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Fluorescent Properties of Neotropical Harvestmen (Arachnida: Opiliones) of Trinidad Sadie Arguello

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Fluorescent Properties of Neotropical Harvestmen (Arachnida: Opiliones) of Trinidad Sadie Arguello Fluorescent Properties of Neotropical Harvestmen (Arachnida: Opiliones) of Trinidad Sadie Arguello Abstract: Although fluorescent creatures have been recognized for hundreds of years, more and more species of fluorescent organisms are being discovered. Opiliones found in Northern Trinidad fluoresce under ultraviolet illumination, and it was found that this phenomenon exists only at specific regions on the body. Differences in families of the Opiliones collected complied with this data, finding that the joints of the legs and the patterns that decorate the abdomens are always fluorescent. Key Words: Opiliones, Harvestmen, fluorescence Introduction: Fluorescent properties were first discovered in marine life, leading to the belief that such fluorescent proteins were limited only to primitive creatures such as jellyfish and corals (Deheyn and Holland 2007). As more advanced technology was developed, more and more fluorescent creatures began coming to light. In just three South Pacific Ocean expeditions, National Geographic explorer David Gruber discovered more than 200 biofluorescent species (Daughtery 2014). Though marine fluorescence is more widely studied, this natural phenomenon is not limited to the depths of the ocean. Many land creatures have recently been found to also fluoresce, with South America boasting the first naturally fluorescent frog species (Daley 2017). Not to be left out, a large number of invertebrates have been discovered to possess this unique ability as well, with Victoria Welch publishing a list of insects in which fluorescence has been documented that includes Blattodea, Coleoptera, Lepidopetera, and Orthoptera (Welch V. et al 2012). There are many uses of fluorescent proteins, both for the creature that possesses the ability, as well as potential human application. The exact function of fluorescence is unknown, but many hypotheses exist, though it is most likely that the function varies depending on the species being observed. For example, marine biologists are now utilizing fluorescence to easily spot and record several species of fish that once had to be stunned and/or killed to be surveyed (Brauwer 2018). Gruber hypothesized that the function of fluorescence in marine fish is for communication, supporting this with the fact that many of these fluorescent fish are heavily preyed upon and only come out to find mates, in which a glowing fluorescent pattern would greatly facilitate that search (Daughtery 2014). Another function includes fluorescent patterns in plants that serve as biological maps to help bees find the pollen source within flowers (Lundeberg 2018). Other hypotheses suggest fluorescence plays a role in a type of ‘sunscreen’ and stress relief (Deheyn and Holland 2007). Biomedically speaking, fluorescent proteins have been isolated and extracted for things such as biological markers and probes for testing environmental qualities (Deheyn and Holland 2007). More recent technological advancements have combined magnetic properties with these fluorescent properties to produce ‘two-in-one’ nanocomposite materials for uses that include biological imaging, cell tracking, nanomedicine and bio and chemo-sensoring, magnetic bio separation, and nanomedicine (Corr et al 2008). Looking into the class Arachnida specifically, scorpions have been known to fluoresce for a long time, with hundreds of studies looking into the inner workings of why or how this may be. More recently, spiders have joined the focus of researchers, with Kindra Andrews finding 45 spiders representing 41 genera and 19 families to contain visible fluophore expression (Andrews et al 2007). Also within the class Arachnida, Opiliones make up the third largest order with nearly 6000 species (Machado et al 2007). Before this article, Opiliones have not been documented as a fluorescent order. This paper serves to investigate some of the fluorescent properties of Opiliones found in Northern Trinidad. Materials and Methods: Sixteen adult Opiliones were collected during May and June 2019 at the Jammev Beach Resort in Toco, Trinidad, WI. The specimens were collected at dusk between 2100 and 2300 in plastic collection jars. Using a GoBe Nightsea Light and yellow glasses that block out the blue light, the Opiliones fluoresced brightly, making them easy to spot in the dark of the night. After collection, the Harvestmen were preserved in 75% alcohol solution. Specimens were identified using the “Taxonomic Key to the Families of Harvestmen Occurring in Trinidad and Venezuela” (Townsend et al 2008). Results and Discussion: In this work, fluorescent patterns were investigated of Opiliones collected in Northern Trinidad. Every specimen collected contained fluorescent properties. Twelve of the sixteen specimens collected were identified as Cranaidae, seven of which were female. Based on the key, the other four specimens were thought to be identified as Stygnidae, but their pedipalps did not match previously documented Stygnidae. For this reason, these specimens remain unknown. It is worth mentioning that each of these unknown specimens were a great deal smaller than the other specimens collected, so it is possible that they are too small or have not yet developed the defining characteristics to be able to correctly identify them. A dissection of a female Cranaidae showed that their hemolymph and other internal organs were not fluorescent. However, the bands surrounding the abdomen were also present on the endoskeleton, which fluoresced the same as the bands on the exoskeleton. There were no significant differences between either male and female fluorescence of the same family nor between the two families collected. Only specific regions of the body were fluorescent, specifically in the joints and the bands around their abdomen. This remained true for every specimen, and the difference in fluorescence stemmed only from the differences between individual characteristics of each specimen (i.e. bands vs spots on the abdomen or larger joints). When discussing fluorescence of Opiliones, they can be most directly compared to Scorpiones, as both orders belong to the class Arachnida. The fluorescent property of scorpions can be traced back the hyaline layer in their cuticle. Because of the developmental process of a scorpion, its exoskeleton does not always fluoresce. The freshly hatched scorplings as well as juveniles who have just molted do not fluoresce until their cuticle has fully hardened. Because no juvenile Opiliones were collected, the same thing could not be observed within these samples. When scorpions are preserved, the liquid preservative that they are placed in begins to fluoresce as well. After ten days of preservation, the same characteristic was not observed in the preservative alcohol that the Opiliones specimens were kept in. Another difference is that the entire cuticle of a scorpion fluoresces while Opiliones only have fluorescent properties localized in specific regions. The three main theories that explain the function of scorpion fluorescence is that it helps them find one another, dazzles prey, or acts as a sunscreen. However, upon further research all of these hypotheses can be disproven, which highly discourages the same ideas in Opiliones. One of the newest hypotheses surrounding a possible function of scorpion fluorescence is a “giant eye” for UV detection that tells the scorpions whether it is dark enough to go out or stay underground. Assuming this hypothesis to be true, this explanation would not be near as effective for Opiliones due to their comparatively huge lack in surface area that actually absorbs the UV light (Wolchover 2011). In general, the function of fluorescence in scorpions and many other land-dwelling creatures that contain this unique characteristic remains a mystery. Figure 1: A female Cranaidae in natural lighting (left) vs under a blue light (right). Figure 2: The same female Cranaidae as figure 1 from a ventral view. Figure 3: A glimpse into just how bright these Cranaidae can appear in natural-type settings. Figure 4: Unknown family of Opiliones in both natural and UV lighting. Conclusion: Now knowing that members of the Opiliones order have the ability to fluoresce opens up more questions than it answers. This knowledge provides abundant ground for more investigations into factors that may show how, when, or why Opiliones developed these properties. After many years of scorpion fluorescence research, some scientists have come to the conclusion that fluorescence serves no function at all; it’s simply a random act of evolution (Wolchover 2011). While several theories have already been disproven, it is near impossible to prove that something is legitimately random. To truly understand the inner workings of fluorescence and how these bright creatures impact their surroundings, further research is clearly necessary. Acknowledgments: I am grateful to Dr. Conway and Dr. Brundage for their guidance and support. I would also like to thank my grandparents and the rest of my family and friends that helped make this opportunity possible. References: Andrews, K., S. Reed, and S. Masta. 2007. Spiders Fluoresce Variable Across Many Taxa. The Royal Societyhttps://royalsocietypublishing.org/doi/full/10.1098/rsbl.2007.0016 Brauwer, M. 2018. Now You See Us: how casting an eerie glow on fish can help count and conserve them. TheConversation <https://theconversation.com/now-you-see-us-how- casting-an-eerie-glow-on-fish-can-help-count-and-conserve-them-86476> Corr, S., Y. Rakovich, and Y. Gun’ko. 2008. Multifunctional Magnetic-fluorescent
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