PARENT SESSION
Poster Session #1: Parasite-Host Interactions.
Monday, August 6, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Examining host/symbiont theory using an obligate commensal: implications for context-dependency.

Pennuto, Christopher¹, ¹

ABSTRACT- Host/symbiont theory suggests that the abundance of an obligate symbiont will correlate positively with the density of its host. I examined this expectation using an aquatic insect host/obligate commensal interaction in 13 streams of southern Maine over two years (1996 and 1998). I also investigated field conditions and macroinvertebrate community composition to search for correlates of commensal population dynamics. No physicochemical condition correlated with commensal population characteristics in both years. Midge commensal presence was negatively correlated with stream conductivity in 1996 and alkalinity in 1998, but positively correlated with embeddedness in 1998. Neither infestation intensity (no. of commensals per host) nor prevalence (% of host population harboring a commensal) was related to host population density across sites. Similarly, commensal infestation intensity was not related to host size. Within-site comparisons, on the other hand, exhibited a trend of increasing infestation intensity with decreasing host density. Commensal density distribution on hosts was significantly clumped at sites with high commensal population densities, low infestation intensities, and small host population size. Commensals showed a strong size-dependent preference for attachment site on their host. These data suggest that intraspecific interactions have a strong influence on population dynamics of this commensal midge and in general, this species pair does not support the expectation of increasing symbiont population size with either increasing host body size or host population size.

KEY WORDS: Chironomidae, species interactions, streams, Maine