Bryophyte and invertebrate interactions abound, but they are poorly understood. I examined the frequency of Bdelloid rotifers within lobular-shaped leaves of an epiphytic liverwort (Frullania eborascensis) in northwestern Pennsylvania. Liverworts were randomly sampled from the bark of three neighboring streamside trees from July through September, 2000. Between 13-68% of the lobules on any given plant were occupied by rotifers (mean=30%; N = 34 samples; 5054 lobules). Of occupied lobules, 71% contained one rotifer, 20% two, and 9% three or more. This distribution is significantly different from that expected at random (Chi-square test using Poisson distribution for expected values, P<0.0001). Although further analyses are needed to confirm this conclusion, the excess of lobules with multiple rotifers supports the hypothesis that rotifers reproduce within lobules and that the plant-animal interaction could have fitness consequences for the rotifer. In addition to this finding, I also show that estimates of rotifer abundance within lobules decreased 20% within three days of sample collection, suggesting that accurate estimates of occupied lobules need to be taken soon after sample collection and that rotifers may be dying as the liverwort dries out.

Key words: Bdelloid rotifers, bryophyte-invertebrate interaction, Frullania eborascensis, liverwort, plant-animal interaction