Karyotypic and genetic variations can provide unique insights into how historical, ecological and cytogenetic factors influence microevolution. Kono et al. study a coastal herb, Lysimachia mauritiana, and find eight cytotypes, including four endemic to Taiwan. Cytotype distributions are highly structured geographically, with single cytotypes present in most populations, and four major cytotypes occuring. Allozyme variation is very low and an extremely high level of population differentiation is found, implying limited gene flow among populations. Cluster analysis of allozyme variation uncovers four geographic groups, each corresponding to the four dominant cytotypes. The geographic structure of cytotype distribution and allozyme variation probably result from severe genetic drift triggered by genetic bottlenecks, suggesting that Taiwanese populations are probably derived from four independent founder events.
Kron and Husband describe a simple method for extracting pollen nuclei for measuring DNA content with flow cytometry, involving the bursting of pollen through a nylon mesh. The method compares favourably to other common protocols, and in tests on 80 taxonomically diverse species the data meet quality control criteria for genome size studies in more than 80% of species tested, and also meet more stringent criteria for cell cycle analysis in more than half of the species. In addition, they estimate genome size for six species using pollen nuclei and obtain results within 2.5% of leaf nuclei estimates. The method should facilitate the use of pollen for measuring genome size and improve estimation of unreduced pollen production using flow cytometry.