Thesis (M.S.)--Villanova University, 2009. / Biology Dept. Includes bibliographical references.

Thesis (M.S.)--Villanova University, 2009. / Biology Dept. Includes bibliographical references.

Thesis (Ph. D.)--University of Canterbury, 2007. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Orientador: João Vasconcellos Neto / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-04T21:51:53Z (GMT). No. of bitstreams: 1 Romero_GustavoQuevedo_D.pdf: 5256133 bytes, checksum: 5c71ea8abd971f76045303bc89c57a3b (MD5) Previous issue date: 2005 / Resumo: O entendimento das interações entre artrópodes e plantas tem crescido consideravelmente nos últimos poucos anos. Embora as aranhas estejam entre os grupos de artrópodes mais abundantes e constituam as principais guildas de predadores sobre a vegetação, poucos estudos envolvendo aranhas e plantas foram desenvolvidos. Aqui, reportamos um conjunto de informações mostrando que algumas espécies de salticídeos são estritamente associadas com Bromeliaceae em várias fitofisionomias sul-americanas, incluindo cerrados, florestas semidecíduas e sazonais, vegetação de dunas costeiras, restingas, afloramentos rochosos, florestas de altitude, chacos e florestas ombrófilas densas, em várias localidades do Brasil, Paraguai, Bolívia e Argentina. Enquanto algumas espécies de aranhas foram especialistas, ocorrendo quase exclusivamente em uma única espécie de planta hospedeira (e.g., Psecas chapoda sobre Bromelia balansae), outras foram generalistas e habitaram até 7-8 espécies de bromélias. Geralmente, as aranhas habitaram e selecionaram as bromélias maiores e/ou aquelas com arquitetura natural (e.g., simulação de inflorescência ou inclusão de folhas secas no centro da roseta). Portanto, as aranhas podem avaliar, em detalhes finos, o estado físico dos seus microhabitats. Bromélias podem muitas vezes fornecer microhabitats apropriados específicos para salticídeos. Suas folhas formam uma arquitetura tridimensional complexa (roseta), que pode ser usada por adultos e imaturos como abrigo contra predadores ou condições climáticas severas, como sítios de forrageamento, acasalamento e de oviposição, e como berçários para as recém emergidas das ootecas. Em troca, as aranhas contribuíram para a nutrição das bromélias. Usando métodos isotópicos (15N), nós verificamos que P. chapoda contribuiu com até 40% do N total de B. balansae no campo. Entretanto, os efeitos benéficos das aranhas foram enfraquecidos onde estas ocorreram em baixa abundância, e a condicionalidade foi gerada pela variação especial na densidade de aranhas / Abstract: The understanding of the interactions between arthropods and plants has grown considerably in the last few years. Although the spiders are among the most abundant arthropod group and compose the main predator guild on vegetation, there exist very few studies involving spiders and plants. Here, we report information showing that some salticid species are strictly associated with the Bromeliaceae in several South American phytophysiognomies, including cerrados (savanna-like vegetation), semideciduous and seasonal forests, coastal sand dune vegetation, restingas, inselbergs, highland forests, chacos and rain forests in several localities of Brazil, Paraguay, Bolivia and Argentina. While some species are specialists, occurring almost exclusively on a single host plant species (e.g., Psecas chapoda on Bromelia balansae), others are generalists and inhabit up to 7-8 bromeliad species. Generally, the spiders inhabited the larger bromeliads and/or those with natural architecture (e.g., simulation of inflorescence or inclusion of dry leaves in the center of the rosette). Therefore, the spiders seem to evaluate, in fine detail, the physical state of their microhabitats. Bromeliads may often provide specifically suitable microhabitats for jumping spiders. Their leaves form a complex tri-dimensional architecture (rosette), which can be used by adults and immature as shelter against predators or harsh climatic conditions, as foraging, mating and laying egg sites, and as nursery for spiderlings. In exchange, the spiders contributed to bromeliad nutrition. By using stable isotope methods (15N), we found that P. chapoda contributed with up to 40% of the total nitrogen of B. balansae in the field. However, the beneficial effects of the spiders were weakened where they occurred in low abundance, and conditionality was generated by spatial variation in spider density / Doutorado / Ecologia / Doutor em Ecologia

Crypsis can be an important mechanism of predator avoidance for organisms. However, many species exhibit sexual dichromatism, in which the males possess a suite of colorations in order to attract female attention. The resulting differences in crypsis between the males and females can provide insight into the relative strengths of the sexually and naturally selective forces shaping the coloration of the organism, as well as clues regarding potential sensory biases of the selecting sex. In this study, I examine variation in the coloration of four Pacific Northwest populations of the sexually dimorphic and dichromatic polygynous species of jumping spider Habronattus oregonensis and compare the coloration of different body regions of the spiders to their habitats. I also investigate differences in relative size of a male sexual ornament, the enlarged first leg tibia. Field work for this study was conducted in June and July of 2009. The three main foci of this study are 1) to compare the degree of color matching of females and their habitat to the degree of color matching of males and their habitat, evaluating whether sexual selection on males has reduced their degree of crypsis relative to that of females, 2) if there is indeed a difference in crypsis between the sexes, to gauge whether there are similar divergences from crypsis among the populations - both in the quantitative amount of divergences as well as the colorimetric direction of such divergences, and 3) whether there is any variation in sexual ornament size among populations. Male first leg tibia size is a sexual character that is presumably not influenced by habitat coloration; differences in male tibia allometry among populations would provide supporting evidence for the hypothesis that sexual selection is indeed maintaining phenotypic differences among the populations, regardless of habitat location and color. I found a high degree of conformity of hue and chroma between male and female spiders and their habitats, with three notable exceptions. The most extreme difference in coloration between spider and habitat was that of the Gorge and Siskiyou population male anteriors. The anteriors had proportionally less green and more ultraviolet reflectance than their habitat. Second, the Mt. Hood and Tillamook population male abdomens diverged from their habitat in a similar, although less pronounced manner to that of the Gorge and Siskiyou population male anteriors: they had proportionally less green and more UV reflectance. Third, female abdomens of all populations were highly variable in chroma, despite having hues that generally matched their habitat. Tibia area relative to body size of Gorge and Siskiyou population males was significantly smaller than that of Mt. Hood and Tillamook population males. The lower level of background hue matching among males compared to females implies that sexual selection has directly conflicted with natural selection, resulting in impaired crypsis. While the reduced crypsis of the Gorge and Siskiyou population males is centered on their anterior (the primary body region presented to the females during courtship), the deviations from crypsis in the Mt. Hood and Tillamook population males are highest on their abdomen, although the degree of contrast is lower than that of the Gorge and Siskiyou population anteriors. These differences in coloration between the Mt. Hood and Tillamook population male abdomens and their habitats are in the same colorimetric direction as those of the Gorge and Siskiyou population anteriors and their habitat; this may indicate a sensory bias of the females, conserved in all four populations, selecting for male reflectance with a higher UV to green ratio. The fact that Mt. Hood and Tillamook population male abdomens have a more modest reduction in background matching compared to Gorge and Siskiyou population male anteriors may be due to the search methods of flying predators (e.g., spider wasps); the dorsum would presumably be more conspicuous to predators than the anterior, and would thus be subject to more intense selection for crypsis despite sexual selection to the contrary. The variability of abdomen coloration of females of both morphs may indicate that selection for crypsis is less strong among females than among males. One possible reason for this would be if females spent less time in the exposed courtship habitat than males, a conclusion implied by a highly male-skewed sex ratio encountered during field collections. Like the differences in coloration between different males of different populations, the significant differences in male tibia size also imply variability in the intensity of sexual selection. Relative importance of male coloration and tibia size may be weighted differently among populations, operating under similar constraints on reductions in survival accrued by developing these characters. The high degree of variation found among the populations implies that there is a degree of reproductive isolation among the chromatically and morphologically dissimilar populations. However, the similarity of the environments in which the populations existed, the close geographic proximity of some of the dissimilar populations, and the lack of any substantial geographic boundaries between the populations imply that this isolation is not maintained through extrinsic factors. Rather, it would seem that the interpopulational diversity is maintained by sexual selection. However, evidence from morphology and coloration suggest that the generation of this diversity is not evolving exclusively under sexual selection pressure, but rather is constrained to a degree by natural selection.

The different ways that animals extract and analyze visual information from their environment is of interest to sensory ecologists. Jumping spiders, well-known for visually guided mating and hunting behavior, are an interesting model for the study of visual attention because they quickly and efficiently integrate information from eight eyes with a small brain. Stimuli in front of the spider are examined by two functionally and morphologically distinct pairs of forward-facing eyes. The principal eyes discern fine details and have small retinas and thus a small visual field. However, their position at the back of moveable tubes within the cephalothorax expands this visual field. The anterolateral eyes, one of the three pairs of secondary eyes, have lower spatial acuity and a larger visual field that overlaps with that of the principal eyes. They act as motion detectors, directing the principal eyes to objects appearing in their visual field. In Chapter 1, using a salticid-specific eyetracker, I explore how characteristics of a stimulus influence whether the secondary eyes redirect the gaze of the principal eyes from a principal stimulus to a new stimulus appearing in the visual field. I found that spiders suppressed redirection of the principal eyes when engaged by a salient stimulus, and redirected to moving peripheral stimuli more frequently than to stationary peripheral stimuli. The principal eyes are also known to engage in a complex behavior called “scanning,” involving both dorsoventral and rotational movement. One hypothesis regarding scanning’s function is that it helps spiders identify important lines and angles in stimuli. However, scanning routines are not well understood. In Chapter 2, I measured scanning behaviors when spiders were watching quickly moving versus still or slowly moving images. I found that spiders spent more time overall looking at still or slowly moving images, and that stimulus speed does not appear to affect rotational movement of the retinas. Overall, I conclude that motion in an appearing stimulus elicits the attention of the principal eyes, but it remains unclear how and whether scanning functions in the extraction of detail from moving stimuli.

Jan Raška: Reactions of the jumping spider Evarcha arcuata to aposematic true bugs Abstract: This paper studies the effect of qualities of a prey on predatory behaviour of Evarcha arcuata (Araneae: Salticidae). Naturally coloured aposematic larveae of Pyrrhocoris apterus have been compared to two types of prey: 1) to identically coloured but in defensive secretion different larvae of Scantius aegyptius, and 2) differently coloured larvae of white mutants of P. apterus. The defensive secretion of S. aegyptius has been found less effective in the first interaction with predator than that of P. apterus, however, after several trials the difference of reactions of the spider has not been noticeable. When changed the species of prey, E. arcuata has symmetrically and considerably generalised between the two species. Significant difference has been established in memory test - while P. apterus has been avoided even after one day, S. aegyptius has been attacked as thought the spiders were naive. The learning sequence has been similar in both colour forms of P. apterus; the generalisation of the two colours has been symetrical as well. Both colour forms succeeded in memory test (e.g. spiders have proven difference in comparison with the naive ones), however, white mutants have been successfully attacked...

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