Does Channel Island Acmispon (Fabaceae) Form Cohesive Evolutionary Groups?

The California Channel Islands are unique relative to other island chains due to their close proximity to the California mainland and the fact that individual islands, or groups of islands, vary in their distance to the mainland and other islands. This orientation raises questions about whether island taxa with widespread distributions form cohesive evolutionary units, or if they are actually composed of several distinct evolutionary entities, either derived from independent mainland-to-island colonization events or divergence due to prolonged allopatric isolation. The 4 northern islands are clustered in a line (6-8 km separation among islands), while the 4 southern islands are widely spaced (34-45 km separation among islands), which should impact the amount of gene flow and genetic connectivity among islands. We used nuclear microsatellite markers to examine the genetic structure and cohesion of 2 island shrubs, Acmispon dendroideus and A. argophyllus, which are widely distributed across the California Channel Islands. Both focal species contain varieties with multi-island distributions, with A. dendroideus exhibiting a greater distribution on the northern islands and A. argophyllus exhibiting a greater distribution on the southern islands. Substantial genetic divergence was observed for 2 single-island endemic varieties, A. dendroideus var. traskiae and A. agrophyllus var. niveus, confirming that allopatric isolation can lead to genetic divergence. The widespread Acmispon dendroideus var. dendroideus and single-island endemic A. dendroideus var. veatchii formed a cohesive evolutionary group that spans all 4 northern islands and 1 southern island, Santa Catalina, indicating that the northern and southern islands have been genetically linked in the past but do not display evidence of contemporary gene flow. In contrast, widespread A. argophyllus var. argenteus was composed of moderately distinct genetic groups on each of the 4 southern islands, with no evidence of recent gene flow among islands. These results demonstrate that isolation among islands has led to significant divergence among the southern islands, but that the commonly recognized split between northern and southern islands does not impact all taxa equally

Missing domesticated plant forms: can artificial selection fill the gap?

In the course of their evolution, the angiosperms have radiated into most known plant forms and life histories. Their adaptation to a recently created habitat, the crop field, produced a novel form: the plant that allocates an unprecedented 30–60% of its net productivity to sexual structures. Long-lived trees, shrubs and vines of this form evolved, as did annual herbs. Perennial herb forms with increased allocation to asexual reproduction evolved, but there are no examples of perennial herbs with high sexual effort. We suggest that sowing seed into annually tilled fields favored shorter-lived herbs because of trade-offs between first-year seed production and relative growth rate and/or persistence. By propagating cuttings, people quickly domesticated tuber crops and large woody plants. Perennial herbs were too small to be efficiently propagated by cuttings, and the association between longevity, allogamy and genetic load made rapid domestication by sexual cycles unlikely. Perennial grain crops do not exist because they could not have evolved under the original set of conditions; however, they can be deliberately developed today through artificial phenotypic and genotypic selection

Genetic differentiation of Hawaiian Bidens

Adaptive radiation is the evolutionary divergence of a group of organisms from a common ancestor to exploit different ecological niches. Bidens has undergone extensive adaptive radiation on the Hawaiian Islands. The 19 Hawaiian species exhibit much more morphological and ecological differentiation than the continental members of the genus. However, the Hawaiian taxa are chromosomally homogeneous and retain the capacity to interbreed in all possible combinations. Thus the morphological and ecological differentiation in Hawaiian Bidens has been attained without the existence of reproductive isolating mechanisms. Although some hybrid populations are known, hybridization usually does not occur in nature because the species are found in different habitats. Preliminary genetic studies have suggested that some of the morphological differences between taxa may be controlled by very few genes. Genetic differentiation may therefore not extend to other parts of the genome, such as to structural genes for enzymes. Most plant groups that have been studied electrophoretically show a correlation between morphological differentiation and genetic differentiation, but opposing predictions can be made about the extent of divergence at isozyme loci in Hawaiian Bidens. The morphological and ecological data suggest that the taxa are highly differentiated genetically, but the chromosomal similarity of species, the genetic studies of morphological characters and the absence of genetically controlled isolating mechanisms suggest that genetic differences among the taxa may be limited to only a small portion of the genome and may not include isozyme loci. Populations of the Hawaiian taxa of Bidens were compared at 23 loci controlling 9 enzyme systems. In general, populations are more polymorphic than populations of most other plant species that have been studied electrophoretically. Little genetic differentiation has occurred among taxa in spite of the high levels of genetic variability, however. Genetic identities calculated for pairs of populations show that populations of the same taxon are genetically more similar than populations belonging to different taxa, but all values are high. The genetic differentiation that has occurred among the taxa of Hawaiian Bidens is comparable to the genetic differences among populations of continental species. Moreover, there is no correlation between the isozyme data and morphological data. No groups of taxa are evident in the genetic data although morphological groups exist. Genetic differentiation at isozyme loci has not occurred at the same rate as the acquisition of adaptive morphological and ecological characters in Hawaiian Bidens. Adaptive radiation therefore does not require genetic change throughout the genome and may be limited to the genes controlling morphological and ecological characters.Science, Faculty ofBotany, Department ofGraduat

Plant Reproductive Ecology: Patterns and Strategies by J. Lovett Doust, L. Lovett Doust

Volume: 39Start Page: 311End Page: 31

Outplanting and differential source population success in Lupinus guadalupensis

Abstract: The choice of appropriate source populations is crucial for the success of outplanting attempts, but this choice is often based on assumptions regarding patterns of adaptation and distribution of genetic variability in natural populations. Although local adaptation is often assumed to exis