PARENT SESSION
Oral Session #56: Aquatic Ecology: Plankton. Presiding: N. Hairston.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas I.

Adjustment in pigmentation level to predation risk and ultraviolet radiation among freshwater copepods.

Hansson, Lars-Anders¹, ¹

ABSTRACT- All organisms are continuously faced with multiple sources of information, and when exposed to multiple sources of conflicting information, an organism may respond differently from when exposed to one stimulus at a time. Ultraviolet (UV) radiation is harmful to all life, but some organisms have evolved adaptations to reduce the radiation damage, such as various types of protective pigmentation among freshwater zooplankton. However, strong pigmentation also increases vulnerability to visually hunting predators. Hence, where both UV radiation and predation are intense, zooplankton may be sandwiched between conflicting selective pressures, to be pigmented and to be transparent at the same time. Here, I show that the level of pigmentation among copepods is up to ten times higher in lakes without predatory fish than where fish are present. In addition, field studies covering more than a year show that both the level and the amplitude in pigmentation is lower in lakes with than without fish predators. Moreover, animals from the same population experimentally exposed to UV light or predator scent showed a 10% difference in pigmentation, suggesting that pigmentation is an inducible trait. Hence, individual copepods are not passive victims of selective predation or radiation damage, but adjust the level of pigmentation according to the prevailing threat.

KEY WORDS: copepod, pigment, predation, UV