CPC Best Plant Conservation Practices

to Support Species Survival in the Wild

Key Messages about Genetics Related to Collecting
  • Planning the quantities to collect from one population and across the range of species will improve the chance of maximizing the genetic diversity of the conservation collection.
  • Maintain maternal lines separately to help approximate potential genetic diversity and allow flexibility for use in future conservation translocations.
  • Collect no more than 10% of a population’s seed crop in a single year and no more than 5 years out of 10.

Prior to collection, ascertain what is known about current distribution, population sizes, and reproductive biology.

  • See CPC Best Practices Section, “Collecting Seeds from Wild Rare Plant Populations” and “Questions to Ask before Acquiring a Conservation  Collection.”
  • Determine the locations and known (or estimated) sizes of populations.
  • Research the reproductive biology including breeding system, self-compatibility, monoecy versus dioecy, and pollination mechanism. Because all influence patterns of genetic diversity of the population, knowing this information will influence the collection protocol. (See Figure 3.2,“Summary of Collecting Recommendations for Numbers of Populations to Sample,” and Figure 3.3, “Summary of Collecting Recommendations for Numbers of Individuals to Sample within a Population.”)
  • Check whether any previous genetic studies (common garden or molecular) have been done on the target species as these might inform collection priorities.
  • If there are known taxonomic issues in the species such as hybridization, taxonomic ambiguity or polyploidy variation, take herbarium vouchers and tissue samples for morphological and genetic studies that may be linked to your collection.
  • If little is known about the species’ breeding system or pollination mechanism, reviewing close relatives may give clues. Note that starting with close relatives may be helpful, but it is not always guaranteed that the biology will be exactly the same as the rare species.

Collect material to capture representative genetic diversity.

  • Collect material (seeds, cuttings, spores, etc.) across the diverse spatial, ecological, temporal and population sizes existing for the species to capture its representative genetic diversity.
  • Collect from as many populations as resources allow, at least five populations that represent the range of variation in distribution, ecology, and population size (Falk and Holsinger 1991). The more populations collected, the greater the probability that the range of genetic variation will be captured. This is particularly true for any selfing or clonally reproducing species, where genetic diversity will be greatest between populations (Schoen and Brown 1991). The ideal would be to capture all populations especially for those species that have less than 20 populations in existence.
  • Collect across the species’ entire range, stratified across environmental features such as soil, elevation, and climate (Guerrant et al. 2014). Collect from both small and large populations, from edge and core parts of distribution.
  • Generally, the amount of genetic variation captured increases with the total number of populations added. However, there is a point where the gain of unique alleles levels off and there is no gain in diversity when adding more individuals or populations. (See Figure 3.1; Griffith et al. 2015; Hoban and Strand 2015; and Hoban and Schlarbaum 2014 for simulation studies related to efficient sampling).

Seed Sampling Improvements for Quercus boyntonii

Sean Hoban, Emma Spence, and Patrick Thompson, The Morton Arboretum The Morton Arboretum seeks to improve the conservation value and genetic representation in ex situ... Read More

Figure 3.1 – Genetic analysis can help quantify whether a conservation collection holds the majority of genetic diversity of a wild population. Griffith et al. (2015) compared the number of alleles measured in 10 microsatellite markers of the cycad Zamia decumbens to the numbers captured in 205 ex situ plants held in botanical garden collections. A single-accession collection (smallest points) would capture between 27% and 57% of in situ alleles, while the entire ex situ collection (7 accessions, 205 plants) captures 78% of wild population alleles.

  • Basey et al. (2015) suggest this sampling strategy to maximize diversity capture:
    • Collect from plants that grow far apart as they are more likely to be unrelated.
    • Collect from large and small maternal plants—robust and spindly, with abundant and few fruits. Collect seeds from very different-looking individuals.
    • Collect multiple times in a season to capture early- or late-flowering plants.
    • Collect from plants in all microhabitats at a site.
    • If collecting from multiple populations of the same species, use the same collecting strategy for all populations.
  • Collect across years and multiple times in a season to capture early-, mid- or late-flowering plants as well as individuals adapted to variable climatic factors (Guerrant et al. 2014; Basey et al. 2015). For small populations with few reproductive individuals, it will be especially important to make collections across multiple years.
  • For species that produce no seed, attempt to collect tissues from up to 50 unrelated individuals from multiple populations. The size of plants at maturity and space available will likely influence the number of plants that can be maintained long-term at any institution.

From how many populations should I collect?

The general rationale is that in highly outcrossing species with extensive gene flow (large neighborhood size), populations are more similar (so one can collect from fewer populations). Whereas in a selfing species or one with limited gene flow (small neighborhood size), we expect populations to be very different, therefore we advise collecting from more populations.

From how many individuals should I collect within a population?

Outcrossing leads to higher diversity within a population than across populations, so focus collection efforts on collecting more individuals within a population. In a highly selfing species, you expect individuals to be similar, so you might be fine to collect from fewer individuals.

– Kay Havens

Plan your sampling strategy.

  • Use population size and fecundity to plan your sampling strategy for the collection.
  • An ideal collection would have a total of 3000 seeds from at least 50 unique unrelated maternal plants to maximize allelic frequencies represented in each accession (Brown and Marshall 1995; Guerrant et al. 2004; Guerrant et al. 2014). Note that the breeding system may adjust the representative number of maternal plants recommended. (See Figure 3.2 below, “Summary of Collecting Recommendations for Numbers of Populations to Sample,” and Figure 3.3 below, “Summary of Collecting Recommendations for Numbers of Individuals to Sample within a Population.”)
  • If maternal plants produce few seeds, it may be necessary to collect from more than 50 maternal plants to obtain a collection of 3000 seeds while collecting within permit restrictions. FAQ – Why should I try to collect 3000 seeds? and FAQ – Why should I try to collect from 50 maternal  plants?
  • If populations are simply too small to produce 3000 seeds in a season, or even across multiple years, collecting a few seeds may be the only option. In these instances, attempt to capture up to 10% of the seeds from each of the reproductive individuals across multiple years. To avoid collecting from the same perennial individual across years, it may be necessary to place tags on individuals so that they can be identified in the future.
  • Realize that extremely small seed collections (<100 seeds) will require making additional collections in the future. If more than 300 seeds cannot be collected within 5 years, try a seed increase rather than wild collection to increase quantities of seeds in storage. (See CPC Best Practice Section, “Curating Small Samples” if it is unlikely that a collection can ever surpass 100 seeds or 300 seeds in 5 years.)? FAQ – Will it be damaging to collect 10% of the seed production in sequential years?

Figure 3.2 – Summary of Collecting Recommendations for Numbers of Populations to Sample. CPC recommends collecting from at least 5 populations across the range of a species. You can use the row factors in this figure to refine your decision. If any of the row factors falls into the red zone, we recommend collecting from all populations. If factors fall into the yellow or green zone, then it is reasonable to collect from fewer populations. (Adapted from Falk and Holsinger 1991.)

Figure 3.3 –  Summary of Collecting Recommendations for Numbers of Individuals to Sample within a Population. CPC recommends collecting from 50 unique maternal plants within a population. You can use the row factors in this figure to refine your decision. If any of the row factors falls into the red zone, we recommend collecting from all individuals. If factors fall into the yellow or green zone, then it is reasonable to collect from fewer individuals. (Adapted from Falk and Holsinger 1991.)

Maintain accessions of each population separately with packages of maternal lines separated.

  • It is always better to collect and maintain maternal lines separately for several reasons. Separation allows flexibility to equalize family lines in reintroductions, may add value to potential projects down the line, or may be useful for a purpose unanticipated at the time of collection. Equalizing family size in a reintroduction maximizes the effective population size and may help prevent genetic problems caused by inbreeding, genetic drift, and artificial selection (Havens et al. 2004).
  • If your species has individuals that produce fewer than 20 seeds, so that collecting 10% of a maternal line equals 1 or 2 seeds, it may be appropriate to bulk the collection, maintaining an equal number of seeds collected from each mother plant. In this scenario, collecting from more than 50 maternal plants will be necessary to achieve a total collection of 3000 seeds.

Collect no more than 10% of the seed output of a population in a season for no more than 5 in 10 years.

Drastic times may call for drastic measures.

  • Extremely small populations or populations with high probability of extirpation in the foreseeable future may warrant rescue collections greater than 10%, up to 100%, to preserve the highest genetic diversity for the species possible (Guerrant et al. 2004).
  • For populations of species with extremely low overall numbers, particularly those that have 10 or fewer reproductive individuals and a poor history of recruitment, or are known to be in precipitous decline, it may be necessary to rescue the population from whatever is threatening it in the wild population. Collect up to 100% of seed or whole plants at the discretion of the permitted collector. Such collection levels assume, of course, that adequate facilities, procedures, and resources are available to care for the material, and that such collections are part of a more inclusive strategy, which is endorsed by the appropriate regulatory agencies (Guerrant et al. 2004).
  • If there are fewer than 50 individuals in the wild, or if viable seed is not available, tissue culture or vegetative reproduction may be required to maintain the species’ genetic diversity. Collecting vegetative tissue should follow the same guidelines as for seed collections. Collect vegetative tissue from as many unrelated individuals from each population as possible. (See CPC Best Practice Section, “Tissue Culture and Cryopreservation.”)

Collect herbarium vouchers, soil samples, and genetic samples (when possible) associated with the seed accession.

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