Abstract
An understanding of genetic diversity and the population genetic processes that impact future population viability is vital for the management and recovery of declining populations of threatened species. Styphelia longissima (Ericaceae) is a critically endangered shrub, restricted to a single fragmented population near Eneabba, 250 km north of Perth, Western Australia. For this population, we sought to characterize population genetic variation and its spatial structure, and aspects of the mating portfolio, from which strategies that optimize the conservation of this diversity are identified. A comprehensive survey was carried out and 220 adults, and 106 seedlings from 14 maternal plants, were genotyped using 13 microsatellite markers. Levels of genetic variation and its spatial structure were assessed, and mating system parameters were estimated. Paternity was assigned to the offspring of a subsection of plants, which allowed for the calculation of realized pollen dispersal. Allelic richness and levels of expected heterozygosity were higher than predicted for a small isolated population. Spatial autocorrelation analysis identified fine-scale genetic structure at a scale of 20 m, but no genetic structure was found at larger scales. Mean outcrossing rate (tm = 0.66) reflects self-compatibility and a mixed-mating system. Multiple paternity was low, where 61 % of maternal siblings shared the same sire. Realized pollen dispersal was highly restricted, with 95 % of outcrossing events occurring at 7 m or less, and a mean pollen dispersal distance of 3.8 m. Nearest-neighbour matings were common (55 % of all outcross events), and 97 % of mating events were between the three nearest-neighbours. This study has provided critical baseline data on genetic diversity, mating system and pollen dispersal for future monitoring of S. longissima. Broadly applicable conservation strategies such as implementing a genetic monitoring plan, diluting spatial genetic structure in the natural population, genetically optimizing ex situ collections and incorporating genetic knowledge into translocations will help to manage the future erosion of the high genetic variation detected.
Highlights
Genetic diversity is widely acknowledged as a critical, yet under-utilized, consideration for the conservation management of threatened species (Allendorf et al 2013; Taylor et al 2017; Laikre et al 2020)
This study has provided critical baseline data on genetic diversity, mating system and pollen dispersal for future monitoring of S. longissima
The present study aims to assess genetic diversity and its spatial structure in S. longissima and to characterize its mating system, breeding system and pollen dispersal
Summary
Genetic diversity is widely acknowledged as a critical, yet under-utilized, consideration for the conservation management of threatened species (Allendorf et al 2013; Taylor et al 2017; Laikre et al 2020). This study is the first to examine population genetic diversity, spatial genetic structure (SGS), mating system and pollen dispersal for any member of the Australian Ericaceae (subfamily Epacridoideae), a large group containing ca 420 species (Crayn et al 2014) It is one of the first to shed light on the ecological genetics of a threatened plant species of the diverse kwongan (Zawko et al 2001; Byrne et al 2014). It is predicted that pollination by insects will result in restricted pollen dispersal, considerable near-neighbour mating and low rates of outcrossing if self-compatible, causing high levels of inbreeding and fine scale SGS In this way, the current study establishes a baseline of understanding of population genetic pattern and process to underpin future genetic monitoring and assessment of conservation and translocation efforts, and to identify strategies for the management of genetic diversity for conservation
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