Are differences in breeding mechanisms and fertility among populations contributing to rarity in Grevillea rhizomatosa (Proteaceae)?

Abstract

Plant breeding systems are seldom studied across the breadth of a species' range. For many systems, this precludes an informed assessment of the evolutionary biology of a species, particularly of the factors that shape fecundity. Grevillea rhizomatosa is a threatened species of shrub known only from a 7 × 8 km area and c. 2000 plants in northern New South Wales, Australia. The species reproduces asexually from rhizomatous suckers, and fruit are only produced in a few populations. Over two flowering seasons, we investigated the extent of sexual reproduction and the mechanisms of infertility in five populations that span the range of the species. Seed were produced in three of the five populations. The breeding system varied among populations from obligate outcrossing to facultative outcrossing to fully sterile. Fruit to flower ratios were below 0.13 in the fertile populations but within the range found in other species of Grevillea. Pollinator limitation was not linked to infertility. Stigmatic opening and receptivity were functional in all populations. Interpopulation crosses using fertile pollen failed to recover fertility in an infertile population. A breakdown in female and male fertility mechanisms was found including a fault in the mechanical release of pollen from anthers, <10% viable pollen, and a post-pollen-deposition event that prevents fertile pollen from effecting seed-set. In the infertile populations pollen was not released from anthers, resulting in flowers projecting barren pollen-presenters. Sexually reproducing populations are threatened by the incursion of asexual forms that may be favored by frequent disturbance from wild-fires.

Divergent levels of genetic variation and ploidy among populations of the rare shrub, Grevillea repens (Proteaceae)

“…Abbott et al 2007). Third, it means that genetic rescue might not be effective in all G. repens populations (c.f., Gross and Caddy 2006) and care needs to be taken to avoid triploid plants when sourcing vegetative and other material from one population for enhancing the size of other populations.…”

“…Plants from this genus play important ecological roles within the Australian biota including the provision of food for numerous vertebrate and invertebrate species (Olde and Marriott 1994) and extinction of populations may have flow-on ecological effects. Many Grevillea species combine both sexual and clonal reproduction (Makinson 2000) however, some populations within these taxa rely predominantly (or exclusively) on vegetative reproduction (Burne et al 2003;Gross and Caddy 2006;Olde and Marriott 1994). Some species appear to currently lack sexual reproduction altogether (Kimpton et al 2002).…”

Evidence for autonomous selfing in grassland Protea species (Proteaceae)

“…; Vaughton & Ramsey, 1991) supplemented by within‐flower self‐pollination due to stigma opening at or soon after anthesis before self‐pollen has been removed (e.g. early receptivity in Grevillea rhizomatosa Olde & Marriott; Gross & Caddy, 2006). Other mechanisms that prevent autonomous self‐pollination include a narrowed stigmatic groove at anthesis (Matthews, Gardner & Sedgley, 1999), and complex stigmatic structures blocking the path for self‐pollen to reach the stigmatic groove such as cellular outgrowths (Ladd et al ., 1998).…”

Reproduction in Wild Populations of the Threatened TreeMacadamia tetraphylla: Interpopulation Pollen Enriches Fecundity in a Declining Species

“…2004). Moreover, the Australian Proteaceae are thought to have very low levels of self‐compatibility and species are often subject to pollen limitation (Goldingay & Carthew 1998, but see Smith & Gross 2002, Gross & Caddy 2006). Macadamia is the only Australian rain forest Proteaceae studied in detail, but most research effort has focused on cultivars in orchards and usually M. tetraphylla × M. integrifolia hybrids.…”

“…Studies of non-rainforest Proteaceae have demonstrated that fragmentation, small population size, and low plant density can have negative impacts on reproduction (Lamont et al 1993, Field et al 2005, survival (Drechsler et al 1999), gene mixing and gene flow (Coates & Sokolowski 1992), and genetic diversity (Ayre et al 1994, Llorens et al 2004. Moreover, the Australian Proteaceae are thought to have very low levels of self-compatibility and species are often subject to pollen limitation (Goldingay & Carthew 1998, but see Smith & Gross 2002, Gross & Caddy 2006. Macadamia is the only Australian rain forest Proteaceae studied in detail, but most research effort has focused on cultivars in orchards and usually M. tetraphylla × M. integrifolia hybrids.…”