Variations of cocoon external lipids during wolf spiderlings' development

This study presents the first characterisation of the silk lipids of the cocoons of a wolf spider (Pardosa saltans). Wolf spiders' maternal behaviour is complex and involves guarding a cocoon for several weeks, and so cocoons must emit cues to ensure their care and the development of juveniles. We investigated cues associated with the cocoon silk. We assessed qualitative changes of the lipid contents and the composition of cocoon silk in relation to the development of P. saltans wolf spider juveniles. Gas chromatography-mass spectrometry of P. saltans' cocoon silk revealed 62 different lipid compounds. The compounds were aliphatic alcohols, glycerides, fatty acids and their methylesters containing 13-29 carbon atoms. We reveal for the first time the presence of ethanolamides and phytosterol on cocoon silk. Qualitative and quantitative changes occur during the embryonic period, as some polar compounds, such as diglycerides and ethanolamides, disappeared while hydrocarbons emerge, and fatty acids disappeared later during the post-embryonic period. Qualitative and/or quantitative changes could play a role in tactochemical communication between mothers and their cocoon. However, mothers do not modify their behaviour in relation to the developmental stage of their cocoon. Mothers' behaviour appears to be linked to both internal (physiological state) and external mechanisms (signals from the cocoon).