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Date Permissions Signed


Date of Award

Winter 2020

Document Type

Masters Thesis

Department or Program Affiliation


Degree Name

Master of Science (MS)



First Advisor

Anderson, Roger A. (Roger Allen)

Second Advisor

Miner, Benjamin G., 1972-

Third Advisor

Donovan, Deborah Anne, 1964-

Fourth Advisor

Ransom, Jason


In the Alvord Desert in Harney County, Oregon, I examined the response of desert horned lizards (Phrynosoma platyrhinos) to a common and abundant gastrointestinal nematode parasite (Skrjabinoptera phrynosoma) transmitted to them through harvester ants (Pogonomyrmex californicus), a principal component of their specialized diet. I examined presumed fitness correlates including foraging, prey choice, energetic endurance, and immune response at varying levels of nematode load in joules/hour while correcting for body size differences in 19 male and 21 female Desert horned lizards in summer 2018. The effects of increasing nematode load were more benign than hypothesized, with the only significant detriments being in reduced energetic endurance and blood immune response. Nematode load was positively correlated with foraging, body condition, and showed a sex-specific influence on prey choice. I posit that male and non-reproductive female desert horned lizards accumulate nematodes with little consequence and may become hyperphagic in order to feed both themselves and their parasites, explaining the enhanced foraging and body condition in more parasitized lizards. I also suggest that reproductive female horned lizards are the cause for the continued relationship, as reproductive females have the obligation to utilize the nematode-transmitting harvester ants to meet their reproductive energy needs, while nematodes have the obligation to be mild enough upon their hosts as to not facilitate mortality during horned lizards’ energetically challenging reproductive season. This study indicates that even nutritionally limited species can support large parasite communities with little fitness costs, and dietary specificity can lead to highly autonomous and stable host-parasite systems.




horned, lizard, nematode, ant, immunity, fitness, endurance, body condition


Western Washington University

OCLC Number


Subject – LCSH

Phrynosoma platyrhinos--Parasites--Oregon--Alvord Desert; Phrynosoma platyrhinos--Behavior--Oregon--Alvord Desert; Skrjabinoptera phrynosoma--Oregon--Alvord Desert; Host-parasite relationships

Geographic Coverage

Alvord Desert (Or.)




masters theses




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