Limiting inbreeding in disjunct and isolated populations of a woody shrub

Abstract

Pollen movements and mating patterns are key features that influence population genetic structure. When gene flow is low, small populations are prone to increased genetic drift and inbreeding, but naturally disjunct species may have features that reduce inbreeding and contribute to their persistence despite genetic isolation. Using microsatellite loci, we investigated outcrossing levels, family mating parameters, pollen dispersal, and spatial genetic structure in three populations of Hakea oldfieldii, a fire‐sensitive shrub with naturally disjunct, isolated populations prone to reduction in size and extinction following fires. We mapped and genotyped a sample of 102 plants from a large population, and all plants from two smaller populations (28 and 20 individuals), and genotyped 158–210 progeny from each population. We found high outcrossing despite the possibility of geitonogamous pollination, small amounts of biparental inbreeding, a limited number of successful pollen parents within populations, and significant correlated paternity. The number of pollen parents for each seed parent was moderate. There was low but significant spatial genetic structure up to 10 m around plants, but the majority of successful pollen came from outside this area including substantial proportions from distant plants within populations. Seed production varied among seven populations investigated but was not correlated with census population size. We suggest there may be a mechanism to prevent self‐pollination in H. oldfieldii and that high outcrossing and pollen dispersal within populations would promote genetic diversity among the relatively small amount of seed stored in the canopy. These features of the mating system would contribute to the persistence of genetically isolated populations prone to fluctuations in size.

Evaluating restoration outcomes through assessment of pollen dispersal, mating system, and genetic diversity

“…The nearest known natural remnant is the reference population located approximately 2 km from the restoration site. Although limited in amount, pollen immigration into the study area may well have occurred over such a distance, as pollen dispersal over this distance has been documented in another Hakea species (Sampson et al 2016). Generalist insect pollinators are known to be capable of extensive pollen dispersal in many fragmented landscapes.…”

“…Standard deviations (population values) or standard errors (means) are in parenthesis. a Values are significantly different to 1 (t m and t s ) or to zero (other estimates (Sampson et al 2016). Combined with a high outcrossing rate, a pattern of random realized pollen dispersal suggests the attraction of effective pollinators for the restoration population of H. nitida.…”

Recovery of threatened plant species and their habitats in the biodiversity hotspot of the Southwest Australian Floristic Region

“…Despite no direct genetic and demographic effects of fragmentation, the associated disturbance has led to high weed densities resulting in a lack of recruitment in populations in degraded remnants (Gibson et al., 2012). In another rare species, Hakea oldfieldii , high outcrossing rates and long distance pollen dispersal appear to maintain connectivity among naturally fragmented populations (Sampson et al., 2016).…”

NMπ—improved re‐implementation of NM+, a software for estimating gene dispersal and mating patterns

“…Some years ago, the neighbourhood model was implemented in the NM+ software (Chybicki & Burczyk, ). The software has been successfully applied in a number of studies (e.g., Llorens, Byrne, Yates, Nistelberger, & Coates, ; Sampson, Byrne, Gibson, & Yates, ; Saro, Robledo‐Arnuncio, González‐Pérez, & Sosa, ). However, the fixed structure of the program makes it of limited applicability to specific study designs or questions (e.g., Chybicki & Burczyk, ; Lagache, Klein, Ducousso, & Petit, ).…”