This is part 1 of a three-part series on using conservation genomics to help restore threatened ecological communities. In part 1, we start at the beginning and describe why genetics is relevant to ecological restoration.
Genetic information can help ensure restoration plantings are of appropriate provenance and sufficiently genetically diverse to be resilient in the long term. Fail to adequately consider genetic diversity when sourcing material for your restoration project and you may end up with populations that are unable to adapt to change and exhibit low or no recruitment.
Why we need to consider genetics in ecological restoration
Determining where seed should be sourced is amongst the primary decisions for ecological restoration projects, particularly when it comes to restoring threatened ecological communities.
Professor Maurizio Rossetto, Senior Principal Research Scientist with the Australian Institute for Botanical Science, illustrated the potential consequence of not adequately considering genetic diversity when sourcing seed for revegetation at a workshop on conservation and restoration genomics for field practitioners hosted by the institute’s Research Centre for Ecosystem Resilience (ReCER).
Using a hypothetical scenario of a koala tree revegetation project, Maurizio demonstrated how sourcing material from only one or few populations can decrease the long-term success of restoration projects.
Maurizio Rossetto illustrates why an understanding of genetic diversity is critical to biodiversity management at a workshop on conservation and restoration genomics for field practitioners hosted by ReCER in March 2022.
In the hypothetical scenario, three eucalypt species were included in a koala corridor revegetation project. Seed of one species were collected from across a large geographic range from a broad range of environmental conditions, whereas the other two species were sampled from a single site, and perhaps even from a single tree. “In talking to some practitioners, that is not an uncommon event, a lot of seed are obtained from a particular tree because it is easy to access, and incredibly prolific,” he said.
Sampling from a restricted geographic range or from one or few populations can decrease survival and recruitment of restored populations. For example, considering climate change, local conditions are likely to change. In the hypothetical scenario, the species that was collected from multiple populations from across a large geographic range is much more likely to include individuals that were already experiencing the new conditions a site may be shifting to; they are more likely to be able to adapt to change. Whereas the probability of individuals collected from only a single location being pre-adapted is much lower.
Another consequence of collecting from one or few trees, particularly for eucalypts, is a lack of recruitment. “Generally, eucalypts are preferential outcrossers.” They don’t like to breed with close kin. “So, unless you have a population with sufficiently distant related individuals, those individuals are not going to produce viable progeny. And inbreeding depression is going to impact successful reproduction.”
“Eucalypts seem to be so desperate for outcrossed pollen that they will rather hybridise than inbreed with a close relative. … So not only are you not going to get new pure recruits from the two narrowly sourced species, but you will start to get hybrids as well,” said Maurizio.
Reduced adaptive capacity and inbreeding depression
Dr Jason Bragg, Scientific Officer with ReCER, provided further insight into what is happening at the genetic level when sampling is too narrow, or populations are too small.
“Populations face two key genetic risks. These risks are particularly relevant for small populations,” said Jason.
“The first is the loss of genetic diversity, which leads to the loss of what we call adaptive capacity, and therefore decreases the ability of a population to respond to future change.”
“The second risk is inbreeding depression. As populations decrease in size, it can be harder for individuals to find unrelated mates.”
Restoration practitioners minimise these genetic risks in enhanced or restored populations by striving to maximise genetic diversity and by ensuring populations are large enough to avoid mating among close relatives.
Jason Bragg describing inbreeding depression, a consequence of mating among close relatives, at a workshop on conservation and restoration genomics for field practitioners hosted by ReCER in March 2022.
Is local provenance always best?
Another important consideration when sourcing seed for ecological restoration is provenance. Local provenance seed is collected from a geographic location close to the restoration site, whereas non-local provenance is collected from a more distant geographic location.
For the past few decades, restoration practitioners have favoured local provenance material because it is more likely to be adapted to local conditions.
But what happens when conditions are rapidly changing? Or when there’s not enough local material nearby to collect, as is often the case for threatened species or threatened ecological communities? Or when genetic diversity within a local provenance is no longer sufficient to maintain adaptive capacity due to the loss of individuals?
In such situations, sampling from further afield may be the only way to ensure a population is sufficiently genetically diverse to maintain adaptive potential and avoid inbreeding depression.
We need genetic data rather than generalisations
Given the extent of habitat loss and our changing climate, limiting ourselves to collecting only local provenance material may no longer be adequate, particularly when it comes to restoring threatened ecological communities, where the consequences of using genetically depauperate material may have great implications for the long-term persistence of a community.
Defining provenance boundaries in the absence of genetic information is also challenging. Generalisations have their limitations, with local provenance ranging from sampling within a few hundred meters to across a bioregion. Underestimating provenance size may unnecessarily reduce options for seed sourcing.
Sample further afield and we may maximise genetic diversity and avoid inbreeding depression, but we may also unintentionally risk outbreeding depression. Outbreeding depression may result in the loss of locally adapted genotypes and therefore a situation where offspring of plantings are less fit than their parents.
We are at a point in time where we need real live genetic data rather than generalisations, especially when it comes to restoring threatened ecological communities because the consequences of using inappropriate material can be dire.
“Conservation genetics has stepped into a new phase. Until 10-15 years ago, genetics was always last resort, was considered all too complex, too expensive, too difficult to manage, and too hard to interpret. But now we have moved away from that era,” said Maurizio Rossetto.
“We can now easily gather a lot of relevant genomic information very quickly, very cost effectively, and use that information to provide all sorts of applied outcomes.”