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.

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 Miomantis binotata 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.

Structural features and life habits of †Alienoptera (Polyneoptera, Dictyoptera, Insecta)

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.

A Predator's Perspective of the Accuracy of Ant Mimicry in Spiders

Among spiders, resemblance of ants (myrmecomorphy) usually involves the Batesian mimicry, in which the spider coopts the morphological and behavioural characteristics of ants to deceive ant-averse predators. Nevertheless, the degree of resemblance between mimics and ants varies considerably. I usedPortia fimbriata,a jumping spider (Salticidae) with exceptional eyesight that specialises on preying on salticids, to test predator perception of the accuracy of ant mimicry.Portia fimbriata’s response to ants (Oecophylla smaragdina), accurate ant-like salticids (Synageles occidentalis), and inaccurate ant-like salticids (females ofMyrmarachne bakeriand sexually dimorphic males ofM. bakeri, which have enlarged chelicerae) was assessed.Portia fimbriataexhibited graded aversion in accordance with the accuracy of resemblance to ants (O. smaragdina>S. occidentalis> femaleM. bakeri> maleM. bakeri). These results support the hypothesis that ant resemblance confers protection from visual predators, but to varying degrees depending on signal accuracy.

Salticid predation as one potential driving force of ant mimicry in jumping spiders

Many spiders possess myrmecomorphy, and species of the jumping spider genus Myrmarachne exhibit nearly perfect ant mimicry. Most salticids are diurnal predators with unusually high visual acuity that prey on various arthropods, including conspecifics. In this study, we tested whether predation pressure from large jumping spiders is one possible driving force of perfect ant mimicry in jumping spiders. The results showed that small non-ant-mimicking jumping spiders were readily treated as prey by large ones (no matter whether heterospecific or conspecific) and suffered high attack and mortality rates. The size difference between small and large jumping spiders significantly affected the outcomes of predatory interactions between them: the smaller the juvenile jumping spiders, the higher the predation risk from large ones. The attack and mortality rates of ant-mimicking jumping spiders were significantly lower than those of non-ant-mimicking jumping spiders, indicating that a resemblance to ants could provide protection against salticid predation. However, results of multivariate behavioural analyses showed that the responses of large jumping spiders to ants and ant-mimicking salticids differed significantly. Results of this study indicate that predation pressure from large jumping spiders might be one selection force driving the evolution of nearly perfect myrmecomorphy in spiders and other arthropods.