Phenotypic plasticity of larval retreat design in a net-spinning caddisfly
Gordon
R. Plague and J Vaun McArthur
Savannah River Ecology Laboratory, University of Georgia, PO Drawer
E, Aiken, SC 29802, USA
Larval Macrostemum carolina caddisflies construct silken catchnets
within protective retreats, often on submerged trees and branches (i.e.,
snags). In the Savannah River, M. carolina larvae construct three
distinct retreats that differ in the configuration of the water entrance
hole: (1 ) at the end of a silken tube, (2) flush with the top of the
retreat, and (3) backed by a -180-degree silken backstop. To identify
the proximate mechanism mediating this retreat polymorphism, we removed
larvae of known phenotype from their original retreats and brought them
into the laboratory, allowing them to construct new retreats. We found
that, (1) larvae can construct more than one type of retreat, so variation
in this behavior is not under strict genetic control; (2) larvae do
not preferentially reconstruct their original retreat design, so these
alternative behaviors apparently exhibit little heritability; and (3)
larvae primarily construct each phenotype in a particular microhabitat
(i.e., "tube" and "backstop" retreats are principally
constructed on the downstream half of the snag, and "flush"
retreats on the upstream-bottom quadrant). Therefore, the retreat polymorphism
in M. carolina is phenotypically plastic and is controlled by
microhabitat location or it correlated environmental variable. Most
net-spinning caddisflies construct their nets in fairly specific microliabitats.
However, behavioral plasticity allows M. carolina larvae to construct
retreats all around a snag, thereby reducing potentially intense competition
for space with other net-spinning caddisflies. Consequently, this may
be the ultimate reason this polymorphism evolved.
Keywords: artifical stream channel, behavioral plasticity, Hydropsychidae, interspecific competition, Macrostemum carolina, microhabitat slection, Trichopters.
SREL Reprint #2663
Plague, G. R. and J V. McArthur. 2003. Phenotypic plasticity of larval retreat design in a net-spinning caddisfish. Behavioral Ecology 14:221-226.
