Spider Silk Adaptations: Sex-Specific Gene Expression and Aquatic Specializations
Spiders are very diverse and inhabit most terrestrial environments. Spiders are renowned for their silk usage, which they rely on for an array of essential, fitness-related tasks such as reproduction, dispersal and prey-capture. Spider silks are proteinaceous and are largely composed of structural proteins called spidroins. Spidroins are encoded by a gene family that has undergone dramatic proliferation. To date, whether specific molecular modifications of silks are associated with success in particular habitats is still unknown. To better understand the specializations of silk sequence and expression levels, I examined the molecular composition of spidroins from terrestrial and aquatic (marine and freshwater) spiders to determine how aquatic spiders are using their silk to thrive in wet environments. I also compared silk gene expression levels of males and females within and across species.
Sex-biased silk expression was observed in genes associated with male- and female-specific tasks (e.g., egg-case production by females, wandering for mates by males). While all females highly expressed egg-case silk genes, male silk gene expression differed across species. Comparison of silks from a semi-aquatic spider to a terrestrial counterpart did not provide obvious evidence for unique specializations of silks that function underwater. Rather, the silks of the semi-aquatic spider appear to have been preadapted for aquatic use. Characterization of silk molecules from a terrestrial cribellate spider (constructs webs with cribellar silk), led to the identification of new protein sequence motifs, including a putative gene for cribellar silk. Finally, by comparing the spidroins from multiple species that independently evolved water-association, I found that they share a sequence motif composed of hydrophobic amino acids [(GV)n]. My research also addressed some of the structural aspects of silk fibers used by different spiders in terrestrial and aquatic settings. Characterization of silks from terrestrial, aquatic, and marine semi-aquatic spiders shows that spiders have developed different silk-related strategies to match their habitat and lifestyle. In addition to contributing to an integrated understanding of spider silks, my research expands the potential of spider silk as a novel biomaterial.