 |
Annette Shears |
Evaluation of Genetic Diversity of Lyonothamnus floribundus ssp. floribundus
Deborah D. Kaska, Academic Coordinator UCSB
Scott Hodges, Assoc. Prof of Ecology and Evolution UCSB
Department of Ecology and Evolution, UCSB, Santa Barbara, CA 93106
The Island Ironwood, Lyonothamnus floribundus is a paleoendemic tree found
only on 4 of the 8 California Channel Islands. Fossil evidence, however, indicates
they were widespread on the mainland in the Miocene (16 million years ago). Two
subspecies of ironwood are characterized by differences in leaf structure, ssp.
aspleniifolius or the "fern leaf ironwood" is native to Santa Cruz,
Santa Rosa and San Clemente islands and, ssp. floribundus, is native only to
Santa Catalina Island. We are currently using molecular methods to investigate
genetic diversity of this species.
Our initial studies on ironwood groves on Santa Cruz Island indicated that
most groves, containing from a few to more than 100 trunks, were clonal, that
is, were derived from one genetic individual. Each grove was distinct, but the
trees within a grove were genetically identical. For years botanists have noted
that, despite abundant flowers, the trees appear to reproduce solely by root
sprouting. Seeds and seedlings are rare on the islands. Groups of ironwoods in
cultivation on the mainland, however, produce abundant seeds and we have demonstrated
that each of these trees is genetically distinct. These observations suggest
that extensive clonality in this species on the islands may have reduced the
out crossing needed for seed production and that that number of genetically distinct
individuals in nature may be far less than the number of trunks.
We are currently investigating clonality and genetic diversity of the ironwoods
on Santa Catalina Island. We have collected leaf material from multiple trees
in groves representing all the geographic regions on the island and are currently
using amplified restriction length polymorphism (AFLP) to analyze the DNA. This
method is based on the polymerase chain reaction (PCR) and allows us to rapidly
survey many regions of the DNA for differences. Clonal trees will be expected
to have identical DNA sequences and therefore will not show differences in this
sampling method. Genetically distinct individuals, on the other hand, will have
unique sequences and these will appear as differences in the ALFP patterns. The
results obtained with the trees on Santa Catalina Island will then be compared
with the results from the other 3 island populations to estimate the total diversity
of this species remaining in the wild and whether the patterns of diversity can
give us clues to the time of the origin and the relationships between these island
populations. |
