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.

Mirror image stimulation could reverse social-isolation-induced aggressiveness in the high-level subsocial lactating spider.

Conspecific aggressiveness often increases after social isolation for species that are not entirely solitary, and this increased aggression could also be reversed after resocialization. However, literature on this aggression plasticity refers to either permanently social or low-level subsocial species in invertebrates. Examinations of conspecific aggressiveness reversibility in high-level subsocial invertebrates, in which offspring cohabitate with parents for a certain period of time after sexual maturation, would enhance the understanding of the role of conspecific-aggression plasticity in social evolution. Here, using the lactating spider Toxeus magnus, which exhibits extremely high-level subsociality, we assessed three questions. (1) Is its conspecific aggression affected by social living and/or kinship? The results indicated that conspecific aggression increased after social isolation, while kinship did not affect aggressiveness. (2) Could the social-isolation-induced higher aggression be reversed after resocialization? The results showed that the increased aggression of the spiders could be reversed 3 days after resocialization. (3) What is the proximate mechanism that caused the aggression reversibility by resocialization? A simulated resocialization experiment in which single spider was provided with mirrors demonstrated that the visual cues of conspecifics alone could reverse the aggression after 6 days. These results indicate that the high-level subsocial invertebrate showed aggressiveness reversibility without chemical cues. This is more similar to permanently social species rather than to low-level subsocial species, and visual cues could be vital to induce aggression change. These results suggest that conspecific-aggression reversibility might play a key role in social evolution and may functionally enhance species' adaptiveness under variable conditions.

Meotipa species (Araneae, Theridiidae) from China.

In an ongoing effort to expand knowledge of the Chinese cobweb spider fauna (Theridiidae), the genus Meotipa Simon, 1894 is reviewed. Two new species are described, Meotipapseudopicturata sp. nov., Meotipastriata sp. nov., and five known species are redescribed: Meotipaargyrodiformis (Yaginuma, 1952), Meotipapulcherrima (Mello-Leitão, 1917), Meotipapicturata Simon, 1895, Meotipaspiniventris (O. Pickard-Cambridge, 1869), and Meotipavesiculosa Simon, 1895.

Two new Eresus species (Araneae, Eresidae) from Xinjiang, China.

Background: Eresidae C. L. Koch, 1845 contains nine genera and 102 species, of which 24 species belong to Eresus Walckenaer, 1805. Four species of the family are known from China: E.granosus Simon, 1895 (Beijing), E.kollari Rossi, 1846 (Hebei), E.lishizheni Lin, Marusik & Li, 2021 (Xinjiang) and Stegodyphustibialis (O. Pickard-Cambridge, 1869) (Yunnan). New information: Two new species of Eresus are described from Xinjiang, China: Eresusda Lin & Li sp. n. and E.yukuni Lin & Li sp. n. Photos and morphological descriptions of new species are given.

Two sexes respond equally to food restriction in a sexually dimorphic but not body mass dimorphic jumping spider.

Natural selection favors animals that evolve developmental and behavioral responses that buffer the negative effects of food restrictions. These buffering responses vary both between species and within species. Many studies have shown sex-specific responses to environmental changes, usually in species with sexual size dimorphism (SSD), less found in species with weak or no SSD, which suggests that sizes of different sexes are experiencing different selections. However, previous studies usually investigated development and behavior separately, and the balanced situation where males and females of sexually dimorphic species respond in the same way to food restriction remains little known. Here, we investigated this in Phintelloides versicolor (Salticidae) that presents sexual dimorphism in color and shape but weak SSD. We examined whether food restriction induced the same responses in males and females in development duration, adult body size and weight, daily time allocated to foraging, and hunting. We found food restriction induced similar responses in both sexes: both exhibited longer development duration, smaller adult body size and weight, higher probability of staying outside nests and noticing prey immediately, and higher hunting success. However, there were sexual differences regardless of food condition: females showed faster development, smaller adult body size, higher probability of staying outside of nests, and higher hunting success. These indicated the differential selection on male and female sizes of P. versicolor could be under a balanced situation, where males and females show equal developmental and behavioral plasticity to environmental constraints.

Prolonged milk provisioning and extended maternal care in the milking spider Toxeus magnus: biological implications and questions unresolved.

Prolonged milk provisioning and extended parental care for nutritionally independent offspring, previously considered to only co-occur in long-lived mammals (Clutton-Brock, 1991; Royle et al., 2012), were recently reported in the reproduction of the milking spider, Toxeus magnus (Chen et al. 2018). Newly hatched T. magnus spiderlings require 53 days to develop to maturity, with an average adult body length of 6.6 mm. The mother provides milk droplets to her newly hatched spiderlings until they develop into subadults (~38 days old), during which their body lengths increase from 0.9 mm at birth to 5.3 mm at weaning. Although spiderlings can forage for themselves at around 20 days old, they remain in the breeding nest for weeks after maturity.

Prolonged milk provisioning in a jumping spider.

Lactation is a mammalian attribute, and the few known nonmammal examples have distinctly different modalities. We document here milk provisioning in a jumping spider, which compares functionally and behaviorally to lactation in mammals. The spiderlings ingest nutritious milk droplets secreted from the mother's epigastric furrow until the subadult stage. Milk is indispensable for offspring survival in the early stages and complements their foraging in later stages. Maternal care, as for some long-lived vertebrates, continues after the offspring reach maturity. Furthermore, a female-biased adult sex ratio is acquired only when the mother is present. These findings demonstrate that mammal-like milk provisioning and parental care for sexually mature offspring have also evolved in invertebrates, encouraging a reevaluation of their occurrence across the animal kingdom, especially in invertebrates.

The spectral transmission of non-salticid spider corneas.

Although many salticid spiders have been shown to have corneas that transmit ultraviolet (UV) light, whether the corneas of non-salticid spiders transmit UV has not been previously investigated. In this study, we determined the spectral corneal transmission properties of 38 species belonging to 13 non-salticid families. We used these data to estimate the T50 transmission cut-off value, the wavelength corresponding to 50% maximal transmission for each species. The corneas of almost all species from the families Deinopidae, Lycosidae, Oxyopidae, Pisauridae, Sparassidae and Thomisidae, all of which have been reported to rely to a substantial extent on vision, transmitted short wavelength light below 400 nm, ranging from 306 to 381 nm. However, species from the families Atypidae and Ctenizidae are not known to rely substantially on vision, and the corneas of these species tended to absorb light of wavelengths below 380 nm, which may not allow UV sensitivity in these spiders. Liphistiidae, the family widely regarded as most basal among spiders, is of particular interest. The species in this family are not known to make substantial use of vision, and yet we found that liphistiid corneas transmitted UV light with a low T50 value (359 nm). T50 values of non-salticid spider corneas also varied with light habitat. Species living in dim environments tended to have UV-opaque corneas, but species inhabiting open areas had UV-transmitting corneas. However, there was no evidence of corneal transmission properties being related to whether a species is diurnal or nocturnal.

Spectral transmission of the principal-eye corneas of jumping spiders: implications for ultraviolet vision.

Ultraviolet (UV) vision plays an important role in interspecific and intraspecific communication in many animals. However, UV vision and its adaptive significance have been investigated in only approximately 1% of more than 5000 species of jumping spiders (Araneae: Salticidae), renowned for their unique, complex eyes that support exceptional spatial acuity and visually based behaviour. To appreciate the adaptive significance of UV vision, it is important to establish whether salticids can perceive UV and whether the perception of UV varies with ecological factors such as light environment. In this study, we measured the UV-transmission properties of the principal-eye corneas of 128 salticid species. We found that the corneas of all measured species were able to transmit UV light, making the perception of UV possible. Three classes of corneal spectral transmission curves were identified; the majority of species had a Class II curve with a less-steep slope and a gradual onset of the transmission cut-off; all the remaining species had a Class I curve with a very steep slope and a sharp cut-off except for one species that had a Class III curve with an intermediate step, which appeared as a shoulder on the descending part of the transmission curve. The T(50) cut-off transmission values (the wavelength at which 50% of the maximum transmission is reached) in salticid corneas vary with species and light habitat. The corneas of species inhabiting open bush had a higher relative transmission at short wavelengths in the UV than forest species. This is the first investigation of corneal transmission in spiders and suggests that UV perception is widespread in salticids.