Divergent life history traits in two closely related species of Simocephalus (Cladocera : Daphnidae) inhabiting lentic environments in Venezuela

We describe life history tactics under laboratory conditions of two species of cladocerans of the genus Simocephalus. The populations live in two habi tats with different characteristics. S. acutirostratus was isolated from a small temporary pool without fish. S. latirostris was found in the marginal vegetation of a reservoir with fish. Their life history was monitored for differences in traits such as clutch size, neonate size, age distribution, reproductive effort and adult survival. Our results show that S. acutirostr atus (the larger-sized species) grows until it reaches the optimal foraging size and then begins to reproduce, while S. latirostris (the smaller-sized species) starts breeding before reaching the optimal foraging size, alloca ting energy mainly to reproduction. We explore the possibility that diverge nces in life history may arise as a response to environmental stress such a s that produced by fishes.