Floral Morphology, Biology and Sex Allocation in Disjunct Populations of Christmas Bells (Blandfordia grandiflora, Liliaceae) With Different Breeding Systems

Abstract

Evolutionary shifts in breeding systems are often accompanied by changes in reproductive attributes such as floral morphology and biology, and pre- and post-zygotic allocation patterns. The effects of breeding system variation on several such attributes were examined in self-fertile tableland and outcrossing coastal populations of Blandfordia grandiflora R. Br. In general, overall flower size was similar in both populations, although pedicel and pistil stipe diameters were greater in coastal plants, and pistil length and stigma-anther separation were greater in tableland plants. Although all floral parts from coastal flowers weighed more, proportional biomass allocation to floral parts was similar in both populations. Daily nectar production per flower was similar in both populations. Tableland flowers produced more ovules but fewer pollen grains than did coastal flowers. Pollen-ovule ratios were 11 500 in coastal flowers and 5600 in tableland flowers. Open-pollinated tableland fruits produced more seeds than coastal fruits, but individual seeds weighed less; total seed biomass of tableland fruits was greater than coastal fruits. Prezygotic relative male biomass did not differ significantly between populations. Relative male biomass, estimated from stamen and seed weights, was 5% greater in coastal plants, although populations did not differ significantly. Similarly, relative biomass allocation to pollinator attraction (i.e. coralla and nectar) did not differ between populations. The onset and duration of stigmatic receptivity and pollen longevity of flowers from the two populations were similar.

The large differences in ovule, seed and pollen production supports sex allocation theory which predicts that in self-fertile plants resource allocation should be female biased whereas in outcrossing plants, allocation should be male biased. The lack of differences between the Christmas bell populations in other aspects of floral morphology, allocation pattterns and biology suggests that changes in ovule and pollen production precedes changes in other traits during the evolution of autonomous selfing. Overall, these findings suggest that tableland plants may have evolved self-fertility only recently and selection has had insufficient time to change floral traits. Alternatively, self-fertility may not have evolved recently and floral traits promoting outcrossing have been maintained by selection, imposed by inbreeding depression and/or overdominance.