Jumping behavior in the oligotrich ciliates Strobilidium velox and Halteria grandinella, and its significance as a defense against rotifer predators

Abstract

The jumping behavior of Strobilidium velox and Halteria grandinella was analyzed videographically. On average, undisturbed cells of these species jumped 1.7–3.6 and 8 times per minute and spent 0.8 and 1.0% of their time jumping, respectively. Both ciliate species initiated jumps after encounters with rotifer predators. S. velox jumped on contact with Asplanchna girodi, traveling a mean distance of 1.5 mm (33 body lengths) at a mean velocity of 7 mm/s (154 body lengths/s) at 17°C. H. grandinella jumped on contact or near contact with Synchaeta pectinata, traveling a mean distance of 0.37 mm (18 body lengths) at a mean velocity of 2.76 mm/s (131 body lengths/s) at 20°C. The maximum velocity recorded during these escape jumps was 16.07 mm/s for S. velox and 3.70 mm/s for H. grandinella. In S. velox, swimming velocity during jumps was not significantly correlated either with swimming velocity just before jumping (mean = 0.15 mm/s) or with distance traveled. In H. grandinella, jumping velocity and distance also were not significantly correlated. Jumping in S. velox and H. grandinella was calculated to require approximately 149% and 41 % of total metabolic rate, respectively. Jumping seemed to be an effective defense against rotifer predation. Only 3% of 93 S. velox cells contacted by A. girodi were captured, and only 12% of 92 H. grandinella cells contacted or closely approached by S. pectinata were captured; all other cells jumped away. A predation experiment showed that A. girodi was about twice as, and significantly more, likely to ingest Paramecium tetraurelia as S. velox in a mixture of equal numbers of these ciliates. The swimming velocity of S. velox during jumps is the highest one so far reported for an oligotrich, and equals the highest one reported for any ciliate (Mesodinium rubrum).