Dm. Bilkovic et Jt. Lehman, LIPID-CONCENTRATION AND SIZE VARIATION OF BYTHOTREPHES (CLADOCERA, CERCOPAGIDAE) FROM LAKES ERIE, HURON, AND MICHIGAN, Journal of Great Lakes research, 23(2), 1997, pp. 149-159
Lipid concentrations of Bythotrephes cederstroemi were compared among
three Great Lakes, Erie, Huron and Michigan, in an effort to investiga
te the phenotypic plasticity in size displayed among the lakes. Four d
evelopmental stages were measured in Lakes Erie and Huron and two stag
es were studied in Lake Michigan. With a gravimetric extraction method
, the total lipid concentration range (mu g lipid mu g dry weight(-1),
expressed as percent)for Bythotrephes was estimated to be 10-19%. Sta
tistically significant differences were found in lipid concentrations
of Bythotrephes among lakes and developmental stages. Lake Erie had si
gnificantly higher lipid concentration values than Lake Huron for stag
es 2 through 4, and had similar values to Lake Michigan for the analyz
ed stages I and 4. The fir-st instar had indistinguishable lipid conce
ntrations among Lakes Erie, Huron, and Michigan. Even though animals f
rom Lake Erie were significantly smaller, the data suggest that they w
ere nor less well nourished. We hypothesize that selective mortality i
mposed by visual predators on larger Bythotrephes and the lack of deep
water refuges in Lake Erie has encouraged the smaller size of Bythotr
ephes found there in comparison to those found in Lakes Huron and Mich
igan.