Term of Award

Fall 2009

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Department

Department of Biology

Committee Chair

Dana Nayduch

Committee Member 1

Lance McBrayer

Committee Member 2

Oscar Pung

Abstract

Author's Abstract: Skrjabinoptera phrynosoma (Ortlepp) Schulz, 1927 is a common parasitic nematode of horned lizards. The life cycle of S. phrynosoma was described by Lee in 1957, but has received little attention since. The present study addressed effect of season as well as host characteristics on the infection dynamics in lizard hosts. In the Alvord Basin in southeastern Oregon, S. phrynosoma were collected from Phrynosoma platyrhinos Gerard 1852 horned lizards via stomach flushes, cloaca flushes and fecal pellet collections. Parasite load variables (number of nematodes per host, length of those nematodes, and total worm burden (ΣL)) were analyzed within three collection periods during the active season of 2008. Number and length of nematodes of different sex categories also was analyzed within collection period and across season. The relationship between parasite variables and host characteristics (sex and SVL) were analyzed. Pogonomyrmex spp. harvester ants were collected and dissected to determine the prevalence of infection in this intermediate host. The number of non-gravid female nematodes as well as the number of juvenile nematodes in lizards' stomachs decreased significantly between the early and late collection periods. While the number of male nematodes in lizards' stomachs did not change across season, the length of male nematodes increased significantly between early, middle and late collection periods. During the early collection period, host SVL was positively correlated with non-gravid female nematode length and juvenile nematode length. Also, in late season, there was a negative relationship between lizard SVL and number of gravid female nematodes. Nematodes were retrieved from cloacal sampling mostly during the middle collection period, and were exclusively gravid female nematodes. Prevalence in the ant intermediate host was extremely low. As the population of male nematodes in lizards' stomachs remains stable, it is proposed that any newly-establishing nematodes (juveniles) develop into non-gravid females and then, after mating, develop into gravid female nematodes. It is also proposed that in larger lizards, newly-establishing nematodes (juveniles) can develop into females, can mate, and can exit the lizard faster because of more space and resources in the larger stomachs. The changing parasite load of S. phrynosoma in P. platyrhinos across the active season is most likely driven by the timing of the unique life cycle of this parasite.

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