Do wolf spiders’ egg-sacs emit tactochemical signals perceived by mothers?

Parent–offspring relationships take many forms. One particular form of parental behavior is egg care when parents brood their eggs after laying them. Parents of many oviparous vertebrates and terrestrial arthropods brood their eggs. Spiders present a particular interesting form of parental behavior, enclosing their eggs in a silk sac (or egg-sac) and can care for it until spiderlings emerge. This study investigated proximal cues which stimulate the wolf spider Pardosa saltans (Lycosidae) to care for their egg-sacs, transport them for 30 days and open it to allow spiderlings to emerge. We showed that mothers discriminate between egg-sacs differencing in mass (empty or not) as they do not hang an empty egg-sacs but do not discriminate between egg-sacs with viable and nonviable juveniles either when manipulating or when hanging them. However, mothers do not open nonviable egg-sacs but abandon them only at the end of the juvenile development period when spiderlings are due to emerge (30-day-old egg-sacs). We investigated egg-sac silk chemical cues that mothers detected by presenting them egg-sacs washed with different polar solvents or chemical egg-sacs silk extracts. We identified the polar and apolar chemical compounds of lipid extracts of egg-sacs detected by mothers during manipulation. Our results demonstrate that these compounds stimulate maternal care, and mothers detect mobility of juveniles at the end of the postembryonic period, when juveniles are ready to emerge from a 30-day-old egg-sacs indicating that tactochemical stimuli are involved in egg-sacs care. Wolf spiders mothers protect their eggs in a silk sac and guard it for 30 days. We show that mothers detect signals (vibrations, odours) emitted by the young through the egg-sac and that they consequently modulate their behavior in response to these signals. These signals inform the mother when she should open the sac to allow her young to emerge or inform that her young are dead.