Geographic Isolation, Environmental Disturbance, and Local Adaptation in a Clonal Aquatic Plant, Lemna minor

Abstract

In a multiyear study we conducted laboratory reciprocal transplant experiments with Lesser Duckweed Lemna minor from two manmade ponds. Runoff Pond (RP) is a catch basin for parking lot runoff and has no outlet. Shingle Creek Pond (SCP) is connected to Shingle Creek. Lemna minor forms clones as fronds grow and separate from the mother plant. We hypothesized that a reduced influx of genotypes in RP relative to SCP would lead to local adaptation of Lemna minor to RP conditions, and greater genetic diversity in SCP would result in greater phenotypic plasticity. In 2004 both hypotheses were supported. Lemna minor from RP performed better (rate of per capita growth and senescence) in RP water. Lemna minor from SCP had similar characteristics in both sources of water. Runoff Pond was significantly disturbed by dredging following the experiment. In 2005, SCP plants outperformed RP plants in both sources of water. Prior to the experiment in 2006, SCP experienced environmental disruption when construction occurred along Shingle Creek upstream of SCP. Despite environmental disturbance, SCP Lemna minor again outperformed RP Lemna minor, faring better in RP water than SCP water. Interestingly, Lemna minor from a nearby lake outperformed SCP and RP plants in both sources of water. In 2008 SCP and RP Lemna minor exhibited a pattern similar to 2004. Overall, SCP Lemna minor exhibited greater ability to respond to environmental change than RP Lemna minor, and significant local adaptation was not observed.