Allozyme Diversity Within and Divergence Among Four Species of Robinsonia (Asteraceae: Senecioneae), a Genus Endemic to the Juan Fernandez Islands, Chile

Abstract

Enzyme electrophoresis was employed to assess genetic diversity within and divergence among four species of Robinsonia (R. evenia, R. gayana, R. gracilis, R. thurifera), a genus endemic to the Juan Fernandez Islands, Chile. The genus consists of treelike perennial plants, and all species are dioecious. Morphological diversity within the genus is reflected by recognition of two subgenera, with three sections in one subgenus. Total gene diversity is highest in the two species (R. gayana and R. gracilis) that are most common and have the largest population sizes. Robinsonia evenia has only half and the rare R. thurifera only 20% of the diversity detected in the other two species. The diversity measured in R. gayana and R. gracilis is comparable to the values typical of continental species of flowering plants with similar life history attributes. The genetic identities between species range from 0.560 to 0.706, which is similar to or below many values for congeneric species, but much lower than most reports for congeners on oceanic islands. The higher diversity within and divergence among species of Robinsonia compared to many insular endemics may result from several factors. The genus probably arose from selfincompatible plants of the genus Senecio, which means that several to perhaps many colonizers carried considerable allozymic variation to the Islands. Large population sizes and obligate outcrossing are additional factors that would account for higher diversity. Sorting of alleles during radiation and the process of mutation probably combined to produce divergence among the species. Estimated divergence times calculated for the species from allozyme data range from 1.7 to 5.5 million years depending on the assumptions made in the calculations; the age of the island (Masatierra) on which these four species are confined is approximately 4.0 million years. The electrophoretic data suggest that Robinsonia arrived early in the archipelago, and radiated and speciated rapidly after colonization.

A General Dynamic Theory of Oceanic Island Biogeography: Extending the MacArthur- Wilson Theory to Accommodate the Rise and Fall of Volcanic Islands

“…Studies from the flora of the Juan Fernández Islands also support the idea of high initial rates of radiation, with faster rates evident on the younger island: 0.33 species per lineage per million years on Mastierra (island age: 4 Myr) vs. 0.96 species per lineage per million years on Masafuera (island age: 1-2 Myr) (Levin, 2000;cited in Levin, 2004). Electrophoretic data for the endemic genus Robinsonia (Asteraceae) suggest that the founding population arrived early in the 4.0-million-year history of Masatierra Island, radiating and speciating rapidly after colonization (Crawford et al, 1992). Similarly, Kaneshiro et al (1995, p. 71), in their analysis of species groups within the picture-wing Drosophila of Hawaii, make the following observation: 'Most of these species, like many other extant terrestrial endemic fauna, show a very strong but by no means exclusive tendency to single-island endemism.…”

High Genetic Diversity and Differentiation in Relict Lowland Populations ofGentianella austriaca(A. and J. Kern.) Holub (Gentianaceae)

“…PAGE: Leaves were ground in a 160 mM tris/107 mM glycine/ HCl-buffer, pH 8.0 (including 20 % sucrose, 1 % DTT, 0.1 % mercaptoethanol, and bromophenol blue). MDH was resolved in a 7.5 % gel (acrylamide/bisacrylamide 19 : 1) in Hoefer Mighty (1) only understorey (2) about 1 month after mowing Mini SE250 chambers. A 250 mM tris/boric acid buffer, pH 8.0, was used for gel and bridge.…”

“…Dolan (1994 [4] ) found potential negative impacts of small population sizes in a genetically depauperate subset of the whole sample. In comparing narrow island endemics, Crawford et al (1992 [2] ) found lowest genetic diversity in the smallest populations.…”

“…In detail, the purposes of this study are: (1) to determine the genetic variation within and among populations from lowland to mountain habitats, (2) to assess variation in morphometric and reproductive characters (including germination) within and among these seven populations, (3) to seek correlations between these traits, environmental features, and population sizes, (4) to suggest evolutionary relations among populations by estimating degrees of differentiation/identity, and (5) to comment on the implications for conservation.…”

Biogeography and Origin of Lilium Longiflorum and L. Formosanum I - Interspecific Isolating Mechanisms and Population Genetic Structure

“…Generally, among insular plants, the lower minimum I values have been barely recorded in very limited 'congeneric' or 'intergeneric' population pairs of the large complex of morphologically and ecologically highly radiating taxa; e.g., Alsinoideae in Hawaii (0.242; Weller, Sakai and Straub, 1996), for silversword alliance in Hawaii (0.426; Witter and Carr, 1988), for woody Sonchus alliance in Canary (0.490; Kim et al, 1999) and Robinsonia in Juan Fernandez (0.560; Crawford et al, 1992). Unlike morphological and ecological phenotypes, protein molecules like allozyme are assumed to evolve much constantly because of their neutrality to natural selection, i.e., the neutral theory of molecular evolution (Kimura, 1983).…”