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Physical structures built by animals challenge our understanding of biological processes and inspire the development of smart materials and green architecture. It is thus indispensable to understand the drivers, constraints, and dynamics that lead to the emergence and modification of building behavior. Here, we demonstrate that spider web diversification repeatedly followed strikingly similar evolutionary trajectories, guided by physical constraints. We found that the evolution of suspended webs that intercept flying prey coincided with small changes in silk anchoring behavior with considerable effects on the robustness of web attachment. The use of nanofiber based capture threads (cribellate silk) conflicts with the behavioral enhancement of web attachment, and the repeated loss of this trait was frequently followed by physical improvements of web anchor structure. These findings suggest that the evolution of building behavior may be constrained by major physical traits limiting its role in rapid adaptation to a changing environment. [ABSTRACT FROM AUTHOR]

Abstract: Among group‐living spiders, subsocial representatives in the family of crab spiders (Thomisidae) are a special case, as they build protective communal leaf nests instead of extensive communal capture webs. It could thus be inferred that antipredator benefits (e.g., enhanced protection in larger nests) rather than foraging‐related advantages (e.g., capture of more and larger prey) promote sociality in this family. Nonetheless, subsocial crab spiders do share prey, and if this behaviour does not reflect mere food scramble but has a cooperative character, crab spiders may offer insights into the evolution of social foraging applicable to many other cooperative predators that hunt without traps. Here, we performed a comparative laboratory feeding experiment on three of the four subsocial crab spider species—Australomisidia ergandros, Australomisidia socialis and Xysticus bimaculatus—to determine if crab spiders derive advantages from foraging in groups. In particular, we tested artificially composed groups of five sibling spiderlings vs. single siblings in terms of prey capture success and prey size preference. Across species, groups had higher prey capture success (measured in terms of capture rates and capture latency) and were more likely to attack large, sharable prey—dynamics leading to reduced food competition among group members in favour of living and foraging in groups. Within groups, we further compared prey extraction efficiency among the three applied social foraging tactics: producing, scrounging and feeding alone. In A. ergandros, individuals were exceptionally efficient when using the non‐cooperative scrounger tactic, which entails feeding on the prey provided by others. Thus, our multispecies comparison confirms foraging advantages in maintaining a cooperative lifestyle for crab spiders, but also demonstrates the relevance of research into exploitation of cooperative foraging in this family. [ABSTRACT FROM AUTHOR]

Throughout the breeding season, changing environmental and biological conditions can lead to variation in the reproductive landscape of many species. In alpine environments temperature is a key driver of behaviour for small ectotherms such as insects, but variable biotic factors such as mate quality and availability can also influence behaviour. Kosicuscola tristis is a small semelparous grasshopper of the Australian alpine region. In a rare behaviour among grasshoppers, K. tristis males engage in vigorous fights over access to females, involving mandible displays, kicking, biting and grappling. In this study we describe the variation in fighting behaviour of K. tristis throughout the breeding season and test several hypotheses related to temperature, body size, mating behaviour, and female quality. We show that K. tristis males are more aggressive toward each other at the end of the breeding season than at the beginning. This increased aggression is associated with decreased daily average temperatures (from ~20°C to ~9°C), decreased mating activity, increased female fecundity, and an unexpected trend toward an increase in female-to-male aggression. These results suggest that K. tristis is likely under increased selective pressure to time key life cycle events with favourable biological and climatic conditions. The stochastic nature of alpine environments combined with a relatively short life span and breeding season, as well as limited mating opportunities toward the end of the season may have contributed to the evolution of this extraordinary mating system. [ABSTRACT FROM AUTHOR]

In groups of socially foraging animals, feeding behaviour may change with group size in response to varying cost-benefit trade-offs. Numerous studies have described group-size effects on group-average feeding behaviour, particularly emphasizing an increase in scrounging incidence for larger groups, where individuals (scroungers) feed from the food sources others (producers) discovered. However, individual variation in feeding behaviour remains unconsidered in the vast majority of these studies even though theoretical models predict individuals to specialize in feeding tactic and anticipate higher scrounger-type frequencies in larger groups. We combined grouplevel and individual-level analyses of group-size effects on social foraging in the subsocial spider Australomisidia ergandros. Lending novel experimental support to model predictions, we found that individuals specialize in feeding tactic and that higher scrounging and lower producing incidence in larger groups were mediated through shifts in the ratio of feeding types. Further, feeding-type specialization was not explained by innate individual differences in hunting ability as all feeding types were equally efficient in prey capture when foraging alone. Context adaptivity of feeding behaviour might allow this subsocial species to succeed under varying socioecological conditions. [ABSTRACT FROM AUTHOR]

In unpalatable prey, long-wavelength colors such as red or yellow are often thought to be aposematic (warning) signals, due to their high conspicuousness. However, conspicuousness depends on the visual physiology of the receivers. Tectocoris diophthalmus is a shieldback stinkbug with highly variable coloration; individuals may be all orange or have blue-green iridescent patches of variable size. Prior research has demonstrated the defenses of T. diophthalmus can induce avoidance learning in birds but not praying mantids, and that geographic patterns in variation may relate to the local density of arthropod predators. In this study, we use visual modeling and behavioral assays to test how praying mantids Hierodula majuscula may impose directional selection pressure on the coloration of T. diophthalmus. Mantids have monochromatic vision with peak sensitivity in the "green" region of the spectrum. Using a receptor excitation model, we show that orange bugs are much less conspicuous than iridescent conspecifics and may be inconspicuous against their typical green leaf background. In behavioral assays, mantids detected iridescent bugs from a greater distance on average. In binary choice experiments, mantids showed no color preference at short range, but approached iridescent bugs significantly more often when the choice had to be made at a greater distance, and could not distinguish between orange bugs and unoccupied leaves at distance. Together, this evidence suggests that H. majuscula should impose strong directional selection against iridescent bugs in nature, and that orange coloration may be performing dual roles of crypsis to mantids but aposematic signaling to birds. [ABSTRACT FROM AUTHOR]

Group activities that require an initial investment are liable to be exploited. This situation can, for example, be found in group-hunting lions, but also in subsocial and social spiders, in which several individuals capture single large prey items. Individuals could save investment by contributing less to the hunt but also during feeding by saving their external digestive enzymes. Such dynamics have been partly explored in subsocial and social web-building spiders, but are likely to differ when groups hunt in the absence of a web. Subsocial crab spiders hunt without webs and forage communally. Their nests usually comprise related individuals, although groups accept immigrating spiderlings from foreign nests, which may affect competition among group members. We aimed to test whether hunting and communal feeding differ depending on spiderling group composition and formed experimental treatments consisting of either (1) family members, (2) family members including two foreigners or (3) assorted spiderlings. Group hunting was more frequently found among family members and was positively correlated with spiderling mass increase. Family groups fed in consistently larger numbers and grew better compared with the assorted groups, but also compared with family groups including only two foreigners. The latter finding suggests that even a few immigrants may negatively affect communal activities. [ABSTRACT FROM AUTHOR]

Australia is a curious place and a popular arena for behavioral research. Here we explore why Australia seems to be particularly rich in organisms that make their living from deceiving others.The Australian continent is renowned for its idiosyncratic flora and fauna and high diversity of endemic taxa (e.g., Eucalyptus, marsupials, and monotremes; Braithwaite RW. 1990. Australia’s unique biota: implications for ecological processes. J Biogeogr. 17:347–354.). Given this diversity, it is perhaps not surprising that Australia is a coveted and productive field site for behavioral ecologists worldwide. The prevalence of some unusual animal behaviors is well documented, such as cooperative breeding in birds, low rates of herbivory, and high rates of pollination by vertebrates. However, other behavioral phenomena, especially those involving deception and exploitation, are also remarkably prevalent in some systems and still require comprehensive treatment. We examine 3 distinct forms of deception in entirely different taxa, cuckoos, crab spiders, and orchids, where there is strong evidence that deception is more prevalent in Australia than in other geographic regions. We offer several explanations addressing environmental conditions, evolutionary isolation, the prevalence of behavioral ecologists, and the research culture in Australia. The aim of this “Idea” paper is to draw attention to intriguing patterns of deception in a limited number of well-studied systems and to generate several testable predictions. It is not intended as a thorough review of all deceptive systems, but we hope to stimulate more research, a systematic review, and further testing in this area. [ABSTRACT FROM PUBLISHER]

Theory suggests that aposematism, specifically the learned avoidance of unprofitable prey via memorable color patterns, should result in selection for pattern uniformity. However, many examples to the contrary are seen in nature. Conversely, honest sexual signals are likely to exhibit greater variation because they reflect underlying variation in mate quality. Here we aim to characterize and quantify the mechanistic causes of color in Tectocoris diopthalmus to shed light on the costs of color production, and thus the potential information content of its color signals. We use Tectocoris diopthalmus because it is a weakly-defended stinkbug, and presents elements that have classically been studied in the context of aposematism (red coloring), and sexual selection (sexual dichromatism and iridescent coloring). Pigment analysis reveals that variation in orange coloration is due to the amount of erythropterin pigment, stored in intracellular granules. This pigment is common in Heteroptera, and as an endogenously produced excretory byproduct is unlikely to reflect mate quality or variation in unprofitability of the bug. Electron microscopy reveals the iridescent patches are caused by an epicuticular multilayer reflector, and the hue and patch size are directly related to the layer widths and extent of coverage of this layering. Furthermore, we identified melanin as an essential component of the multilayer reflector system; therefore, the quality of the iridescent patches may be affected by aspects of rearing environment and immunocompetence. We posit that T. diopthalmus has co-opted the melanic patches of a ‘typical’ red and black aposematic signal, transforming it into a complex and variable iridescent signal that may enhance its capacity to display individual quality. [ABSTRACT FROM AUTHOR]

Scramble competition polygyny is expected when females and/or resources are widely dispersed and not easily monopolized by males, or when there is an abundance of mates during an extremely restricted reproductive period. Additional factors such as first male sperm precedence or low female re-mating rate might further explain the propensity of males to engage in scramble competition. The sexually cannibalistic praying mantid Pseudomantis albofimbriata exhibits a polygynous mating system, where females exist in low-density populations and male competition manifests as the race to find females rather than as direct physical fighting. Here, we aim to determine whether there is a paternity advantage for the first-male to mate and/or a low frequency of female re-mating. First, we determined sperm precedence patterns in P. albofimbriata using the sterile male technique. Second, we tested the likelihood of female re-mating in P. albofimbriata by comparing the close-range approach behaviour and frequency of successful mating attempts for males when paired with virgin as opposed to recently mated females, and by comparing the frequency of long-distance male attraction between virgin and mated females. We found no paternity advantage for the first male to mate, rather a second male advantage. Although mated females were not rejected by males when approached from close-range, they were chemically unattractive to males searching from a distance. Since initial mate attraction in many praying mantids, including P. albofimbriata, is mediated via long-distance chemical communication, we believe the latter result is more ecologically relevant and therefore more important. These results suggest that the relatively low frequency of female re-mating observed in P. albofimbriata may be an additional factor driving scramble competition in this system. [ABSTRACT FROM AUTHOR]

In cases where sexual cannibalism represents a sexual conflict, we should expect to find male traits that reduce the risk of cannibalism. In fact, a wide variety of such traits have been proposed, including elaborate courtship displays, cautious approach behaviours, and opportunistic mating whilst a female is feeding. However, there is very little direct evidence that these behaviours actually reduce the risk of sexual cannibalism for males, and the evidence that does exist comes mainly from spider studies. In this study of Pseudomantis albofimbriata praying mantids we found evidence of various male behaviours that reduced the risk of sexual cannibalism. Most males attempted to avoid detection entirely and others moved in a slow and stealthy manner. We also observed five cases of opportunistic mating, but saw no evidence of any male courtship routine. It seems that mounting from the rear of a female or slowly approaching her from the front, allows many males to go unnoticed and, therefore, substantially reduces the risk of sexual cannibalism in this mating system. Interestingly, we could not identify any female traits that males use to assess the risk of sexual cannibalism. It may be that P. albofimbriata males use alternative means to assess these risks. The presence of these behavioural strategies by males suggests a net cost of being consumed, and that sexual cannibalism is likely to be a female strategy in this system. [ABSTRACT FROM AUTHOR]

Several hypotheses have been proposed to explain the evolution of sexual cannibalism. The foraging strategy hypothesis states that sexual cannibalism may arise as an adaptive foraging strategy, providing females with the nutrients to increase future fecundity. Yet, very few studies have found that nourishment through cannibalism translates into increased fecundity. One explanation for this may be that most of these investigations have concentrated on sexually dimorphic spider species with tiny males that do not significantly increase female body mass on consumption. The current study focuses on the praying mantid, Pseudomantis albofimbriata, a moderately size dimorphic species with relatively large males. Cannibalistic females of such species may be more likely to gain nutritional benefits from male consumption, which translate into increased fecundity. Here, cannibalistic females substantially improved their body condition and subsequently produced heavier egg cases than their noncannibalistic counterparts. An additional prediction of the foraging strategy hypothesis is that sexual cannibalism will increase with decreasing female condition. We found that the prevalence of sexual cannibalism in this system was indeed affected by female body condition; females in poor condition were more likely to consume their potential mates than females in good condition. Additional analysis of the data refuted the relevance of each of the remaining hypotheses for this species, providing clear evidence for the foraging strategy hypothesis as an explanation for the maintenance of sexual cannibalism in this species. [ABSTRACT FROM PUBLISHER]

The article discusses research by Nagata et al. in this issue about the depth perception of jumping spiders. Topics covered include binocular stereoscopic vision in humans, the multilayered retina of the jumping spider, and the method of defocus for depth perception used by spiders. It is noted that the neural mechanism for focused and unfocused images is not known.