Is fish predation on Enallagma selective pressure?

Abstract

Attempts to explain female color polymorphism in various species of damselfly—particularly Enallagma—have failed to yield convincing data. Increased risk of fish predation on the more conspicuous female Enallagma morph is a worthwhile hypothesis to test because Enallagma are found co-existing with species of fish that are able to detect differences in UV reflection, such as rock bass (Ambloplites rupestris). Rock bass caught in Douglas Lake, Michigan were tested for the ability to differentiate between a conspicuous blue male Enallgama carunculatum damselfly, a male E. carunculatum whose UV reflectance had been diminished with sunscreen (in order to mimic the UV reflectance of a female heteromorph) and male Ishnura, whose color morphology is similar to the female E. carunculatum heteromorph. Attempts to mimic a natural setting failed at obtaining data due to no reactivity from the fish being tested. Rock bass were responsive to a line and hook test. No trend in the reaction time of the rock bass to each of the morphs tested was observed. This does not sufficiently accept the null hypothesis, and more testing should be done on how much UV reflection has an effect on fish prey choice, and also how that relates to polymorphic damselflies.