- Email: [email protected]
Developing quantitative seed sampling protocols using simulations: A reply to comments from Guja et al. and Guerrant et al.
Biological Conservation 184 (2015) 469–470
Contents lists available at ScienceDirect
Biological Conservation journal homepage: www.elsevier.com/locate/biocon
Letter to the Editor Developing quantitative seed sampling protocols using simulations: A reply to comments from Guja et al. and Guerrant et al.
We appreciate and largely agree with both Comments (Guerrant et al., 2015; Guja et al., 2015), to our recent article (Hoban and Schlarbaum, 2014), whose main points are: (1) We did not sufficiently acknowledge prior scholarship on seed collections, especially regarding species’ characteristics and collection purpose. (2) Our sample size recommendations were minimum estimates, and may need increasing due to redundancy needs, loss during storage, use, and reintroduction. First we acknowledge that scholarly exists work regarding considerations for seed collections, and that collectors are not always naïve regarding biological realities. The conceptual framework for sampling in light of species’ attributes (among-population structure, environmental variation, population histories) is wellestablished. CPC and other commentaries also emphasize carefully considering collection goals (e.g. ‘backup’ or restoration). Nonetheless, to our knowledge all prior work is qualitative, and has not attempted to quantitatively develop collection protocols tailored to species’ distribution and dispersal. While general recommendations are a valuable resource, we argue that only a quantitative treatment of seed sampling can reveal diminishing return points, statistically compare different practices, and give practical evidence-based advice. A quantitative approach (based on realistic models incorporating population history, distributions and environment) will help managers produce relevant estimates of where/how to sample, similar to how demographic-genetic modeling guides in situ protection. While our current models (Hoban and Schlarbaum, 2014) are simple, we assert that modeling will be an essential component of future collection planning, complementing existing strategies. The simulation approach formally incorporates parameters on biological data. Future work is needed to simulate relevant adaptive diversity for breeding and restoration, and contemporary evolution. Of course, model-based recommendations may be assessed and adjusted, on a case-by-case basis, by managers possessing multiple lines of evidence. Second, we acknowledge that diverse operational factors influence sample size. Our minimum recommendations (Hoban and Schlarbaum, 2014) may often (but not always) need adjustment upwards. Important factors include attrition during storage, using seeds to monitor viability, experiments on seed storage, distributing seed to researchers and backup storage, and survival and
http://dx.doi.org/10.1016/j.biocon.2015.02.021 0006-3207/Ó 2015 Elsevier Ltd. All rights reserved.
recruitment during reintroduction. In our model, we assumed all seeds survive storage and 100% germination. We concede that our minimum sample sizes are inadequate if these assumptions are not met. Therefore it will be valuable and necessary to link our sampling models to models of storage, regeneration, and reintroduction demography, a feasible research agenda. Subsequently, a planner could choose which processes apply to their species and project goal, utilize appropriate models of these processes, and calculate sufficient sample sizes. For example, Rancho Santa Ana Botanic Garden evaluates germination at regular intervals, and separates collections into three ‘‘bins’’: active (for use and testing), base (for long-term storage), and back-up. A decision tree to guide samplers through operational decisions in a quantitative manner could complement our model-based advice. A further operational consideration is that many collectors keep maternal lines separate, for research purposes, which is relevant when determining whether to sample more maternal plants or more seed per maternal plant. Sampling many maternal plants and keeping them isolated poses storage and cataloguing challenges. Furthermore, some species produce copious but small seeds (<1 mm), and separating only few seeds is logistically impractical. Our models have not yet considered these practicalities. We agree that ideal collections be of sufficient size to meet diverse conservation, research, sharing, and backup needs. In non-resource limited situations, minimum sampling is not recommended. Nonetheless, first-approximation minimum recommendations are needed now for species and populations ‘‘on the brink’’ due to imminent challenges (pests/disease, climate change). Collectors often make ‘‘salvage’’ decisions with limited resources, or have limited opportunity (e.g. scientists making field studies, or citizen participants). Our recommendations for butternut would indeed preclude screening for traits or research. Such activities, though, may be low priority for butternut and other species for which collection and storage resources are minute, with no foreseeable research budget. In the absence of concrete advice about feasible minimum collection sizes, a major risk is that collections will not be made- indeed in spite of decades of demographic collapse, limited butternut collections were only recently accomplished. Many species, even those of economic importance, face similar destinies. Though some small collections are inadequate under a comprehensive approach, our modeling work demonstrates their potential genetic value (Hoban and Schlarbaum, 2014). We also agree that ‘‘collections inevitably change over time,’’ due to adaptation and drift, and need replenishing. As others demonstrate (Jensen et al., 2012; Greene et al., 2014), a mix of models and empirical data can help determine how often to resample wild populations. Lastly, economics of scale are worth
470
Letter to the Editor / Biological Conservation 184 (2015) 469–470
considering. We plan to link our work to economic models to test the hypothesis noted by the Comments: that large-scale collections are ‘‘more resource efficient.’’ This is an exciting, useful area for future simulation-based sample planning work. We thank the authors for their comments. This ongoing conversation is crucial for ex situ conservation programs. We argue that quantitative estimates of sample size for achieving sufficient genetic representation, based on optimality criteria and recognizing diminishing returns, will promote and assist such conversations. Acknowledgements
Jensen, H.R., Dreiseitl, A., Sadiki, M., Schoen, D.J., 2012. The Red Queen and the seed bank: pathogen resistance of ex situ and in situ conserved barley. Evolut. Appl. 5, 353–367.
⇑
Sean Hoban National Institute for Mathematical and Biological Synthesis (NIMBioS), University of Tennessee, Knoxville, TN 37919, United States ⇑ Corresponding author. E-mail address: [email protected] Allan Strand Department of Biology, College of Charleston, Charleston, SC 29424, United States E-mail address: [email protected]
SH acknowledges postdoctoral funding from the National Institute for Mathematical and Biological Synthesis (NIMBioS), funded through NSF Awards #EF-0832858 and #DBI-1300426, and The University of Tennessee, Knoxville.
Naomi Fraga Rancho Santa Ana Botanic Garden, Claremont, CA 91711, United States E-mail address: [email protected]
References
Chris Richards Plant Germplasm Preservation Unit, National Center for Genetic Resources Preservation, USDA-ARS, Fort Collins, CO 80521, United States E-mail address: [email protected]
Greene, S.L., Kisha, T.J., Yu, L.-X., Parra-Quijano, M., 2014. Conserving plants in gene banks and nature: investigating complementarity with Trifolium thompsonii Morton. PloS One 9, e105145. Guerrant, EO., Havens, K., Fiedler, PL., et al, 2015. Population structure integral to seed collection guidelines: a response to Hoban and Schlarbaum. Biol. Conserv. Guja, LK., Broadhurst, L., Brown, AHD., et al, 2015. Genetic diversity is a significant but not the only consideration for effective ex situ plant conservation: response to Hoban and Schlarbaum. Biol. Conserv. Hoban, S., Schlarbaum, S., 2014. Optimal sampling of seeds from plant populations for ex-situ conservation of genetic biodiversity, considering realistic population structure. Biol. Conserv. 177, 90–99.
Scott Schlarbaum Department of Forestry, Wildlife and Fisheries, University of Tennessee, Knoxville, TN 37919, United States E-mail address: [email protected] Available online 6 March 2015
Contents lists available at ScienceDirect
Biological Conservation journal homepage: www.elsevier.com/locate/biocon
Letter to the Editor Developing quantitative seed sampling protocols using simulations: A reply to comments from Guja et al. and Guerrant et al.
We appreciate and largely agree with both Comments (Guerrant et al., 2015; Guja et al., 2015), to our recent article (Hoban and Schlarbaum, 2014), whose main points are: (1) We did not sufficiently acknowledge prior scholarship on seed collections, especially regarding species’ characteristics and collection purpose. (2) Our sample size recommendations were minimum estimates, and may need increasing due to redundancy needs, loss during storage, use, and reintroduction. First we acknowledge that scholarly exists work regarding considerations for seed collections, and that collectors are not always naïve regarding biological realities. The conceptual framework for sampling in light of species’ attributes (among-population structure, environmental variation, population histories) is wellestablished. CPC and other commentaries also emphasize carefully considering collection goals (e.g. ‘backup’ or restoration). Nonetheless, to our knowledge all prior work is qualitative, and has not attempted to quantitatively develop collection protocols tailored to species’ distribution and dispersal. While general recommendations are a valuable resource, we argue that only a quantitative treatment of seed sampling can reveal diminishing return points, statistically compare different practices, and give practical evidence-based advice. A quantitative approach (based on realistic models incorporating population history, distributions and environment) will help managers produce relevant estimates of where/how to sample, similar to how demographic-genetic modeling guides in situ protection. While our current models (Hoban and Schlarbaum, 2014) are simple, we assert that modeling will be an essential component of future collection planning, complementing existing strategies. The simulation approach formally incorporates parameters on biological data. Future work is needed to simulate relevant adaptive diversity for breeding and restoration, and contemporary evolution. Of course, model-based recommendations may be assessed and adjusted, on a case-by-case basis, by managers possessing multiple lines of evidence. Second, we acknowledge that diverse operational factors influence sample size. Our minimum recommendations (Hoban and Schlarbaum, 2014) may often (but not always) need adjustment upwards. Important factors include attrition during storage, using seeds to monitor viability, experiments on seed storage, distributing seed to researchers and backup storage, and survival and
http://dx.doi.org/10.1016/j.biocon.2015.02.021 0006-3207/Ó 2015 Elsevier Ltd. All rights reserved.
recruitment during reintroduction. In our model, we assumed all seeds survive storage and 100% germination. We concede that our minimum sample sizes are inadequate if these assumptions are not met. Therefore it will be valuable and necessary to link our sampling models to models of storage, regeneration, and reintroduction demography, a feasible research agenda. Subsequently, a planner could choose which processes apply to their species and project goal, utilize appropriate models of these processes, and calculate sufficient sample sizes. For example, Rancho Santa Ana Botanic Garden evaluates germination at regular intervals, and separates collections into three ‘‘bins’’: active (for use and testing), base (for long-term storage), and back-up. A decision tree to guide samplers through operational decisions in a quantitative manner could complement our model-based advice. A further operational consideration is that many collectors keep maternal lines separate, for research purposes, which is relevant when determining whether to sample more maternal plants or more seed per maternal plant. Sampling many maternal plants and keeping them isolated poses storage and cataloguing challenges. Furthermore, some species produce copious but small seeds (<1 mm), and separating only few seeds is logistically impractical. Our models have not yet considered these practicalities. We agree that ideal collections be of sufficient size to meet diverse conservation, research, sharing, and backup needs. In non-resource limited situations, minimum sampling is not recommended. Nonetheless, first-approximation minimum recommendations are needed now for species and populations ‘‘on the brink’’ due to imminent challenges (pests/disease, climate change). Collectors often make ‘‘salvage’’ decisions with limited resources, or have limited opportunity (e.g. scientists making field studies, or citizen participants). Our recommendations for butternut would indeed preclude screening for traits or research. Such activities, though, may be low priority for butternut and other species for which collection and storage resources are minute, with no foreseeable research budget. In the absence of concrete advice about feasible minimum collection sizes, a major risk is that collections will not be made- indeed in spite of decades of demographic collapse, limited butternut collections were only recently accomplished. Many species, even those of economic importance, face similar destinies. Though some small collections are inadequate under a comprehensive approach, our modeling work demonstrates their potential genetic value (Hoban and Schlarbaum, 2014). We also agree that ‘‘collections inevitably change over time,’’ due to adaptation and drift, and need replenishing. As others demonstrate (Jensen et al., 2012; Greene et al., 2014), a mix of models and empirical data can help determine how often to resample wild populations. Lastly, economics of scale are worth
470
Letter to the Editor / Biological Conservation 184 (2015) 469–470
considering. We plan to link our work to economic models to test the hypothesis noted by the Comments: that large-scale collections are ‘‘more resource efficient.’’ This is an exciting, useful area for future simulation-based sample planning work. We thank the authors for their comments. This ongoing conversation is crucial for ex situ conservation programs. We argue that quantitative estimates of sample size for achieving sufficient genetic representation, based on optimality criteria and recognizing diminishing returns, will promote and assist such conversations. Acknowledgements
Jensen, H.R., Dreiseitl, A., Sadiki, M., Schoen, D.J., 2012. The Red Queen and the seed bank: pathogen resistance of ex situ and in situ conserved barley. Evolut. Appl. 5, 353–367.
⇑
Sean Hoban National Institute for Mathematical and Biological Synthesis (NIMBioS), University of Tennessee, Knoxville, TN 37919, United States ⇑ Corresponding author. E-mail address: [email protected] Allan Strand Department of Biology, College of Charleston, Charleston, SC 29424, United States E-mail address: [email protected]
SH acknowledges postdoctoral funding from the National Institute for Mathematical and Biological Synthesis (NIMBioS), funded through NSF Awards #EF-0832858 and #DBI-1300426, and The University of Tennessee, Knoxville.
Naomi Fraga Rancho Santa Ana Botanic Garden, Claremont, CA 91711, United States E-mail address: [email protected]
References
Chris Richards Plant Germplasm Preservation Unit, National Center for Genetic Resources Preservation, USDA-ARS, Fort Collins, CO 80521, United States E-mail address: [email protected]
Greene, S.L., Kisha, T.J., Yu, L.-X., Parra-Quijano, M., 2014. Conserving plants in gene banks and nature: investigating complementarity with Trifolium thompsonii Morton. PloS One 9, e105145. Guerrant, EO., Havens, K., Fiedler, PL., et al, 2015. Population structure integral to seed collection guidelines: a response to Hoban and Schlarbaum. Biol. Conserv. Guja, LK., Broadhurst, L., Brown, AHD., et al, 2015. Genetic diversity is a significant but not the only consideration for effective ex situ plant conservation: response to Hoban and Schlarbaum. Biol. Conserv. Hoban, S., Schlarbaum, S., 2014. Optimal sampling of seeds from plant populations for ex-situ conservation of genetic biodiversity, considering realistic population structure. Biol. Conserv. 177, 90–99.
Scott Schlarbaum Department of Forestry, Wildlife and Fisheries, University of Tennessee, Knoxville, TN 37919, United States E-mail address: [email protected] Available online 6 March 2015