PARENT SESSION
Oral Session # 48: Mutualism - Parasitism I: Plants; Modeling.
Presiding: K Jayachandran
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 203.

Effect of the parasitic plant, Cuscuta gronovii, on size inequality in populations of Pilea pumila.

Alers-Garcia, Janice ^*,1, Bever, James ¹, Clay, Keith¹, ¹ Indiana University - Bloomington, Bloomington, IN

ABSTRACT- Parasitic plants are characterized by obtaining water and nutrients from one or a few host individuals causing some harm but not their immediate death. Given the antagonistic fitness effects present in this parasite-host interaction, we predict that host choice and its effects on individual host plant sizes can affect the development of size inequality in host populations. We used a matched pair design (n=36) to examine whether Cuscuta gronovii (dodder) a holoparasite, affects the development of size inequality of its host Pilea pumila. Cuscuta gronovii did not affect the mean population size of its host(F_df3=1.63, P=0.193). Nevertheless, parasitized populations had a significantly high size inequality for height (F=23.87, P=0.0001) and shoot biomass (F=6.57, P=0.0126) throughout the growing season compared to non-parasitized populations. This increase in size inequality was accompanied by an increase in negative skewness for height and a decrease in positive skewness for shoot biomass by the end of the season. This indicates that parasitized populations contained a small group of extremely small individuals (short and low biomass). On the other hand, Cuscuta exhibited a significant increase in biomass (F_df2=4.646, P=0.0167) during the growing season, but did not increase in number of hosts infected. These data indicate that parasitic dodder selects its hosts early in the growing season, which are then intensively parasitized throughout the growing season. Indeed, examination of mean size differences among parasitized and unparasitized individuals on population assemblages with Cuscuta showed that taller individuals of Pilea pumila are preferentially parasitized. This preferential parasitism strongly depressed their height and biomass throughout the season. These results suggest that size dependent parasitism by highly selective holoparasites such as Cuscuta gronovii could have strong effects in the development of size inequality and thus potential competitive interactions of its host population.

Key words: Pilea pumila, Cuscuta gronovii, parasitism