Ontogenetic shifts in the migratory behavior of Chaoborus flavicans Meigen: field and experimental evidence
Gliwicz, Z. Maciej; Biernack, Anna; Pijanowska, Joanna; Korak, Rafal
published: Sep 29, 2000
ArtNo. ESP141014902002, Price: 29.00 €
Wide range diel vertical migrations of fourth-instar Chaoborus larvae have been shown in many field and experimental studies, but little comparative information is available for the pupae and first three larval instars. In this study we monitored the midday and midnight depth distributions of different instars in a stratifying lake with abundant planktivorous fish as well as in experimental chambers with and without fish kairomones. In both the field population exposed to natural fish predation in the lake, and experimental animals exposed to fish kairomones, we found that the range of migration changed ontogenetically in relation to size/instar-specific vulnerability to predation, from a nonmigratory behavior among the 1st and 2nd instar larvae, to an intermediate-range diel migration in the 3rd instar larvae, and a wide-range migration in the 4th instar larvae and pupae (no experimental support available for pupae), that are largest and thus most vulnerable prey to planktivorous fish. The midday depth and the midnight depth selected by the late larvae and the pupae, were also both greater than those selected by the early larvae. Under laboratory conditions, the range of migration in the 3rd and 4th instar larvae from the field population in the lake was significantly smaller in animals transferred to a medium free of fish kairomones than in those transferred to a medium with fish kairomones, but the migration behavior did not fade away completely in 17 days, and nor did the midday depth selected by larvae decrease to the level observed in animals grown in kairomone-free medium from the time of hatching. The reverse shift in behavior was much faster: when naive 4th instar larvae grown in fish kairomone-free medium were transferred to medium with fish kairomones, the midday mean depth selected by these larvae increased within 12 h, and their behavior was changed from nonmigratory to migratory in 48 h.