REPRODUCTIVE BEHAVIOR IN HARVESTMEN (ARACHNIDA): MATING SYSTEMS AND PARENTAL CARE

Abstract

Opiliones (harvestmen) undergo a prolonged process of reproduction, which consists of finding a suitable mate, persuading the mate to copulate, succeeding in fertilization and oviposition, and, in some cases, protecting the brood. In most harvestman species studied so far the manner of mate acquisition is a type of resource defense polygyny in which males fight over territories containing the preferred sites for oviposition by females. In at least one species, Acutisoma proximum, there is a discontinuous variation in the lengths of the sexually dimorphic second pair of legs, which are used as weapons by larger males when fighting over territories. Males with a shorter pair of second legs do not fight for territories, but instead adopt an alternative mating tactic of furtively invading the harems of the larger males to copulate. After oviposition, females of many harvestman species of the superfamily Gonyleptoidea take care of their eggs and young nymphs. Maternal care in harvestmen is expected to evolve when: (1) females live long enough to watch over the offspring after oviposition, (2) females are capable of defending their offspring against potential predators, and (3) females have a single reproductive event during the breeding season, so that they can achieve greater reproductive success by defending their eggs until hatch. Although caring for the offspring negatively affects the fecundity of females, this behavior was demonstrated to play a crucial role in enhancing egg survival and preventing predation by conspecifics and other arthropods. In at least seven lineages of harvestmen of the suborder Laniatores, males are responsible for watching over the offspring. Whereas maternal care most likely evolved as a result of natural selection, paternal care in harvestmen seems to have evolved as a result of sexual selection. According to experimental evidence, males capable of providing paternal care are preferred by females and thus produce more brood than males unable and/or unwilling to provide paternal care. Additionally, it was shown that males tend to care for egg clutches from other males that were experimentally removed, as the eggs attract females. The reproductive biology of harvestmen is fascinating, and the clade provides an ideal and yet unexplored system for the study of sexual selection.