In this thesis, the succession of spider assemblages in five limestone quarries of different ages in Bohemian Karst has been studied. The main goal of this paper was studying changes of spider assemblages along successional gradient. Furthermore, different environmental factors affecting spider communities and also assemblages of spider communites in different terraces of the quarry have been studied. Standardized methods (pitfall traps, hanging desk traps, shifting leaf litter, sweeping of herb vegetation, and beating shrubs) have been used for recording the highest possible richness of spiders. The results showed that position of the terraces and the age of the quarry do not affect species richness and density. Species density of epigeic spiders increased significantly with number of the plant species. The results showed that spiders do not have their own succession, but they are following vegetational succession. The environmental factors which affect species composition of spiders from the pitfall traps are positon of terraces, shading and moss cover. Although the age of the quarry was insignificant for spiders from pitfall traps, every quarry was inhabited by different spider communities. Shrubs and tree-dwelling spiders showed correlations with the age of the quarry. Data recorded from...

Circadian rhythms are ubiquitous among eukaryotic organisms and have evolved several times independently which strongly suggests that the presence of a biological clock is adaptive. A prevailing, though relatively untested, hypothesis is that having an internal clock allows organisms to anticipate daily changes in the environment and physiologically and/or behaviorally prepare for them. Locomotor activity is commonly interpreted as an indicator of neurological arousal, and, thus, is a useful indicator in studies of circadian rhythm. We have observed that some species of spiders exhibit a tight and predictable band of activity at a particular time of day, while in other species activity is more spread out through the day. Such patterns tend to continue, or are exaggerated, under conditions of constant darkness. We hypothesize that these predators with tight activity bands are ‘circadian specialists’ using their internal clocks to focus their attention in the narrow temporal window when prey are available to them. On the other hand, the species with broader activity bands are employing a ‘circadian generalist’ strategy, and are able to be more opportunistic with temporally unpredictable prey. Some support of this hypothesis comes from the observation that species that forage only at night tend to have tighter bands of locomotor activity than those species which forage continuously day and night. In this study we present a simulation model that supports this idea that a tight distribution of neurological alertness is advantageous when prey is predictable, but an evenly clumped distribution of alertness is favored when prey are unpredictable. We also tested the abilities of four nocturnal spider species to opportunistically respond to an unexpected period of darkness. Consistent with our hypothesis, we found that in the predicted circadian specialist species activity could not be elicited with unexpected darkness at any time of day, while the predicted circadian generalist showed activity in mid and late day. In two species intermediate on the specialist-generalist scale we only elicited activity in late day. This work represents a test of a novel hypothesis regarding the adaptiveness of circadian rhythms.

Changes to vegetation architecture within a natural habitat can have profound impacts upon ecological community function, but the relative influence of vegetation architecture itself and potential indirect influences of associated food resources are often difficult to disentangle. I present the results of a three-year study designed to address the community level impacts of changes in big sagebrush (Artemisia tridentata) architecture and associated prey availability upon the ground-dwelling arthropod community. Three experimental sagebrush architecture treatments (low, intermediate, and high foliage density) and two levels of prey insect availability treatment (natural and baited/increased prey availability) were imposed in a sage-steppe ecosystem. The ground-dwelling spider (top predators) and insect (prey) response to all combinations of the six treatments were assessed through abundances in pitfall traps. Chapter 2 demonstrates that changes in a single shrub’s architecture did not markedly impact prey arthropod availability on the ground, though an overall increase in arthropod abundance was detected within baited shrubs. This indicates changes to vegetation architecture do not impact prey insect availability for ground-dwelling spiders. Thus, changes in shrub architecture and not the associated prey base directly alter the ground-dwelling spider community. Chapter 3 shows that architectural manipulation of a single sagebrush directly influences the ability of certain ground-dwelling spider guilds to persist beneath the shrub. Data within Chapters 2 and 3 support the conclusion that vegetation architecture directly affects ground-dwelling spider community structure and composition. Finally, Chapter 4 explores how the relative impacts of vegetation architecture and prey availability upon ecological communities can shift depending upon the spatial context in which the manipulations take place, given the differences in mobility of species within the grounddwelling spider and insect prey communities. Within this study, Diurnal and Nocturnal Wanderers responded to manipulations in prey availability at a larger spatial context (patches of 15 shrubs) while more stationary Trappers and Ambushers did not. Through simultaneous manipulation of vegetation architecture (Artemisia tridentata, big sagebrush) and associated insect prey base in different spatial contexts, this dissertation demonstrates that vegetation architecture directly affects ground-dwelling spider community organization at the species and guild levels of diversity. Shifts in spider (predator) functional diversity can ultimately impact arthropod decomposer and herbivore populations, influencing fundamental ecosystem processes such as decomposition and productivity.

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.

Spider dragline silk is a biomaterial with outstanding material properties, possessing high-tensile strength and toughness. In nature, dragline silk serves a central role during spider locomotion and web construction. Today, scientists are racing to elucidate the molecular machinery governing silk extrusion, attempting to translate this knowledge into a mimicry process in the laboratory to create synthetic fibers for a wide range of different applications. During extrusion, it has been established that biochemical and mechanical forces govern spidroin folding, aggregation, and assembly. In black widow spiders, at least 7 different proteins have been identified as constituents of dragline silk fibers. These represent the major ampullate spidroins, MaSp1 and MaSp2, and several low-molecular weight cysteine-rich protein (CRP) family members that include CRP1, CRP2, and CRP4. Molecular modeling studies have predicted that CRPs contain a cystine slipknot motif. To advance scientific knowledge regarding CRP function, we expressed and purified recombinant CRP1 and CRP4 from bacteria and investigated their secondary structure using circular dichroism (CD) under different chemical and physical conditions. We demonstrate by far-UV CD spectroscopy that CRP1 and CRP4 contain similar secondary structural characteristics in solution, displaying substantial amounts of random coil conformation, followed by lower levels of beta sheet, alpha helical and beta-turn structure. Additionally, we show that native structures of CRP1 and CRP4 have high thermal stability and are resistant to conformational changes under acidic pH conditions. Taken together, the chemical and thermal stability of CRP1 and CRP4 are experimentally consistent with biochemical properties of cystine slipknot proteins.

Little is actually known about the transcriptional regulation of spider silk as most studies have focused on the material properties of silks. We isolated and mapped the TuSp1 core promoter from the black widow spider, Latrodectus hesperus. Using a genomic DNA walking strategy, we have isolated an upstream segment (581 bp) of genomic DNA containing the promoter as well as the first exon of the TuSp1 gene. This upstream regulatory element was able to initiate transcription in insect cells when placed upstream the promoterless firefly luciferase reporter gene. Initiation of transcription was orientation dependent, as insertion of this upstream regulatory module in the reverse orientation led to inefficient transcriptional initiation. Only 170 bp of upstream sequence was required for strong transcriptional initiation, showing that core promoter resides within the first 170 bp of upstream 5' -flanking DNA. We also demonstrate the bHLH factor SGSF1 can repress gene transcription of the TuSp1 core promoter, implying SGSF I might participate in the transcriptional regulation of the TuSp1 gene in vivo.

While development in flies is well understood, pattem formation and the evolution thereof in arachnids have yet to be clarified. Flies and other metazoans primarily use two families of genes called Hox genes and Pax genes to regulate embryogenesis. Because of the high evolutionary conservation of Hox and Pax proteins, I hypothesize that arachnids also use this system to organize their body pattern. To enable studies of the Westem black widow spider, Latrodectus hesperus, an embryonic eDNA library and a fixation protocol were developed for L. hesperus embryos. The generation of these tools will allow comprehensive analysis of black widow spider development and give insight into whether, and how, spiders use Hox and Pax genes to organize their bodies. Finally, it will provide a more thorough understanding of how different developmental mechanisms have evolved and ultimately how changes in gene expression can lead to a change in overall body plan.

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