PhD theses

All Wageningen University PhD theses

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    Wageningen PhD theses


    This database contains bibliographic descriptions of all Wageningen University PhD theses from 1920 onwards. It is updated on a daily basis by WUR Library.

    Author abstracts and/or summaries are added to all descriptions. A link to the full text dissertation is added to the bibliographic description. In a few cases, no electronic version is available, mostly because of copyright issues.

    Hard copies of all theses are available for loan at WUR Library. To request them, click the link Request this publication in the full record presentation. This is a fee based service.

    mail icon WUR Library, 9 july 2012

     

Record number 2221724
Title Community ecology of Neotropical ticks, hosts, and associated pathogens
show extra info.
Helen J. Esser
Author(s) Esser, Helen J. (dissertant)
Publisher Wageningen : Wageningen University
Publication year 2017
Description 200 pages figures, diagrams
Description 1 online resource (PDF, 200 pages) figures, diagrams
Notes Includes bibliographical references. - With summaries in English and Dutch
ISBN 9789463436908; 9463436901
Tutors Prins, Prof. dr. H.H.T. ; Bongers, Prof. dr. F.J.J.M. ; Jansen, Dr. P.A.
Graduation date 2017-10-09
Dissertation no. 6763
Author abstract show abstract

The ongoing loss of global biodiversity is unprecedented in both magnitude and pace, raising urgent questions as to how this loss will affect ecosystem functioning and human well-being. Control of infectious diseases has been proposed as an important ecosystem service that is likely to be affected by biodiversity loss. A negative relationship between biodiversity and disease risk could offer a win-win situation for nature conservation and human health. However, the generality of this relationship remains the subject of contentious debate. The aim of this thesis was to contribute to a better understanding of the interactions between ticks and their vertebrate hosts in a biodiversity hotspot, and how loss of biodiversity affects these interactions and ultimately, tick-borne disease risk. My study was unique in that I simultaneously considered and directly assessed broader communities of Neotropical wildlife, ticks, and tick-borne pathogens across an anthropogenic disturbance gradient.

Determining whether and how biodiversity loss affects tick-borne disease risk in tropical forests requires a thorough understanding of tick-host associations, which are a function of tick-host specificity as well as host biological and ecological traits. In chapter 2, I therefore quantified the degree to which adult ticks are host-specific in my study region: Panama. Using quantitative network analyses and phylogenetic tools with null model comparisons, I found that the adult life stages of most tick species were specific to a limited number of host species that were phylogenetically closely related. In Chapter 4 I showed that species assemblages of adult ticks became increasingly diverse on larger-bodied host species, indicating that adult ticks in Panama tend to select for large reproduction hosts.

In contrast to adult ticks, understanding the ecological interactions between immature ticks and their hosts in the tropics has long been hampered by a lack of morphological identification keys. Therefore, in Chapter 3, I describe the development of a DNA barcode reference library for the molecular identification of larvae and nymphs. This reference library was highly effective in species-level identification of immature ticks collected from birds (Chapter 3) and small mammals (Chapter 4 and 6). Several avian ecological traits were positively associated with tick parasitism, but the potential role of wild birds in tick-borne disease transmission seems to be limited in Panama. Immature ticks did not show any specificity to particular bird species or avian ecological traits (Chapter 3), and species assemblages of immatures ticks were equally diverse across a large number of host taxa (Chapter 4). This suggests that larvae and nymphs may feed more opportunistically than their adult counterparts.

High host specificity in adult ticks implies high susceptibility to tick-host coextinction, even if immature ticks feed opportunistically. In chapter 5, I tested this hypothesis by surveying tick and vertebrate host communities across a forest fragmentation gradient. Forest fragments consisted of previously connected islands and peninsulas in the Panama Canal and ranged 1000-fold in size. Abundance and species richness of ticks was positively related to that of wildlife, which in turn was related to the size of the forest fragment. Specialist tick species were only present in fragments where their specific reproduction hosts were captured by camera traps. Further, less diverse tick communities were dominated by a generalist tick species. These results indicate that loss of wildlife had cascading effects on tick communities through local host-parasite coextinction.

In Chapter 6, I studied how communities of wildlife, ticks, and tick-borne microbes changed along a more ‘typical’ disturbance gradient, in which forest fragments were embedded in an agricultural and sub-urban landscape, rather than surrounded by water. I found that wildlife community disassembly either diluted, amplified, or had no effect on infection prevalence in ticks, depending on the pathogen and degree of disturbance. However, hyperabundance of medium- to large-sized frugivores and herbivores (important reproduction hosts for adult ticks) in sites that lacked apex predators was related to exponential increases in tick density, negating any effect of reduced pathogen prevalence. Moreover, high tick species richness in these sites was related to high microbial and pathogen richness. High parasite diversity is thus a source of infectious diseases. When medium- to large-sized frugivores and herbivores also disappeared, densities of infected ticks declined, suggesting a non-linear relationship between biodiversity loss and tick-borne disease risk, in which initial loss of apex predators increases disease risk, but further loss of species decreases disease risk again.

In this thesis, I have quantified host-feeding relationships of adult and immature Neotropical ticks, many of which (in the case of larvae and nymphs) were largely unknown. I have shown that adult ticks tend to be highly host-specific, particularly to larger-bodied vertebrates, whereas immature ticks appear to have broader host-use patterns. I found that ticks are susceptible to local host-tick coextirpation, and that the relationship between biodiversity loss and tick-borne disease risk is non-linear. My results emphasize the importance of directly assessing host community composition and suggest that the presence of specific (reproduction) hosts are a more important factor than species richness per se for tick population and tick-borne disease dynamics.

Online Embargo on full text. Full text available from 2018-10-09
On paper FORUM ; STACKS ; NN08202,6763 ; Not for loan
Keyword(s) metastigmata / host specificity / host parasite relationships / biodiversity / species diversity / pathogens / size / community ecology / tickborne diseases / panama / tropics / hosts
Categories Terrestrial Ecology / Arachnida
Publication type PhD thesis
Language English
Comments
There are no comments yet. You can post the first one!
Post a comment
 

To support researchers to publish their research Open Access, deals have been negotiated with various publishers. Depending on the deal, a discount is provided for the author on the Article Processing Charges that need to be paid by the author to publish an article Open Access. A discount of 100% means that (after approval) the author does not have to pay Article Processing Charges.

For the approval of an Open Access deal for an article, the corresponding author of this article must be affiliated with Wageningen University & Research.

Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.