Spider silk-secreting systems likely evolved from pre-existing glandular structures in an onychophoran-like ancestor.
The evolution of spider silk is a fascinating journey tracing back to the ancient ancestors of modern arthropods. Research suggests that the complex silk-producing systems we see in spiders today did not appear out of nowhere but evolved from simpler, pre-existing glandular structures found in their evolutionary lineage.
Comparative data and phylogenetic analyses indicate a deep connection between the silk-secreting systems of spiders and insects. These studies suggest that the systems are homologous, meaning they share a common evolutionary origin. This shared ancestry is believed to be linked to the glandular structures of a creature resembling an onychophoran (velvet worm), which is an ancient relative of arthropods.
Specifically, this ancestral onychophoran-like creature possessed glands and secretions that served as the foundation for the two main pathways of silk production seen in modern spiders and insects:
- Systemic Pathway: This pathway, responsible for producing silks like dragline silk (the main web line), is thought to have originated from the crural gland of the onychophoran-like ancestor.
- Surficial Pathway: This pathway, potentially related to secretions used for protection or adhesion, is linked to the cuticular secretions (secretions from the outer body layer) of the ancestral creature.
Over millions of years, these primitive glandular systems underwent significant modification and diversification, leading to the incredible variety and sophistication of silks produced by spiders for various purposes, including web building, prey capture, protection, and reproduction.
This evolutionary perspective highlights that the remarkable biomaterial that is spider silk is not a unique spider invention but rather a highly adapted and specialized form of a system inherited from much older ancestors.
