The effects of fish presence on mayfly allometry

The presence of predatory fish in a stream can change body size, behavioral patterns, and life history in some pieces of mayflies that seek to minimize the threat of predation.  While there is some evidence for altered morphology in certain mayfly taxa, it is not known whether the presence of fish impacts the allometry of their prey.  We examined Baetis sp. (summer), an un-described species to examine how reduced size at emergence may affect Baetis body shape.  We measured head-capsule width, body length, and ash-free dry mass of male and female mayfly larvae collected from fish and fishless reaches of a Rocky Mountain stream.  Body length more accurate predicted body mass than did head-capsule width.  Maximum likelihood analysis revealed little difference in the parameter estimates between body length and body mass for mayflies from fish versus fishless reaches.   Our results suggest that while mayflies mature at smaller size in streams that contain fish, their allometries are similar to those from fishless streams.