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Evaluation of the Existence of Chemosensory Glomeruli in Spiders

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Evaluation of the Existence of Chemosensory Glomeruli in Spiders EVALUATION OF THE EXISTENCE OF CHEMOSENSORY GLOMERULI IN SPIDERS Item Type Electronic Thesis; text Authors Mortensen, Michael Citation Mortensen, Michael. (2020). EVALUATION OF THE EXISTENCE OF CHEMOSENSORY GLOMERULI IN SPIDERS (Bachelor's thesis, University of Arizona, Tucson, USA). Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 07/10/2021 21:15:57 Item License http://rightsstatements.org/vocab/InC/1.0/ Link to Item http://hdl.handle.net/10150/651338 EVALUATION OF THE EXISTENCE OF CHEMOSENSORY GLOMERULI IN SPIDERS By MICHAEL SAMUEL MORTENSEN ____________________ A Thesis Submitted to The Honors College In Partial Fulfillment of the Bachelors degree With Honors in Neuroscience and Cognitive Science THE UNIVERSITY OF ARIZONA M A Y 2 0 2 0 Approved by: ____________________________ Dr. Wulfila Gronenberg Department of Neuroscience Abstract Spiders sit at the forefront of fearful minds of people across the globe, but scientific knowledge of these creatures is surprisingly far from complete. For instance, the current body of work that describes a spider’s olfactory capabilities is lacking, specifically in narrowing down the possible locations for receptors by which odors are sensed. To push knowledge in this area forward, this study analyzed the region of the CNS known as the suboesophageal ganglion, referenced in the work done by Babu & Barth (1984), in five species of spider in an attempt to determine if glomeruli, globular arrangements of synaptic connections typically underlying olfactory processing in most animals (as described in Hildebrand & Shepherd, 1997), could be found. In all species studied, glomeruli-like structures were identified in the regions of the suboesophageal’s leg ganglia which contain synaptic connections between the leg nerves and the CNS. This study presents evidence suggesting that olfactory receptors may be more abundant on the legs of spiders, and that the sense of smell may be more pronounced than previously thought. Dedication This body of work is lovingly dedicated to the Nephila clavipes who gracefully excluded herself from this study by means of ignoring her provided meal and instead choosing to eat so much dried glue that she choked and died. Also dedicated to my lab instructor, Wulfila Gronenberg. Without him and the time he spent making countless revisions, this thesis would have been much shorter and vastly inferior in quality. Table of Contents Abstract ..................................................................................................................................... 2 Introduction ............................................................................................................................... 5 Methods .................................................................................................................................. 15 Results ..................................................................................................................................... 19 Discussion ................................................................................................................................ 33 Acknowledgements ................................................................................................................. 38 Bibliography ............................................................................................................................ 39 Introduction General Introduction/Terminology The phylum of arthropoda is home to several fascinating classes and orders of animals, with some of the most well-known being the order of araneae, belonging to the family arachnida. The term araneae refers, of course, to what is commonly known as a spider. Spiders come in a huge variety of families, such as the Agelenidae (funnel-web spider), Lycosidae (wolf spider), and Salticidae (jumping spider). These families, despite their differences, all hold several attributes that qualify them for classification as araneae, including the existence of eight legs, silk glands, and chelicerae (fangs) (Foelix, 2011). There exist a wide variety of spider families, with each having a species count ranging from around 100 to several thousand (reviewed in Foelix, 2011). As expected with such a wide range of families and species, there exist notable differences between them, clearly shown in hunting behavior. Spiders within the Araneidae family (orb-web spiders), which contains the Nephila clavipes used in this study, take a more passive approach when it comes to finding a meal. These spiders prefer a strategy of patience (Nyffeler et al., 1994; Nyffeler, 1999) and the laying of careful traps with their webs. These web-weaving spiders will spin their web in a way that is most beneficial to trapping a certain type of prey, whether they fly (Kajak, 1965; Chacon & Eberhard, 1980; all as cited by Nyffeler, 1999) crawl, or jump, and then simply wait for the time to strike to arrive. As such, web-weaving spiders are thought to rely on prey that is, in order to fall into their web, capable of moving (Turnbull 1973, as cited by Nyffeler, 1999). Other spiders are known best as hunters, such as ones from the Lycosidae family (wolf spiders) (Nyffeler et al., 1994), including the Hogna lenta and Tigrosa californica used in this study, or the Sparassidae family (giant crab spiders) (Airamé & Sierwald, 2000), including the Olios gigantius used in this study. Spiders from these families place an active approach to finding a meal, and have been thought to have a broader plate of prey to choose from, so to speak, due to this (Jackson & Tarsitano, 1993; Nyffeler et al., 1990; Turnbull 1973, as cited by Nyffeler, 1999). Interestingly, this broader plate has been observed to include other spiders (Wise 1993, as cited in Nyffeler, 1999). Biology of a Spider A good place to start before delving into the subject of this paper is to briefly explain the basic biology of a spider as laid out by Foelix (2011). The body of a spider consists of two sections strung together. The anterior section, called the prosoma, carries the central nervous system (CNS). The prosoma is also the location of four pairs of legs, a single pair of pedipalps, which are used as feelers (and, in males, as copulatory organs), and a pair of chelicerae, which are used to bite. The posterior section, called the opisthosoma (or abdomen), instead deals with tasks such as silk production, reproduction, and digestion, amongst other things. The opisthosoma is also home to a spider’s spinnerets, which are essential for web-building. The prosoma and opisthosoma are connected by a stalk called the pedicel. The primary focus of this paper lies in the CNS that sits inside the prosoma. As can be imagined, the actual CNS of a spider is quite different from that of a vertebrate. The most notable feature of a spider’s CNS is that its ganglia are fused into two parts that both lie in the prosoma. These sections are known as the supraoesophageal and Figure 1: Diagram of Spider CNS. Left Figure: Dorsal view of the two sections of a spider (Tegenaria)’s body, with the CNS in the prosoma shown to extend via nerve bundles to suboesophageal ganglion (SOG) (Babu the opisthosoma. Right Figure: Lateral view of the CNS of a spider of the same species. SUPRA: supraoesopageal ganglion. SUB: subeosophageal gaglion. Eso: esophagous, & Barth, 1984). The which divides the two areas of the CNS. PG: palpal ganglion. 1-4: Leg ganglia. Image taken from Foelix 2011. (p119) supraoesophageal ganglion (the brain proper) sits anteriorly and dorsally to the SOG, and the two parts are divided by the spider’s esophagus (Babu & Barth, 1984; Foelix, 2011). The supraoesophageal ganglion is a higher order processing center, where information from visual and other sensory pathways are integrated (Babu & Barth, 1984; Foelix, 2011). It comprises the protocerebrum (which supplies the eyes) and the deutocerebrum, which supply the chelicera (Babu & Barth, 1984; Foelix, 2011; Tanaka et al. 2013). The SOG is instead made up of the fused ganglia of the legs, pedipalps, and the abdominal ganglia (Babu & Barth, 1984; Foelix, 2011). The traditional term ‘suboesophageal ganglion’ is an unfortunate choice, as in other arthropods it refers to a more specific ganglion which only supplies the mouthparts. A less misleading term would be ‘fused post-oral ganglia’, but I will use the traditional term ‘suboesophageal ganglion’ because it is used by many of the relevant previous studies. As Babu & Barth (1984) and Foelix (2011) summarize, the ganglia composing the SOG can still be recognized as individual neuromeres, each of which supplies a leg (or pedipalp). The neuromeres are separated ventrally but fused dorsally in the SOG. Each neuromere contains areas known as neuropils where synaptic connections are located. It is here that the CNS receives incoming sensory fibers and gives rise to outgoing axons that originate from large motoneurons whose cell bodies reside in the peripheral cell body cortex, which lies below the central neuropil (Gronenberg, 1989; 1990; Milde & Seyfarth; 1988; all as cited in Foelix 2011; Babu & Barth, 1984). Senses of a Spider Perhaps the most striking and well understood aspects of a spider’s biology are their mechanical senses based
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