Phylogenetic inferences in the dung-moss family Splachnaceae from analyses of cpDNA sequence data and implications for the evolution of entomophily

The moss family Splachnaceae is characterized by half of its members relying on insects for spore dispersal. These species grow on dung or other animal substrates. They produce small and aggregated spores, and their capsule is modified to attract coprophilous insects or carrion flies using olfactory and visual cues. Systematic concepts and implicit evolutionary inferences have relied much on variation in characters associated with the spore dispersal syndrome. Phylogenetic reconstructions based on sequence variation of two chloroplast loci (trnL-trnF region and the rps4 gene) suggest that most supraspecific taxa are poly- or paraphyletic. Transformations in morphological characters associated to the syndrome thus offer little if any phylogenetically informative signal. Brachymitrion is resolved in a nested position within Tayloria. A new combination, Tayloria immersa (Goffinet) Goffinet, Shaw & Cox is proposed for B. immersum. Only one of the five subgenera of Tayloria (subg. Orthodon) is potentially monophyletic. Voitia shares a common ancestor with Tetraplodon and is thus nested within the Splachnoideae. The affinities of Aplodon remain ambiguous. Reconstruction of shifts between wind and insect spore dispersal syndromes suggests that entomophily arose more than once and may have been followed by a reversal to the generalist strategy in two lineages.     

Odour-genes eovariance and differential investigation of individual odours in the Mus species complex

Previous research using habituation techniques has demonstrated that greater genetic similarity between two individuals is associated with more similarity in the qualities of their individual odours ('odour-genes eovariance'). We assessed odour similarities across species in two pairs of genetically close species within the Mus species complex (M. musculus and M. domesticus; M. spicilegus and M. macedonicus). Subjects treated odours within each species pair as similar compared with an odour from the other species pair. Subjects also treated odours of M. spicilegus males from the same population as similar compared with the odour of M. spicilegus males from a different population. This confirms odour-genes eovariance across species and within populations and also supports previous findings that odour similarities are more salient than specific odour markers. When adult males were presented with odours of females from two different heterospecific species, subjects spent more time investigating the odour from his own species pair than the other species pair, indicating greater interest in the odour of the closer heterospecific and demonstrating that odour-genes eovariance is reflected in behavioural responses to odours. Implications of odour-genes eovariance as a basis for identifying degrees of genetic relatedness of unfamiliar individuals through similarities in individual odours are discussed.     

Structural changes in plastids of developing Splachnum ampullaceum sporophytes and relationship to odour production

Many mosses of the family Splachnaceae are entomophilous and rely on flies for spore dispersal. Splachnum ampullaceum produces a yellow‐ or pink‐coloured hypophysis that releases volatile compounds, attracting flies to the mature moss. The biosynthetic sources of the visual and aromatic cues within the hypophysis have not been identified, and may be either symbiotic cyanobacteria or chromoplasts that break down lipids into volatile compounds. Here, we used transmission electron microscopy and gas chromatography‐mass spectrometry (GC‐MS) to investigate the sources of these attractants, focusing on different tissues and stages of maturation. Microscopy revealed an abundance of plastids within the hypophysis, while no symbiotic bacteria were observed. During plant maturation, plastids differentiated from amyloplasts with large starch granules to photosynthetic chloroplasts and finally to chromoplasts with lipid accumulations. We used GC‐MS to identify over 50 volatile organic compounds from mature sporophytes including short‐chain oxygenated compounds, unsaturated irregular terpenoids, fatty acid‐derived 6‐ and 8‐carbon alcohols and ketones, and the aromatic compounds acetophenone and p‐cresol. The hypophysis showed localised production of pungent volatiles, mainly short‐chain fermentation compounds and p‐cresol. Some of these volatiles have been shown to be produced from lipid oxidase degradation of linolenic acid within chromoplasts. However, other compounds (such as cyclohexanecarboxylic acid esters) may have a microbial origin. Further investigation is necessary to identify the origin of fly attractants in these mosses.     

Trends in floral scent chemistry in pollination syndromes: floral scent composition in hummingbird-pollinated taxa

We studied an assemblage of 17 species of bird-pollinated Ecuadorian plants (from 14 angiosperm families), including taxa pollinated by short-billed (trochiline) and sickle-billed (hermit) hummingbirds. Hummingbirds are widely supposed to ignore fragrance while visiting flowers. We collected floral headspace odours in order to test the general prediction that specialist hummingbird-pollinated flowers are scentless. In nine out of 17 of these species we failed to detect any odours using gas chromatography-mass spectrometry (GC-MS), whereas the remaining eight species produced trace levels of volatile compounds. Most of these odour compounds were of terpenoid or lipoxygenase derivation and are commonly emitted by vegetative as well as floral plant tissues. Further studies will be required to determine whether these weak odours attract alternative pollinators, repel enemies or represent vestiges of a scented ancestry.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 191–199.     

Individual odour similarities across species parallel phylogenetic relationships in the S. ehrenbergi superspecies of mole-rats

Research using habituation techniques has shown that rodents from the same kin group, population, or species share similarities in their individual odours that covary with shared genetic similarities between them, that is, the closer their genetic relatedness, the more similar their odours. We assessed similarities in individual odours across four sibling species of subterranean mole-rats from the Spalax ehrenbergi superspecies in Israel. Mole-rats were habituated to the urine odour of a same-sex individual from one species then tested with urine odours of individuals from two different species of the superspecies. Subjects treated urine odours of individuals from more closely genetically related species as similar compared with the odours of individuals from a less closely related species, showing that the covariance between odours and genes extends across species. These similarities in odour also paralleled genetic similarities determined by molecular analysis: odours of descendent species were perceived as similar to those of their closest ancestral species, suggesting that some qualities of the odour of the ancestral species persist in the descendent species. It is generally assumed that during speciation incipient species develop species-specific markers, including, for example, odour markers, to facilitate discrimination of conspecifics from close ancestral heterospecifics. Our findings indicate that similarities in odours across species are more salient than species-specific odour markers. Such findings may also have important implications for mechanisms of species recognition. Copyright 2000 The Association for the Study of Animal Behaviour.     

Oviposition preferences and antennal size in carrion flies

Carrion-feeding flies use odours emanating from the decomposing corpse as cues for oviposition and are described as generalists because the larvae feed on the corpses of diverse species. Whereas several features of the corpse may influence the oviposition choices of these flies, it is not known whether there is a preference for a particular species of corpse. We provided carrion flies with ovipositional (and feeding) choices in a field experiment, in which various odour sources were presented simultaneously. We found novel evidence of broadly consistent choices of carrion by flies from four families. Traps baited with decaying fish flesh captured the greatest number of individuals, whereas traps baited with decaying pig liver typically attracted the least. We also asked whether individuals captured in the various baits vary in antennal size, perhaps reflecting different capacities for odour detection. There was a trend for individuals of Lucilia sericata Meigen (Diptera: Calliphoridae) and the platystomatid collected from the traps baited with pig liver to have significantly larger antennae, whereas individuals of Muscina stabulans (Fallen) (Diptera: Muscidae) captured in traps baited with marine fish flesh had relatively longer antennae for their body size. Our data reveal a more nuanced pattern of oviposition behaviour in these generalist carrion flies, which may reflect differences in their preference of carrion with different nutrients, and in their capacity to detect particular odours.     

A tangerine-scented social odour in a monogamous seabird

Social odours, conspecific chemical signals, have been demonstrated in every class of vertebrate except birds. The apparent absence is surprising, as every bird examined has a functional olfactory system and many produce odours. The crested auklet (Aethia cristatella), a monogamous seabird, exhibits a distinctive tangerine-like scent closely associated with courtship. Using T-maze experiments, we tested whether auklets preferred conspecific odours and whether they distinguished between different types of scent, two prerequisites of chemical communication. Crested auklets exhibited: (i) an attraction to conspecific feather odour; (ii) a preference for two chemical components of feather scent (cis-4-decenal and octanal), which we identified as seasonally elevated; and (iii) differential responses to odours, as indicated by a preference for auklet odour, an aversion to mammalian musk, but no significant response to banana essence (amyl acetate). Our results suggest that crested auklets detect plumage odour and preferentially orientate towards this stimulus. The striking and well-described courtship display that involves the scented neck region, the 'ruff sniff', provides a conspicuous behavioural mechanism for odour transmission and the potential for scent assessment during sexual selection. Although the importance and full social function of chemical signals are just beginning to be understood in birds, including crested auklets, social odours promise to reveal a largely unexplored and possibly widespread means of avian communication.     

Effect of food deprivation on attractiveness of food sources, containing natural and artificial sugar and protein, to three African fruit flies: Ceratitis cosyra, Ceratitis fasciventris, and Ceratitis capitata

The effects of food deprivation, age, and mating status on the responses of three fruit fly species, Ceratitis cosyra (Walker), Ceratitits fasciventris (Bezzi), and Ceratitits capitata (Wiedemann) (Diptera: Tephritidae) to natural and artificial sugar and protein food sources were investigated. Natural food sources included guava [Psidium guajava L. (Myrtaceae)] juice (a common host fruit for all three fruit fly species) and bird faeces (farm chicken). Artificial food sources included molasses (obtained from a local sugar factory) and a locally produced protein bait (the International Centre of Insect Physiology and Ecology yeast). In all species studied, sugar deprivation of immature (1–2‐day‐old) male and female flies increased their response to food odours, although it did not change their preference for the type of odour (protein or sugar). Protein deprivation of mature (14–17‐day‐old) male and female flies also increased their response to food odours compared to protein‐fed flies. Protein‐deprived females were highly attracted to odours from protein sources in particular. Odours from natural food sources, guava juice, and chicken faeces, were more attractive to food‐deprived flies than were odours from artificial sugar and protein sources. Attraction to food odours increased significantly with increasing age for protein‐deprived females of all species. For males and females of all species, nutritional state was a more important factor than mating status in influencing responses of flies to food odours. Practical implications of these findings are discussed in terms of strategies for fruit fly control using food baits.     

Chemosensory processing in the fruit fly,Drosophila melanogaster: generalization of a feeding response reveals overlapping odour representations

Insects are capable of detecting, and discriminating between, a very large number of odours. The biological relevance of many of those odours, particularly those related to food, must first be learned. Given that the number of sensory receptors and antennal lobe (AL) glomeruli is limited relative to the number of odours that must be detectable, this ability implies that the olfactory system makes use of a combinatorial coding scheme whereby each sensory cell or AL projection neuron can participate in coding for several different odours. An important step in understanding this coding scheme is to behaviourally quantify the degree to which sets of odours are discriminable. Here we evaluate odour discriminability in the fruit fly,Drosophila melanogaster, by first conditioning individual flies to not respond to any of several odourants using a nonassociative conditioning protocol (habituation). We show that flies habituate unconditioned leg movement responses to both mechanosensory and olfactory stimulation over 25 unreinforceed trials. Habituation is retained for at least 2 h and is subject to dishabituation. Finally, we test the degree to which the conditioned response generalizes to other odourants based on molecular features of the odourants (e.g. carbon chain length and the presence of a target functional group). These tests reveal predictable generalization gradients across these molecular features. These data substantiate the claim that these features are relevant coding dimensions in the fruit fly olfactory system, as has been shown for other insect and vertebrate species.     

Pollination of the “carrion flowers” of an African stapeliad (<Emphasis Type="Italic">Ceropegia mixta</Emphasis>: Apocynaceae): the importance of visual and scent traits for the attraction of flies

Flowers that mimic carrion or faeces exhibit unusual traits, the evolution and functional significance of which remain poorly understood. Odour is an important pollinator attractant, but visual traits and interactions between visual and scent traits have seldom been considered. We studied pollination of the “carrion flowers” of Ceropegia mixta [= Orbea variegata], analysed floral traits and used manipulative experiments to explore the contributions of visual and scent traits to pollinator attraction. Flowers were pollinated primarily by Musca domestica (Muscidae), with lesser contributions by Calliphoridae and Sarcophagidae flies. The floral odour (analysed using gas chromatography–mass spectrometry) was dominated by oligosulphides and phenol. Comparison of floral and abiotic background colours (analysed using reflectance spectrometry) using a fly colour vision model suggested that flowers would be chromatically indistinguishable from the background. Comparison of fly arrival rates at concealed (but still scented) versus exposed flowers showed that flies can locate flowers without visual cues, but visitation was higher when the flowers were visible. Experiments using model flowers with odour supplied by real flowers (to explore the significance of dark flowers and dark spots on a pale background, which both occur frequently in flowers that mimic carrion or faeces) showed that scented black flowers attracted significantly more flies than similarly scented human-yellow flowers, while the presence or size of black spots on the corolla had no effect on the attraction of flies. Our results suggest that there is a visual component to fly attraction, but some traits, such as the mottled patterning, may not have evolved to enhance pollinator attraction.     

Patterns of Detection and Capture Are Associated with Cohabiting Predators and Prey

Avoidance behaviour can play an important role in structuring ecosystems but can be difficult to uncover and quantify. Remote cameras have great but as yet unrealized potential to uncover patterns arising from predatory, competitive or other interactions that structure animal communities by detecting species that are active at the same sites and recording their behaviours and times of activity. Here, we use multi-season, two-species occupancy models to test for evidence of interactions between introduced (feral cat Felis catus) and native predator (Tasmanian devil Sarcophilus harrisii) and predator and small mammal (swamp rat Rattus lutreolus velutinus) combinations at baited camera sites in the cool temperate forests of southern Tasmania. In addition, we investigate the capture rates of swamp rats in traps scented with feral cat and devil faecal odours. We observed that one species could reduce the probability of detecting another at a camera site. In particular, feral cats were detected less frequently at camera sites occupied by devils, whereas patterns of swamp rat detection associated with devils or feral cats varied with study site. Captures of swamp rats were not associated with odours on traps, although fewer captures tended to occur in traps scented with the faecal odour of feral cats. The observation that a native carnivorous marsupial, the Tasmanian devil, can suppress the detectability of an introduced eutherian predator, the feral cat, is consistent with a dominant predator – mesopredator relationship. Such a relationship has important implications for the interaction between feral cats and the lower trophic guilds that form their prey, especially if cat activity increases in places where devil populations are declining. More generally, population estimates derived from devices such as remote cameras need to acknowledge the potential for one species to change the detectability of another, and incorporate this in assessments of numbers and survival.     

Search strategies of fruit flies in steady and shifting winds in the absence of food odours

Abstract. Flight behaviour by females of two species of fruit flies, Drosophila funebris and Drosophila immigrans , was videorecorded in a wind tunnel in still air and in wind with a constant or shifting direction. Flies which were deprived of food overnight took flight in the absence of food odours. Both species responded to the presented winds in agreement with two models that predict the shortest distance to an odour plume. According to these models, the shortest distance to an odour plume is travelled when insects fly at right angles to the wind with a steady direction. In winds shifting over more than 60, the shortest distance to an odour plume is achieved when insects fly parallel to the time-averaged wind direction. We propose a behavioural mechanism which accomplishes the observed flight directions taken by the two species of fruit flies in response to the tested wind regimes.     

Individual Odour Similarity and Discrimination in the Coruro (Spalacopus cyanus, Octodontidae)

Previous studies of subterranean, fossorial and above‐ground rodents have demonstrated that similarities in individual odours covary with genetic similarities thus supporting the theory of odour‐genes covariance (i.e. the closer the individuals are genetically, the greater the similarities between their odours). We used the habituation‐generalization paradigm, where the subject is exposed to the same odour stimulus in three consecutive habituation trials followed by two test trials in which the odour from two other individuals are presented successively. Using this test design, we showed that the socially living coruros (Spalacopus cyanus) discriminate individuals on the basis of their ano‐genital odours and also respond to odour similarities between individuals. Male and female subjects treated ano‐genital odours of two same‐sex family members and also the odours of two sibling strangers as different to each other. At the same time, they treated the odours of siblings as similar compared with the odour of an unrelated individual. No gender differences were detected. Our results contrast with those from other rodent species that did not spontaneously discriminate between individual odours of siblings from a different family than their own. The polygyneous lifestyle may provide the selective background for that difference. Additional research will be necessary to explore this hypothesis and to rule out differences due to dietary preferences and due to the type of paradigm chosen for the tests.     

Evidence for olfactory learning in procellariiform seabird chicks

Burrow nesting procellariiform seabirds use olfactory cues for both foraging and nest recognition. As chicks, burrow nesters develop in the dark, but are exposed to both prey‐related and individual‐specific scents through contact with their parents. This exposure suggests that chicks may have the opportunity to learn odours while still in the nest. In this study, we examined whether exposure to odourants during development might influence olfactory search behaviour expressed later in life. To test this idea, we exposed eggs of thin‐billed prions Pachyptila belcheri to a rosy‐scented novel odour (phenyl ethyl alcohol, PEA) or a control (water) just before hatching; chicks were then tested with these odours in a simple wind tunnel. Prior to fledging, subjects who had received pre‐exposure to PEA displayed head sweeps nearly twice as frequently as control birds did when presented with PEA. This study demonstrates that under natural rearing conditions, procellariiforms learn odour characteristics of their rearing environment in the nest.     

Convergent evolution of carrion and faecal scent mimicry in fly-pollinated angiosperm flowers and a stinkhorn fungus

Flowers of many angiosperms attract fly pollinators through mimicry of animal carrion and faeces. This phenomenon of “sapromyiophily” is also evident in the sporophytes of some mosses and fruiting bodies of “stinkhorn” fungi, both of which use flies as agents of spore dispersal. We studied the scent chemistry of a stinkhorn fungus (Clathrus archeri) and seven fly-pollinated plant species with foetid odours to determine the degree to which these organisms mimic the scent of carrion and faeces (reference scent samples were collected from rotting meat, a rat carcass and horse and dog faeces), as well as the degree of convergent evolution between the fungus and angiosperm flowers. We found that scents of both the fungus and angiosperms tended to contain compounds typical of carrion, such as oligosulphides, and of faeces, such as phenol, indole and p-cresol. This study provides compelling new evidence for mimicry of carrion and faeces, as well as a striking pattern of convergence in the putrid scents of the fungus and the angiosperms, relative to those of confamilial species. The syndrome of sapromyiophily thus encompasses at least two kingdoms (Plantae and Fungi) and provides an effective means of exploiting flies as agents of pollen and spore dispersal.     

Behavioural responses of free‐ranging western grey kangaroos (Macropus fuliginosus) to olfactory cues of historical and recently introduced predators

Predation risk influences foraging decisions and time allocation of prey species, and may result in habitat shifts from potentially dangerous to safer areas. We examined a wild population of western grey kangaroos (Macropus fuliginosus) to test the efficacy of predator faecal odour in influencing time allocated to different behaviours and inducing changes in habitat use. Kangaroos were exposed to fresh faeces of a historical predator, the dingo (Canis lupus dingo), a recently introduced predator, the red fox (Vulpes vulpes), a herbivore (horse, Equus caballus) and an unscented control simultaneously. Kangaroos did not increase vigilance in predator‐scented areas. However, they investigated odour sources by approaching and sniffing; more time was spent investigating fox odour than control odours. Kangaroos then exhibited a clear anti‐predator response to predator odours, modifying their space use by rapidly escaping, then avoiding fox and dingo odour sources. Our results demonstrate that wild western grey kangaroos show behavioural responses to predator faeces, investigating then avoiding these olfactory cues of potential predation risk, rather than increasing general vigilance. This study contributes to our understanding of the impact of introduced mammalian predators on marsupial prey and demonstrates that a native Australian marsupial can recognize and respond to the odour of potential predators, including one that has been recently introduced.     

A sheep in wolf's clothing: do carrion and dung odours of flowers not only attract pollinators but also deter herbivores?

Carrion and dung odours of various flowers have traditionally been considered an adaptation for attracting the flies and beetles that pollinate them. While we accept the role of such odours in pollinator attraction, we propose that they may also have another, overlooked, anti‐herbivore defensive function. We suggest that such odours may deter mammalian herbivores, especially during the critical period of flowering. Carrion odour is a good predictor for two potential dangers to mammalian herbivores: (1) pathogenic microbes, (2) proximity of carnivores. Similarly, dung odour predicts faeces‐contaminated habitats that present high risks of parasitism. These are two new types of repulsive olfactory aposematic mimicry by plants: (1) olfactory feigning of carcass (thanatosis), a well‐known behavioural defensive strategy in animals, (2) olfactory mimicry of faeces, which also has a defensive visual parallel in animals.     

Olfactory Sex Recognition Investigated in Antarctic Prions

Chemical signals can yield information about an animal such as its identity, social status or sex. Such signals have rarely been considered in birds, but recent results have shown that chemical signals are actually used by different bird species to find food and to recognize their home and nest. This is particularly true in petrels whose olfactory anatomy is among the most developed in birds. Recently, we have demonstrated that Antarctic prions, Pachyptila desolata, are also able to recognize and follow the odour of their partner in a Y-maze.However, the experimental protocol left unclear whether this choice reflected an olfactory recognition of a particular individual (i.e. partner) or a more general sex recognition mechanism. To test this second hypothesis, male and female birds'' odours were presented simultaneously to 54 Antarctic prions in a Y-maze. Results showed random behaviour by the tested bird, independent of its sex or reproductive status. Present results do not support the possibility that Antarctic prions can distinguish the sex of a conspecific through its odour but indirectly support the hypothesis that they can distinguish individual odours.     

Confusing tastes and smells: how odours can influence the perception of sweet and sour tastes

This study investigated the relationship between perception of an odour when smelled and the taste of a solution to which the odour is added as a flavorant. In Experiment 1 (E1) sweetness, sourness, liking and intensity ratings were obtained for 20 odours. Taste ratings were then obtained for sucrose solutions to which the odours had been added as flavorants. Certain odours were found to enhance tasted sweetness while others suppressed it. The degree to which an odour smelled sweet was the best predictor of the taste ratings. These findings were extended in Experiment 2 (E2), which included a second tastant, citric acid, and employed four odours from E1. The most sweet smelling odour, caramel, was found to suppress the sourness of citric acid and, as in E1, to enhance the sweetness of sucrose. Again, odours with low sweetness suppressed the sweetness of tasted sucrose. The study demonstrated that the effects of odours on taste perception are not limited to sweetness enhancement and apply to sour as well as sweet tastes. The overall pattern of results is consistent with an explanation of the taste properties of odours in terms of prior flavour-taste associations.     

Nestling tree swallows (Tachycineta bicolor) alter begging behaviour in response to odour of familiar adults,but not their nests

Communication using chemical cues is important for many taxa, including birds, but the use of olfaction for intraspecific communication has been investigated only recently in passerines and is understudied in nestlings. To address this knowledge gap, we explored whether nestling tree swallows (Tachycineta bicolor) would recognize and respond to chemical cues of conspecifics, specifically testing begging responses to familiar and unfamiliar nest and adult odours. For the nest odour experiment, nests were treated with either orange essential oil or distilled water to create scented and unscented (control) odour environments, respectively. For the adult odour experiment, adults attending the nestlings were considered “familiar adults” and adults attending a different brood in the population were considered “unfamiliar adults.” We found that begging responses of nestlings did not differ in response to orange oil odour or water, but nestlings begged significantly longer and more intensely in response to odours of a familiar than an unfamiliar adult, regardless of adult sex. This provides evidence that tree swallows use chemical cues to alter their behaviour and opens up many exciting avenues of future research.