Morphological changes in Daphnia mendotae in the chemical presence of Bythotrephes longimanus

Induction of helmet formation in Daphnia mendotae was demonstrated experimentally through chemical exposure to the predatory cladoceran Bythotrephes longimanus. The degree of helmet formation recorded in two of three clone lines of D. mendotae is comparable to other published studies on D. mendotae and Daphnia ambigua in the chemical presence of Chaoborus. The results are the first demonstration that B. longimanus, a recent invader of North America, elicits chemical induction of helmet formation in daphniids and, importantly, may help explain recent trends in the post-invasion success of D. mendotae in Lake Michigan and Harp Lake, Ontario, following species invasion by B. longimanus.