Maternal care, defensive behavior, and sociality in neotropical Goniosoma harvestmen (Arachnida, Opiliones)

Abstract

Goniosoma includes large and conspicuous species of harvestmen that occur exclusively in the Brazilian Atlantic forest. This paper reports on the parental activities, defensive behavior, and gregariousness of five species of Goniosoma, and also summarizes the published biological data for the genus. The behavioral patterns within the genus are discussed and a hypothesis for the emergence of gregariousness in the group is presented. Several Goniosoma live inside caves, mainly as trogloxenes. Although species of the genus comprise only 5 % of the harvestmen fauna in Brazil, they account for 20.6 % of all harvestmen species recorded in Brazilian caves. In addition to several morphological and physiological features that may favor the occupation of caves, species of Goniosoma also present subsocial behavior, which may confer a special advantage in this particular environment. Female protection is crucial for egg survival since predators may consume entire batches in a single night. Most species of Goniosoma form dense diurnal aggregations ranging from three to 200 individuals (mainly subadults and adults of both sexes). In a hypothetical scenario for the evolution of sociality in the Goniosoma, physiological constraints acting on individual harvestmen would lead to a behavioral response for the selection of sites with appropriate microclimatic conditions. The lack of cannibalism among adults and subadults may favor tolerance towards conspecifics, and may represent a pre-adaptation to gregariousness. The derived functions of gregarious behavior may include strengthening of the defensive signal through the collective release of a repugnant secretion, the dilution effect, and promptness in fleeing a predator attack as a consequence of the additional alarm role of scent gland secretions. These defensive functions may overcome the costs of group living and may be responsible for the maintenance of gregariousness in Goniosoma.

Chemical Defense in Harvestmen (Arachnida, Opiliones): Do Benzoquinone Secretions Deter Invertebrate and Vertebrate Predators?

“…Many gonyleptids show gregarious habits, and among the representatives of the subfamily Goniosomatinae, this behavior is especially common (Machado, 2002). Recently, it was demonstrated that the defensive secretion of Goniosoma aff.…”

“…All individuals of G. longipes used in this study were collected inside caves at the Parque Florestal do Itapetinga (23-15 ¶S, 46-45 ¶W, 900-to 1300-m altitude, 1600 mm rain/year), Atibaia, São Paulo state, southeastern Brazil (for details on the study site, see Machado andOliveira, 1998 andMachado et al, 2000). In the laboratory, adult G. longipes were maintained in a communal terrarium (60 Â 40 cm base, 35 cm high) containing cotton wetted with water to maintain the humidity and fed with dead insects twice a week.…”

“…Most laniatorean harvestmen, including G. longipes, have spines covering the body and legs and present a variety of defensive behaviors that may be divided in evasive responses (fleeing and dropping from the substrate) and aggressive responses (Machado, 2002). The latter includes several mechanisms that threaten, harm, or deter aggressors, such as attacking with the pedipalps, biting with the chelicerae, pinching with the sharp projections of the femora and coxae IV, and releasing scent gland secretions (Machado, 2002;Hara and Gnaspini, 2003).…”

“…The latter includes several mechanisms that threaten, harm, or deter aggressors, such as attacking with the pedipalps, biting with the chelicerae, pinching with the sharp projections of the femora and coxae IV, and releasing scent gland secretions (Machado, 2002;Hara and Gnaspini, 2003). To test the potential defensive role of the glandular secretion only, and prevent other possible defensive mechanisms, individuals of G. longipes were not offered to the predators.…”

“…We recorded the time elapsed between the presentation of the crickets and the attack of the opossums, as well as the behavioral response of the animals to each type of prey. Because species of the genus Goniosoma are capable of ejecting their secretion forcibly as a spray (Machado, 2002;Hara and Gnaspini, 2003), one adult individual of G. longipes was also introduced in each cage after the presentation of the crickets to investigate the response of the opossums to this special type of emission.…”