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Cyclops insignis; Cyclops strenuus; developmental plasticity; diapause; ephemeral habitats; juvenile development
Abstract:
Temporary-pond species can be expected to use environmental cues to predict the onset
of adverse conditions, while permanent-pond species may be insensitive to such cues.
Temperature is such a potential cue in temporary waterbodies, as it fluctuates more widely
with decreasing pond size than in deeper permanent ponds. We compared the temperatureinduced
response of a permanent-pond and a temporary-pond cyclopoid copepod focusing
on juvenile development duration, diapause induction and survival during diapause. Nonlinear
regression analysis suggested a stronger effect of temperature on the duration of
juvenile development in the temporary-pond species. This species also showed a higher and
temperature-dependent variation in development duration (highest coefficient of variation
26%) compared with the permanent species, for which variation was lower and similar at
all temperatures (maximal coefficient of variation 6%). Temperature significantly influenced
the induction of diapause in the temporary-pond species, where the percentage of individuals
entering diapause increased from 0% at 5°C and 10°C to 63% at 15°C and 91% at 20°C. In
the permanent-pond species, diapause induction was independent of temperature and was
induced in 100% of experimental specimens. This suggests an obligatory diapause in
the permanent-pond species, a type of dormancy that has not been described previously
for cyclopoid copepods. Survival during diapause in both species was higher when the
diapausing copepodid stage was reached at lower temperatures. At higher temperatures,
the temporary-pond species survived longer than the permanent-pond species. These
results suggest different temperature optima of the two species. The strategy displayed by the
permanent-pond species might be selected for in more stable habitats and may preclude
the colonization of temporary ponds. Higher flexibility in life-history traits and the use of
temperature as an environmental cue in the temporary-pond species could be favoured
in unpredictable habitats.
