The Anatomical Distribution Patterns, Physiological Effects, and Quantification of Biogenic Amines in the Central Nervous Systems of Araneae and Scorpiones (Arthropoda: Chelicerata)

University of Minnesota Ph.D. dissertation. August 2019. Major: Entomology. Advisor: Karen Mesce. 1 computer file (PDF); xviii, 268 pages.The arthropod subphylum Chelicerata is one of the most diverse groups of organisms on the planet, and yet relatively little is known about the structural and functional organization of chelicerate central nervous systems (CNSs). To address this knowledge gap, I conducted a comparative study of biogenic amines in the CNSs of three representative chelicerates: the wolf spider Hogna lenta (Araneae: Lycosidae), the jumping spider Phidippus regius (Araneae: Salticidae), and the bark scorpion Centruroides sculpturatus (Scorpiones: Buthidae). In H. lenta and P. regius, I mapped the anatomical distribution of catecholaminergic neurons (i.e., those that produce dopamine [DA] or norepineprhine [NE]) in the CNS, using an antiserum against tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis. TH immunoreactivity was detected throughout the spider CNS, including in the visual system, the arcuate body (a site of sensorimotor integration), and the neuromeres of the appendages and opisthosoma, thus suggesting that catecholamines play vital roles in many different behaviors and other physiological processes in spiders. Using similar immunocytochemical methods, I also described the distribution of catecholaminergic neurons in the ventral nerve cord (VNC) of C. sculpturatus, as well as neurons that contain octopamine (OA) and serotonin (5-hydroxytryptamine, 5-HT). Of particular note in the scorpion were clusters of large efferent TH-ir neurons, which exited the CNS to directly innervate the tissues of the book lungs, implying a role for catecholaminergic modulation of respiratory functions. These studies include the first description of catecholamines in any chelicerate taxon, and provide a much-needed foundation upon which future functional studies of biogenic amines in chelicerates can be based. Additionally, I utilized a combination of immunocytochemistry, quantitative chemistry, electrophysiology, and bioinformatics techniques to examine the possibility that NE is an endogenous signaling molecule in chelicerates, despite the widespread notion that invertebrates lack NE. Using ultra-performance liquid chromatography and mass spectrometry, I detected non-trace amounts of NE in the CNSs of both C. sculpturatus and H. lenta. Endogenous NE was localized to cells of the supraneural lymphoid glands in the scorpion, which implies a previously unrecognized secretory role for these structures. NE was also shown to elicit robust patterned electrophysiological activity in the terminal nerves of the scorpion, which was distinct from the patterns produced by other amines. Finally, I identified genes for distinct NE, OA, and DA receptors in the C. sculpturatus genome. Taken together, my results support the idea that NE is an endogenous and physiologically active modulator in scorpions, and possibly in the Chelicerata more broadly, thus challenging the idea that adgrenergic signaling is exclusive to the vertebrates. The implications of these findings are discussed in relation to the evolution of aminergic systems within the Arthropoda and the Bilateria as a whole

An examination of the differential production of silk by juvenile male and female Aposthonia ceylonica (Enderlein, 1912) (Embiidina: Oligotomidae)

Members of the elusive insect order Embiidina are known for their prolific use of silk, and are unusual among insects in that silk is produced by both sexes and all life stages. However, the relative costs of silk spinning might vary considerably between the sexes, as male embiids do not feed as adults and are thus expected to be more resource-limited than females, which feed continuously throughout their lifetimes. Previous research on this group has also shown that the tarsal silk glands of male embiids contain significantly larger silk reservoirs than those of females, and it has been suggested that juvenile males may use these enlarged reservoirs to store silk proteins for use during adulthood, when the amount of energy available for silk production is low. The purpose of this study was to evaluate the plausibility of these conclusions by comparing the silk spinning behaviors of immature male and female embiids in the Indian species Aposthonia ceylonica (Enderlein, 1912) (Embiidina: Oligotomidae). Since this species is gregarious, spinning was also examined in a group context in order to test the hypothesis that males can adjust the amount of silk production in response to group composition, as they may be expected to conserve their own silk in the presence of spinning females. The quantity of silk produced and the amount of time spent spinning were measured over 24 hours for solitary late instar male and female nymphs, as well as for nymphs in single sex and mixed sex groups. The results of this study suggest that juvenile males do produce significantly less silk than juvenile females, but no significant differences were found between groups and solitary individuals or between single sex and mixed sex groups. These findings corroborate the suggestion that males store silk as juveniles, which is likely a strategy to compensate for limited energy availability during adulthood. However, the data do not provide any evidence for social contextdependent silk spinning in the Embiidina. This study is among the first to address these questions in this little-studied insect order, but further research which incorporates more species of embiids as well as field observations is necessary to fully assess sex-related differences in silk production

Preferential prey sharing among kin not found in the social huntsman spider, Delena cancerides (Araneae: Sparassidae)

Although the benefits of group foraging are important for evolution of sociality in spiders, the factors that influence group-level benefits of prey sharing in social spiders are still poorly understood. In the unusual transitional social spider Delena cancerides Walckenaer 1837 (Sparassidae), prey sharing almost certainly occurs occasionally among non-kin in the wild, and so we tested the effects of kin relationships and familiarity on the amount of prey consumed in this species. To determine whether the amount of prey sharing increased with relatedness or with familiarity, we fed treatment groups containing spiderlings of varying relatedness and familiarity a single prey item and measured the amount of weight gained by sharing groups. We found no effect of relatedness or familiarity on the amount of prey consumed by prey-sharing groups of D. cancerides. Increased duration of sharing, number and age of the spiders involved, and size of the prey item all increased the amount of prey consumed. The benefits of prey sharing in this species likely overwhelm any possible inclusive fitness benefits derived from kin discrimination in this highly outbred social spider. Hence, we reject the hypothesis that groups of kin consumed proportionately larger amounts of prey biomass than groups of non-kin, as proposed by Schneider and Bilde in 2008 with Stegodyphus lineatus Latreille 1817 (Eresidae)

Preferential prey sharing among kin not found in the social huntsman spider, Delena cancerides (Araneae: Sparassidae)

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First Description of the Nuclear and Mitochondrial Genomes and Associated Host Preference of <i>Trichopoda pennipes</i>, a Parasitoid of <i>Nezara viridula</i>

Trichopoda pennipes is a tachinid parasitoid of several significant heteropteran agricultural pests, including the southern green stink bug, Nezara viridula, and leaf-footed bug, Leptoglossus phyllopus. To be used successfully as a biological control agent, the fly must selectively parasitize the target host species. Differences in the host preference of T. pennipes were assessed by assembling the nuclear and mitochondrial genomes of 38 flies reared from field-collected N. viridula and L. phyllopus. High-quality de novo draft genomes of T. pennipes were assembled using long-read sequencing. The assembly totaled 672 MB distributed among 561 contigs, having an N50 of 11.9 MB and a GC of 31.7%, with the longest contig at 28 MB. The genome was assessed for completeness using BUSCO in the Insecta dataset, resulting in a score of 99.4%, and 97.4% of the genes were single copy-loci. The mitochondrial genomes of the 38 T. pennipes flies were sequenced and compared to identify possible host-determined sibling species. The assembled circular genomes ranged from 15,345 bp to 16,390 bp and encode 22 tRNAs, two rRNAs, and 13 protein-coding genes (PCGs). There were no differences in the architecture of these genomes. Phylogenetic analyses using sequence information from 13 PCGs and the two rRNAs individually or as a combined dataset resolved the parasitoids into two distinct lineages: T. pennipes that parasitized both N. viridula and L. phyllopus, and others that parasitized only L. phyllopus.</i