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Readel, A. M. (2009). Effects of habitat on physiology and infection in aquatic turtles. Unpublished thesis , University of Illinois, Urbana-Champaign.
Added by: Admin (29 Jan 2012 12:39:07 UTC) |
| Resource type: Thesis/Dissertation BibTeX citation key: Readel2009 View all bibliographic details  |
Categories: General Keywords: Bakterien = bacteria, Chelydra, Chelydra serpentina, Chelydridae, Chrysemys, Chrysemys picta, Emydidae, Habitat = habitat, Nordamerika = North America, Parasiten = parasites, Physiologie = physiology, Schildkröten = turtles + tortoises, Stress = stress, Trachemys, Trachemys scripta, Veterinärmedizin = veterinary medicine Creators: Readel Publisher: University of Illinois (Urbana-Champaign) |
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| Abstract |
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Conservation efforts often rely on tools such as population viability analysis (PVA) that attempt to predict species extinction risk and identify effective management strategies for species conservation. Information on the physiology and health of organisms is important but rarely incorporated into viability models. These data can help biologists understand how animals are impacted by environmental change, identify the causative mechanisms underlying conservation threats, and help prevent species extinctions. Additionally, they can provide information on individual and population dynamics much quicker than time-intensive behavioral or demographic studies. To illustrate the importance and usefulness of physiologic and health data for conservation, I used slider (Trachemys scripta), painted (Chrysemyspicta), and snapping (Chelydra serpentina) turtles that were collected from ponds throughout east and southeast Illinois. At each pond, I measured 48 habitat variables that included both physical pond characteristics and the land use surrounding ponds at multiple spatial scales. The relationships between and among habitat characteristics and patterns of glucocorticosteroids, heterophil/lymphocyte (H/L) ratios, parasitism, and infection with the zoonotic bacterium, Salmonella were examined. Habitat characteristics strongly influenced slider turtle corticosterone levels in the first two years of our study. In 2004, baseline corticosterone levels and the adrenocortical response of 46 turtles varied more extensively between the two ponds sampled than with any host characteristic measured. When 78 turtles were sampled from additional ponds in 2005, baseline corticosterone levels were higher in ponds that lacked vegetation, and increased with the percentage of agriculture surrounding ponds. The fact that habitat characteristics in 2005 increased turtle baseline corticosterone levels but were not generally associated with decreased adrenocortical responsiveness may suggest that they act as chronic stressors without impairing hypothalamic-pituitary-adrenal (HPA) function. Unlike 2004 and 2005, habitat characteristics did not influence baseline corticosterone levels or the adrenocortical responses of 46 turtles in 2006. Nevertheless, turtles had elevated baseline corticosterone levels and impaired adrenocortical responsiveness to adrenocorticotropic hormone (ACTH) injections that year, possibly due to a decline in regional habitat quality and a corresponding production of corticosterone at maximal or near maximal physiological limits. H/L ratios were positively correlated with the percentage of water surrounding (within 125 m) ponds. Since both turtle abundance in ponds and average body condition declined from 2004/2005 to 2006, these data may suggest that turtles with higher body conditions emigrated from ponds when additional water bodies were available while turtles with lower body condition, higher baseline corticosterone levels, higher H/L ratios, and lower adrenocortical responsiveness remained in the ponds. Turtle parasitism was also altered by habitat characteristics. When five turtle species were pooled, leech intensity was higher in more turbid ponds. When we used a more restrictive model that examined slider, painted, and snapping turtle data separately, we did not identify a relationship between turbidity and leech parasitism. The prevalence and/or abundance of almost all parasite species in slider turtles increased significantly with the percentage of development and water surrounding ponds within 5000 and 10,000 m, however. Slider turtles in ponds with high human use also had a higher abundance of two of three gastrointestinal parasites that required intermediate hosts than individuals in ponds with low human use. Other habitat characteristics, such as the percentage of agriculture surrounding ponds, whether ponds were natural or manmade, and basking site availability, also significandy affected some parasites; however, the direction of the relationships varied among parasite species. Gastrointestinal parasite richness, measured as the average number of species identified in each pond, did not vary significantly among ponds. Although my data suggested that some parasites could impact host fitness, no parasites appeared to affect turtle population stability in the timeframe of this study. Finally, Salmonella infections in slider turtles were not significantly affected by the host or habitat characteristics measured in this study. No turtles out of 100 were shedding Salmonella. Dissections of 73 turtles, however, revealed that turtles in the region had a moderate prevalence (11%) of Salmonella infection. This study illustrates the usefulness of health and infection data and fills gaps in our understanding of the effects of habitat on wildlife. This study identified specific habitat characteristics that may be applicable to turtle management and conservation. Additionally, it demonstrates that anthropogenic habitat alterations of both the aquatic and adjacent terrestrial habitats may affect turtle physiology and parasitism. This study also demonstrates that health data could be useful for identifying landscape scales that are relevant to turtle conservation. For example, landscape scales identified by corticosterone levels and H/L ratios were nearly identical to those suggested for turtle conservation based on behavioral data. These methods may be particularly useful for turtle studies since these data can provide information on individual and population dynamics much quicker than time-intensive behavioral or demographic studies. Perhaps most importantly, however, our data suggests that large-scale land use and regional effects could have far-reaching negative influences on turtle physiology and parasitism in localized habitats. These findings lay the groundwork for future studies that wish to investigate the effects of broad-scale landscape changes, such as might be caused by agricultural expansion, development, or climate change, on turtle health and the capacity of turtle populations to adapt physiologically. Although in this thesis project I did not apply our data to a PVA model since slider turtles are common and ubiquitous, our findings indicate that physiologic and infection information can be as informative as data on demography, community structure, and behavior for species conservation.
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