Genetic Structure of the Florida Key Tree Cactus, Pilosocereus robinii, Using Restriction Site Associated DNA (RAD) Markers

Rare plant conservation efforts must utilize current genetic methods to ensure the evolutionary potential of populations is preserved. One such effort involves the Key Tree Cactus, Pilosocereus robinii, which is an endangered columnar cactus native to the Florida Keys.   The five populations have precipitously declined over the past decade due to habitat loss and increasing soil salinity from rising sea levels and storm surge.  We employed restriction site associated DNA sequencing (RAD) to analyze genetic variation and mortality status of P. robinii. Forty individuals that are representative of both wild andextirpated cacti from the populations in the Keys and stable populations in the Bahamas and Dominican Republic were chosen for RAD sequencing. Samples were processed using HindIII and NotIII restriction enzymes and we obtained 151,829,113 high quality reads of which 82,382,440 were used for mapping. In total, 5,265 SNPs were discovered. Population genetic analysis revealed that the Keys populations are closely related with low pairwise PhiPT values and only four significant differences. Additionally, AMOVA indicated that 86% of the genetic variation was shared across the group and only 14% of the overall variation was restricted to a particular population (F=0.139, p=0.020). The populations of P. robinii display evidence of inbreeding with all FIS estimatesbeing positive. Our genetic analysis informs an ongoing reintroduction of P. robinii, providing insight into the current diversity and evolutionary history of these imperiled plants, and guiding efforts to select clones for reintroduction onto higher ground in the Florida Keys.