Elucidating the ecological determinants of community structure and how they vary spatially has a long history in ecology, but there still is no consensus on the mechanisms behind diversity patterns. The primary objective of this dissertation was to focus on spider assemblages to investigate how the fine-scale habitat associations of organisms may drive their community composition at larger scales. Research was conducted in the Bear River Mountains, Utah, in an attempt to elucidate the potential role of species-microhabitat associations in driving three well-known patterns of community composition that have typically been investigated at broad scales: 1) elevation gradients of species diversity, 2) the response of species assemblages to neighboring habitat structure and 3) community composition at the edges of habitat patches. Slope aspect was a significant predictor of spider density and species richness when communities were compared at the same elevation, suggesting that fine-scale topographic variables may play an important role in shaping elevational patterns of species composition. Cursorial spider composition was strongly linked to site temperature only, whereas differences across web spider assemblages significantly increased with dissimilarities in woody plant cover and temperature. The study on the effects of neighboring habitat structure revealed markedly reduced cursorial spider densities in shrubs without surrounding structure, and more cursorial species in control shrubs, whereas web spiders lacked any significant response to treatments. These contrasting responses indicate that data should be collected at larger spatial extents for mobile species, and that mobility may mediate the outcome of surrounding habitat modifications on the local composition of communities. In the last study, I focused on communities in which the edge-dwelling spiders Theridion and Dictyna strongly differed in terms of concealment and substrate generalization and found that microhabitat choice may affect the sensitivity of species to habitat geometry, a characteristic associated with habitat fragmentation. This work suggests that a better understanding of the links between the biological traits of species and their fine-scale environmental requirements may help uncover the mechanisms behind spatial patterns of community composition at larger scales.

To improve measurement reliability and repeatability and resolve the orders of magnitude discrepancy between the two different measurements (via reduced model transient electrothermal and lock-in IR thermography), this dissertation details the development of three complementary methods to accurately measure the thermal properties of the natural and synthetic Nephila (N.) clavipes spider dragline fibers. The thermal conductivity and diffusivity of the dragline silk of the N. clavipes spider has been characterized by one research group to be 151-416 W m−1 K −1 and 6.4-12.3 ×10−5 m2 s −1 , respectively, for samples with low to high strains (zero to 19.7%). Thermal diffusivity of the dragline silk of a different spider species, Araneus diadematus, has been determined by another research group as 2 ×10−7 m2 s −1 for un-stretched silk. This dissertation seeks to resolve this discrepancy by three complementary methods. The methods detailed are the transient electrothermal technique (in both reduced and full model versions), the 3ω method (for both current and voltage sources), and the non-contact, photothermal, quantum-dot spectral shape-based fluorescence thermometry method. These methods were also validated with electrically conductive and non-conductive fibers. The resulting thermal conductivity of the dragline silk is 1.2 W m−1 K −1 , the thermal diffusivity is 6 ×10−7 m2 s −1 , and the volumetric heat capacity is 2000 kJ m−3 K −1 , with an uncertainty of about 12% for each property

Spider silk has received significant attention due to its fascinating mechanical properties. Given the solitary and cannibalistic behavior of spiders, spider silk farming is impractical. Unlike spiders, silkworms are capable of producing large quantities of a fibrous product in a manner mimetic to spiders, and there already exists an industry to process cocoons into threads and textiles for many applications. The combination of silk farming (sericulture), a millennia old practice, and modern advancements in genetic engineering has given rise to an innovative biomaterial inspired by nature; transgenic silkworm silk. This project focuses on the creation of chimeric silkworm-spider silk fibers through the genetic modification of silkworms. Advanced genetic engineering techniques were used to introduce the minor ampullate spider silk (MiSp) genes into the silkworm genome. A subset of these transgenic silkworms was cross-bred with other transgenic silkworms containing the same spider silk gene in a different section of the silkworm genome to create hybrid, dual-transgenic silkworms. The transgenic silk samples showed increased mechanical properties compared to native silkworm fibers, with the strongest fibers approaching or surpassing the mechanical properties of native spider silk. The transgenic silk retained the elasticity of the native silkworm silk and gained the strength of the spider silk. Ultimately, genetic engineering opens the door to mass produce synthetic spider silk in an established organism and industry, and the results of this project demonstrate that the properties of silkworm silk can be predictably altered through this technology.

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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.

Spiders are capable of producing a variety of silk types, each with their own unique protein composition and function. Dragline silk in particular, has been of great interest due to its high tensile strength and extensibility. In the past, synthetically produced dragline fibers have not been able to match the superior properties of natural silk. A recent discovery in the western black widow spider, Latrodectus hesperus, might be the missing link between the current state of synthetic silks and naturally produced fibers. Our research is centered around the discovery a new family of five low-molecular-weight cysteine-rich proteins (CRPs) and their potential function within dragline silk. This study focuses on the characterization of recombinantly expressed CRP1, CRP2, and CRP4. Through structural analysis using circular dichroism, it has been determined that the CRP family members have mostly alpha-helical secondary structure and exhibit small differences in their ability to maintain their structure in the presence of changing environmental conditions. The study also covers the effects of temperature and pH on the folding and unfolding of the CRPs. It appears that pH is the dominant influence on protein unfolding within the major ampullate gland.

PART I The basic helix-loop-helix (bHLH) family of transcription factors are involved in a variety of developmental processes. MyoR is the mouse homologue of the human transcription factor ABF-1 . MyoR is classified as a class II basic-helix-loop-helix transcription factor. In order to better understand the relationship between MyoR and muscle cell differentiation, we analyzed the temporal expression at both the mRNA and protein level. Unlike previous studies, we have utilized reverse transcriptase quantitative PCR to analyze mRNA expression. This allows quantitative analysis of MyoR mRNA levels during muscle cell differentiation. We have also analyzed MyoR expression at the protein level. Our studies suggest that the temporal expression of MyoR at the mRNA level is similar to the expression profile seen at the protein level. To ascertain differences in the MyoR DNA-binding activity during myogenesis we performed EMSA. Results suggest that changes in MyoR expression fail to account for differences in the DNAbinding complexes to an E-box site. Part II Members of the basic helix-loop-helix (bHLH) family are required for a number of different developmental pathways, including lymphopoiesis, myogenesis, neurogenesis and sex determination. Screening a eDNA library prepared from silk-producing glands of the black widow spider, we have identified a new bHLH transcription factor named BW6. Within the bHLH region, BW6 shows considerable conservation with other HLH proteins, including Drosophila melanogaster achaete and scute, as well as three HLH proteins identified by gene prediction programs. The expression pattern of bw6 is restricted to a subset of silk producing glands, which includes the tubuliform and major ampullate glands. BW6 is capable of binding an E-box element as a heterodimer with E2A, but was unable to bind this motif as a homodimer. BW6 is also capable of inhibiting the transactivation of rE47 in mammalian cells. BW6 represents the first example of a silk-gland-restricted bHLH protein, and its expression pattern suggests that BW6 may play a role in regulating differentiation of cells in the spider that control silk gland formation or egg case silk gene expression.

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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