Effects of Inbreeding in Three Populations of the Dioecious Annual Amaranthus cannabinus (Amaranthaceae)

Inbreeding depression in dioecious populations of the plant Mercurialis annua: comparisons between outcrossed progeny and the progeny of self-fertilized feminized males

“…In fact, Amaranthus cannabinus (Amaranthaceae), a dioecious perennial, was found to have surprisingly low inbreeding depression, too (Bram, 2002), similar to that found in the dioecious M. annua lineages studied here. Bram (2002) suggested that low inbreeding depression in A. cannabinus could have been due to the fact that only early life history traits were measured in this long-lived perennial, plants were not allowed to compete with one another and plants were not grown in the field. In contrast, we measured inbreeding depression in M. annua under field conditions, allowing for inter-and intra-specific competition, and we accounted for all life-history stages from germination through late survivorship and fertility.…”

“…In contrast, we found that inbreeding depression was on average low in the dioecious lineages we sampled. A low inbreeding depression in outcrossing plant populations is uncommon but not unprecedented (Bram, 2002;AEgisdó ttir et al, 2007). In fact, Amaranthus cannabinus (Amaranthaceae), a dioecious perennial, was found to have surprisingly low inbreeding depression, too (Bram, 2002), similar to that found in the dioecious M. annua lineages studied here.…”

“…A low inbreeding depression in outcrossing plant populations is uncommon but not unprecedented (Bram, 2002;AEgisdó ttir et al, 2007). In fact, Amaranthus cannabinus (Amaranthaceae), a dioecious perennial, was found to have surprisingly low inbreeding depression, too (Bram, 2002), similar to that found in the dioecious M. annua lineages studied here. Bram (2002) suggested that low inbreeding depression in A. cannabinus could have been due to the fact that only early life history traits were measured in this long-lived perennial, plants were not allowed to compete with one another and plants were not grown in the field.…”

“…In some gynodioecious species, inbreeding depression is sufficiently high to explain the maintenance of females (Kohn and Biardi, 1995;Schultz and Ganders, 1996;Sakai et al, 1997;Thompson et al, 2004;Medrano et al, 2005; but see Ashman, 1992;Eckhart, 1992;Koelewijn and van Damme, 2005). However, for dioecious plant species, which are obligate outcrossers, there are currently estimates of inbreeding depression only in two species, one showing high levels (Dorken et al, 2002) and the other showing low levels (Bram, 2002). It is thus difficult to make generalizations about the level of inbreeding depression in dioecious species.…”

Moving to mate: the evolution of separate and combined sexes in multicellular organisms

“…However, alternate theory and recent work highlights the benefits of investing in either male or female function (i.e. sexual specialization) as a factor influencing the evolution of separate sexes in plants (Charnov, 1982; Charlesworth & Morgan, 1991; Charlesworth, 1999; Bram, 2002; Gleiser & Verdu, 2005; Eppley & Pannell, 2007a). Selection for combined vs. separated sexes is also expected to be influenced by population‐level effects, particularly density.…”