Structural complexity and prey availability shape spider communities under retention forestry

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 Abstract Retention forestry is promoted as a conservation-oriented management strategy to sustain forest biodiversity by preserving key structural elements, such as single old trees and deadwood. However, the effectiveness of this approach in conserving the diversity of spiders as generalist predators remains unclear, particularly because the effect of structural elements under retention forestry on spiders may be mediated by its effect on prey availability. We sampled spiders (Araneae) and potential prey (Diptera, Hemiptera, Collembola) in 55 1-hectare plots across mixed temperate forests of the Black Forest, Germany. We used pitfall traps targeting species active on the forest floor. We studied spider abundance, taxonomic diversity, ecological diversity (combined measure of functional and phylogenetic distance) and community composition along gradients of forest structure (canopy cover, proportion of conifers, stand structural complexity, volume of lying deadwood, herb cover and...

From fibres to adhesives: evolution of spider capture threads from web anchors by radical changes in silk gland function

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From fibres to adhesives: evolution of spider capture threads from web anchors by radical changes in silk gland function

Abstract

Spider webs that serve as snares are one of the most fascinating and abundant type of animal architectures. In many cases they include an adhesive coating of silk lines—so-called viscid silk—for prey capture. The evolutionary switch from silk secretions forming solid fibres to soft aqueous adhesives remains an open question in the understanding of spider silk evolution. Here we functionally and chemically characterized the secretions of two types of silk glands and their behavioural use in the cellar spider, Pholcus phalangioides. Both being derived from the same ancestral gland type that produces fibres with a solidifying glue coat, the two types produce respectively a quickly solidifying glue applied in thread anchorages and prey wraps, or a permanently tacky glue deployed in snares. We found that the latter is characterized by a high concentration of organic salts and reduced spidroin content, showing up a possible pathway for the evolution of viscid properties by hygroscopic-salt-mediated hydration of solidifying adhesives. Understanding the underlying molecular basis for such radical switches in material properties not only helps to better understand the evolutionary origins and versatility of ecologically impactful spider web architectures, but also informs the bioengineering of spider silk-based products with tailored properties.

2024From fibres to adhesives: evolution of spider capture threads from web anchors by radical changes in silk gland functionJ. R. Soc. Interface.2120240123, http://doi.org/10.1098/rsif.2024.0123