Increased spatial-genetic structure in a population of the clonal aquatic plant Sagittaria latifolia (Alismataceae) following disturbance

The spatial genetic structure (SGS) of plant populations is determined by
the outcome of key ecological processes, including pollen and seed
dispersal, the intensity of local resource competition among newly
recruited plants, and patterns of mortality among established plants.
Changes in the magnitude of SGS over time can provide insights into the
operation of these processes. We measured SGS in a population of the
clonal aquatic plant, Sagittaria latifolia that had been disturbed by
flooding, both before and after the flood. . Over the four-year interval
between measurements, we found substantial changes in the magnitude of
SGS. In the first measurement (pre-flood), SGS was weak, even over short
distances. By contrast, there was substantial SGS in the second
measurement (post-flood), particularly over short distances. This change
in SGS was accompanied by near complete turnover in the genotypic
composition of the population. The genotypic richness of the population
(the number of unique clones scaled by the sample size) was halved over
the four-year interval. The clonal subrange – the distances between shoots
within clones – also shrank considerably, with more than 5% of shoots
having clone-mates at distances greater than 10 m before the flood, but
fewer than 5% of shoots having clone-mates at distances beyond 2 m
afterwards. Clonal turnover and the re-establishment of SGS in clonal
populations are both expected following local extirpation and recruitment.
These data reveal the genetic signatures of disturbance and a subsequent
flush of seedling recruitment and subsequent clonal expansion.