Estrutura da teia e estratégias de defesa de Wixia abdominalis O. Pickard-Cambridge, 1882 (Araneae, Araneidae)

Abstract

Foraging activities and defense are the most fundamental aspects involved with survivorship. Thus, morphology, physiology and behavior of an animal reflect how trade-offs between foraging and defense are solved in its evolution, through the influence prey types and predators involved in its interactions. Orb-web weaver spiders are good models to assess both aspects. They are predators and usually are included in diet of other animals. The orb-web allow the evaluation on the solution of trade-offs during foraging. Its components exert different functions and their arrangement influences the size and kinds of prey captured. However, the architectural functionality of orb-webs is not completely understood. Thus, several hypotheses, some of them conflicting with each other, were proposed to explain the differential investment in distict parts of the web and other aspects of its design. In chapter 1, using orb-webs of Wixia abdominalis (Araneae, Araneidae) as a model, we assessed which of the hypotheses previously presented in literature better explain the observed pattern and how incidental mechanisms interfere in this pattern. Our analyzes indicate that multiple hypotheses are necessary to explain the orb-web architecture. Some, however, were not corroborated by our data on W. abdominalis. Orb-web weaver spiders are usually prey of visually oriented predators, such as wasps and birds. Different kinds of passive defenses, such as crypsis and masquerade, have been proposed to be the result of selective pressures by these predators. However, these assumptions are still subjective, since visual systems of predators, such as wasps and birds, are different from that of human and are different between them. Therefore, the function of masquerade is directed to specific kinds of observers, which are the sources of selective pressure. In chapter 2, by means of visual models, we assessed whether indeed the color of W. abdominalis and its microhabitat provides the masquerade against its potential main predators, wasps and birds. Our tests corroborate that indeed there is masquerade when W. abdominalisis seen in its microhabitat by visual systems of hymenopterans and birds. We also discussed the potential influence of both kinds of predators over the evolution of this kind of defense.