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Sensory exploitation in a sit-and-wait predator: Exploring the functions of stabilimenta in the banded garden spider, Argiope trifasciataCROWE, SUSAN ALLISON 28 September 2009 (has links)
Attracting prey by exploiting a visual sensory bias is a common theme in stationary predators across many taxa, particularly for obligate ambush predators, such as orb-weaving spiders, because they construct complex prey traps. Mimicry of UV-reflecting floral-guides has been suggested as the mechanism behind the tendency for spiders and silk web decorations (stabilimenta) to reflect in the UV, to attract pollinators that they then prey upon. Also, many insects are attracted to UV because it most commonly indicates open sky, or a safe flight path. My study focuses on the prey attraction function of stabilimenta, in Argiope trifasciata in eastern Ontario. Decorated webs were no more likely to contain prey than undecorated webs, but for adult spiders, longer stabilimenta were associated with increased likelihood of prey capture. For both adults and juveniles, larger webs were more likely to contain prey in undecorated webs, but for decorated webs, web size was not a predictor of prey presence. I interpret this as evidence for a trade-off between two alternative prey capture strategies: building a web with a large capture area, or building a small web with a stabilimentum. In further support of this trade-off, smaller webs were more likely to contain a stabilimentum, for both juveniles and adults. My data also suggest that close neighbours compete rather than cooperate with each other. Adult webs were spaced farther apart from each other than juvenile webs, more than would be expected based on web diameter difference. For juveniles, webs with a closer neighbour were more likely to be decorated, implying an increased need for prey attraction in the presence of a nearby competitor. For adults, prey was more likely to be found in webs that were more solitary. My results do not support the hypothesis that visually attractive spiders increased prey capture by aggregating. / Thesis (Master, Biology) -- Queen's University, 2009-09-28 10:57:18.156
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O papel da interação com presas e predadores na variação cromática de Gasteracantha cancriformis (Araneidae) / The role of interaction with prey and predators on the chromatic variation of Gasteracantha cancriformis (Araneidae)Gonçalves, Nathalia Ximenes 18 August 2017 (has links)
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Previous issue date: 2017-08-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The sensory drive theory predicts that signals, sensory systems, and signaling behavior should
coevolve. Variation in the sensory systems of prey and predators may explain the diversity of color
signals, such as color polymorphism. The spider Gasteracantha cancriformis (Araneidae)
possesses several conspicuous color morphs. The aim of the present study was to assess whether
the color polymorphism of G. cancriformis may be maintained by pressure from multiple signal
receivers, such as prey and predators with distinct color vision systems. In orb-web spiders, the
prey attraction hypothesis states that conspicuous colors are prey lures that increase spider foraging
success via flower mimicry. However, in highly defended species, conspicuous colors could also
be a warning signal to predators. We used color vision modelling to estimate chromatic and
achromatic contrast of G. cancriformis morphs as perceived by potential prey and predator taxa. To
assess the role of prey, we conducted a prey capture experiment in the field, in which webs were
assigned to four treatments: yellow, red, and black models, or no model. For each treatment, we
counted the number of prey trapped on the webs and the calculated webs damaged area. To assess
the role of predators on the evolution of conspicuous color patterns and polymorphism, we
conducted a second field experiment, allocating yellow, red and black spider models in nylon
threads along the vegetation, and observed the number of attack markings for each of them. Our
results revealed that individual prey and predator taxa perceive the conspicuousness of morphs
differently. Therefore, the multiple prey and multiple predator hypotheses may explain the
evolution of color polymorphism in G. cancriformis. The results of prey capture experiment did
not corroborate the prey attraction hypothesis nor the prey specific adaptation of color
polymorphism. On the predation experiment, we found that black spider models presented more
markings, which indicates that yellow and red models were less preferred, possibly suggesting that
spider coloration may play a role on predator avoidance. Our results, however, do not corroborate
the hypothesis that multiple predators influence polymorphism evolution. Color polymorphism in
this species is possibly a multi-functional attribute, where some morphs benefits from
aposematism, whereas others may alternative fitness advantages. Non-adaptive explanation should
also be considered in future experiments of the evolution and maintenance of color
polymorphisms. / A teoria de “sensory drive” prediz que sinais, sistemas sensoriais e comportamentos de sinalização
devem coevoluir. Variação no sistema sensorial de presas ou predadores pode explicar a
diversidade de colorações existentes e polimorfismos de cores. A aranha de teia orbicular
Gasteracantha cancriformis apresenta padrões de coloração conspícuos e polimorfismo de cor. A
evolução e manutenção de tal variação cromática pode ser influenciada por presas e predadorescom sistemas visuais diferentes, já que um mesmo morfo é percebido distintamente por potenciais
presas e predadores. A coloração conspícua, entretanto, não se assemelha à coloração de flores.
Tampouco influencia na captura de presas, visto que modelos dessa aranhas apresentaram números
similares de presas nas teias. Portanto, ao contrário de outras aranhas de teia orbicular, para as
quais a coloração chamativa é atribuída ao mimetismo floral, para G. cancriformis, esta hipótese
não é corroborada. Os morfos amarelo e vermelho apresentam coloração típica de organismos
aposemáticos e são conspícuos para a visão de uma ave. O morfo vermelho apesar de não ser
conspícuo na visão de vespas, ainda assim poderia estar protegido de predação por camuflagem.
Dessa forma, esses morfos poderiam ser mantidos na população devido à pressão de diferentes
predadores, morfos vermelhos sinalizariam impalatabilidade para aves, enquanto morfos amarelos,
para vespas. Porém, essas diferenças não foram observadas experimentalmente. Em campo,
modelos pretos de aranha apresentaram mais marcas de predação do que modelos amarelos e
vermelhos, também sugerindo que em G. cancriformis a coloração chamativa pode ser um sinal de
advertência para predadores. Porém, a multiplicidade de predadores por si só não explica a
variação cromática em populações dessa espécie de aranha. Consequentemente, o polimorfismo de
cor em G. cancriformis pode ser uma característica multi-funcional, onde morfos não aposemáticos
seriam mantidos nas populações devido a outras funções adaptativas, como camuflagem ou
termorregulação.
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