Pollen dispersal and gene flow by pollen in Araucaria angustifolia

Abstract

Araucaria angustifolia (Bert.) O.Ktze. is an economically important tree in southern Brazil. Indiscriminate exploitation is threatening this species with extinction. Conservation programs are urgently needed to save the remaining forest, and such programs must be guided by biological studies that genetically characterise the remaining populations. Pollen and seed dispersion patterns determine the distance of gene flow and directly influence genetic structure and effective population size. A. angustifolia is a wind-pollinated dioecious tree. For pollen-dispersal airflow, physical characteristics of pollen grain, such as size and shape, must be considered. The aim of this work was to determine the homogeneity of effective pollen clouds as well as to infer the physical characteristics of pollen. The homogeneity of pollen clouds of A. angustifolia was assessed for 70 trees of natural population in Brazil. Analysis of genetic variability and differentiation of the effective pollen clouds detected high diversity at the MDH-B and 6-PGDH-B loci. Heterogeneity G-tests indicated pollen pool heterogeneity in four of seven examined loci (GOT-B, PGM-A, SKDH-B and 6-PGDH-B). The pollen grains measured 61.50 μm. The floating rate ranged from 12.02 to 18.98 cm s^–1. The physical characteristics of the pollen suggest that pollen dispersion is likely to be limited.