BERGH, N G*, T A J HEDDERSON, H P LINDER, and W J BOND. Botany Department, University of Cape Town, Rondebosch, 7700, Cape Town, South Africa. - Genetic variation in the renosterbos, Elytropappus rhinocerotis (Asteraceae) in the southwestern Cape, South Africa.
Renosterbos is a shrub which is extremely common on the Cape coastal
forelands. Together with several other fynbos species, it also occurs
in isolated interior populations, confined to mesic high-altitude
sites separated by large tracts of arid country. How did the outliers
come to occupy such sites? Was fynbos previously more extensive, and
is it currently in a contracted state due to widespread aridification
since the last glacial maximum (vicariance hypothesis)? Or are the
outliers the results of long-distance dispersal events (dispersal
hypothesis)? These conflicting scenarios would produce different
genetic signatures in extant populations, which should be detectable
(in the absence of confounding factors such as subsequent gene flow)
using highly polymorphic genetic markers. In the case of vicariance,
long-isolated populations should have distinct genetic signatures and
contain unique genotypes, and genetic difference should be correlated
with duration of isolation. Neighbouring isolated populations would
not necessarily be more closely related than very distant isolated
populations. In the case of dispersal, colonies should consist of a
subset of genotypes present in the founder population, and founder
populations are likely to be those closest to colony populations. In
this study we use three ISSR-PCR primers to survey the genomes of at
least five individuals from each of ten populations across the entire
species range, as a first step in constructing a phylogeographic
hypothesis. The survey shows high levels of variation, most of which
is partitioned among populations. Examination of geographic
structuring in this variation may allow us to make inferences on
population histories in renosterbos, which could be extrapolated to
the history of fynbos as a whole.
Key words: fynbos, intraspecific variation, ISSR, phylogeography, population history