Abstract |
This study investigates how the presence of symbiotic crabs (Pinnixa chaetopterana or
Polyonyx gibbesi) in the tubes of the polychaete Chaetopterus variopedatus affects the worms’
pumping activity and growth rates under laboratory and field conditions. In the field, worms whose
tubes are inhabited by Pinnixa beat their fan segments significantly more frequently than do
worms hosting Polyonyx, but other measures of pumping activity do not differ according to
symbiont species. In the lab, worms tend to move water through their tubes at higher rates when
crabs are present. In 7-month laboratory experiments, growth rates of worms hosting either species
of crab did not differ from growth rates of worms without crab symbionts. Although worms
hosting Polyonyx are, on average, significantly larger than worms hosting Pinnixa, this appears to
be due to competition between the crab species for hosts and not due to differential effects on host
growth. Unlike the crabs in this study, pea crab species inhabiting bivalves are known to have
strong deleterious effects on host growth and reproduction, suggesting that the evolution of
virulence in symbiotic interactions is dependent upon specific ecological context. |