Potential inbreeding in a small population of a mass flowering species, Xanthorrhoea johnsonii (Xanthorrhoaceae): is your mother my father?

Abstract

Xanthorrhoea johnsonii is a long lived slow growing perennial understorey species, that produces a large quantity of passively dispersed seed every 3-5 years. Reproductive maturity is not reached until 20-30 years of age. The temporal asynchrony of the flowering event in this population was analogous to geographic isolation through fragmentation. A small population of plants flowering in isolation provided the opportunity to examine outcrossing rates, genetic diversity and the paternity of progeny at a small spatial scale (0.2 ha). The geographic location and physical characteristics of the adult plants were recorded, and both adults and their seed were sampled for genetic analysis. Four microsatellite loci were screened for genetic diversity and spatial structure analysis. A population outcrossing rate was estimated, as well as the number of paternal parents required to resolve the progeny multilocus genotypes. High genetic diversity was found in both adults and progeny with an estimated 97% outcrossing rate. All maternal lines required several paternal contributors, with no evidence of dominant paternal genotypes. Pollen transfer occurred between both geographically close and distant plants.