Navegando por Palavras-chave "Arachnida"

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    Defences of a Neotropical harvestman against different levels of threat by the recluse spider
    (Brill Academic Publishers, 2015-01-01) Segovia, Julio M. G.; Del-Claro, Kleber; Willemart, Rodrigo Hirata [UNIFESP]; Inst Biol; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP)
    The threat sensitive hypothesis predicts that animals modulate the defensive behaviour with the level of threat. Therefore, responses to predator cues may differ from responses to the actual predator in close range. Also, in high threat situations, prey would be expected to use their most dangerous defences. the recluse spider Loxosceles gaucho (Araneae, Sicariidae) is known to prey upon well defended harvestmen such as the laniatorid Mischonyx cuspidatus (Opiliones, Gonyleptidae), which has been reported to use tanathosis, chemical defences, pinching with sharp apophyses on legs, chelicerae and pedipalps. Because of harvestmen's dependence on chemical stimuli, we tested if M. cuspidatus would change its locomotory behaviour in the presence of chemicals of the recluse spider (low threat situation: spider vs blank vs chemical control; one at a time). Subsequently, we tested harvestmen behaviour in the presence of the spider in close range, a high-threat situation. Finally, we looked at the survival rate of spiders after being pierced by sharp apophyses that M. cuspidatus have on legs IV. the harvestmen only showed defensive behaviours in the high threat situation. Surprisingly, their mostly known defensive behaviours (chemical defence, tanathosis, pinching with chelicerae and pedipalps) were not seen even in the high threat situation. This is the first evidence that these behaviours are not used against a natural predator that has an almost 80% predation success when attacking harvestmen. Pinching with the sharp legs IV apophyses may perforate but do not kill the spiders. We highlight the importance of the traditional descriptive approach with natural predators to understand the specificities of defensive behaviours against different types of predator.
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    Delicate fangs, smart killing: the predation strategy of the recluse spider
    (Elsevier B.V., 2015-03-01) Segovia, Julio M. G.; Del-Claro, Kleber; Willemart, Rodrigo Hirata [UNIFESP]; Inst Biol; Universidade de São Paulo (USP); Universidade Federal de São Paulo (UNIFESP)
    Prey consumption depends on the predator's ability to locate, capture and handle prey. We investigated these three steps in interactions between the delicate-bodied recluse spider Loxosceles gaucho (Araneae) and a heavy-bodied and armoured harvestman, Mischonyx cuspidatus (Opiliones). Although previous research suggested that the hard integument of such harvestmen protects them from being preyed upon by spiders larger than Loxosceles, indirect evidence suggested that Loxosceles spiders can subdue these prey. in the present study, we tested the following three hypotheses with regard to L. gaucho: (1) spiders use chemical cues left by prey to select foraging sites; (2) vibratory cues of prey are essential information in the predatory process; and (3) the spider's web sheet allows adequate handling of prey so vulnerable body regions of the prey can be bitten. To understand how a delicate predator can overcome the defences of a heavy-bodied and well-defended prey, we also quantitatively described the spider's behaviour. To test hypothesis 1, we compared the time spent in areas with harvestmen, crickets and no cues. for hypothesis 2, we compared latency to bite and number of bites in the presence or absence of vibratory information, and for hypothesis 3, we compared latency to detect prey, latency to capture prey and predation success. All three hypotheses were rejected. Loxosceles gaucho seems to be exceptional among spiders by not needing its web, indirect prey chemical cues, or prey's substrate borne vibrations to hunt the tested prey. What enables L. gaucho to prey upon M. cuspidatus is its unique hunting strategy, compared to previously studied spiders: it touches the prey with its tarsi possibly to locate weak parts of the prey's body, such as joints and distal parts of the legs, then it delivers several bites to these vulnerable areas. Our study is the first to document and describe how recluse spiders overcome the defences of an armoured harvestman. (C) 2015 the Association for the Study of Animal Behaviour. Published by Elsevier B.V. All rights reserved.
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    Do sexually dimorphic glands in the harvestman gryne perlata (arachnida: opiliones) release contact pheromones during mating?
    (Assoc Arquivos Neuro- Psiquiatria, 2016) Dias, Jessica M.; Willemart, Rodrigo H. [UNIFESP]
    There are records of glands that produce sexual pheromones that are released into the environment or applied directly on sexual partners. Within Opiliones (Arachnida), several harvestmen in the suborder Laniatores have sexually dimorphic glands on legs I and IV, the mode of use of which is recorded only in two species but their function is unknown: while walking, males rub the glands against the substrate or against their body. Here we test an alternative and non-exclusive hypothesis that the glands present on the legs of male Gryne perlata (Cosmetidae) produce contact pheromones used in mating. We predicted that males would touch the females with the gland openings or with other male body parts previously rubbed by these glands. We also predicted that there are chemoreceptors on those parts of the females where males touch them. We analyzed 13 videos of G. perlata mating, a species in which the males have glands on legs I and IV of unknown function. We also analyzed 14 videos of Discocyrtus pectinifemur (Gonyleptidae) mating as a control, a species that lacks these glands. Finally, we looked for chemoreceptors on the legs of female G. perlata using a scanning electron microscope. During copulation, males of both species rubbed the legs of females with their first pair of legs, but not with the regions of these legs where the openings of the glands are. The fourth pair of legs were only used to support the body. Rubbing other body parts of the female by males with their glands was not observed during mating. Setae on the legs of the female did not have tip pores and therefore do not seem to be chemoreceptors. We therefore did not find any evidence that these sexually dimorphic glands in G. perlata release contact pheromones during mating.
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    Proximate factors and potential benefits influencing selection of Psychotria suterella for shelter by the harvestman Jussara spec.
    (Wiley, 2017) Pagoti, Guilherme Ferreira; Gomes Villalba Penaflor, Maria Fernanda; Marabesi, Mauro Alexandre; Simoes Bento, Jose Mauricio; Willemart, Rodrigo Hirata [UNIFESP]
    Harvestmen (Arachnida, Opiliones) are arachnids that rely on chemicals for communication and are particularly dependent on high humidity. The harvestman Jussara spec. (Sclerosomatidae) clearly prefers to rest on the stem and leaves of Psychotria suterella Muell. Arg. (Rubiaceae), a plant having a complex architecture of overlapping branches. So far, few studies have focused on understanding how harvestmen find their host plant and the benefits associated with the selected plant. Here, we investigated cues harvestmen may exploit to find P.suterella and the potential benefits for harvestmen of this interaction. To address how harvestmen find the plant, we tested two non-exclusive hypotheses: harvestmen use chemicals from conspecifics, and/or harvestmen use chemicals from plants. For the first hypothesis, we assessed the number of harvestmen choosing P.suterella with or without chemicals of Jussara spec. on the main stem. We did not find evidence that Jussara spec. uses chemicals from conspecifics to select P.suterella, at least in isolation, without any mechanical stimuli such as stem texture or size. For the second hypothesis, we tested harvestman behavior exposed to volatiles from P.suterella, a non-preferred host plant - Impatiens walleriana Hook.f. (Balsaminaceae) - and a blank treatment, both in a triangular arena and in a Y-tube olfactometer. We also found no evidence that the harvestmen use plant volatiles to find it. We also tested two non-exclusive hypotheses regarding the benefits of selecting P.suterella for harvestmen. The first hypothesis is that P.suterella offers a higher humidity than other plants in the micro-environment surrounding the leaves because of a high leaf transpiration rate. Harvestmen could benefit from this because they rest with the body in contact with the leaf or at less than 5mm from it. We did not find evidence that leaf transpiration rate is important for Jussara spec., as P.suterella did not present high rates compared to other local species. The second hypothesis is that the leaves of P.suterella provide a better shadow than other plants, acting as a sun shade due to its complex architecture with overlapping leaves. We measured light passage through the leaves of P.suterella and three other local species and found that less light passes through the leaves of P.suterella, which therefore provides darker shadow. This potentially provides a favorable micro-climate for harvestmen, which might help to explain the micro-habitat preference of Jussara spec.