Potential Inbreeding in a Small Population of a Mass Flowering Species, <i>Xanthorrhoea johnsonii</i> (Xanthorrhoeaceae): 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.

Outcrossing rates and reproductive success inXanthorrhoea johnsonii(Xanthorrhoeaceae), in south east Queensland, Australia

“…The low levels of inbreeding estimated in these populations are most likely a result of true selfing (within a plant) rather than biparental inbreeding and are in agreement with results from another study on outcrossing rates in this species (King & Zalucki, ). In cases of biparental inbreeding, individual loci often indicate different levels of potential selfing (Ritland & El‐Kassaby, ).…”

“…This is interesting because it indicates that, if plants in close proximity are closely related (as a result of limited seed dispersal), this does not result in high levels of biparental inbreeding. As a long‐lived perennial with an asynchronous flowering pattern, it is possible that temporal separation within a flowering season, and across years, limits matings among kin (King & Zalucki, ). More information on the relatedness of the individuals, and their spatial distribution in the flowering population at any given time, would be required to confirm this.…”

Fine-scale spatial genetic structure in the frankincense tree Boswellia papyrifera (Del.) Hochst. and implications for conservation

“…From the kinship analyses, a significant genetic structure was also detected for both B. papyrifera populations, although in Kurmuk, no significant spatial genetic structure was detected for the seedlings over the whole distance range. Limited gene flow reinforces FSGS across generations (Smouse et al 2008;King and Zalucki 2012;Moran and Clark 2012). In B. papyrifera, FSGS did not significantly change from adult to seedling populations.…”

“…A long life span ensures the representation of many cohorts within a population. This enables such species to maintain diverse individuals across cohorts, ensuring a high genetic diversity within populations (King and Zalucki 2012;Moran and Clark 2012). As a long-lived, widespread species with extensive gene dispersal, B. papyrifera may maintain its genetic diversity across generations in continuous natural forest landscapes, but it may be at risk of losing the genetic diversity in the future in highly fragmented landscapes.…”

“…Due to limited gene flow and the effects of these factors, genetically related individuals aggregate, producing finescale spatial genetic structure (FSGS), which is a decrease of pairwise kinship with increasing pairwise distance (Vekemans and Hardy 2004). The structure is reinforced in subsequent generations due to bi-parental inbreeding and genetic drift if pollen movement and seed dispersal are limited (King and Zalucki 2012;Moran and Clark 2012). On the other hand, extensive dispersal and immigration would weaken FSGS over generations.…”