Petal-shaped femoral lobes facilitate gliding in orchid mantises.

To glide in forest canopies, arboreal vertebrates evolved various skin-derived aerodynamic structures, such as patagial membranes or webbing, but no comparable structure has been reported from wingless arboreal arthropods.1,2,3 Orchid mantises (Hymenopus coronatus) have been traditionally considered a textbook example of flower mimicry for ∼200 years due to their highly expanded, petal-shaped femoral lobes. However, the empirical evidence substantiating the petal-mimicry function of the femoral lobes has not been entirely conclusive.4,5,6 Observational and experimental evidence suggests that these lobes do not contribute to flower mimicry for luring pollinators6,7 and likely serve other functions.7,8 After observing their aerial escape initiated with active jumping, we hypothesized that orchid mantises can glide and that their femoral lobes are used for gliding. Through behavioral investigations and morphological analyses, we show that orchid mantis nymphs are excellent gliders, exhibiting the shallowest gliding trajectories observed in terrestrial invertebrates.9,10,11,12,13 The lobe extensions on their femoral segments are cambered airfoils, which increase the mantis projected area by ∼36% and play a vital role in the aerodynamic underpinning of the observed gliding. Despite a 165-fold increase in body mass throughout ontogeny, older female mantis nymphs maintained a persistent gliding capability. We further showed a notable 40%-56% reduction in wing loading attributed to the positive size allometry of these lobes, indicating a clear promotion of gliding throughout ontogeny. This is the first documentation of gliding-adapted "leg wings" in a wingless arthropod. The evolution of such structures is potentially common among arboreal arthropods and demands a systematic re-examination.

Camouflage in lichen moths: Field predation experiments and avian vision modelling demonstrate the importance of wing pattern elements and background for survival.

Background matching is perhaps the most ubiquitous form of defensive camouflage in the animal kingdom, an adaptive strategy that relies on the visual resemblance between a prey organism and its background to promote concealment from predators. The importance of background matching has been acknowledged for over a century, yet despite its renown and apparent pervasiveness, few studies exist that have objectively quantified its occurrence and tested the functional significance of background matching in a specific animal study system. The North Island lichen moth Declana atronivea presents a fascinating system to investigate such anti-predator coloration. This species possesses high contrast black and white forewings that appear to resemble lichen. Here we assessed the contribution of background matching to the antipredator defence of D. atronivea using field predation experiments with realistic models. We found that D. atronivea coloration confers a significant survival advantage against native avian predators when on lichen backgrounds compared to bark backgrounds, with an intermediate level of predation occurring when models were near, but not on lichen. This suggests that D. atronivea wing patterns are an adaptation for background matching. We subsequently used calibrated digital photography, avian vision modelling and image analysis techniques to objectively quantify the degree of background matching exhibited by D. atronivea and assessed the contribution of different visual elements (colour, luminance and pattern) to camouflage in this species. Only the pattern elements of D. atronivea presented a close match to that of the lichen backgrounds, with both chromatic and achromatic cues found to be poor predictors of background matching in this species. This study is one of the first to integrate vision modelling, quantitative image analysis and field predation experiments using realistic models to objectively quantify the level and functional significance of background matching in a real species, and presents an ideal system for further investigating the interrelation between multiple mechanisms of camouflage.

The evolution of startle displays: a case study in praying mantises.

Anti-predator defences are typically regarded as relatively static signals that conceal prey or advertise their unprofitability. However, startle displays are complex performances that deter or confuse predators and can include a spectacular array of movements, colours and sounds. Yet, we do not fully understand the mechanisms by which they function, their evolutionary correlates, or the conditions under which they are performed and evolve. Here, we present, to our knowledge, the first phylogenetically controlled comparative analyses of startle displays including behavioural data, using praying mantises as a model system. We included 58 species that provide a good representation of mantis diversity and estimated the strength of phylogenetic signal in the presence and complexity of displays. We also tested hypotheses on potential evolutionary correlates, including primary defences and body size. We found that startle displays and morphological traits were phylogenetically conserved, whereas behavioural traits were highly labile. Surprisingly, body size was not correlated with display presence or complexity in phylogenetically controlled analyses. Species-rich clades were more likely to exhibit displays, suggesting that startle displays were probably involved in lineage diversification. We suggest that to further elucidate the conditions under which startle displays evolve, future work should include quantitative descriptions of multiple display components, habitat type, and predator communities. Understanding the evolution of startle displays is critical to our overall understanding of the theory behind predator-prey dynamics.

The dynamic eggs of the Phasmatodea and their apparent convergence with plants.

The egg stages of animal life cycles are underappreciated in terms of their capacity for dispersal, protection, and biotic and abiotic interactions. Some of the most intriguing egg morphologies are seen in stick and leaf insects (Phasmatodea). Phasmids are charismatic insects, particularly due to their incredible camouflage, though a lesser-known fact is that their eggs are incredibly diverse in shape and structure, reflecting varying ecological niches. Perhaps most remarkable are those eggs which appear to resemble plant seeds in both their appearance and means of dispersal, such as via water and animal vectors. Numerous hypotheses surrounding the function of these egg morphologies and their apparent convergence with seeds have been proposed; however, empirical evidence remains lacking. Here, we present an initial synthesis of available evidence surrounding the ecology and dispersal strategies of phasmid eggs and weigh up the evidence for convergent evolution between phasmid eggs and seeds. In doing so, we highlight areas where further research is needed and discuss how the ecology of phasmid eggs may interplay with other aspects of phasmid ecology, distribution, and evolution.

Short and fast vs long and slow: age changes courtship in male orb-web spiders (Argiope keyserlingi).

Male reproductive performance can vary with condition, age and future reproductive opportunities. Web-building spiders are ideal models to examine the effects of senescence on fitness-related behaviours due to strong selection on male courtship to reduce pre-copulatory sexual cannibalism. Argiope keyserlingi spiders generate courtship vibrations, or 'shudders', that reduce female aggression. We found that male A. keyserlingi courtship slowed with chronological age. Older males took longer to travel across the courtship thread, and overall number of shudders increased. Males retained some ability to modulate courtship quality (shudder duration and number of rocks within each shudder) in response to female quality. A change in courtship performance over time, despite strong selection for repeatability, indicates that ageing in male A. keyserlingi may have direct impacts on reproductive performance.

Selection for predation, not female fecundity, explains sexual size dimorphism in the orchid mantises.

Here we reconstruct the evolutionary shift towards floral simulation in orchid mantises and suggest female predatory selection as the likely driving force behind the development of extreme sexual size dimorphism. Through analysis of body size data and phylogenetic modelling of trait evolution, we recovered an ancestral shift towards sexual dimorphisms in both size and appearance in a lineage of flower-associated praying mantises. Sedentary female flower mantises dramatically increased in size prior to a transition from camouflaged, ambush predation to a floral simulation strategy, gaining access to, and visually attracting, a novel resource: large pollinating insects. Male flower mantises, however, remained small and mobile to facilitate mate-finding and reproductive success, consistent with ancestral male life strategy. Although moderate sexual size dimorphisms are common in many arthropod lineages, the predominant explanation is female size increase for increased fecundity. However, sex-dependent selective pressures acting outside of female fecundity have been suggested as mechanisms behind niche dimorphisms. Our hypothesised role of predatory selection acting on females to generate both extreme sexual size dimorphism coupled with niche dimorphism is novel among arthropods.

Orchid mantis.

James O'Hanlon introduces the orchid mantis, a species of preying mantis that resembles flowers.

Egg Dispersal in the Phasmatodea: Convergence in Chemical Signaling Strategies Between Plants and Animals?

Numerous tree species' seeds contain an 'elaiosome' that acts as a food reward for ants and thus induces dispersal of the seeds. Many stick and leaf insect species appear to have evolved a convergent adaptation for dispersal whereby the egg 'capitulum' serves to induce ants to pick up and carry their eggs. Here, we investigated whether the capitulum facilitates egg dispersal by ants in the Australian stick insect Eurycnema goliath. The total fatty acid composition of E. goliath egg capsules and egg capitula were characterized to identify potential signaling compounds. Removing capitula from E. goliath eggs significantly reduced the likelihood of eggs being carried into the nests of Rhytidoponera metallica ants. Furthermore, attaching capitula to inert objects (polystyrene balls) resulted in these objects being carried into nests by R. metallica. Several fatty acids were present on the egg capsule surface in only trace amounts, whereas they made up over 10% of the dry weight of egg capitula. The fatty acid composition of egg capitula consisted mostly of palmitic acid (C16:0), linoleic acid (C18: 2n6c), oleic acid (C18:1n9c), linolenic acid (C18:3n3), and stearic acid (C18:0). Previously reported research has found that a diglyceride lipid species of oleic acid induces carrying behavior in R. metallica when added to inert artificial stimuli. Therefore, we propose that the dispersal mechanism of E. goliath eggs has converged upon the same chemical signaling pathway used by plants to exploit ant behavior.

The Functional Significance of Chiral Genitalia: Patterns of Asymmetry, Functional Morphology and Mating Success in the Praying Mantis Ciulfina baldersoni.

Genital asymmetry is relatively common and widespread throughout the animal kingdom. The functional significance of genital asymmetry is however, poorly understood for most species. Male praying mantids of the genus Ciulfina are remarkable in possessing complex and directionally asymmetric genital phallomeres in some species, and chirally dimorphic/antisymmetric genitalia in others. Here we explore the chiral dimorphism in male genitalia of Ciulfina baldersoni which appear to exhibit genital antisymmetry. We test whether genital orientation influences mating success, copulation duration and the attachment duration of spermatophores. Additionally we investigate genital interactions between male and females using x-ray micro-computed tomography (micro-CT) and scanning electron microscopy (SEM). Lastly we assess whether genital asymmetry is associated with non-genital morphological asymmetry of a range of traits. Our results highlight the complex functional morphology of genitalia in this praying mantis species and yet demonstrate no functional difference between dextral and sinistral morphs other than the direction of attachment with both morphs enjoying equal levels of mating success. Chiral morphs also did not strongly associate with any other forms of asymmetry. We therefore conclude that genital chirality in Ciulfina baldersoni is a likely case of antisymmetry with no functional significance to genital orientation, and is likely to be selectively neutral.

Sexually selected UV signals in the tropical ornate jumping spider, Cosmophasis umbratica may incur costs from predation.

Sexually selected ornaments and signals are costly to maintain if they are maladaptive in nonreproductive contexts. The jumping spider Cosmophasis umbratica exhibits distinct sexual dichromatism with males displaying elaborate UV body markings that signal male quality. Female C. umbratica respond favorably to UV-reflecting males and ignore males that have their UV masked. However, Portia labiata, a UV-sensitive spider-eating specialist and a natural predator of C. umbratica, is known to use UV reflectance as a cue when hunting prey. We investigated the cost of these UV signals in C. umbratica in terms of their predation risk. Under experimental conditions, three choice scenarios were presented to P. labiata individuals. Choices by P. labiata were made between male C. umbratica with and without the UV signal; a UV-reflecting male and non-UV-reflecting female; and a UV-masked male and female. The presence and absence of UV signals was manipulated using an optical filter. Portia labiata exhibited a strong bias toward UV+ individuals. These results suggest the sexually selected trait of UV reflectance increases the visibility of males to UV-sensitive predators. The extent of this male-specific UV signal then is potentially moderated by predation pressure. Interestingly though, P. labiata still preferred males to females irrespective of whether UV reflectance was present or not. This suggests P. labiata can switch cues when conditions to detect UV reflectance are not optimal.

Pollinator deception in the orchid mantis.

Mimicry has evolved in contexts such as camouflage, predator deterrence, luring of prey, and pollinator attraction. Mimicry of flowers has until now been demonstrated only in angiosperms, yet it has been hypothesized that the Malaysian orchid mantis Hymenopus coronatus mimics a flower to attract pollinators as prey. Despite the popularity of this charismatic insect, this long-discussed hypothesis has never been experimentally investigated. We found that, as predicted for mimicry, the color of H. coronatus is indistinguishable from the color of sympatric flowers for hymenopteran pollinators. Field experiments show that isolated mantises attract wild pollinators at a rate even higher than flowers and capture these pollinators as prey items. After more than a century of conjecture, we provide the first experimental evidence of pollinator deception in the orchid mantis and the first description of a unique predatory strategy that has not been documented in any other animal species.