Limited pollen-mediated dispersal and partial self-incompatibility in the rare ironstone endemic Tetratheca paynterae subsp. paynterae increase the risks associated with habitat loss
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Patterns of mating and dispersal are key factors affecting the dynamics, viability and evolution of plant populations. Changes in mating system parameters can provide evidence of anthropogenic impacts on populations of rare plants. Tetratheca paynterae subsp. paynterae is a critically endangered perennial shrub confined to a single ironstone range in Western Australia. Mining of the range removed 25% of plants in 2004 and further plants may be removed if the viability of the remaining populations is not compromised. To provide baseline genetic data for monitoring mining impacts, we characterised the mating system and pollen dispersal over two seasons in T. paynterae subsp. paynterae and compared mating system parameters with two other ironstone endemics, T. paynterae subsp. cremnobata and T. aphylla subsp. aphylla that were not impacted by mining. T. paynterae subsp. paynterae was the only taxon showing evidence of inbreeding (t m = 0.89), although hand pollination revealed pre-zygotic self-incompatibility limits the production of seed from self-pollen. In a year of lower fruit set (2005), the estimate of correlated paternity increased from 20 to 35%. Direct estimates of realised pollen dispersal, made by paternity assignment in two small populations where all adult plants were genotyped, revealed a leptokurtic distribution with 30% of pollen dispersed less than 3 m and 90% less than 15 m. Restricted pollen dispersal maintains the strong genetic structuring of the adult populations in succeeding generations. As a consequence of preferential outcrossing, any reduction in effective population size, flowering plant density and/or the abundance and activity of pollinators may impact negatively on population viability through reduced seed set, increased inbreeding and increased correlated paternity.
KeywordsTetratheca Breeding system Paternity analysis Pollen flow Microsatellite Mining impacts
Funding from Portman Iron Ore Pty Ltd and access to unpublished technical reports is gratefully acknowledged. We also acknowledge support provided by Piers Goodman, James Hesford and Rob Howard from Portman Iron Ore Pty Ltd, field assistance provided by Janet Anthony from Kings Park and Botanic Garden (BGPA), Geoff Cockerton, Shapelle McNee and Gemma McLean from Western Botanical, Colin Yates and Rebecca Dillon from the Department of Environment and Conservation and technical advice on pollination provided by Patrick Courtney from BGPA. Constructive comments from two anonymous referees are also acknowledged. Seed was collected under permit No. SW010813 issued under the Western Australian Wildlife Conservation Act 1950.
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