Breeding biology of the cavernicolous harvestman Goniosoma albiscriptum (Arachnida, Opiliones, Laniatores): sites of opposition, egg batches characteristics and subsocial behaviour

Summary

We present field data on seasonality, mating behaviour, sites of oviposition, characteristics of egg batches, and parental care of a cavernicolous population of the Brazilian harvestman Goniosoma albiscriptum. We also tested if guarding females became more aggressive than non-guarding ones by allowing a potential predator to approach G. albiscriptum females. Field work was conducted in several visits to a cave, from September 1999 to April 2001. Reproductive activity was detected almost the whole year, with a minor peak in the spring (October-November) and a major peak in the summer (February-March). Average sex ratio throughout the year was female biased. Proportionally, guarding females were found significantly more often in exposed places than females without eggs. No significant difference was detected between the number of eggs laid in exposed and non-exposed places. The mean number of eggs per batch was 69.58±26.96, and the average minimum time of embryonic development was 33.26±9.78 days. Twenty-nine females produced two egg batches, with no significant difference between the number of eggs laid in the first and second batch. Intervals between the two ovipositions ranged from 3 to 17 months. Laboratory tests showed that conspecifics and other cave inhabitants, such as other harvestmen species and crickets, preyed on G. albiscriptum eggs. Guarding females reacted aggressively to a non-conspecific approaching harvestman. Non-guarding females never reacted aggressively. Con-specific males near females during the day attacked conspecifics males but not males of another species. Once, a male was seen standing next to eggs and immatures, possibly guarding them.

Key words:

• Behaviour
• egg-guarding
• Gonyleptidae
• offspring defence
• parental care