Ph.D. - Zoology

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https://hdl.handle.net/10125/2173

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Now showing 1 - 10 of 184
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    Source to sink: Modeling marine population connectivity across scales in the Main Hawaiian Islands
    (2024) Conklin, Emily Elizabeth; Toonen, Robert; Zoology
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    THE PHYSIOLOGY AND MOLECULAR ECOLOGY OF VISION IN HAWAIIAN SEABIRDS
    (2024) Moon, Hannah E.; Porter, Megan; Zoology
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    ECOLOGY OF FISHES AND INVERTEBRATES INHABITING THE CORAL POCILLOPORA GRANDIS IN HAWAIʻI
    (2024) Brush, Erik Grosvenor; Hixon, Mark; Zoology
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    Competition And Resource Partitioning Between Congeneric Coral- Dwelling Scorpionfishes (sebastapistes Spp.) In Hawai‘i
    (University of Hawaii at Manoa, 2023) Jones, Ryan Neil; Hixon, Mark A.; Zoology
    Exposed coral reefs in Hawai‘i are largely dominated by the small branching cauliflower coral (Pocillopora meandrina), which supports diverse communities of fishes and invertebrates. Two of the most common fishes that reside in these corals are the Speckled Scorpionfish (Sebastapistes coniorta) and the Galactic Scorpionfish (S. galactacma). These small nocturnal reef mesopredators use the complex branching morphology of cauliflower coral as protection during the day and feed in and around their host corals at night. Despite their apparent ecological similarities, these species coexist locally, at times even co-occupying the same host coral. Surveys of cauliflower coral communities around O‘ahu revealed inverse depth distributions, with Galactic Scorpionfish found across all depths surveyed, though more commonly in deeper reef areas (> 11 m), while Speckled Scorpionfish almost exclusively occurred in shallow reef areas (5 – 10 m deep). These species also used microhabitat in subtly different ways, with the larger species (Speckled Scorpionfish) being more associated with coral colonies with wider spacing between branches. Reciprocal removal experiments across depths, among clusters of corals, and within individual colonies suggest that competition between these species is not currently occurring, and recolonization experiments showed that colony characteristics played a large role in determining which species recolonized corals. Diet analyses using both visual examination and DNA metabarcoding of stomach contents revealed that Speckled Scorpionfish and Galactic Scorpionfish have minimally overlapping diets with significantly different compositions, though both species typically consume small crustaceans that co-occur with them in cauliflower corals. Further, the diets of these species did not significantly differ whether they co-occurred or not, suggesting that these species have evolved different diets, possibly due to past competition. Thus, these species partition food and microhabitat resources to a degree that presently allows for their coexistence on reefs in Hawai‘i.
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    Impact Of Environment, Host Microbiome, And Stress On Angiostrongylus Cantonensis (rat Lungworm) Transmission
    (University of Hawaii at Manoa, 2023) Rollins, Randi; Cowie, Robert; Zoology
    Angiostrongylus cantonensis, commonly known as rat lungworm, is a nematode parasite widely distributed in tropical and subtropical regions, and is the causative agent of neuroangiostrongyliasis, a leading cause of eosinophilic meningitis globally. This parasite completes its life-cycle in various gastropod species (intermediate host) and rat species (definitive host). Humans are accidental hosts, becoming infected by ingesting infectious stage larvae, present in snails. Symptoms of neuroangiostrongyliasis can be severe, occasionally leading to death. Other mammals and birds also serve as accidental hosts. Although A. cantonensis was originally discovered in 1935, it wasn’t linked to human disease until 1961, when found in the brain of a deceased Hawaiʻi State Hospital patient. Since 1961, the parasite’s life-cycle and distribution have been discovered, but relatively little is known about A. cantonensis. Therefore, I developed three projects to explore the effects of the environment, stress, and host microbial communities on host-parasite dynamics and human transmission. The first project involved the collection of 16 snail species from 39 sites across Oʻahu, where A. cantonensis infection prevalence and intensity were determined using qPCR targeting the ITS1 region of DNA. Generalized linear mixed models (GLMMs) were constructed, incorporating environmental data to assess the influence of rainfall and temperature on these infection metrics. The analysis revealed higher infection prevalence and intensity in snails inhabiting wetter, cooler regions compared to snails in hotter, drier areas. In the second project, 196 snails (Parmarion martensi) were subjected to stress, leading to the release of infectious larvae in 13.3% of the stressed snails’ slime, while non-stressed snails did not release any larvae. Permutation tests and GLMMs demonstrated that stress significantly alters the parasite-host relationship, with snail infection intensity positively correlated with the presence of A. cantonensis larvae in their slime. These findings suggest that snail slime may serve as an alternative zoonotic transmission pathway. The third project involved a comparison of the effect of A. cantonensis infection on the microbial communities of snail guts (Parmarion martensi and Lissachatina fulica), rat feces and rat skin (Rattus rattus and R. norvegicus) using high-throughput sequencing of 16S ribosomal RNA. Analysis of microbial abundance with GLMMs revealed a significant interaction between infection status, host species, and individual bacteria. Shifts in individual bacterial abundances in response to A. cantonensis infection were most pronounced in the gut microbiota of infected snails, characterized by large log2FoldChange values. Changes in microbial abundance in rat feces were less pronounced, and relatively minor in rat skin. Notably, certain bacterial groups displayed remarkable increases in abundance in both taxa, suggesting potential protective symbiosis in response to A. cantonensis infection. Furthermore, differences in host susceptibility were observed to be associated with varying degrees of microbial disturbance. Parmarion martensi, a highly susceptible snail host, exhibited less microbial dysbiosis than L. fulica, a less susceptible host, suggesting the existence of unique adaptations and coadaptations in host-parasite interactions, potentially driven by the evolutionary history of the parasite and host. These projects contribute to the understanding of host-parasite relationships and provide valuable ecological insights for future research on A. cantonensis. The findings highlight the risk for human neuroangiostrongyliasis in different environments, the influence of stress in disease transmission, and the potential for microbial targets to be developed for therapeutic intervention and disease prevention. Furthermore, these discoveries have implications for ongoing efforts to mitigate human transmission and disease caused by A. cantonensis.
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    Vision and Bioluminescence of Marine Crustaceans
    (University of Hawaii at Manoa, 2023) Iwanicki, Tom; Porter, Megan L.; Zoology
    The overarching theme of this dissertation research was to understand light as the cue for life in the ocean. I approached this dissertation with a background in molecular biology, animal behavior, and vertebrate opsin evolution, and upon my arrival was tasked with familiarizing myself with invertebrate opsins and bioluminescence. Chapter 1 briefly describes my rationale for this dissertation research and puts it into a broader context for understanding light as a cue for light in the ocean. Chapter 2 contains a literature review of the many multiple origins, forms and functions, cellular biology, and ecology of bioluminescence, with an emphasis on marine taxa. I point to recent discoveries in bioluminescent systems that challenge orthodoxies and present a systematic review of plausible human impacts on bioluminescence via ocean acidification. In chapter 3, I present a fully resolved molecular phylogeny for metridinid copepods, with an emphasis on the genus Pleuromamma, and characterize the opsin and luciferase diversity in the group using transcriptomics. Within the transcriptomes, I found evidence for the origin of copepod bioluminescence possibly arising from a blood clotting protein. In chapter 4, I used immunohistochemistry to localize opsin proteins in ocular and non-ocular tissues from four species in the superfamily Oplophoroidea, a group of bioluminescent decapod shrimp. These data provide molecular confirmation for previously described single- and dual-sensitivity visual systems in the superfamily, and offer the first evidence for co-localization of opsins in the R8 cells – or distal rhabdom – of a decapod crustacean retina. In chapter 5, I sequenced metatranscriptomes from zooplankton communities at Station ALOHA, Oʻahu, Hawaiʻi to describe community structure across the epipelagic and lower mesopelagic during the day and night for small and large zooplankton. We found that Station ALOHA was dominated by copepods, followed by euphausiids, amphipods, and ostracods, with a faunal shift toward fishes in large bodied, deep samples, and time of day had no influence on overall community structure. Further, we tested the utility of metatranscriptomes for functional analysis leveraging gene expression estimates of the opsin gene family. We found that opsin abundance does not conform with community patterns and that depth, size, and taxa influenced opsin expression, but time of day had no effect. Combined, these chapters leverage tools at multiple levels of organization to understand why bioluminescence is such a prevalent phenomenon throughout the worlds oceans, and to understand how visual ecology structures where species are horizontally, temporally, and vertically through the water column.
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    The Power Of Poop: Insights Into Hawaiian Honeycreeper Conservation Through DNA Metabarcoding
    (University of Hawaii at Manoa, 2022) Costantini, Maria Sara; Reed, Floyd A.; Zoology
    The Hawaiian honeycreeper lineage (subfamily: Carduelinae) is one of the quintessential examples of an adaptive radiation. In modern human history, however, most of the 56+ species that evolved from a Eurasian finch have gone extinct, and most of the extant species are experiencing severe population declines. Currently, urgent management actions are being taken to prevent the extinction of the lineage, including captive breeding and translocation efforts. In this dissertation, I used DNA metabarcoding of fecal samples to study the diets and gut microbiomes (GM) of Hawaiian honeycreepers and inform management decisions of these imperiled species. I first focused on two critically endangered species that have recently been brought into captivity for conservation breeding efforts. Previous work on other species have shown that captivity can negatively affect individuals’ gut microbiome. The GM is known to strongly influence the health, fitness, and behavior of its hosts, yet what drives its formation and how the GM is affected by environmental changes is not well understood across species. I then characterized the diet of the forest birds on the island of Kauaʻi, which has been an island of particular concern due to the recent rapid population declines of several species. I found that Lepidoptera are key components of all bird diets regardless of foraging guild, that there is evidence for resource partitioning between closely related species, and that the diet of an introduced bird is not distinct from native species. Finally, I investigated how three main factors contribute to the composition of GMs across the extant Hawaiian honeycreeper lineage. I looked at the relative roles of host phylogeny, diet, and geography, and found that geographic distance was associated with the largest effect on the variation within honeycreeper microbiomes. The results from this dissertation work can be used by wildlife managers to improve Hawaiian honeycreeper conservation strategies, protecting and bolstering the populations of these stunning species into the future.