Meeting Abstract

52.1  Monday, Jan. 5  Silk filaments facilitate larval dispersal through freshwater stream pools FINGERUT, J*; SCHAMEL, L; FAUGNO, A; MESTRINARO, M; HABDAS, P; Saint Joseph’s University; Saint Joseph’s University; Saint Joseph’s University; Saint Joseph’s University; Saint Joseph’s University jfingeru@sju.edu

For species that use ambient flow to facilitate dispersal, the heterogeneous nature of the lotic environment can have serious fitness consequences. For non-swimming larvae such as those of the black fly Simulium tribulatum, the presence of large regions of slow flow (pools) may impede downstream movement and act as a sink, limiting population size and spatial distributions. Extended time spent in pool habitat increases predation and greatly reduces feeding opportunities. S. tribulatum may, however, use silk threads, already known to aid settlement in riffles, to increase their chances of successfully transiting pools by reducing fall velocity and/or increasing the chance of resuspension after deposition. In this study we employ video analysis to determine the fall velocity of larvae both with and without naturally produced silk threads. In addition we measure the drag forces exerted on larvae both with and without silk threads under simulated pool-bed flow conditions using scale models. We find that the presence of silk caused a significant reduction in fall velocity ranging from ~50% for the smallest neonates (0.6mm) to ~20% for the largest (7mm) late-instar larvae. In addition, analysis of the scale models revealed that the presence of silk threads should significantly increase the drag force exerted on larvae already settled to the bed. This drag should increase the chance that larvae are resuspended from the bed, allowing them to continue their downstream transport. The combined effect should be to increase the chances for all larvae to successfully transit unsuitable pool habitat. However, the success rate should be much greater for the youngest/smallest larvae and may be important in determining the spatial and demographic distributions of larval populations.