Reciprocal Garden Study Reveals Acute Spatial-Edaphic Adaptation for Cycas micronesica

Abstract

A long-term reciprocal garden study was used to determine adaptive variation between Cycas micronesica K.D. Hill plants from north versus south Guam. Half-siblings from each location were planted as one-leaf seedlings in north and south gardens and monitored for 15 years. Stem height and diameter, and leaf number and maximum length were measured yearly. Survival and plant size traits were evaluated using a two-way factorial. In both locations, the local genotypes out-performed the foreign genotypes in terms of survival and growth. Survival of the foreign genotypes began to decline by year 4 and was less than 10% by year 15. Survival of the local genotypes was 70% for the north garden and 100% for the south garden. The north site was more hostile to plant performance because overall survival and plant growth were less than for the south site. The most likely environmental factor provoking local adaptation was highly contrasting soil characteristics between north and south Guam. The results indicates that long-term conservation success for C. micronesica and other cycad species must include the concept of local adaptation into decisions for transplantation and restoration projects.

Metals and Metalloids Increase in Cycas micronesica Seed Gametophyte Tissue in Shaded Growth Conditions

“…Second, the genetic structure of the Guam population of C. micronesica is characterized by genetically distinct sub-populations exhibiting allopatric distribution [ 49 ]. When genotypes from northern Guam were grown in these southern Guam soils, mortality reached 90% in less than 15 years [ 50 ]. More sub-population genetics research may reveal if genetic differences among the allopatric sub-populations are partly causal of the elevated Al and Se content in gametophyte tissues in the southern Guam sub-population.…”