Behavioral consistency, sexual and day/night differences in defenses of the harvestman Mischonyx cuspidatus

Author(s)

Júlio do Monte Gonzalez de Segovia

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2018-11-30

Examining board members

Rodrigo Hirata Willemart; Cibele Biondo; Regina Helena Ferraz Macedo; Patricia Izar Mauro; Laura Carolina Leal de Sousa

• Advisor: Rodrigo Hirata Willemart

Abstract

Prey-predator interactions play a major role in species evolution. Failing in an interaction with a predator may represent death for prey. Consequently, prey´s genes would not be represented in the future generations. In response to the strong selective pressures imposed by predators, prey have evolved several defensive strategies. Prey defenses may hinder detection by predators (e.g. anachoresis and crypsis). Other defensive strategies may play a role after predators are in close-range or already attacked the prey, for example retaliation (both mechanical and chemical) and thanatosis. All the aforementioned defenses have been described to harvestmen. Thus, harvestmen are potentially good models to study the evolution of defensive strategies. In this thesis, we used the harvestman Mischonyx cuspidatus as our experimental model. In the first chapter, we tested if individuals of M. cuspidatus are consistent in boldness levels (propensity to take risks, herein measured by the time spent performing thanatosis and freezing). We also tested if boldness is influenced by starvation. We found that M. cuspidatus behaved consistently regarding boldness, but we did not find any effect of starvation. In the second chapter, we looked for sexual differences in defensive behavior of M. cuspidatus. Taking into account the sexually dimorphic characters of this species (males have sharp structures in the fourth pair of legs, but females do not) we tested the following predictions i) males would rely more upon mechanical defenses than females and ii) females would rely more on other kinds of defenses, such as chemical and passive defenses than males. We found that males performed mechanical retaliation more often than females and females performed thanatosis more often than males. We did not find any sexual difference with respect to chemical defense. In the third chapter we tested if there are differences in the frequency of thanatosis performed by females of M. cuspidatus between the periods of night and day. By performing thanatosis more often during the day, females of M. cuspidatus might be able to avoid being detected by visual predators. As expected, females performed thanatosis more often during the day than at night. Taken together, our results contribute to the understanding of the evolution of defensive strategies, as well as provide results that might be a first step to address new questions about behavioral consistency in harvestmen and their implications in this group (AU)

• FAPESP's process: 14/19191-3 - Natural history, behavioral syndromes and learning in Charinus asturius (Arachnida: Amblypygi: Charinidae)
• Grantee: Júlio do Monte Gonzalez de Segovia
• Support Opportunities: Scholarships in Brazil - Doctorate