Ecosystems Plants & People

Estimating genetic variation in seed collections using seed morphology

Can variation in seed morphological traits allow us to estimate genetic variation in seed banks of vulnerable plant species?

Ex situ seed collections, commonly referred to as seed banks, preserve the genetic diversity of plant species outside of their native range, providing the raw material for species reintroduction and ecosystem regeneration efforts. Ensuring such seed collections represent the wide genetic variation found in natural populations is critical to both contemporary conservation and potential future restoration efforts. In conifers, seed morphology is primarily genetically controlled. As such, morphological variation assessed within conifer seed collections could potentially be used as a low cost tool to estimate within- and between-population genetic variation, providing a unique approach to inform sampling techniques for future seed collections.

Torrey pine stand on Santa Rosa Island, Channel Islands National Park, California. Image credit: L. Di Santo).

In their new study published in AoBP, Di Santo et al. evaluate morphological trait variation in a large ex situ conservation collection of Torrey pine (Pinus torreyana) seeds sourced from the two native extant populations, in La Jolla, California and Santa Rosa Island, California, USA. The species is one of the rarest pines in the world and is of critical conservation concern due to low population size, low genetic diversity, climate change, and environmental- and human-mediated disturbances. In their work, the authors quantified the distribution of variation for 14 seed morphological traits (including those shown in the image below) and assess differences in emergence between island and mainland seedlings. Ultimately, using a simulation-based approach, they used estimates of within-population variance to assess the number of maternal families required to capture 95% of trait variation within each existing seed collection.

Visual of morphological measurements for seeds collected on Santa Rosa Island and at the Torrey Pine State Reserve. (A) Seed length (cm). (B) Seed width (cm). (C) Embryo length (cm). (D) Embryo width (cm). (E) Seed coat width (cm). (F) Embryo area (cm2). (G) Endosperm area (cm2). (H) Seed area (cm2). Image credit: Di Santo et al.

Di Santo et al. show that seed trait variation may aid in the establishment of population-specific guidelines to optimize genetic diversity preserved in ex situ collections of Torrey pine (Pinus torreyana), and possibly across any plant species with largely heritable seed morphological variation. From a conservation perspective, the results indicate that to optimise genetic diversity captured in Torrey pine seed collections, maximizing the number of maternal families sampled within each population will be necessary. The authors conclude by stating that while their results and conclusions may be specific to Torrey pine, the empirical, statistical and simulation-based approaches presented in their work could likely be applied to heritable traits across ex situ seed collections of other endangered plant species.

RESEARCH ARTICLE

Di Santo, L.N., Polgar, M., Nies, S., Hodgkiss, P., Canning, C.A., Wright, J.W., Hamilton, J.A., 2021. Seed morphological traits as a tool to quantify variation maintained in ex situ collections: a case study in Pinus torreyana. AoB PLANTS. https://doi.org/10.1093/aobpla/plab058

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