BRAM, MARGOT R. Department of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ 08901. - The effects of inbreeding on Amaranthus cannabinus (L.) Sauer (Amaranthaceae), a dioecious annual.
The effects of inbreeding were investigated in the greenhouse in three
populations of Amaranthus cannabinus (L.) Sauer, a dioecious
annual. The degree of inbreeding depression varied among populations
and among maternal lineages within populations. However, all three
populations exhibited some negative effects of inbreeding within just
two generations of inbred crosses. Inbreeding depression was observed
in the percentage of germination, leaf size, and plant height. The
plants which exhibited the most inbreeding depression were from a salt
marsh population while the plants which exhibited the least amount of
inbreeding depression were from a freshwater marsh. Differences in
habitat structure among the populations may partly explain the
variation in degree of inbreeding depression observed in the
greenhouse. The need to reduce inbreeding may have been involved in
the evolution of dioecy in A. cannabinus.
Key words: Amaranthus cannabinus, dioecy, inbreeding depression