Michiels, N. K.; Beukeboom, L. W.; Pongratz, N.; Zeitlinger, J.: Parthenogenetic flatworms have more symbionts than their coexisting, sexual conspecifics, but does this support the Red Queen? Journal of Evolutionary Biology 14 (1), pp. 110 - 119 (2001)
Michiels, N. K.; Beukeboom, L. W.; Greeff, J. M.; Pemberton, A. J.: Individual control over reproduction: An underestimated element in the maintenance of sex? Journal of Evolutionary Biology 12 (6), pp. 1036 - 1039 (1999)
Weinzierl, R. P.; Beukeboom, L. W.; Gerace, L.; Michiels, N. K.: Spatial and ecological overlap between coexisting sexual and parthenogenetic Schmidtea polychroa (Tricladida; Platyhelminthes). Hydrobiologia 392 (2), pp. 179 - 185 (1999)
Beukeboom, L. W.; Sharbel, T. F.; Michiels, N. K.: Reproductive modes, ploidy distribution, and supernumerary chromosome frequencies of the flatworm Polycelis nigra (Platyhelminthes: Tricladida). Hydrobiologia 383 (1-3), pp. 277 - 285 (1998)
Pongratz, N.; Sharbel, T. F.; Beukeboom, L. W.; Michiels, N. K.: Allozyme variability in sexual and parthenogenetic freshwater planarians: Evidence for polyphyletic origin of parthenogenetic lineages through hybridization with coexisting sexuals. Heredity 81 (1), pp. 38 - 47 (1998)