Restricted gene flow within the morphologically complex species Persoonia mollis (Proteaceae): contrasting evidence from the mating system and pollen dispersal

Abstract

Severely restricted gene flow may be a factor contributing to the remarkable amount of morphological variation within the complex species Persoonia mollis, in which nine subspecies are recognized. The mating system and realized pollen dispersal were studied to assess their effect on gene flow. Mating system parameters were estimated in seven natural populations over two seasons using allozyme electrophoresis. Realized pollen dispersal was measured in two natural populations over two seasons by monitoring the dispersion of a rare allozyme from a known source plant in each population. Single-and multilocus estimates of outcrossing rate (t) were consistently equal to or greater than one (i.e. complete outcrossing). Realized pollen dispersal distances showed that 99 per cent of the pollen received by given females was donated by males on average within 33 m. However, 70 per cent of all pollen dispersal was on average to the paternal plant's immediate neighbour. Genetic neighbourhood sizes due to pollen dispersal alone ranged from one to five plants and paternity pool sizes ranged from four to 22 plants. These population sizes are small enough to allow genetic differentiation in the absence of selection. However, in contrast to the expectation that small population size leads to biparental inbreeding and reduced heterozygosity compared with Hardy-Weinberg expectations, the mean fixation index (F) of -0.035 indicated a slight excess of heterozygotes in the seed cohort. This apparent paradox could be the result of selection for heterozygous seeds, disassortative mating or more likely because gene flow through seed dispersal substantially increases the neighbourhood sizes estimated here through pollen dispersal alone.

Genetic divergence and the mating system in the endangered and geographically restricted species, Lambertia orbifolia Gardner (Proteaceae)

“…, 1988 ; Coates & Sokolowski, 1992). Very high outcrossing rates were observed in another member of the family, Persoonia mollis ( Krauss, 1994). In contrast, consistently low levels of outcrossing were found in all four populations of L. orbifolia.…”

Pollination ecology and the possible impacts of environmental change in the Southwest Australian Biodiversity Hotspot

“…Studies using pollen tracking and paternity assignment (e.g. Krauss 1994;Kropf & Renner 2008) are not directly comparable with those based on pollinator observation due to the prevalence of pollen carryover (Broyles & Wyatt 1991). However, use of these techniques will provide the most direct test of the effectiveness of a pollinator at dispersing genes, assuming that the pollinator responsible for each pollen movement can be isolated.…”

Comparison of pollinator flight movements and gene dispersal patterns in Mimulus ringens

“…Pollinators frequently move short distances (Bateman, 1947b;Levin & Kerster, 1969a,b;Fenster, 1991), potentially limiting gene dispersal. However, pollinator flight data may underestimate the extent of gene movement within populations because of the effects of pollen carryover (Price & Waser, 1979;Schaal, 1980;Thomson & Plowright, 1980;Thomson & Thomson, 1989) and post-pollination events influencing fertilization (Campbell, 1991;Marshall & Folsom, 1991;Krauss, 1994). Several researchers have quantified patterns of gene dispersal by introducing one or two marker genotypes into populations lacking the novel alleles (Bateman, 1947a;Schaal, 1980;Levin, 1981;Ennos & Clegg, 1982;Handel, 1982;Galen, 1992).…”