Can a botanic garden cycad collection capture the genetic diversity in a wild population?

Premise of research. Conservation of plant species often requires ex situ (off-site) cultivation of living collections. Cycads constitute the most imperiled major group of plants, and ex situ collections are an important part of conservation planning for this group, given seed recalcitrance, difficulties with tissue culture, and ongoing in situ threats. Very little is known about the genetics of ex situ conservation collections of cycads. Thus, this study seeks to illuminate how well an ex situ collection of a cycad can capture the diversity in a wild population.

Methodology. A model species, Zamia decumbens, was chosen on the basis of geographic isolation and detailed census knowledge, which allowed near-total sampling of in situ plants. Overall, 375 in situ plants were compared to 205 ex situ plants via 10 microsatellite markers.

Pivotal results. Genetic-distance analysis shows high fidelity of the ex situ collections to their in situ source populations as well as clustering of ex situ progeny by accession and strong identity with their respective mother plants. Structured resampling of allele capture from the in situ populations by the ex situ collections shows that allele capture increases as number of ex situ plants maintained increases, but with a diminishing rate of increase.

Conclusions. These data demonstrate that botanic garden collections can better conserve the genetic diversity of in situ cycad populations if four recommendations are followed: (1) use the species biology to inform the collecting strategy; (2) manage each population separately; (3) collect and maintain multiple accessions; and (4) collect over multiple years.