Australasian Plant Conservation
Originally published in Australasian Plant Conservation 19(3) December 2010 - February 2011, p 23-24
A practical genetic contribution towards best-practice seed-sourcing guidelines for ecological restoration
Siegy Krauss, Liz Sinclair, Jessica Stingemore and Kristina Hufford
Kings Park and Botanic Garden, West Perth, WA, and School of Plant Biology, University of Western Australia, Crawley, WA.
Figure 1. Banksia prionotes seedlings sourced from plants growing 70 km apart at Eneabba and Badgingarra (south-west Western Australia), grown in soil from the Eneabba site. The relatively poor growth of the non-local Badgingarra seedlings on the right compared to the local Eneabba seedlings on the left, demonstrate a strong home-site advantage for local provenance seeds due to substrate.
Seed sourcing issues are of fundamental importance for successful ecological restoration. Where biodiversity objectives are a high priority in an ecological restoration project, the sourcing of diverse, local provenance seed has been long recognised as best practice. There are situations where local provenance seed may not be a priority (e.g. restoring highly altered landscapes) and other issues such as source population properties require consideration (Broadhurst et al. 2008). However there remain numerous reasons, described below, why local provenance must be considered a starting point for seed sourcing decisions.
It has been known for more than 300 years that all species display genecological variation throughout their range. Thus, populations of plants are adapted such that their phenotypes respond as well as possible to the environmental factors of their particular habitats. In an ecological restoration context, this has been termed home-site advantage, where local genotypes display greater fitness than non-local genotypes. For example, local (Eneabba) Banksia prionotes seed grown in a glasshouse in local (Eneabba) soil displayed seedling biomass and vigour three times that of non-local (Badgingarra) seed (Figure 1). This home-site advantage can result in ineffective and inefficient restoration if using poorly adapted non-local provenance seed.
The introduction of non-local provenance genotypes can have negative genetic effects of poor integration with local genotypes. Mating between non-local and local genotypes can result in outbreeding depression in their offspring (Hufford and Mazer 2004). Impacts of outbreeding depression can be as severe as negative impacts from inbreeding depression. For example, artificial cross pollinations between Stylidium hispidum (triggerplant) plants sourced from populations separated by 120 km resulted in less than half the number of established seedlings compared to crosses between local plants, as a consequence of outbreeding depression.
Poor genetic integration of non-local genotypes can also result in the genetic swamping of local genotypes. For example, the local variety of Chamelaucium uncinatum in Bold Park, Perth, called Wembley Wax, is threatened by genetic swamping caused by the introduction of a cultivated northern variety, the Geraldton Wax. Without the removal of the introduced variety, the loss of the locally significant variety through genetic dilution or swamping is likely.
Through the extended phenotype, genetically differentiated provenances can have a marked effect on the biological communities they support. For example, assessment of a provenance trial in Eucalyptus globulus showed different provenances harbour different fungi and arthropod communities (Barbour et al. 2009). Sourcing seed from non-local populations can have negative flow-on effects on the biological communities they support.
Biological diversity is recognised through the Convention on Biological Diversity at landscape, ecosystem, species and population genetic levels. Mixing of genetically differentiated provenances leads to an erosion of the natural genetic structure of populations within species, leading to a loss of biodiversity.
How local is local?—a practical genetic contribution
A key question for restoration practitioners, then, is how far from a restoration site can seed be collected before it impacts negatively on restoration outcomes. Negative impacts can be felt through inefficient or ineffective restoration, or through local biodiversity impacts.
For the past 10 years, we (with support from other research staff, university collaborators, and Australian Research Council and industry funding) have been applying molecular markers and an efficient sampling approach to make a practical genetic contribution to the delineation of local provenance seed collection zones. Whilst the molecular markers we have used are largely neutral, recent reviews indicate that (i) neutral genetic variation estimates of genetic structure are positively correlated with adaptive (quantitative trait) markers, and (ii) genetic structure found with neutral markers typically hides a lot of cryptic genetic differentiation in genes coding quantitative traits (Savolainen et al. 2007). That is, neutral markers almost always substantially under-estimate the genetic differentiation among populations found with adaptive markers, further emphasising the importance of local provenance because they are best adapted to local conditions.
In our pursuit of a genetic provenance atlas for south-west Western Australia, we now have population genetic data for more than 35 native plant species (Bussell et al. 2006). These data are visualised in two key ways. Firstly, ordinations of all samples show the degree of genetic overlap among populations. Strongly differentiated populations will show no overlap, while undifferentiated populations will show marked overlap. Secondly, we use a measure (Fst) that indicates the proportion of total genetic variation that is partitioned among populations compared to that within populations. A high Fst indicates most variation is partitioned among populations, and the genetic differentiation among populations is strong.
For general utility, we have interpreted these ordination and Fst results and classified species into one of three provenance classes—narrow, intermediate and broad—to guide seed collectors on the relative importance on sourcing seed locally. For example, Acacia rostellifera showed very high Fst and marked non-overlap of population clusters in ordinations of genetic data, and was classified as having a narrow genetic provenance, so seed should be collected very locally. At the other scale, wind pollinated Restionaceae and Cyperaceae were found to have very low Fst and marked overlap of populations in ordinations, indicating a broad provenance, with wide seed collection acceptable. The widespread tree species Jarrah (Eucalyptus marginata), Marri (Corymbia calophylla) and She-oak (Allocasuarina fraseriana) were found to have similarly broad provenances for seed sourcing.
Our continuing studies are providing practical genetic seed sourcing guidelines for restoration practitioners, and are re-emphasizing the importance of local provenance seed sourcing where there are biodiversity objectives.
Barbour, R.C., O’Reilly-Wapstra, J.M., De Little, D.W., Jordan, G.J., Steane, D.A., Humphreys, J.R., Bailey, J.K., Whitham, T.G. and Potts, B.M. (2009). A geographic mosaic of genetic variation within a foundation tree species and its community-level consequences. Ecology 90:1762–72.
Broadhurst, L.M., Lowe, A., Coates, D.J., Cunningham, S.A., McDonald, M., Vesk, P.A. and Yates, C. (2008). Seed supply for broadscale restoration: maximizing evolutionary potential. Evolutionary Applications 1:587–97.
Bussell, J.D., Hood, P., Alacs, E.A., Dixon, K.W., Hobbs, R.J. and Krauss, S.L. (2006). Rapid genetic delineation of local provenance seed-collection zones for effective rehabilitation of an urban bushland remnant. Austral Ecology 31: 164–75.
Hufford, K.M. and Mazer, S.J. (2004). Plant ecotypes: genetic differentiation in the age of ecological restoration. Trends in Ecology and Evolution 18: 147–55.
Savolainen, O., Pyhajarvi, T. and Knurr, T. (2007). Gene flow and local adaptation in trees. Annual Review of Ecology, Evolution and Systematics 38: 595–619.