Ant-like Research Articles

Small Brains: Body Shape Constrains Tissue Allocation to the Central Nervous System in Ant‐Mimicking Spiders

ABSTRACTIn Batesian mimicry, mimetic traits are not always as convincing as predicted by theory—in fact, inaccurate mimicry with only a superficial model resemblance is common and taxonomically widespread. The “selection trade‐offs hypothesis” proposes a life‐history trade‐off between accurate mimetic traits and one or more vital biological functions. Here, using an accurate myrmecomorphic (ant‐mimicking) jumping spider species, Myrmarachne smaragdina, we investigate how myrmecomorphic modifications to the body shape impact the internal anatomy in a way that could be functionally limiting. Specifically, via x‐ray micro‐computed tomography (microCT), we quantify how the spider's constricted prosoma, which emulates the head and thorax of ants, impacts the size of the central nervous system (CNS) and the venom glands. Although, relative to their whole‐body mass, we found no significant difference in venom gland volume, the CNS of the ant‐mimicking jumping spider was significantly smaller when compared with a relatively closely related non‐mimic jumping spider, indicating that some trade‐off between mimic accuracy and size of neural anatomy, as articulated by the “selection trade‐offs hypothesis,” is a possibility. Our explorative evidence enables and encourages broader investigation of how variable mimic accuracy impacts the neuroanatomy in ant mimics as a direct test of the “selection trade‐offs hypothesis.”

Myrmecium colombianum (Poinar, 2024) n. comb.-the second known fossilized castianeirine spider, illustration of a further specimen of Myrmecium in Colombian copal and notes on transformational ant mimicry and evolution of the genus.

Myrmecium colombianum (Poinar, 2024) n. comb.-the second known fossilized castianeirine spider, illustration of a further specimen of Myrmecium in Colombian copal and notes on transformational ant mimicry and evolution of the genus.

And the Oscar goes to… – Species‐specific ant behaviour related to predator defence in ant‐mimicking spiders

AbstractMimicry, the superficial resemblance between organisms of two or more species, is considered a textbook example for natural selection, for which it is assumed that predators are important selective agents. Ant mimicking spiders have received considerable attention in studies on mimicry because they include examples with remarkable, species‐specific morphological adaptations. Ant‐like behaviours such as erratic locomotory patterns, abdomen bobbing and vertical movements of the first or second pair of legs to imitate antennal movements, are assumed to have evolved before morphological mimicry and may be considered adaptations to general ant resemblance. Species‐specific behavioural ant mimicry (behaviour that is only observed in specific ants and imitated by their mimics) was very rarely documented and ant resembling behaviour that repels predator attacks has not been confirmed yet. In this study we report and discuss such species‐specific behaviour, a spray display (SD), in the castianeirine spiders Myrmecotypus iguazu (a morphologically accurate mimic of the carpenter ant Camponotus sericeiventris), and M. tahyinandu (a morphologically accurate mimic of C. crassus). The SD consisted of the raising of the cephalothorax and moving of the abdomen ventrally under the cephalothorax, pointing the apex forward, and holding the antennae (ant) or first pair of legs (spiders) at an angle of about 45°–120°. The morphological adaptations that are required to perform the SD and the lack of an alternative explanation for the purpose of this display suggest that the SD has evolved to enhance both general behavioural and morphologically accurate ant resemblance. The two observed Myrmecotypus species may be considered the behaviorally most accurate ant‐resembling spiders known to date, as the SD may provide protection against spider‐ and ant‐eating predators at a point in predator interactions where other myrmecomorph spiders may abandon their ant‐resembling behaviour.

Myrmarachne colombiana sp. n. (Araneae: Salticidae), a new species of ant-mimic spider in copal from Colombia, South America

ABSTRACT Ant-mimicking spiders (Araneae: Salticide) are fascinating creatures that have evolved modified morphology and behaviours to resemble those of ants (Hymenoptera: Formicidae). Ant-mimicking spiders are cosmopolitan but currently, there are no records of such spiders in fossilised resin, nor any records of extant ant- mimicking spiders in Colombia, S.A. The present study describes Myrmarachne colombiana sp. n. (Araneae: Salticidae) as the first species of ant-mimicking spider in fossilised resin (copal) from Colombia, discusses possible ages of copal inclusions around the world, and examines various scenarios showing why spiders have become ant mimics. The LSID for the paper is:urn:lsid:zoobank.org:pub:DA4E7993-C1B7-46DF-9863-47BD1DAA6686 And for the new species:urn:lsid:zoobank.org:act:849971BF-D641-41C7-AB67-7B01B6CBEE77

Morphological ant mimics: constrained to imperfection?

Adaptive evolution relies on both heritable variation and selection. Variation is the raw material upon which selection acts, so any mechanism that limits or prevents the generation of heritable variation reduces the power of selection to lead to adaptation. Such limitations are termed evolutionary constraints. While it is widely accepted that constraints play an important role in shaping evolutionary outcomes, their relative importance, as opposed to adaptation, in determining evolutionary outcomes remains a subject of debate. Evolutionary constraints are often evoked as the reason behind the persistence of inaccurate mimicry. Here, we compared the variation and accuracy of body-shape mimicry in ant-mimicking spiders with that of ant-mimicking insects, predicting greater constraints, and hence inaccuracy, in spiders mimicking ants, due to their evolutionary distance from the ant model. We found high inter-species variation in mimetic accuracy, but dorsally, no overall difference in mimetic accuracy between spider and insect mimics, which is inconsistent with a constraint causing inaccurate mimicry. Our study provides empirical evidence suggesting that imperfect mimicry in spiders and insects is predominantly shaped by adaptive processes rather than constraints or chance. Our findings contribute to our understanding of the mechanisms underlying evolutionary diversity and the processes that shape phenotypic outcomes.

Castianeira swiftay sp. nov., a new species of ant-mimicking spider from Costa Rica, and further new records of castianeirines from Central America.

Castianeira swiftay sp. nov., a new species of ant-mimicking spider from Costa Rica, and further new records of castianeirines from Central America.

Imperfect ant mimicry contributes to local adaptation in a jumping spider

Putative ant mimicry is a remarkable example of an evolutionary strategy that can be well integrated into the framework of natural selection and adaptation. However, challenges remain in understanding imperfect ant mimicry. Here, we combine trait quantification and behavioral assays to investigate imperfect ant mimicry in the jumping spider Siler collingwoodi. We performed trajectory analysis and gait analysis to show that the locomotor characters of S.collingwoodi generally resemble those of the putative ant models, supporting the multiple models hypothesis. We then performed background-matching analysis, revealing that body coloration may be involved in background camouflage. We further carried out antipredation assays and found that S.collingwoodi had a significantly lower risk of predation than nonmimetic salticids, suggesting an overall protective effect of Batesian mimicry. Our findings quantitatively demonstrate a combination of mimicry and camouflage in S.collingwoodi and thus highlight the significance of a complex phenomenon driven by natural selection.

An arachnid’s guide to being an ant: morphological and behavioral mimicry in ant-mimicking spiders

Abstract Batesian mimicry imposes several challenges to mimics and evokes adaptations in multiple sensory modalities. Myrmecomorphy, morphological and behavioral resemblance to ants, is seen in over 2000 arthropod species. Ant-like resemblance is observed in at least 13 spider families despite spiders having a distinct body plan compared to ants. Quantifying the extent to which spiders’ shape, size, and behavior resemble model ants will allow us to comprehend the evolutionary pressures that have facilitated myrmecomorphy. Myrmaplata plataleoides are thought to closely resemble weaver ants, Oecophylla smaragdina. In this study, we quantify the speed of movement of model, mimic, and non-mimetic jumping spiders. We use traditional and geometric morphometrics to quantify traits such as foreleg size and hindleg size, body shape between the model ant, mimic, and non-mimics. Our results suggest that while the mimics closely resemble the model ants in speed of movement, they occupy an intermediate morphological space compared to the model ants and non-mimics. Ant-mimicking spiders are better at mimicking ants’ locomotory movement than morphology and overall body shape. Some traits may compensate others, suggesting differential selection on these mimetic traits. Our study provides a framework to understand the multimodal nature of mimicry and helps discern the relative contributions of such traits that drive mimetic accuracy in ant-mimicking spiders.

On the behavioural biology of a morpho-variant of Myrmaplata plataleoides (O. Pickard-Cambridge, 1869) (Araneae: Salticidae) with taxonomic notes

Abstract We hereby report an isolated population of a rare morpho-variant of the ant-mimicking jumping spider Myrmaplata plataleoides (O. Pickard-Cambridge, 1869) from Hazaribagh Wildlife Sanctuary, Hazaribagh, Jharkhand, India, which is also the first record of this species from the state of Jharkhand, India. Descriptions of both male and female spiders, the female’s exuviae, its eggs and habitat are presented. We have studied its moulting, feeding and sexual behaviour in detail, and have recorded various behavioural aspects that were never documented before, such as debris-rolling behaviour, photokinetic response, starvation response and oxygen deprivation response. We here report the occurrence of this spider near the colonies of the ground-nesting ant Camponotus compressus (Fabricius, 1787). This spider is known to mimic the Asian weaver ant Oecophylla smaragdina (Fabricius, 1775), which are greenish orange to red in colour. Specimens collected by us are dark brown to black in coloration whereas the commonly reported specimens are often greenish orange to red. We propose that the darker coloration would have been naturally selected in this isolated population of M. plataleoides as an adaptation to coexist with C. compressus, which is also black in coloration and abundant around the spiders. Study of the moulting behaviour of the morpho-variant further reveals the display of a novel mechanism of ant mimicry among these spiders which we have named as temporal myrmecomorphy. Temporal myrmecomorphy has been proposed to be a protective mechanism used by a harmless mimic against the attacks of the aggressive models so that it can co-exist with the models. Present study establishes the usefulness of a morpho-variant as an important model in understanding the evolution and behaviour of a species holistically.

A new genus of jumping spider from the Bolivian Yungas forest, a new country record for Erica eugenia Peckham & Peckham, 1892, and notes on turtle ant mimicry (Araneae: Salticidae: Simonellini)

A new genus and species of the ant-resembling jumping spider tribe Simonellini, Flurica sikimira gen. et sp. nov., from the Yungas mountain forest in the Bolivian Andes is described. Erica eugenia Peckham & Peckham, 1892 is recorded from Bolivia for the first time. Adults of both species are possibly mimics of the turtle ant Cephalotes pusillus (Klug, 1824). Juveniles of E. eugenia resemble workers of black Crematogaster ants, indicating transformational mimicry.

Measuring mimicry: methods for quantifying visual similarity

The existence of substantial variation in the accuracy of resemblance of mimics to their models remains a fundamental evolutionary question, and the ability to quantify mimetic accuracy is key to addressing this question. Mimicry researchers have used a wide variety of methods to measure accuracy, which can be broadly grouped into (1) receiver responses, such as predator trials, and (2) trait measurements. While receiver responses are fundamental to mimicry research, logistical and ethical concerns mean that only a minority of studies include tests with relevant predator receivers. Trait measurement methods are therefore vital, both to supplement receiver response methods and as standalone methods for quantifying accuracy. Here, we collect and describe five methods for measuring the accuracy of visual mimicry. Three of the methods quantify the similarity of mimetic phenotypic traits: linear morphometrics, geometric morphometrics and biometric trait table. Two methods measure the responses of proxy receivers: machine learning and human assessment. These methods are applicable to any type of visual mimetic traits. We evaluate and compare the effectiveness and cost of these methods by assessing the accuracy of a variety of visual ant mimics to their ant models. The methods vary in the types and number of traits being measured, whether traits are measured directly (trait measurement methods) or indirectly (receiver responses) and in the effort and skills required for implementation. Despite the methods measuring different visual characteristics, the accuracy scores from all five methods were positively correlated when applied to ant mimics, suggesting some generality in how mimics rank in their accuracy. We provide practical advice on the use of these five methods and provide open-source implementations of the scripts used in our analysis. The scripts may be freely reused or used as the basis for new implementations. Our aim is to aid researchers to select and implement methods that are appropriate and suitable for future mimicry research.

Mimicry in motion and morphology: do information limitation, trade-offs or compensation relax selection for mimetic accuracy?

Many animals mimic dangerous or undesirable prey as a defence from predators. We would expect predators to reliably avoid animals that closely resemble dangerous prey, yet imperfect mimics are common across a wide taxonomic range. There have been many hypotheses suggested to explain imperfect mimicry, but comparative tests across multiple mimicry systems are needed to determine which are applicable, and which—if any—represent general principles governing imperfect mimicry. We tested four hypotheses on Australian ant mimics and found support for only one of them: the information limitation hypothesis. A predator with incomplete information will be unable to discriminate some poor mimics from their models. We further present a simple model to show that predators are likely to operate with incomplete information because they forage and make decisions while they are learning, so might never learn to properly discriminate poor mimics from their models. We found no evidence that one accurate mimetic trait can compensate for, or constrain, another, or that rapid movement reduces selection pressure for good mimicry. We argue that information limitation may be a general principle behind imperfect mimicry of complex traits, while interactions between components of mimicry are unlikely to provide a general explanation for imperfect mimicry.

Increased speed of movement reduced identification of Batesian ant-mimicking spiders by surrogate predators.

In Batesian mimicry, the mimic gains protection from predators by imitating a noxious model. Some myrmecomorphic species use ants as models as ants have strong defensive capabilities. Ants are highly mobile models, and besides colour, shape, and size, mimics also imitate their movement. Yet, former studies focused mainly on static traits. Here, I tested the hypothesis that artificially increased speed of movement reduces the probability of the mimic being identified. First, images of 14 myrmecomorphic spider species and their models were used for humans to rank their mimetic accuracy. Humans were used as surrogate predators to obtain scores for each mimetic pair. In the second experiment, the effect of movement playback speed on the probability of identification was investigated, again using humans. Videos of mimics were played at different speeds, and the identification probability was recorded. While ants were correctly identified at any playback speed, the identification of myrmecomorphic spiders declined with increasing playback speed. In other words, the latency to correct identification increased with playback speed. Overall, mimics with higher accuracy scores were more difficult to identify while moving. The natural speed of movement of accurate mimics was similar to that of inaccurate ones. Movement is thus an important trait for myrmecomorphic species.

Constraints on the jumping and prey-capture abilities of ant-mimicking spiders (Salticidae, Salticinae, Myrmarachne)

Accurate morphological ant mimicry by Myrmarachne jumping spiders confers strong protective benefits against predators. However, it has been hypothesized that the slender and constricted ant-like appearance imposes costs on the hunting ability because their jumping power to capture prey is obtained from hydraulic pressure in their bodies. This hypothesis remains to be sufficiently investigated. We compared the jumping and prey-capture abilities of seven Myrmarachne species and non-myrmecomorphic salticids collected from tropical forests in Malaysian Borneo and northeastern Thailand. We found that the mimics had significantly reduced abilities compared with the non-mimics. The analysis using geometric morphometric techniques revealed that the reduced abilities were strongly associated with the morphological traits for ant mimicry and relatively lower abilities were found in Myrmarachne species with a more narrowed form. These results support the hypothesis that the jumping ability to capture prey is constrained by the morphological mimicry and provide a new insight into understanding the evolutionary costs of accurate mimicry.

Non-mimetic jumping spider responses towards three species of ants and their mimics

Ants and jumping spiders are prominent invertebrate predators in terrestrial ecosystems. Many jumping spiders are thought to avoid ants and their ant mimicking spiders, yet little is known if they discriminate among different species of ants or mimics. Chances of encountering multiple ants, and mimics all in a relatively short stretch of time and space is fairly common in the tropics, but how all these species interact with each other is not known. In a laboratory setup, we first examined the behavioral response of three ant species (Oecophylla smaragdina, the weaver ants; Camponotus sericeus, the golden backed carpenter ants, and Leptogenys processionalis, the procession ants), and their mimics in the genus Myrmarachne towards the non-mimetic jumping spider Plexippus paykulli. We then examined the response of P paykulli towards the three ant species, and their mimics. Our results suggest that weaver ants and procession ants are more aggressive towards non-mimetic jumping spiders as compared to golden backed ants. The three mimics also differed in their response towards the non-mimetic jumping spider: both weaver ant mimics and golden backed ant mimics charged at the non-mimetic jumping spiders as compared to the procession ant mimics. On the other hand, P. paykulli did not treat all ants similarly: while they looked, and approached the black procession ants by visual cues, they stayed away from weaver ants and golden backed ants. However, P. paykulli treated the three ant mimicking spiders similarly: while they looked at the mimics, they rarely approached or attacked them. Jumping spiders and ants are sympatric, and it may be advantageous to selectively avoid some ants over others. Studies, such as ours go a step closer in understanding multispecies predator–prey interactions.

Contributions to the knowledge of Neotropical ant-like spiders: Myrmecotypus tahyinandu sp. n. from Bolivian Chiquitano forest, a new country record for M. niger, and indirect evidence for species-specific mimicry (Araneae: Corinnidae: Castianeirinae).

Myrmecotypus tahyinandu sp. n. is described from the Bolivian Chiquitano forest, and M. niger Chickering, 1937 is recorded from Bolivia for the first time. The morphological differentiation among the closely related M. tahyinandu sp. n. and M. iguazu Rubio Arbino, 2009 is likely attributable to the selection for specific ant mimicry. Adults of M. tahyinandu sp. n. are accurate mimics of the ant Camponotus crassus Mayr, 1862, M. iguazu of C. sericeiventris (Guérin-Méneville, 1838), and M. niger of Dolichoderus bispinosus (Olivier, 1792). This study is the first to identify ant models for morphologically closely related Castianeirinae, providing a promising starting point for future research on ant mimicry.

The early stages of <em>Miomantis binotata</em> and their bearing on the question whether ant mimicry is a larval feature of first stage praying mantises (Mantodea: Mantidae)

Ant mimicry, i.e., the mimicking of ant workers by another organism, is a widespread phenomenon among different groups of Euarthropoda, including spiders and different insect species. One example of ant mimicry occurs among praying mantises (Mantodea); here the first stage nymphs have been recorded to perform ant mimicry. In this study, we investigated different nymphal instars of Miomantis binotata for possible morphological similarities to ants. The different instars were compared as stages supposed to perform ant mimicry would differ morphologically from those stages not supposed to resemble ants. The specimens were investigated under different microscopic settings and measurements were performed. Our results do not show significant differences concerning morphological measurements or shape of structures between the different nymphal instars of M. binotata. One prominent difference between stage one nymphs and later stages occurs in the colouration of the body, which is very dark in the earliest nymph. This difference might explain why young nymphs of Miomantis binotata are interpreted as ant-mimicking, despite the apparent lack of other morphological resemblances.

Cryptic diversity in ant‐mimic Micaria spiders (Araneae, Gnaphosidae) and a tribute to early naturalists

AbstractSpiders of the genus Micaria are ground‐living mimics of ants. Species delineation in these spiders is challenging, mainly because of exceptional high levels of intraspecific variation masking species boundaries. As implied by preliminary DNA barcode data from Central Europe, the Holarctic and very widely distributed glossy ant‐spider M. pulicaria shows cryptic diversity. Here, we disentangle the hidden diversity by means of an integrative taxonomy approach, using mitochondrial DNA, morphometrics, traditional genitalic characters and ecology. Our data suggest the clear delineation of two distinct species, which supports the conception of 19th century taxonomists. These early naturalists distinguished M. pulicaria and a second closely related species based on morphology and natural history, which were synonymized in subsequent taxonomic studies. Therefore, we re‐circumscribe M. pulicaria and revalidate the long forgotten M. micans. These two Micaria species co‐occur sympatrically in vast areas of the western Palearctic, while the Nearctic region is populated by M. pulicaria alone. Male genitalic traits are more dissimilar in the area of sympatry than in allopatry, suggesting a decisive role of reproductive character displacement in species diversification. Our study emphasizes the value of the early taxonomic literature in integrative taxonomic studies, as it may contain crucial information on natural history that are not regularly recorded by modern taxonomists.

<p><strong>Structural features and life habits of †Alienoptera (Polyneoptera, Dictyoptera, Insecta)</strong></p>

Structural features and life habits of described species of the extinct †Alienoptera are evaluated based on previously published studies on the group. Head structures and feedings habits are addressed, as are the locomotor organs, especially the wings and adhesive devices. Suggested pollen feeding habits and the possible role as pollinators are discussed, as well as hypothesized ant and wasp mimicry and myrmecophily. Species of †Alienoptera were likely predators, in the case of †Caputoraptor elegans Bai, Beutel et Wipfler, 2018 with a unique cephalo-prothoracic prey grasping mechanism. They were likely strong fliers with anatomical dipterism with functional hind wings. Wing joints protected by scale-like sclerotized fore wings probably allowed them to move very efficiently in dense foliage of trees or shrubs and to prey upon smaller insects. Ant mimicry, myrmecophily and “weevil mimicry” are rejected. †Meilia Vršanský et Wang, 2018 is a possible case of wasp mimicry but more evidence is required. Other suggested cases of mimicking wasps are unfounded.

Ant-mimicking spiders: Reflection of ant-diversity in ant-mimics in tropical forests

Ant-mimicking spiders: Reflection of ant-diversity in ant-mimics in tropical forests