Allozyme Variation and Evolutionary Relationships among Three Species of Wahlenbergia (Campanulaceae) in the Juan Fernandez Islands

Abstract

Enzyme electrophoresis was employed to measure variation within and divergence among three species of Wahlenbergia (W. berteroi, W. fernandeziana, and W. masafuerae) endemic to the Juan Fernandez Islands at gene loci encoding soluble enzymes. Two species, W. berteroi and W. fernandeziana, occur only on the older island of Masatierra while W. masafuerae is endemic to the younger island, Masafuera. A high genetic identity (.947) was calculated for W. berteroi and W. masafuerae, with both species monomorphic for the same allele at all loci except one, where the latter species has a novel allele. Wahlenbergia fernandeziana exhibits lowered identities (ca. .680-.770) with the other two species. This divergence results from W. berteroi and W. masafuerae having only a subset of the allelic variation detected in W. fernandeziana. That is, the former two species contain a limited extraction of the variation found in the latter. Isozyme data are concordant with morphological information in suggesting a close relationship between W. berteroi and W. masafuerae. The electrophoretic data also support the hypothesis, based on morphology and geographic distribution, that W. berteroi was derived from W. fernandeziana (or an ancestor of it) and that W. masafuerae evolved from W. berteroi following dispersal to Masafuera. Founder events associated with speciation probably account for the lowered variation in W. berteroi and W. masafuerae. In the present study, chromosome counts of n = 11 were determined for W. berteroi, the same number as previously reported for W. fernandeziana and W. masafuerae. Six new populational counts are also reported here for the latter species. Electrophoretic banding patterns suggest that the number of isozymes detected for several enzymes is greater than the expected minimal conserved number for diploid plants. This suggests either that the plants are diploid with extensive gene duplications or that they are polyploids.