Dairyland populations of bur cucumber (Sicyos angulatus) as a possible seed source for riverbank populations along the Abukuma River, Japan

Abstract

In 2006, the distribution of bur cucumber (Sicyos angulatus L.) along the river bank of the Abukuma River, Japan, was examined. Twenty‐six populations were found in the area surrounding the upper reach of the river and they were limited to dairy land. On the basis of polymerase chain reaction–restriction fragment length polymorphism analysis for four of the six polymorphic loci that were detected in 16 non‐coding regions of the chloroplast DNA from 300 samples, five multilocus haplotypes (A–E) were identified. Despite its smaller size, the surrounding area's population showed a higher genetic diversity at the haplotype level than did the riverbank population. The haplotype composition of the surrounding area's population was similar to that of the riverbank population in the upper‐stream region. The distribution of haplotype D was biased towards the upper reach of the river, possibly because of migration from the surrounding area's population. The distribution of haplotype E was biased towards the middle‐to‐lower reaches of the river and was associated with the existence of source populations other than the surrounding area's population. The results also showed that the estimated seed flow from another dairy land could transport seeds into the middle reach of the river at a high frequency, suggesting that dairy land is largely responsible for the development of the riverbank populations. The eradication of dairyland populations should be given priority in order to prevent future migration along the river bank and to protect the existing endangered wetland species from invasive S. angulatus.