Multiple Lines of Egg Defense in a Neotropical Arachnid with Temporary Brood Desertion

Abstract

Egg predation is the one of the main costs of brood desertion in many ectothermic animals. When stressful environmental conditions constrain parental activities to only some periods of the day, the combination of physical or chemical defenses may attenuate the costs related to egg loss during periods of temporary parental absence. Females of the harvestman Neosadocus maximus periodically abandon their clutches to shelter or forage. They also cover their eggs with a hygroscopic mucus coat and seem to lose fewer eggs to predation than other syntopic harvestmen whose eggs lack the mucus coat. Using two species of N. maximus egg predators, we demonstrate that eggs whose mucus coat was experimentally removed suffered higher predation rate than eggs whose mucus coat was left intact. We argue that this mucus provides physical protection against egg predators, especially small arthropods. A similar mucus coat has independently evolved in other two clades of Neotropical harvestman in which males care for the eggs and typically leave their clutches unattended for several hours a day. We propose that the presence of multiple lines of egg defense may have evolved as a way of lowering the costs imposed by intra- and interspecific egg predation during periods of temporary brood desertion.