Earle, J. D.. Eastern Washington University, jearle@ewu.edu
Buchanan, M. D.. Eastern Washington University, mbuchanan@ewu.edu
Krestian, B. J.. Eastern Washington University, bkrestian@ewu.edu
Black, A. R.. Eastern Washington University, rblack@ewu.edu

We investigated the size selective nature of a predatory aquatic mite, Forelia (Hydracina), on the waterflea, Daphnia pulex (Branchiopoda) in two electivity experiments. In the first electivity experiment, single Forelia were isolated into 500 mls of water and presented with 20 Daphnia from each of three size classes (small juveniles less than 1.0 mm; large juveniles 1.1-2.0 mm; and adults of 2.1mm or greater) for 24-hours. Forelia avoided small juveniles (e=-0.42), preferred larger juveniles (e=0.19), and exhibited neither an avoidance or a preference for adult Daphnia (e=-0.03). To gain insight concerning mite size preference in a more natural environment, Forelia were exposed to D. pulex size structure and densities which reflect spring populations in NE Washington (USA) fishless ponds. Individual Forelia were placed in one liter jars and exposed to 26 D. pulex from five different size classes (1. 0.6-1.15 mm; 2. 1.16-1.71 mm; 3. 1.72-2.28 mm; 4. 2.29-2.83 mm; and 5. 2.84-3.39 mm) for 24 hours. Forelia avoided D. pulex in size class 1 (e=-0.46), exhibited no preference for Daphnia in size class 2 (e=0.03), and tended to prefer the largest juveniles and adults (electivity values equal 0.3, 0.15, and 0.26 for size classes 3-5, respectively). Our results suggest Forelia exhibit body size preferences for Daphnia similar to several predaceous aquatic insects.
Day: Tuesday, Feb. 2
Time: Poster
Location: Sweeney Center
Code: CS67TU1517S