Reproductive constraints: Changes in pollen viability over the flowering season in Banksia
Honors research project by Rose Hyde
The genus Banksia (family Proteaceae) is a plant group with intriguing biogeography and reproductive biology. All but one species are endemic to Australia, and most are pollinated by marsupials and birds rather than insects. The flowering seasons last up to 6 months, and span periods of drought.
The purpose of my study was to determine whether pollen viability changes across the flowering season in four species of Banksia, two in the mid-late blooming period, and two which had just begun blooming. All four were located in an abandoned plantation near Happy Valley, South Australia. Pollen was hand-collected and viability was assessed using two methods: 1) In-vitro pollen tube germination and 2) triphenyl tetrazolium chloride stain. In addition, the effect of temperature on pollen germination was investigated in one species.
The results show that there is a statistical difference between viability percentages from the beginning of the study and those from the end in all four species.
Changes in pollen viability may be a resource allocation strategy. Non-viable pollen may be energetically cheaper to produce, yet ensure pollinator visitation during times when resources are not scarce. Periods of greater viability may also coincide with times of increased outcrossing possibility.