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

Biology, ecology, and biogeography of eremic praying mantis Blepharopsis mendica (Insecta: Mantodea)

Background

Blepharopsis mendica (Fabricius, 1775) is a large mantid species found from the Canary Islands across North Africa, the Middle East, and Pakistan. Research on this species has been limited, especially in Iran, despite the country's potential significance for studying its biology and distribution. Adults of this species are easily recognizable by their marble-white pattern and rhomboidal leaf-like pronotum. They are sit-and-wait predators that inhabit various open environments.

Methods

Field observations were conducted across various regions of the Egyptian Flower mantis (Blepharopsis mendica) global distribution, with a focus on Morocco, Tunisia, and Iran. Distribution data for B. mendicawere gathered from fieldwork, museum collections, online biodiversity databases, and publications, totaling 593 occurrence points. Ecological niche modeling was performed using environmental data, and various models were evaluated for suitability. Phylogeographic analyses involved DNA sequencing and construction of a haplotype network to examine genetic relationships between populations. Divergence time estimation and biogeographical range expansion models were applied to explore historical distribution shifts of the species across different regions. The study provided comprehensive insights into the biology, distribution, and genetic history of B. mendica.

Results

We provide information on the life cycle, ootheca, defense behavior, habitat, and biogeography of the Egyptian Flower mantis Blepharopsis mendica. This mantid is an overwintering univoltine species with nymphs emerging in summer and becoming adults in spring. In the wild, females start oviposition in April and can lay their first ootheca within a week after mating. The species is distributed from the Canary Islands to Pakistan in the dry belt. Thus, its distribution is associated with xeric areas or desert and semi-desert habitats. Phylogeographic analyses revealed three major genetic lineages, (i) in the Maghreb, (ii) from Egypt via Arabia to Iran (with internal substructures), and (iii) likely in Pakistan; the estimated onset of differentiation into these lineages is of Pleistocene age. Defense behavior involves flying away or extending wings broadly and lifting forelegs. Performing laboratory breeding, we documented life cycle and color changes from first instar to adulthood. Due to overwintering, the last larval instar needs considerably longer than the others. At 25 °C (±2), average adult life span was 118 days (±6 SD) for females (range: 100-124) and 46 days (±5 SD) for males (range: 39-55), with a significant difference among sexes. On average, oothecae contained 32.3 eggs (±10.1 SD) and the mean incubation period was 36.8 days (±2.9 SD). We did not find evidence of parthenogenesis. In general, the biology of B. mendica shows a variety of adaptations to its often extreme and little predictable type of habitat.

Evolutionary transitions from camouflage to aposematism: Hidden signals play a pivotal role

The initial evolution of warning signals in unprofitable prey, termed aposematism, is often seen as a paradox because any new conspicuous mutant would be easier to detect than its cryptic conspecifics and not readily recognized by naïve predators as defended. One possibility is that permanent aposematism first evolved through species using hidden warning signals, which are only exposed to would-be predators on encounter. Here, we present a large-scale analysis of evolutionary transitions in amphibian antipredation coloration and demonstrate that the evolutionary transition from camouflage to aposematism is rarely direct but tends to involve an intermediary stage, namely cryptic species that facultatively reveal conspicuous coloration. Accounting for this intermediate step can resolve the paradox and thereby advance our understanding of the evolution of aposematism.

The protective value of the colour and shape of the mountain katydid's antipredator defence

Deimatic behaviour is performed by prey when attacked by predators as part of an antipredator strategy. The behaviour is part of a sequence that consists of several defences, for example they can be preceded by camouflage and followed by a hidden putatively aposematic signal that is only revealed when the deimatic behaviour is performed. When displaying their hidden signal, mountain katydids (Acripeza reticulata) hold their wings vertically, exposing striking red and black stripes with blue spots and oozing an alkaloid-rich chemical defence derived from its Senecio diet. Understanding differences and interactions between deimatism and aposematism has proven problematic, so in this study we isolated the putative aposematic signal of the mountain katydid's antipredator strategy to measure its survival value in the absence of their deimatic behaviour. We manipulated two aspects of the mountain katydid's signal, colour pattern and whole body shape during display. We deployed five kinds of clay models, one negative control and four katydid-like treatments, in 15 grids across part of the mountain katydid's distribution to test the hypothesis that their hidden signal is aposematic. If this hypothesis holds true, we expected that the models, which most closely resembled real katydids would be attacked the least. Instead, we found that models that most closely resembled real katydids were the most likely to be attacked. We suggest several ideas to explain these results, including that the deimatic phase of the katydid's display, the change from a camouflaged state to exposing its hidden signal, may have important protective value.

Increasing intensity of deimatic behaviour in response to repeated simulated attacks: a case study on the mountain katydid (Acripeza reticulata)

Abstract

How and when deimatic behaviours are performed can change during encounters between predators and prey. Some predators attack repeatedly, investigating and manipulating prey, and in response, an individual’s deimatic behaviour may intensify or may diminish in favour of escaping. The presence of a resource can further force a trade-off between displaying and escaping. Here, we examined the intensity of the katydid’s deimatic behaviour, a visual display, the propensity of their escape response under repeated simulated attacks, and how these responses change in the presence of foraging resources. We found that display intensity increased with repeated simulated attacks and that females displayed at a greater intensity than males. The presence of their preferred food plant had no significant effect on display intensity, but reduced escape probability in both sexes. Some katydids were predictable in their display intensity and at the population level we found that strong display intensity is moderately repeatable. Overall, our results suggest that 1) display intensity increases with repeated attacks and might indicate a cost in performing at maximum intensity upon first attack, 2) deploying a deimatic display while feeding can reduce the need to flee a rich foraging patch and 3) some individuals are consistent in their display intensities. Future experiments that aim to determine causal mechanisms such as limitations to perception of predators, sensitisation to stimuli and physiological constraints to display intensity will provide necessary insight into how deimatic displays function.

Significance statement

Though often regarded as success or failure, interactions between predators and prey during the attack phase of a predation event are complex, especially when predators make repeated investigative attacks in quick succession. Our study shows that in mountain katydids, intensity of deimatic behaviour increases with repeated attacks, perhaps indicating that prey sensitise or that maximal displays during initial attacks carry high costs such as conspicuousness. The intensity of the display does not change with the introduction of a valuable food resource, but the probability of fleeing decreased, suggesting that displaying may reduce the opportunity costs of leaving a patch. We also show that individuals vary in the repeatability of their display, suggesting that deimatic display may be highly adaptable, nuanced and targeted.

Context dependent effects on attack and defense behaviors in the praying mantis Tenodera sinensis

Most behavior needs to strike a balance between the competing needs to find food and protect an animal from predators. The factors that influence this balance and the resulting behavior are not well understood in many animals. Here we examined these influences in the praying mantis Tenodera sinensis (Saussure) by presenting perching individuals with alternating sinusoidally moving prey-like stimuli and rapidly expanding looming stimuli then scoring their behavior on a defensive - aggressive scale. In this way, we tested the hypothesis that such behaviors are highly context dependent. Specifically, we found that defensive responses, which are normally very consistent, are decreased in magnitude if the animal has just performed an aggressive response to the previous sinusoid. A thrash behavior not normally seen with looming alone was often seen following aggression. In thrashing the animal tries to push the looming stimulus away. It almost exclusively followed aggressive responses to the sinusoid stimulus. Moreover, aggression levels were found to shift from low to high and back to low as adult animals aged and, in general, female mantises were more aggressive than males. Finally, the specific nature of the mid-life spike in aggressive behaviors differed according to whether the animals were lab-raised or caught in the wild. Lab raised animals showed roughly equal amounts of increased attention to the stimulus and very aggressive strike behaviors whereas wild caught animals tended to either ignore the stimulus or react very aggressively with strikes. Therefore, our hypothesis regarding context dependent effects was supported with all 4 factors influencing the behaviors that were studied.

A tree of leaves: Phylogeny and historical biogeography of the leaf insects (Phasmatodea: Phylliidae)

The insect order Phasmatodea is known for large slender insects masquerading as twigs or bark. In contrast to these so-called stick insects, the subordinated clade of leaf insects (Phylliidae) are dorso-ventrally flattened and therefore resemble leaves in a unique way. Here we show that the origin of extant leaf insects lies in the Australasian/Pacific region with subsequent dispersal westwards to mainland Asia and colonisation of most Southeast Asian landmasses. We further hypothesise that the clade originated in the Early Eocene after the emergence of angiosperm-dominated rainforests. The genus Phyllium to which most of the ~100 described species pertain is recovered as paraphyletic and its three non-nominate subgenera are recovered as distinct, monophyletic groups and are consequently elevated to genus rank. This first phylogeny covering all major phylliid groups provides the basis for future studies on their taxonomy and a framework to unveil more of their cryptic and underestimated diversity.

Survival Sounds in Insects: Diversity, Function, and Evolution

Insect defense sounds have been reported for centuries. Yet, aside from the well-studied anti-bat sounds of tiger moths, little is understood about the occurrence, function, and evolution of these sounds. We define a defense sound as an acoustic signal (air- or solid-borne vibration) produced in response to attack or threat of attack by a predator or parasitoid and that promotes survival. Defense sounds have been described in 12 insect orders, across different developmental stages, and between sexes. The mechanisms of defensive sound production include stridulation, percussion, tymbalation, tremulation, and forced air. Signal characteristics vary between species, and we discuss how morphology, the intended receiver, and specific functions of the sounds could explain this variation. Sounds can be directed at predators or non-predators, and proposed functions include startle, aposematism, jamming, and alarm, although experimental evidence for these hypotheses remains scant for many insects. The evolutionary origins of defense sounds in insects have not been rigorously investigated using phylogenetic methodology, but in most cases it is hypothesized that they evolved from incidental sounds associated with non-signaling behaviors such as flight or ventilatory movements. Compared to our understanding of visual defenses in insects, sonic defenses are poorly understood. We recommend that future investigations focus on testing hypotheses explaining the functions and evolution of these survival sounds using predator-prey experiments and comparative phylogenetics.

Towards an ecology of protective coloration

The strategies underlying different forms of protective coloration are well understood but little attention has been paid to the ecological, life-history and behavioural circumstances under which they evolve. While some comparative studies have investigated the ecological correlates of aposematism, and background matching, the latter particularly in mammals, few have examined the ecological correlates of other types of protective coloration. Here, we first outline which types of defensive coloration strategies may be exhibited by the same individual; concluding that many protective coloration mechanisms can be employed simultaneously, particularly in conjunction with background matching. Second, we review the ecological predictions that have been made for each sort of protective coloration mechanism before systematically surveying phylogenetically controlled comparative studies linking ecological and social variables to antipredator defences that involve coloration. We find that some a priori predictions based on small-scale empirical studies and logical arguments are indeed supported by comparative data, especially in relation to how illumination affects both background matching and self-shadow concealment through countershading; how body size is associated with countershading, motion dazzle, flash coloration and aposematism, although only in selected taxa; how immobility may promote background matching in ambush predators; and how mobility may facilitate motion dazzle. Examination of nearly 120 comparative tests reveals that many focus on ecological variables that have little to do with predictions derived from antipredator defence theory, and that broad-scale ecological studies of defence strategies that incorporate phylogenetics are still very much in their infancy. We close by making recommendations for future evolutionary ecological research.