Date of Award
Master of Science (MS)
Margaret Silliker, PhD
Timothy Sparkes, PhD
Windsor Aguirre, PhD
Parasites are organisms that live on or in hosts, which they typically require to complete their life cycles. Acanthocephalus dirus is an acanthocephalan parasite that exhibits an indirect life cycle that requires two hosts, with a Caecidotea intermedius isopod as the intermediate host and fishes as the definitive hosts, in order to complete its life cycle. Infected C. intermedius individuals have been observed to have altered hiding behavior, in which they have an increased amount of time exposed to predators. Also, infected C. intermedius individuals have demonstrated an increase in activity patterns, which could increase their conspicuousness to visual predators. Infected C. intermedius individuals also exhibit pigmentation dystrophy, which makes infected isopods more conspicuous to visual predators than uninfected isopods.
Using a combination of field-based and laboratory-based behavioral trials, I examined the associations of A. dirus infection with behavior (hiding and activity) and body color of male and female isopods. I also examined the relationships between parasite characteristics (intensity and volume) and host trait modification. This study is the first to examine the relationships between effects of infection status in individual C. intermedius and multiple host traits, as well as the correlations among modified host traits and behaviors in both the field- and laboratory-based settings.
I tested for sex-associated effects on each of the traits using a Mann-Whitney U test. Spearman rank-order correlations were used to analyze the relationships between pairs of traits both in the field and laboratory experiments. To determine the potential impact of parasite characteristics (intensity and volume) on each of the traits, I used Spearman rank-order correlation analysis on trait measures obtained in the field for behavior (hiding behavior and activity) and the laboratory for color (color score and % color).
Infected and uninfected isopods (males and females) differed in hiding behavior in the laboratory. Only infected and uninfected males differed in hiding behavior in the field. Infected and uninfected males did not differ in activity in the field and laboratory. Infected females crossed fewer grid lines than uninfected females in the field and laboratory. These changes in female activity appear to be more likely associated with pathological effects of infection than adaptive manipulation.
Infected isopods were lighter in color than uninfected isopods. The pigmentation dystrophy observed in this system may have been an adaptive mechanism used by parasites or a pathological side effect of infection. When using color score as the color measure, there was a positive correlation between color and activity that was present in only uninfected females in the field. However, there was not a correlation between these traits in the laboratory. The correlation between color and activity in uninfected females in the field may not be a meaningful correlation because it was expected that the correlation would occur in a different context, the laboratory, in addition to occurring in the field. Future research is needed to determine the potential significance of the correlations among traits identified in nature and disruptions to these correlations.
For the results obtained here, it appears that different traits may be modulated by different mechanisms because the correlations among traits were not consistent between different contexts.
Park, Tracey J., "Parasite-related modification of multiple traits in an isopod host" (2016). College of Science and Health Theses and Dissertations. 190.