The Mating System and Genetic Diversity of the Australian Arid Zone Mallee, Eucalyptus rameliana

Abstract

Estimates of parameters of the mixed mating model were made for three populations of the bird-pollinated arid zone eucalypt, Eucalyptus rameliana F. Muell. Levels of outcrossing ((t) over cap) varied significantly between populations from mixed mating with substantial selfing ((t) over cap = 0.54) to almost completely outcrossed ((t) over cap = 0.95). Comparison of single-locus and multilocus estimates suggested that the drop in outcrossing was due to increased self-pollination. The lowest outcrossing rate was attributed to the reduced ability of a population with low numbers of buds to attract bird pollinators. Outcrossing rates in E. rameliana are proposed to be a more direct reflection of pollination than estimates made for mass flowering, i.e. small-fruited eucalypts. The distribution of allozyme diversity in E. rameliana also appeared to reflect the impact of bird pollinators in promoting gene flow as well as the species capacity for outcrossing and introgression. Levels of diversity were comparable with other eucalypts, but the proportion of diversity between populations (GST = 9.2%) was only about half the mean for other eucalypts. Genetic distances between populations were low, but there was same significant differentiation of populations which was attributed to non-random bird migrations. The importance of bird pollination in the mating system and the distribution of genetic diversity in E. rameliana emphasises that enough habitat to support nomadic birds should be preserved in order to conserve this eucalypt species.

Mating system and early viability resistance to habitat fragmentation in a bird-pollinated eucalypt

“…However, these inferences remain to be tested. The high degree of outcrossing contrasts with observations of other closely related species, where 60-80% outcrossing has generally been observed for Eucalyptus species (Sampson et al, 1989(Sampson et al, , 1995Sampson and Byrne, 2008;Mimura et al, 2009), although self-incompatibility is expected for some Eucalyptus species on the basis of controlled pollination experiments (Horsley and Johnson, 2007). On the basis of optimal foraging theory, pollinators are expected to spend extended periods in maternal plants in lower density stands, increasing the probability of self-pollination (Ottewell et al, 2009), which is supported by data from other tree species (Lowe et al, 2005;Sork and Smouse, 2006;Eckert et al, 2010).…”

“…E. incrassata generally grows from 4 to 8 m in height, with small hermaphroditic flowers, pollinated primarily by honeyeaters (Family Meliphagidae; for example, Phylidonyris novaehollandiae, New Holland honeyeater; Anthochaera carunculata, red wattlebird) and to a lesser degree, insects (Bond and Brown, 1979). E. incrassata is likely to have a mixed mating system with preferential outcrossing on the basis of observations of other Eucalyptus species (Sampson et al, 1989(Sampson et al, , 1995Horsley and Johnson, 2007;Sampson and Byrne, 2008;Mimura et al, 2009). Eucalypt flowers are protandrous, however, the development of flowers within and between inflorescences is sequential and gradual so that flowers in male or female phase may be in close proximity, allowing geitonogamous selfing to occur (House, 1997).…”

Multiple paternity in Eucalyptus rameliana (Myrtaceae)

“…24°12 S long. 120°26 E. This population was known from a previous study to be highly outcrossed (t m 0.90), whereas other populations had outcrossing rates as low as 0.54 (Sampson et al, 1995).…”

“…Eucalyptus rameliana is a long-lived eucalypt found in scattered populations of a few to several hundred individuals on the slopes and swales of red sand dunes in a restricted area of the Little Sandy Desert in Western Australia (Sampson et al, 1995). It has an open to bushy multistemmed growth form known as mallee, where stems are derived from an underground organ, the lignotuber.…”

“…In Australia many plant species are pollinated predominantly by birds, and although there are several estimates of outcrossing for these species (Hopper & Moran, 1981;Sampson et al, 1989Sampson et al, , 1994Sampson et al, , 1995Sampson et al, , 1996Coates & Sokolowski, 1992), investigations of the correlation of mating in bird-pollinated species have not been made.…”