The Genetic Basis of Silk-Spinning Organs spiders: Complex trait evolution in spiders

• Applicant: Dr. Marco Meyer
• Subject Area: Evolutionary Cell and Developmental Biology (Zoology) ; Developmental Biology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569927611

The silk-spinning apparatus of cribellate spiders represents a remarkable evolutionary key innovation that played a pivotal role in the early spider diversification. In contrast to most extant spiders, which rely on viscid silk, cribellate spiders produce dry adhesive capture threads using a complex spinning system that extends across multiple body parts. The cribellum, a specialised spinning plate on the spider's abdomen, produces adhesive nanofibres through thousands of silk spigots. These fibres are then processed by the calamistrum, a comb of modified bristles on the fourth pair of legs, into three-dimensional capture threads. Cribellum and calamistrum are not only functionally interdependent but also closely linked in their morphology and development. Both traits appear together in the third instar stage and grow in concert throughout the subsequent development. With the maturing moult, males lose the calamistrum and cribellum, whereas females retain the traits for web building. The cribellate spinning apparatus represents the plesiomorphic form of silk production in "true spiders" (Araneomorphae) and offers a compelling model for studying the evolutionary dynamics of complex morphological traits. Despite its role in spider evolution, the cribellate trait complex (CTC) has been lost multiple times independently, often coinciding with ecological shifts and the emergence of alternative silk-spinning strategies. Notably, the cribellum and calamistrum are consistently lost together and do not occur as independent functional structures. This coordinated development and coinciding loss both in evolution and within an individual’s lifetime strongly suggests a shared genetic basis, forming a cribellate trait complex (CTC). Investigating this system is key to understanding how complex morphological traits evolve, are regulated, and can be lost. This project will employ RNA-Seq to analyse differentially expressed genes in the cribellum, the fourth (calamistrum-bearing) leg, and the third (non-calamistrum-bearing) leg. Samples will be taken from four developmental stages as well as adult males and females. The aim is to identify candidate genes underlying the CTC and investigate their regulation. These candidate genes will then be analysed in a broad phylogenetic framework to trace their evolutionary history and identify conserved regulatory networks. By integrating developmental genetics with comparative genomics, this research will not only provide new insights into the genetic basis of spider silk production but also contribute to a broader understanding of how complex morphological structures emerge, persist, and are lost throughout evolution. The findings will offer valuable perspectives on fundamental principles of evolutionary biology and genomics.

• DFG Programme: WBP Fellowship
• International Connection: United Kingdom
• Host: Dr. Joana Isabel Meier