Population genetics of hydrophilous angiosperms

Abstract Comparisons between genetic variation and life history and ecological characteristics have been produced for over 400 plant species since the advent of starch gel electrophoresis. Knowledge of how aquatic life histories relate to population genetic structure is lacking, however. Four hydrophilous species — Zostera marina L., Vallisneria americana Michx., Ceratophyllum demersum L., and Ceratophyllum echinatum Gray — have been studied using allozyme estimates of variation within and among populations. At the species level, the percent of polymorphic loci is equal to, or higher than, the average reported for all plant species. At the population level, however, hydrophilous taxa have lower percent of polymorphic loci, fewer alleles per locus, and lower levels of heterozygosity than non-hydrophiles. Except for Z. marina , hydrophilous species show much greater partitioning of variation among populations than non-hydrophiles, particularly when compared with anemophilous species. Explanations for these patterns include sexuality ( Ceratophyllum ), extensive clonal spread (all four species), and the greater isolation of freshwater populations (lakes as islands) relative to most terrestrial species and to coastal species such as Z. marina .