Effects of Web Design on the Prey Capture Efficiency of the Uloborid Spider Octonoba sybotides under Abundant and Limited Prey Conditions

Intraspecific niche partition without speciation: individual level web polymorphism within a single island spider population

Early in the process of adaptive radiation, allopatric disruption of gene flow followed by ecological specialization is key for speciation; but, do adaptive radiations occur on small islands without internal geographical barriers? Island populations sometimes harbour polymorphism in ecological specializations, but its significance remains unclear. On one hand, morphs may correspond to ‘cryptic’ species. Alternatively, they could result from population, developmental or behavioural plasticity. The spider Wendilgarda galapagensis (Araneae, Theridiosomatidae) is endemic to the small Isla del Coco and unique in spinning three different web types, each corresponding to a different microhabitat. We tested whether this variation is associated with ‘cryptic’ species or intraspecific behavioural plasticity. Despite analysing 36 803 loci across 142 individuals, we found no relationship between web type and population structure, which was only weakly geographically differentiated. The same pattern holds when looking within a sampling site or considering only F_st outliers. In line with genetic data, translocation experiments showed that web architecture is plastic within an individual. However, not all transitions between web types are equally probable, indicating the existence of individual preferences. Our data supports the idea that diversification on small islands might occur mainly at the behavioural level producing an intraspecific niche partition without speciation.

Caught in the web: Spider web architecture affects prey specialization and spider-prey stoichiometric relationships

Quantitative approaches to predator-prey interactions are central to understanding the structure of food webs and their dynamics. Different predatory strategies may influence the occurrence and strength of trophic interactions likely affecting the rates and magnitudes of energy and nutrient transfer between trophic levels and stoichiometry of predator-prey interactions. Here, we used spider-prey interactions as a model system to investigate whether different spider web architectures-orb, tangle, and sheet-tangle-affect the composition and diet breadth of spiders and whether these, in turn, influence stoichiometric relationships between spiders and their prey. Our results showed that web architecture partially affects the richness and composition of the prey captured by spiders. Tangle-web spiders were specialists, capturing a restricted subset of the prey community (primarily Diptera), whereas orb and sheet-tangle web spiders were generalists, capturing a broader range of prey types. We also observed elemental imbalances between spiders and their prey. In general, spiders had higher requirements for both nitrogen (N) and phosphorus (P) than those provided by their prey even after accounting for prey biomass. Larger P imbalances for tangle-web spiders than for orb and sheet-tangle web spiders suggest that trophic specialization may impose strong elemental constraints for these predators unless they display behavioral or physiological mechanisms to cope with nutrient limitation. Our findings suggest that integrating quantitative analysis of species interactions with elemental stoichiometry can help to better understand the occurrence of stoichiometric imbalances in predator-prey interactions.

Study on Web-Site Attributes and Predatory Efficiency of Dark Tetragnathid Spider in Point Calimere Wildlife and Bird Sanctuary

Spiders represent one of the most abundant components of the predatory arthropods in terrestrial ecosystem. Their effectiveness at restricting pest populations, both alone and as part of natural enemy complex has well demonstrated in many countries. The web, web-site attributes and predatory efficiency of Dark Tetragnathid Spider Tetragnatha mandibulata were assessed in Point Calimere Wildlife and Bird Sanctuary between August 2015 and March 2016. In the present study, the spiders used limited number of plants species. The relationship between web architecture and web-site attributes was estimated using Pearson’s correlation. Number of spiders recorded in the web showed the positive correlation with web horizontal and vertical length of the capture areas (p<0.05). Similarly, the web circumference showed the positive interaction with plant height and canopy width (p<0.05), which clearly indicated the importance of vegetations across the webs of Dark Tetragnathid Spider. Further, the microhabitat selection and utilization could also be impacted by non-trophic factors like structural features of plants that provide architectural supports to spiders. A total of 4620 insect pests comprising seven orders were entangled by the webs of dark tetragnathid spiders. Number of spiders in the web were positively correlated with number of insect pests (p<0.05), which clearly explained that the Dark Tetragnathid spiders restricting pest populations and therefore they are considered as useful organism in biological control.

Study on Web-Site Attributes and Predatory Efficiency of Dark Tetragnathid Spider in Point Calimere Wildlife and Bird Sanctuary

Spiders represent one of the most abundant components of the predatory arthropods in terrestrial ecosystem. Their effectiveness at restricting pest populations, both alone and as part of natural enemy complex has well demonstrated in many countries. The web, web-site attributes and predatory efficiency of Dark Tetragnathid Spider Tetragnatha mandibulata were assessed in Point Calimere Wildlife and Bird Sanctuary between August 2015 and March 2016. In the present study, the spiders used limited number of plants species. The relationship between web architecture and web-site attributes was estimated using Pearson’s correlation. Number of spiders recorded in the web showed the positive correlation with web horizontal and vertical length of the capture areas (p<0.05). Similarly, the web circumference showed the positive interaction with plant height and canopy width (p<0.05), which clearly indicated the importance of vegetations across the webs of Dark Tetragnathid Spider. Further, the microhabitat selection and utilization could also be impacted by non-trophic factors like structural features of plants that provide architectural supports to spiders. A total of 4620 insect pests comprising seven orders were entangled by the webs of dark tetragnathid spiders. Number of spiders in the web were positively correlated with number of insect pests (p<0.05), which clearly explained that the Dark Tetragnathid spiders restricting pest populations and therefore they are considered as useful organism in biological control.

Microfluidic Fabrication of Bio-Inspired Microfibers with Controllable Magnetic Spindle-Knots for 3D Assembly and Water Collection

A simple and flexible approach is developed for controllable fabrication of spider-silk-like microfibers with tunable magnetic spindle-knots from biocompatible calcium alginate for controlled 3D assembly and water collection. Liquid jet templates with volatile oil drops containing magnetic Fe3O4 nanoparticles are generated from microfluidics for fabricating spider-silk-like microfibers. The structure of jet templates can be precisely adjusted by simply changing the flow rates to tailor the structures of the resultant spider-silk-like microfibers. The microfibers can be well manipulated by external magnetic fields for controllably moving, and patterning and assembling into different 2D and 3D structures. Moreover, the dehydrated spider-silk-like microfibers, with magnetic spindle-knots for collecting water drops, can be controllably assembled into spider-web-like structures for excellent water collection. These spider-silk-like microfibers are promising as functional building blocks for engineering complex 3D scaffolds for water collection, cell culture, and tissue engineering.

Foraging decisions and behavioural flexibility in trap-building predators: a review

Foraging theory was first developed to predict the behaviour of widely-foraging animals that actively search for prey. Although the behaviour of sit-and-wait predators often follows predictions derived from foraging theory, the similarity between these two distinct groups of predators is not always obvious. In this review, we compare foraging activities of trap-building predators (mainly pit-building antlions and web-building spiders), a specific group of sit-and-wait predators that construct traps as a foraging device, with those of widely-foraging predators. We refer to modifications of the trap characteristics as analogous to changes in foraging intensity. Our review illustrates that the responses of trap-building and widely-foraging predators to different internal and external factors, such as hunger level, conspecific density and predation threat are quite similar, calling for additional studies of foraging theory using trap-building predators. In each chapter of this review, we summarize the response of trap-building predators to a different factor, while contrasting it with the equivalent response characterizing widely-foraging predators. We provide here evidence that the behaviour of trap-building predators is not stereotypic or fixed as was once commonly accepted, rather it can vary greatly, depending on the individual's internal state and its interactions with external environmental factors.

Insects from the grazing food web favoured the evolutionary habitat shift to bright environments in araneoid spiders

The Araneoidea comprises a diverse group of web-building spiders, and part of this diversity is believed attributable to habitat expansion to bright environments. We clarified the fitness-related advantages of living in such environments by examining prey availability and the growth rates of 10 species in three families inhabiting grassland (bright) and forest understory (dim) habitats. Spiders in the grassland habitat captured more prey, derived mainly from the grazing food web, than those in the forest-floor environment, and this difference was manifested in their growth rate. Independent contrasts indicated that increased utilization of insects from the grazing food web led to an evolutionary increase in adult body size. These results suggest that the shift to bright environments enabled araneoid spiders to evolve diverse life-history traits, including rapid growth and large size, which were not possible in dim environments.

Changes in composition of spider orb web sticky droplets with starvation and web removal, and synthesis of sticky droplet compounds

The sticky spiral of araneoid spider orb webs consists of silk fibers coated with adhesive droplets. The droplets contain a variety of low-molecular-mass compounds (LMM). Within a species, a fairly consistent ratio of LMM is often observed, but substantial variability can exist. To gain insight into factors influencing LMM composition, spiders of three araneid species were starved and LMM from their webs were analyzed for changes in composition. To determine if these changes were consistent with the spider's ability to synthesize the different organic LMM, synthetic capacities were estimated following the feeding of radiolabeled metabolites. Some changes in droplet composition were broadly consistent with differing synthetic capacities: molar percentages of less readily synthesized compounds (e.g. choline, isethionate, N-acetyltaurine) typically declined with starvation, at least during a portion of the imposed fast, while more readily synthesized compounds (e.g. GABamide, glycine) tended to increase. Most striking was the apparent partial substitution of N-acetylputrescine by the more readily synthesized GABamide in fasting Argiope trifasciata. However, departures from expected compositional shifts demonstrated that synthetic capacity alone does not adequately predict sticky droplet compositional shifts with starvation. Moreover, feeding controls exhibited some changes in composition similar to starving spiders. As the webs of both feeding and starving spiders were removed for chemical analysis and could not be recycled, the loss of LMM contained in these webs likely contributed to similarities between treatments. In addition, feeding spiders molted, oviposited and/or built heavier webs. The added metabolic demands of these activities may have contributed to changes in composition similar to those resulting from starvation.

Spider webs designed for rare but life-saving catches

The impact of rare but positive events on the design of organisms has been largely ignored, probably due to the paucity of recordings of such events and to the difficulty of estimating their impact on lifetime reproductive success. In this respect, we investigated the size of spider webs in relation to rare but large prey catches. First, we collected field data on a short time-scale using the common orb-weaving spider Zygiella x-notata to determine the distribution of the size of prey caught and to quantify the relationship between web size and daily capture success. Second, we explored, with an energetic model, the consequences of an increase in web size on spider fitness. Our results showed that (i) the great majority of prey caught are quite small (body length less than 2mm) while large prey (length greater than 10mm) are rare, (ii) spiders cannot survive or produce eggs without catching these large but rare prey and (iii) increasing web size increases the daily number of prey caught and thus long-term survival and fecundity. Spider webs seem, therefore, designed for making the best of the rare but crucial event of catching large prey.

Growth factor array fabrication using a color ink jet printer

We have developed a novel method for growth factor analysis using a commercial color ink jet printer to fabricate substrata patterned with growth factors. We prepared substrata with insulin printed in a simple pattern or containing multiple areas of varying quantities of printed insulin. When we cultured the mouse myoblast cell line, C2C12, on the insulin-patterned substrata, the cells were grown in the same pattern with the insulin-printed pattern. Cell culture with the latter substrata demonstrated that quantity control of insulin deposition by a color ink jet printer is possible. For further applications, we developed substrata with insulin-like growth factor-I (IGF-I) and basic fibroblast growth factor (bFGF) spotted in 16 different areas in varying combinations and concentrations (growth factor array). With this growth factor array, C2C12 cells were cultured, and the onset of muscle cell differentiation was monitored for the expression of the myogenic regulator myogenin. The ratio of cells expressing myogenin varied with the doses of IGF-I and bFGF in the sections, demonstrating a feasibility of growth factor array fabrication by a color ink jet printer. Since a printer manipulates several colors, this method can be easily applied to multivariate analyses of growth factors and attachment factors affecting cell growth and differentiation. This method may provide a powerful tool for cell biology and tissue engineering, especially for stem cell research in investigating unknown conditions for differentiation.