorants, from their eggs and ovarian fluid (Chinook and coho salmon only). They then tested juvenile coho salmon, an egg predator, for responses to ovarian fluid and egg odours using the electro-olfactogram (EOG) recording technique. The amino acid compositions of the salmon species were significantly and positively correlated with each other, and the interspecific differences were comparable to those between individuals of the same species. The egg water samples were, on average, dominated by lysine, alanine and glutamine (12.6%, 12.4% and 10.9%, respectively). The ovarian fluid samples were dominated by lysine (20.5%), followed by threonine (9.7%), glycine (9.2%) and arginine (8.8%). EOG recordings demonstrated the ability of juvenile coho salmon to detect the chemical traces of eggs and ovarian fluid. It is concluded that salmon eggs are a potent source of odours for potential predators but likely not highly differentiated among salmon species.     

Disparity between Adult and Juvenile American Robins Turdus migratorius Foraging for Ground Invertebrates and Cherry Fruits

Although it has long been known that juveniles often have foraging skills inferior to those of adults, it has generally been assumed that animal prey are more difficult to capture than fruit, and thus that juveniles foraging on fruit should be similar to adults in their efficiency. To examine these ideas, we investigated the abilities of juvenile and adult American robins Turdus migratorius to forage for ground invertebrates and fruits of the black cherry tree Prunus serotina. We hypothesized that juveniles, lacking the experience of adults, would not have the skills of adults and therefore would be less proficient invertebrate and fruit foragers. Juveniles captured 69% of invertebrates at which they struck compared with 80% of adults’ strikes that ended in capture. However, juveniles made more strikes than adults, so mean prey capture per minute was the same. Juveniles were also less skilled fruit foragers. Juveniles were twice as likely as adults to fail to pick a cherry (55% of adults’ vs. 28% of juveniles’ attempts ended in success). However, there was no significant difference in the proportion of juveniles and adults that dropped a cherry once it was picked. As a result of their low levels of success, juveniles consumed about half the number of cherries per minute as did adults. Contrary to prior assumptions, skills involved in fruit foraging may not be so easily acquired and many omnivorous species, like the American robin, must learn both invertebrate and fruit foraging skills.     

Drosophila melanogaster males respond differently at the behavioural and genome‐wide levels to Drosophila melanogaster and Drosophila simulans females

Drosophila melanogaster are found in sympatry with Drosophila simulans, and matings between the species produce nonfertile hybrid offspring at low frequency. Evolutionary theory predicts that females choose mates, so males should alter their behaviour in response to female cues. We show that D. melanogaster males quickly decrease courtship towards D. simulans females. Courtship levels are reduced within 5 min of exposure to a heterospecific female, and overall courtship is significantly lower than courtship towards conspecific females. To understand changes at the molecular level during mate choice, we performed microarray analysis on D. melanogaster males that courted heterospecific D. simulans females and found nine genes have altered expression compared with controls. In contrast, males that court conspecific females alter expression of at least 35 loci. The changes elicited by conspecific courtship likely modulate nervous system function to reinforce positive conspecific signals and dampen the response to heterospecific signals.     

The influence of desiccation and predation on vertical size gradients in populations of the gastropod Oxystele variegata (Anton) on an exposed rocky shore

Summary Oxystele variegata (Anton.) exhibits a vertical size gradient contrary to the model proposed by Vermeij (1972) for low/mid intertidal species, as shell size increases in an upshore direction. Settlement occurs in the lowest zones and juveniles are restricted to the lower shore by conditions of desiccation higher up the beach. Juveniles suffer rapid water loss due to a relatively large opercular surface area and circumference and have a much lower resistance to water loss than adults. This leads to high mortality under conditions of low humidities, and juveniles caged at the top of the balanoid zone, where adults normally occur, die within a few days. As animals increase in size their resistance to desiccation rises allowing them to migrate upshore. This is a response to high rates of predation by the whelk Burnupena delalandii in the lower balanoid zone. Predation is so intense as to override the advantages of higher food availability which lead to a greater body weight for adults protected by cages on the lower shore.     

Behavioural development of conspecific odour preferences in Brandt’s voleMicrotus brandti

The behavioural development of conspecific odour preferences in Brandt’s voleMicrotus brandti (Radde, 1861) was evaluated in laboratory tests. During the weaning period (15th-30th day after the birth), the preference of pups to individual odours of their parents, novel adult males and females were examined. Pups investigated odours of unfamiliar adults significantly more than those of their parents and they displayed significantly more jumping and upward visual investigating behaviours on the bedding soiled by unfamiliar adults than they did on the bedding of their parents. However, the frequency of crossing the parent’s bedding was significantly higher than the frequency of crossing the bedding of alien adults. It is suggested that odour discrimination ability was associated with the age of pups. The Brandt’s vole pups might keep themselves away from unfamiliar environments by keeping away from the novel conspecific odours.     

Damage released prey alarm substances or predator odours? Risk assessment by an aquatic oligochaete

Although the abilities of prey to detect and respond to chemical substances associated with a predator have been widely reported, the factors promoting the evolution of responses to prey alarm cues vs. predator odours are still vague. In this article, we combined field research with laboratory experiments to explore which chemical substance associated with predator activity (predator odour, conspecific or heterospecific alarm substances) induces defence responses in the aquatic oligochaete Stylaria lacustris, which is vulnerable to common littoral predators. The field results indicated that predators injure the oligochaetes and a great proportion, up to 45% of individuals in the population, were found to be damaged. The results of the laboratory experiments revealed that chemical odours from damselfly larvae feeding on S. lacustris did not induce the defence response in the oligochaetes. On the contrary, oligochaetes detected and responded to alarm substances from damaged conspecifics alone and substances from damaged cladoceran Daphnia magna. We discussed conditions favouring the responses to damage released prey alarm cues instead of predator odours in Stylaria lacustris. Our data suggest that the selection of responses to alarm cues from damaged prey vs. predator odours may be dependent on three factors: (1) non-species-specific predation, (2) divergence of food niche of the different stages of the predator and (3) complex food web with multiple predators. Handling editor: S. Declerk     

The smell of danger: chemical recognition of fish predators by the invasive crayfish Procambarus clarkii

1. Since avoiding predation can compromise animal fitness, prey are expected to respond to different predator species with an intensity appropriate to the level of risk. In fresh waters, the threat of predation is typically assessed by chemical cues, in particular by odours released by either injured/disturbed conspecifics (conspecific alarm odour) or predators (predator odours). Here, we used the most widely distributed crayfish in the world, the invasive North American Procambarus clarkii, to investigate the relative effectiveness of odours emitted by fish predators compared with conspecific alarm odour. We also tested whether P. clarkii is able to discriminate between fish predators of which it has ‘experience’ (either recent, via introduction to the same water body, or old, by sharing a native range), as well as between fish predators that pose low or high risk. 2. The study was carried out on introduced populations of P. clarkii from two sites, characterised by different fish assemblages: the Malewa River (a tributary of Lake Naivasha, Kenya) and Lake Trasimeno (Italy). Laboratory experiments consisted of three sequential phases (‘water’, ‘food’ and ‘smell’ phases) and five treatments. Treatments differed in the odour presented during the smell phase, i.e. no odour (plain water) and odours from either injured conspecifics or three fish species per site. Crayfish from the Malewa River population were confronted with the odours of largemouth bass (Micropterus salmoides), common carp (Cyprinus carpio) and tilapia (Tilapia zillii) (all introduced to Lake Naivasha but absent from the Malewa River), and those from the Lake Trasimeno population with the odours of the introduced largemouth bass and carp and the native chub (Squalius cephalus). Largemouth bass is the only predator that imposes a high risk to crayfish, and it also shares its native range with P. clarkii. We analysed the time spent by crayfish feeding, in locomotion and in adopting a raised or lowered posture. A reduction in the time spent feeding and in locomotion, and an increase in the time spent in the lowered posture were considered to indicate alarm. 3. Crayfish from both populations responded with a more pronounced reduction in feeding to conspecific alarm odour rather than to predator odours. Crayfish from the Malewa River reacted with the same intensity to the odours of the three fish species tested, whereas, in Lake Trasimeno, the odour of largemouth bass was significantly more threatening than the odours of the other two species. 4. Procambarus clarkii seems to perceive a general fish odour that alerts it to possible predation risk without the need of either a direct recent experience or via sharing a common native range. However, where they coexist with fish, crayfish become able to distinguish among species, adapting the intensity of their response to the effective risk. Our results confirm the relatively high learning capacity of P. clarkii reported in previous studies and suggest the existence of mechanisms that make predator recognition particularly efficient in this extraordinarily successful invader.     

棉铃虫成虫对两种关键花香气味的联系性学习

为了明确棉铃虫对苯乙醛和乙酸苯甲酯两种关键花香气味的联系性学习行为,在室内分别测定了不同学习训练的棉铃虫雌雄成虫对两种关键花香气味的选择偏好性反应和雄成虫的触角电位反应。偏好性测定结果表明,无花香气味接触经历的棉铃虫对苯乙醛和乙酸苯甲酯的选择频次均无显著差异,且单纯的花香气味接触经历也不能诱导棉铃虫气味偏好性的显著改变,唯有花香气味接触经历伴随蔗糖溶液进行强化训练时,才能诱导气味偏好性的显著性改变。从对两种花香气味的联系性学习看,棉铃虫更容易将苯乙醛与蔗糖溶液进行联系性学习,而不容易将乙酸苯甲酯与蔗糖溶液进行联系性学习。从性别差异看,雌虫比雄虫具有更强的将花香气味与蔗糖溶液进行联系性学习的能力。触角电位测定结果表明,不同学习训练的棉铃虫雄成虫对两种花香气味和绿叶气味顺-3-己烯-1-醇的EAG反应值之间不存在显著性差异。总之,花香气味伴随食物资源的联系性学习经历,能够明显提高棉铃虫成虫对花香气味的选择偏好,可以此为基础进一步优化花香引诱剂的配方设计和应用技术。     

Wild fledgling tits do not mob in response to conspecific or heterospecific mobbing calls

Mobbing, where birds harass a predator through a combination of vocalizations and stereotyped behaviours, is an effective anti-predator behaviour for many species. Mobbing may be particularly important for juveniles, as these individuals are often more vulnerable than adults. Although the component behaviours of mobbing are often considered to be un-learned, there are few confirmatory data, and the developmental trajectory of mobbing is unknown. In this study, we tested whether conspecific or heterospecific mobbing calls initiated mobbing behaviour in juvenile Blue Tits Cyanistes caeruleus. We located wild adult and recently fledged juvenile Blue Tits and presented them with playback recordings of adult conspecific (Blue Tit) and heterospecific (Great Tit Parus major) mobbing alarm calls. Although adult birds readily mob in response to these types of playbacks, juveniles did not exhibit characteristic mobbing behaviour. Some juveniles did, however, exhibit individual components of mobbing behaviour found in mobbing, despite not producing adult-like mobbing behaviour in response to either conspecific or heterospecific playback. These results suggest that, although birds might be capable of mobbing as juveniles, the associations between the non-vocal stereotyped mobbing behaviours and mobbing calls may be learned.     

Ontogenetic shift in buoyancy and habitat in the Antarctic toothfish, <Emphasis Type="Italic">Dissostichus mawsoni</Emphasis> (Perciformes: Nototheniidae)

Buoyancy measurements and depth of capture were taken on 70 individuals of Dissostichus mawsoni collected from the Southern Scotia Arc and McMurdo Sound, Antarctica, to examine the effect of age on buoyancy and habitat use. Standard lengths (SL) ranged from 10.4 to 138.0 cm. Juveniles were not buoyant (heavy in water), whereas adults were neutrally buoyant. The slope of the relationship between buoyancy and SL was significantly negative for juveniles (individuals less than 81 cm SL), but there was no significant relationship for adults (individuals greater than 81 cm SL). These results demonstrate an ontogenetic shift in buoyancy. For juveniles, depth of capture and SL had a significantly positive relationship. As individuals reach adulthood they achieve neutral buoyancy and appear to use deeper water habitats. This interpretation is supported by a significant positive correlation between buoyancy and depth of capture for juveniles. Changes in buoyancy with maturation of juveniles may also be associated with a shift in habitat use. Juveniles appear to exploit benthic habitats, whereas adults use the entire water column over deeper water. Given the differences in prey species available in these habitats and based on our results, we predict that diets of juveniles and adults should differ significantly. We also hypothesize that accumulation of lipid deposits from the diet during maturation of juveniles may account for the ontogenetic shift in buoyancy and allow neutral buoyancy to be achieved in adulthood.     

Faecal pellets as burrow markers: intra- and interspecific odour recognition by western plethodontid salamanders

Chemical communication is widespread among plethodontid salamanders (Caudata: Plethodontidae), but little information exists on the role of odours in interspecific competition in general and among species in western North America in particular. The present study examined the potential of faecal odours for intra- and interspecific communication among sympatric plethodontids in two-choice tests in the laboratory. In experiment 1, Plethodon vehiculum and Aneides ferrus from Vancouver Island, B.C., Canada, were presented with two burrows marked with (1) a faecal pellet of male P. vehiculum versus a control clay pellet, and (2) a faecal pellet of male A. ferreus versus a control pellet. In experiment 2, responses of P. vehiculum, P. dunni and P. vandykei from Washington, U.S.A., were tested towards faecal pellets of conspecific males and females, and towards pellets of congeneric males. Both P. vehiculum and P. dunni distinguished odours of conspecific males and females, based on their behavioural responses towards faecal and control pellets. Only P. dunni, however, avoided burrows marked with faeces of conspecific individuals. In contrast, neither A. ferreus nor P. vandykei appeared to distinguish faecal odours of conspecific salamanders from control pellets. In tests with odours of heterospecific individuals, P. dunni and P. vehiculum distinguished odours of each other, and P. vandykei distinguished odours of P. vehiculum. The data from these two experiments suggest that P. dunni use faecal pellets as territorial markers both in intraspecific communication and in interspecific encounters with P. vehiculum.     

Life cycle and mating behavior of <Emphasis Type="Italic">Helicotylenchus multicinctus</Emphasis> (Nematoda: Hoplolaimidae) on excised <Emphasis Type="Italic">Musa cavendishii</Emphasis> roots

The life cycle and mating behavior of Helicotylenchus multicinctus (Nematoda: Hoplolaimidae) were observed in vitro on excised roots of Musa cavendishii in gnotobiotic culture. Eggs hatched into juveniles whose appearance and structure were similar to those of the adults. Juveniles grew in size and each juvenile stage was terminated by a molt. H. multicinctus had four juvenile stages. The first molt occurred outside the egg shortly after hatching. After the final molt the juveniles differentiated into adult males and females. Mating was required for reproduction. After mating, fertilized females began to lay eggs. The life cycle from second stage juvenile to second stage juvenile was completed in 39 days.     

Communication via sex pheromones within and among Arrenurus spp. mites (Acari: Hydrachnida; Arrenuridae)

We present direct experimental evidence of pheromone use in six species of Arrenurus and indirect evidence for four species, including members of the subgenera Megaluracarus, Truncaturus, and Arrenurus. Water in which females were housed elicited arrestant behaviour in males, males oriented to the source, and at least some individuals in each species assumed the male readiness posture, a precursor to coupling. Most species responded to water treated with conspecific females, but there was also interspecific sex pheromone responsiveness. Arrenurus manubriator and A. megalurus demonstrated reciprocal pheromone cross-attractancy. Males of A. major, A. marshallae, and A. birgei responded to water from females of related species from within their subgenera. Arrenurus apetiolatus males failed to respond to conspecific female-treated water, but the same water elicited arrestant behaviour and orientation in A. manubriator. Heterospecific reactions to female-conditioned water were limited to cases involving members of the same species group and were not seen between species representing different species groups or different subgenera. The species for which cross-attractancy has been demonstrated commonly co-occur in nature, so apparently these pheromones are of limited value for species recognition. Shared reaction to sex pheromones provides additional evidence for inferring close phylogenetic relationship among species, and thus far, corresponds with morphological evidence based on adult males and larvae.     

Pattern and mortality in Colorado Desert plants

Summary We tested for intraspecific interference among Colorado Desert shrubs using an integrated analysis of spatial pattern and juvenile mortality. The data set included 7,000 woody perennials of 24 species in a mapped hectare of Joshua Tree National Monument, California. The site is dominated by Ambrosia dumosa (62.0% of the stems), with Larre tridentata a conspicuous secondary species (2.3% of the stems). Analyses of static pattern for common species showed: (1) aggregated adults and juveniles for Ambrosia dumosa, Erigonum fasciculatum, Mirabilis bigelovii, and Sphaeralcea ambigua, with more aggregation among juveniles than adults; (2) randomly distributed adults and juveniles for Krameria grayi, Opuntia rasmosissima, Simondsia chinensis, and Yucca schidigera. The summed volumes and distances between nearest conspecific neighbors were positively correlated for Ambrosia dumosa and Larrea tridentata, but not significantly correlated for eight remaining species with 100 individuals. Static pattern suggests only weak evidence for negative interactions in Ambrosia and Larrea, and little evidence for other species. Alternative mechanisms other than negative interaction that could give rise to these static patterns are discussed. Juvenile mortality was documented for four common species (Ambrosia dumosa, Eriogonum fasciculatum, Mirabilis bigelovii, and Sphaeralcea ambigua) that experienced substantial mortality. Analyses show: (1) the proportion of individuals that died was independent of the initial density of conspecifics; (2) distance to conspecific adults did not differ for juveniles that died versus those that survived; and (3) death was no more likely for juveniles that contacted other plants than for those that were isolated. The exception was a vine, Mirabilis bigelovii, whose juveniles survived better in contact with other plants. In sum, neither spatial pattern nor patterns of mortality showed clear evidence of negative intraspecific interference.     

Extended Mother–Offspring Relationships in Crayfish: The Return Behaviour of Juvenile Procambarus Clarkii

Crayfish shows a relatively complex parental behaviour compared with other invertebrates, but the literature provides only anecdotal accounts of this phenomenon. In Procambarus clarkii, we described the ‘return’ behaviour of third‐stage juveniles when offered four types of adults: biological mothers, foster mothers, non‐brooding females and males. Then, we analysed the posture and behaviour of the adults to understand the role played by the putative mother in attracting the juveniles. Contrary to non‐brooding individuals, both biological and foster mothers displayed a relatively rare locomotion, executed few cleaning and feeding acts, and never attempted to prey on juveniles. They often assumed a ‘spoon‐like telson posture’ that seemed to facilitate offspring’s approaches. Juveniles increased the frequency of tail‐flips away in the presence of non‐brooding adults; conversely, they accepted foster mothers, along with biological mothers, but not as fast as the latter. Taken together, these results suggest that mother–offspring relationships in P. clarkii are more refined than previously thought, being possibly a key factor enabling this species to thrive in harsh environmental conditions.