I. Tso’s research while affiliated with Tunghai University and other places

Understanding the complex interplay of factors shaping polymorphic changes within individuals represents a longstanding conundrum in biology. Some crab spiders (Thomisidae) are examples of sit-and-wait predators that can change their body coloration. Many factors may influence crab spider color polymorphism with multiple explanations receiving various levels of support. Here we examined the daytime and nighttime activities and predator and prey interactions for two yellow-white polymorphic crab spiders, Thomisus labefactus and Ebrechtella tricuspidatus in the field. We thereupon conducted a manipulative experiment using dummies with color morphs visibly resembling the spiders when placed on background-matched flowers. We measured the spectra reflected from the dummies and their floral backgrounds and used insect visual models to determine if they are likely to be visible to a range of insects by night and day. We found that both color morphs of each species were more active by night than by day. Our visual models revealed that the spider’s bodies were unlikely to be cryptic. Together, these results suggest that the crab spiders might exploit flower colorations during the night but not during the day. They also indicated that explanations of why crab spiders utilize certain color polymorphs are context dependent and will vary with time, and whether predators, prey, or both, are present. Crab spiders are an excellent model for investigating a long-standing challenge in evolutionary biology: understanding the causes and consequences of polymorphic coloration in animals. Studies have postulated a range of explanations with some support for each. Broader studies encompassing all interactions between spiders and their predators and prey across the day and night are urgently needed. Here we combined an around-the-clock spider activity survey with field experiments and insect visual models to show that the types of interactions between spider color morphs and their predators and prey differ over the day and night. Our study suggests that outcomes of experiments examining the adaptive drivers of polymorphisms may be dependent upon the context within which the observations were made, and that examining interactions across temporal contexts is required to fully uncover the various drivers of the polymorphisms.

Visual prey luring in animals is typically achieved by brightly colored body parts or excretions of the signal sender, and using signals from other organisms is rarely reported. However, certain species of kleptoparasitic Argyrodes spiders usually reside in the webs of Cyrtophora spiders, and their brightly colored bodies have been demonstrated to serve as a visual lure that attracts prey to host webs. The golden orb-web spider Nephila pilipes spins giant orb webs and also attracts web coinhabitants such as mate-seeking males and kleptoparasitic spider Argyrodes miniaceus. These two types of spiders have similar orange-red body coloration, leading us to investigate the function of this shared trait by manipulating their body color and recording the response of prey insects in the field using video cameras. Our results showed that, in both diurnal and nocturnal conditions, female N. pilipes webs with naturally colored male N. pilipes and A. miniaceus had a significantly higher prey attraction rate than those with body color altered coinhabitants. Specifically, A. miniaceus lure more prey at nighttime. These results indicate that the conspicuously colored web coinhabitants may potentially bring foraging benefits to the hosts through prey luring and provide new perspectives on the ecology and evolution of symbiotic relationships between animals. Significance statement It has been known that the body coloration of some spiders can lure prey to their webs, and even some kleptoparasitic Argyrodes spiders can lure prey to their hosts’ webs. However, whether the conspicuous body coloration of mate-seeking males plays any role remains untested. We showed for the first time that the orange-red body coloration shared by male Nephila pilipes and kleptoparasitic Argyrodes miniaceus spiders inhabiting webs of female N. pilipes can visually lure prey. Findings of this study can potentially strengthen our current understanding of the function of body coloration of spiders, shed light on evolution of spider body coloration, and provide new perspectives on symbiotic relationships between animals.

Bioluminescent glow-worms (Arachnocampa spp.) capture prey in glue-coated silk capture threads hung from their nests on damp cave and wet forest substrates. In a dry environment, these animals are very susceptible to desiccation as their bodies can become life threateningly dry and their silk has been anecdotally observed to become non-sticky. Water has a plasticizing effect on the structural proteins of several invertebrate silks, including those used in caddisfly nets, mussel byssus and spider webs. Moreover, water facilitates interfacial adhesion by spreading adhesive biomolecules in functionally analogous velvet worm slime and spider silk glue. We tested the effects of water on the mechanics and adhesion of Arachnocampa tasmaniensis capture threads sampled within damp caves. We found that threads tested at high humidity were three times more compliant and over 10-fold more extensible than those tested at low humidity (30% RH). We also found the threads to be significantly more adhesive in high humidity with force at detachment increasing two orders of magnitude and work of adhesion increasing by five orders of magnitude compared to threads tested at low humidity. Our results unequivocally demonstrate that A. tasmaniensis capture thread functionality is dependent upon exposure to high humidity. Our results both confirm previous reports and indicate that the foraging habitat of these animals is restricted to caves and cave-like environments, such as wet forests.

Animal morphological traits may vary across life stages. Web‐building spiders are diverse insectivores that can display ontogenetic shifts in the design and properties of their webs. Nevertheless, we know little about how a critical component of their webs, major ampullate silk (MAS), varies in property across life stages, inferably owing to a difficulty in finding suitable model species. The Tasmanian cave spider Hickmania troglodytes presents as a good model as it is long‐lived and grows to a large body size with overlapping generations. We collected MAS from the webs of different‐sized H. troglodytes and performed tensile tests on MAS fibers collected from their webs to search for shifts in properties over life stages. We found that strength and toughness (i.e. ability to deform and absorb energy) of the MAS increased with spider carapace width and body length. We expect that such a shift in silk performance across life stages has distinctive advantages, including enhanced prey capture capabilities, an improvement in the economy of silk production and ability of the web to support the spider's larger body.

Predators have been shown to alter their foraging as a regulatory response to recent feeding history, but it remains unknown whether trap building predators modulate their traps similarly as a regulatory strategy. Here we fed the orb web spider Nephila pilipes either live crickets, dead crickets with webs stimulated by flies, or dead crickets without web stimulation, over 21 days to enforce spiders to differentially extract nutrients from a single prey source. In addition to the nutrients extracted we measured web architectures, silk tensile properties, silk amino acid compositions, and web tension after each feeding round. We then plotted web and silk “performance landscapes” across nutrient space. The landscapes had multiple peaks and troughs for each web and silk performance parameter. The findings suggest that N. pilipes plastically adjusts the chemical and physical properties of their web and silk in accordance with its nutritional history. Our study expands the application of the geometric framework foraging model to include a type of predatory trap. Whether it can be applied to other predatory traps requires further testing.

The frequency and form of visual signals can be shaped by selection from predators, prey or both. When a signal simultaneously attracts predators and prey selection may favour a strategy that minimizes risks while attracting prey. Accordingly, varying the frequency and form of the silken decorations added to their web may be a way that Argiope spiders minimize predation while attracting prey. Nonetheless, the role of extraneous factors renders the influences of top down and bottom up selection on decoration frequency and form variation difficult to discern. Here we used dummy spiders and decorations to simulate four possible strategies that the spider Argiope aemula may choose and measured the prey and predator attraction consequences for each in the field. The strategy of decorating at a high frequency with a variable form attracted the most prey, while that of decorating at a high frequency with a fixed form attracted the most predators. These results suggest that mitigating the cost of attracting predators while maintaining prey attraction drives the use of variation in decoration form by many Argiope spp. when decorating frequently. Our study highlights the importance of considering top-down and bottom up selection pressure when devising evolutionary ecology experiments.

Masquerading comes at various costs and benefits. The principal benefit being the avoidance of predators. The orb-web spider Cyclosa ginnaga has a silver body and adds a white discoid-shaped silk decoration to its web. The size, shape and colour of C. ginnaga's body resemble, when viewed by the human eye against its decoration, a bird dropping. We therefore hypothesized that their body colouration might combine with its web decoration to form a bird dropping masquerade to protect it from predators. We measured the spectral reflectance of: (i) the spider's body, (ii) the web decoration, and (iii) bird droppings, in the field against a natural background and found that the colour of the spider bodies and decorations were indistinguishable from each other and from bird droppings when viewed by hymentopteran predators. We monitored the predatory attacks on C. ginnaga when the spider's body and/or its decorations were blackened and found that predator attack probabilities were greater when only the decorations were blackened. Accordingly, we concluded that C. ginnaga's decoration and body colouration forms a bird dropping masquerade, which reduces its probability of predation.

The unique combination of high mechanical strength, extensibility and toughness, and its ability to be synthesized in a benign environment make spider major ampullate (MA) silk a desirable material for a medical and other applications. Despite the effort invested in bioengineering spider silks, a synthetic analog mimicking MA silk in performance is yet to be made. It is becoming clear that spider silk is a highly variable material whose properties are affected by genes as well as the environment acting on the spinning processes via their affects on spider physiology. The environment may further directly adjust the properties of silk post-spinning; how water acts on silk to induce supercontraction is a classic example. We identify variations in prey type, ambient and spider body temperature, wind speed and water availability as environmental variables that have been shown to induce alterations in spider silk performance. How these variables directly induce the appropriate genetic or physiological adaptations are not known, but recent research suggests nutrients such as protein and water availability are important. We propose that understanding the ecophysiological processes affecting spider silk performance is crucial to enable the commercial synthesis of materials mimicking the properties of spider silks. Further, an understanding of these processes may be harnessed in order to create materials that are adaptable and/or resistant to environmental degradation for utilization by the medical industry, or other industries.

Building structures and aggregating can increase an animal’s fitness, but the benefits come at a cost. Some orb web spiders build multiple structures or build in aggregations, which may have the same effect on prey capture success as the addition of a structure. As these structures often appear together, they may bestow interactive benefits not realized if the structures were added alone. We performed field experiments to investigate whether the multiple structures associated with the orb webs of two spider species provide interactive benefits. The orb web spider Nephila clavata adds barrier webs and prey carcass decorations to its webs. We manipulated their webs in the field by removing either, both or neither the barrier webs or the carcass decorations. We found that prey interception rate was greatest when neither barrier webs nor carcasses were present but, for the prey caught, the prey retention rate was greatest with both structures present. Another orb web spider, Cyclosa mulmeinensis, adds prey carcass decorations and forms aggregations. We manipulated the decorations and aggregations of C. mulmeinensis in the field to determine their interactive influences. In solitary webs and webs with decorations, prey capture rates were lower than those without structures. These negative foraging effects, however, did not exist in decorated webs that were in aggregations. Our results thus show that multiple structures, individually, are costly, but interactively they provide substantial benefits.