Microstructure, elemental composition and fatty acid compounds of spider egg sacs featuring Parasteatoda sp. and Pardosa sp. spiders

Spider egg sacs provide a valuable system for investigating offspring protection strategies. In this study, we examined both the silk and egg components of egg sacs from two model spiders, Pardosa sp. and Parasteatoda sp. chosen for their contrasting ecotypes, parental-care strategies, and egg sac organization. Egg sac morphology, elemental composition, and fatty-acid (FA) profiles were characterized using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) and gas chromatography combined with mass spectrometry and flame-ionization detection (GC-MS/GC-FID). SEM revealed that Pardosa sp. produced dense, highly organized silk, whereas Parasteatoda sp. formed a looser silk matrix but exhibited a denser layer of chorionic microstructures on the egg surface than Pardosa sp. EDX showed that both silk and eggs were composed primarily of C, N, and O, with smaller contributions of K, Cl, Na, Al, and Mg, and elemental maps revealed their spatial distribution within the analysed structures. GC-MS/GC-FID identified 29 FAs in eggs and 17 in silk, ranging from C9 to C20. Egg samples were dominated by 16:0, 16:1, 18:0, 18:1 ω7c/ω9c, 18:2 ω6,9c, and 20:4 ω6,9,12,15c, whereas silk samples contained mainly 13:0, 14:0, 14:1, 15:0, 16:0 anteiso, 16:0, 17:0 anteiso, 18:3 ω6c, 18:2 ω6,9c, 18:1 ω9c, and 18:0. Although FA profiles were broadly similar between species, species-specific differences were observed in eggs (9:0, 17:1 ω8c, 20:2 ω6,9c, 18:1 ω7c, 18:1 ω5c) and silk (16:0 anteiso, 16:1 ω9c, 17:0 anteiso, 9:0, 15:0). Some of the identified FAs have been reported in the literature to exhibit antimicrobial potential. Overall, these findings expand current knowledge of the structural and biochemical diversity of spider egg sacs and provide a further basis for future in vitro studies on the biological significance of egg sac components.