Abstract: Female St Andrewâs Cross spiders control copulation duration by timing sexual cannibalism and may thereby control paternity if cannibalism affects sperm transfer. We have investigated the effect of copulation duration on sperm transfer and documented sperm storage patterns when we experimentally reduced the ability of females to attack and cannibalise the male. Virgin males and females were paired and randomly allocated either to a
control treatment, where females were allowed to attack and cannibalise the male during copulation, or to an
experimental treatment, where females were unable to cannibalise the male. The latter was achieved by placing a paintbrush against her chelicerae during copulation. Our experimental manipulation did not affect copulation duration or sperm storage. However, the number of sperm stored by the female increased with copulation duration only if the male was cannibalised, suggesting that cannibalism increases relative paternity not only through prolonged copulation duration following a fair raffle model but also through the cannibalism act itself. Future studies should explore whether cannibalised males ejaculate more sperm or whether females electively store the sperm of cannibalised males.
Abstract: The extraordinary taxonomic and morphological diversity of orchids is accompanied by a remarkable range of pollinators and pollination systems. Sexually deceptive orchids are adapted to attract specific male insects that are fooled into attempting to mate with orchid flowers and inadvertently acting as pollinators. This review summarises current knowledge, explores new hypotheses in the literature, and introduces some new approaches to understanding sexual deception from the perspective of the duped pollinator. Four main topics are addressed: (1) global patterns in sexual deception, (2) pollinator identities, mating systems and behaviours, (3) pollinator perception of orchid deceptive signals, and (4) the evolutionary implications of pollinator responses to orchid deception, including potential costs imposed on pollinators by orchids. A global list of known and putative sexually deceptive orchids and their pollinators is provided and methods for incorporating pollinator perspectives into sexual deception research are provided and reviewed.
At present, almost all known sexually deceptive orchid taxa are from Australia or Europe. A few sexually deceptive species and genera are reported for New Zealand and South Africa. In Central and Southern America, Asia, and the Pacific many more species are likely to be identified in the future. Despite the great diversity of sexually deceptive orchid genera in Australia, pollination rates reported in the literature are similar between Australian and European species. The typical pollinator of a sexually deceptive orchid is a male insect of a species that is polygynous, monandrous, haplodiploid, and solitary rather than social. Insect behaviours involved in the pollination of sexually deceptive orchids include pre-copulatory gripping of flowers, brief entrapment, mating, and very rarely, ejaculation. Pollinator behaviour varies within and among pollinator species.
Deception involving orchid mimicry of insect scent signals is becoming well understood for some species, but visual and tactile signals such as colour, shape, and texture remain neglected. Experimental manipulations that test for function, multi-signal interactions, and pollinator perception of these signals are required. Furthermore, other forms of deception such as exploitation of pollinator sensory biases or mating preferences merit more comprehensive investigation. Application of molecular techniques adapted from model plants and animals is likely to deliver new insights into orchid signalling, and pollinator perception and behaviour.
There is little current evidence that sexual deception drives any species-level selection on pollinators. Pollinators do learn to avoid deceptive orchids and their locations, but this is not necessarily a response specific to orchids. Even in systems where evidence suggests that orchids do interfere with pollinator mating opportunities, considerable further research is required to determine whether this is sufficient to impose selection on pollinators or generate antagonistic coevolution or an arms race between orchids and their pollinators.
Botanists, taxonomists and chemical ecologists have made remarkable progress in the study of deceptive orchid pollination. Further complementary investigations from entomology and behavioural ecology perspectives should prove fascinating and engender a more complete understanding of the evolution and maintenance of such enigmatic plant-animal interactions.
Abstract: Typically, floral colour attracts pollinators by advertising rewards such as nectar, but how does colour function when pollinators are deceived, unrewarded, and may even suffer fitness costs? Sexually deceptive orchids are
pollinated only by male insects fooled into mating with orchid flowers and inadvertently transferring orchid pollinia. Over long distances, sexually deceptive orchids lure pollinators with counterfeit insect sex pheromones, but close-range deception with colour mimicry is a tantalising possibility. Here, for the first time, we analyse the colours of four sexually deceptive Cryptostylis orchid species and the female wasp they mimic (Lissopimpla excelsa, Ichneumonidae), from the perspective of the orchidsâ single, shared pollinator, male Lissopimpla excelsa. Despite appearing different to humans, the colours of the orchids and female wasps were effectively
identical when mapped into a hymenopteran hexagonal colour space. The orchids and wasps reflected predominantly red-orange wavelengths, but UV was also reflected by raised bumps on two orchid species and by female wasp wings. The orchidsâ bright yellow pollinia contrasted significantly with their overall red colour. Orchid deception may therefore involve accurate and species-specific mimicry of wavelengths reflected by female wasps, and potentially, exploitation of insectsâ innate attraction to UV and yellow wavelengths. In general, mimicry may be facilitated by exploiting visual vulnerabilities and evolve more readily at the peripheries of sensory perception. Many sexually deceptive orchids are predominantly red, green or white: colours that are all potentially difficult for hymenoptera to detect or distinguish from the background.
Abstract: Sexually deceptive orchids lure pollinators by mimicking female insects. Male insects fooled into gripping or copulating with orchids unwittingly transfer the pollinia. The effect of deception on pollinators has been considered negligible, but we show that pollinators may suffer considerable costs. Insects pollinating Australian tongue orchids (Cryptostylis species) frequently ejaculate and waste copious sperm. The costs of sperm wastage could select for pollinator avoidance of orchids, thereby driving and maintaining sexual deception via antagonistic coevolution or an arms race between pollinator learning and escalating orchid mimicry. However, we also show that orchid species provoking such extreme pollinator behavior have the highest pollination success. How can deception persist, given the costs to pollinators? Sexually-deceptive-orchid pollinators are almost exclusively solitary and haplodiploid species. Therefore, female insects deprived of matings by orchid deception could still produce male offspring, which may even enhance orchid pollination.
Notes: Free access from Am. Nat. at www.journals.uchicago.edu/doi/abs/10.1086/587532
Abstract: Spiders and their mating systems are useful study subjects with which to investigate questions of widespread interest about sexual selection, pre- and post-copulatory mate choice, sperm competition, mating strategies, and sexual conflict. Conclusions drawn from such studies are broadly applicable to a range of taxa, but rely on accurate understanding of spider sexual interactions. Extensive behavioural experimentation demonstrates the presence of sex pheromones in many spider species, and recent major advances in the identification of spider sex pheromones merit review. Synthesised here are the emission, transmission, structures, and functions of spider sex pheromones, with emphasis on the crucial and dynamic role of sex pheromones in female and male mating strategies generally. Techniques for behavioural, chemical and electrophysiological study are summarised, and I aim to provide guidelines for incorporating sex pheromones into future studies of spider mating.
In the spiders, pheromones are generally emitted by females and received by males, but this pattern is not universal. Female spiders emit cuticular and/or silk-based sex pheromones, which can be airborne or received via contact with chemoreceptors on male pedipalps. Airborne pheromones primarily attract males or elicit male searching behaviour. Contact pheromones stimulate male courtship behaviour and provide specific information about the emitterâs identity. Male spiders are generally choosy and are often most attracted to adult virgin females and juvenile females prior to their final moult. This suggests the first male to mate with a female has significant advantages, perhaps due to sperm priority patterns, or mated female disinterest. Both sexes may attempt to control female pheromone emission, and thus dictate the frequency and timing of female mating, reflecting the potentially different costs of female signalling and/or polyandry to both sexes. Spider sex pheromones are likely to be lipids or lipid soluble, may be closely related to primary metabolites, and are not necessarily species specific, although they can still assist with species recognition. Newer electrophysiological techniques coupled with
chemical analyses assist with the identification of sex pheromone compounds. This provides opportunities for more targeted behavioural experimentation, perhaps with synthetic pheromones, and for theorising about the biosynthesis and evolution of chemical signals generally. Given the intriguing biology of spiders, and the critical
role of chemical signals for spiders and many other animal taxa, a deeper understanding of spider sex pheromones should prove productive
Abstract: Study of Australian Tongue Orchids addresses questions of widespread interest about the evolution of sexually deceptive pollination, and provides information for conservation and management. We present recent data on flowering, pollination, and fruit set for three Cryptostylis species: the Bonnet Orchid C. erecta R. Br., the Small Tongue Orchid C. leptochila F. Muell. Ex Benth., and the Large Tongue Orchid C. subulata (Labill.) H. G. Reichb. (Jones 1988). These species are pollinated by male Orchid Dupe wasps Lissopimpla excelsa (Ichneumonidae) when they âpseudocopulateâ with the flowers. C. subulata flowered December-February, and C. erecta flowered November-March. C. leptochila began flowering in December, and pollination was still occurring in late April. This species had the most flowers, but the lowest fruit set. In most field sites, the earliest flowers on a raceme were pollinated most often, although this was absent when pollinators were scarce. Orchids may attract pollinators more easily at the start of the flowering season before the female wasps emerge, or pollinators could learn the locations or appearance of orchids and avoid later-opening flowers. We also found that pollinator abundance varied during and between seasons, no evidence of self-pollination, and that C. erecta racemes were more likely to be eaten by predators after fruit set.
Abstract: Floral traits such as odor, color, and morphology are important pollinator attractants. Variation in floral traits may influence floral
constancy, the tendency of pollinating insects to visit flowers of only one type. We investigated for the first time variation in odor between floral morphs in heterostylous species. We analyzed inter- and intraspecific odor variation in the Bpin^ and Bthrum^ floral morphs of sympatric Primula elatior and P. farinosa (Primulaceae). Floral volatiles were sampled with headspace sorption. Quantitative analysis and chemical identification were performed by gas chromatography coupled to mass spectrometry. The species produced different floral bouquets. P. elatior emitted mostly limonene with small amounts of a-pinene, myrcene, and sabinene. P. farinosa produced
benzaldehyde, 4-oxoisophorone (2,6,6-trimethyl-2-cyclohexene-1,4-dione), benzyl alcohol, and benzyl acetate. These interspecific differences may play a role in promoting floral constancy and maintaining species integrity. Conversely, no differences were detected between the scents of pin and thrum morphs within each species. Heterostyly relies on pollinators visiting both floral morphs. There may be stabilizing selection against divergences in traits that may cause pollinators to develop floral constancy to only one of the
floral morphs.
Abstract: Sexual cannibalism is common among orb-web spiders and may limit male copulation frequency. Each copulation by male St Andrew's Cross spiders (Argiope keyserlingi) involves the transfer of sperm from one pedipalp only. Almost half of the males survive their first copulation, but all of the surviving males are cannibalized when they copulate with the other pedipalp. We investigated why males cannot copulate more than twice. Experimentally fatigued males were not cannibalized more frequently than control males. Experimental removal of one pedipalp in virgin males did not increase cannibalism during their first copulation, but the surviving males were unable to copulate with a subsequent female, suggesting they cannot use a pedipalp more than once. Un-manipulated males always inserted their unused pedipalp during their second copulation. Sperm counts from males preserved immediately after copulation and from males maintained for an additional 3 wk show that used pedipalps are not replenished over such a period.
Abstract: In theory, male mate choice should occur when the costs of copulation, in terms of future mating opportunities, are high. The criteria males use to choose mates may change depending upon male mating history and the potential for future matings. We examine male mate choice in the St. Andrew's Cross Spider (Argiope keyserlingi Araneae: Araneidae). Laboratory experiments revealed that death and injury caused by female sexual cannibalism limits males to a maximum of two copulations. We assessed the mate choices of virgin and mated males for females of different reproductive status. We used field and laboratory choice bioassays involving airborne and web-based pheromones. In field experiments, wild males were strongly attracted to webs built by laboratory-raised virgin females. Webs from mated females did not attract males. Male mate choice was affected by male reproductive status: while virgin males strongly preferred penultimate and virgin females to mated females, mated males were apparently indifferent to females of different mating status. Such post-copulatory changes in male mate choice have not been previously documented, and may reflect a decreased potential for future mating.
Abstract: Studies that investigate patterns of paternity in polyandrous species typically employ double-mating trials, in which the paternity share of each male is established by either the sterile male technique or using genetic markers. However, polyandrous females may mate with more than two males and, in some species, triple-mating trials produce different patterns of paternity from double-mating trials. We investigated patterns of paternity share in triple-mating trials of the sexually cannibalistic orb-web spider Nephila plumipes. These experiments reveal little quantitative changes to paternity share when more than two males mate with the female; the third male apparently diluted the fertilisation success of the second male but not of the first male. Sexual cannibalism had little impact on the fertilisation success of the first male, but greatly increased the fertilisation success of the third male. When offered a choice, males did not prefer to mate with virgin over mated females, but males that chose virgin females were significantly heavier than those that chose mated females.
Abstract: Mesopelagic (200-1000 m) and bathypelagic (> 1000 m) fish near Macquarie Island, Australia, are important in the diets of seals, seabirds, and Patagonian toothfish. They also form important links between the productivity at shallow and deeper water depths. Here we analyse the diets of 23 fish species, 13 of which are from the family Myctophidae from 254 stomach samples. Crustaceans (particularly copepods, amphipods, and euphausiids) were the dominant prey in 18 species. Fishes were the dominant prey in five species. Further analysis showed that five of the 13 myctophid fishes had a low level of similarity in diet composition between individuals of each species, whereas the other eight species had significantly high levels of similarity. Cluster analysis and randomisation procedures suggested the existence of five trophic guilds among the Myctophidae.
Abstract: Orb-web spiders may anticipate their future prey environment by detecting the presence of prey and adjusting their web building behavior accordingly. Here we investigate the effect of different prey sizes and density on the web size and mesh height of the orb webs constructed by Argiope keyserlingi. The experimental design allowed the transmission of prey vibrations but prevented any capture. We found that A. keyserlingi constructed webs more frequently in the presence of prey, but did not alter the web size or mesh height of their webs.
