LIFE-HISTORY VARIATION IN A HYBRID SPECIES COMPLEX OF DAPHNIA

Life-history variation was examined among members of the Daphnia longispina group, which consists of D. galeata, D. hyalina, D. cucullata, and hybrids. Factorial experiments were conducted at two temperatures (14-degrees and 20-degrees-C) and two food concentrations (0.2 and 1.0 mg C l-1). Differences in life-history features (size at maturity, age at first reproduction, size of first clutch, offspring size in first clutch) under the different environmental conditions were assessed among eight Daphnia clones, which represented members of this species complex. Significant differences between parentals and hybrids for most life-history features were observed under various treatments; generally, hybrid clones showed intermediate life-history traits when compared with parentals. When comparisons were made among clones within a given species (i.e. D. galeata, D. galeata x cucullata, D. cucullata), clonal differences were also noted for certain life-history traits. The data are discussed with reference to the formation and maintenance of hybrid species complexes in nature.