Geographic patterns of clonal propagation
Having detected extensive clonality among the wild-collected P.
vaginatum samples, we next assessed the distribution of geographic and
environmental distances between clones of the same genotype in our wild
collections. Specifically, we investigated the extent to which they
showed patterns consistent with a “frozen-niche” strategy (multiple
geographically and environmentally restricted clones) or a
“general-purpose genotype” strategy (a few broadly distributed
clones). For the fine-textured ecotype, the four genotypes with multiple
clones in the wild tended to have relatively small geographic ranges;
two of the four had genotypes restricted to a single location, while the
two found in multiple locations had a maximum range of 126 km (Table S1;
Fig. 1; Fig. 2A). Consistent with their narrow geographical
distributions, assessments of pairwise environmental distances among
locations (based on local climatic and salinity conditions; see Methods)
indicated a low level of environmental dispersion (Fig. 2B). These
patterns are generally consistent with a “frozen-niche” reproductive
strategy for fine-textured P. vaginatum .
In contrast to the fine-textured ecotype, genotypes of the
coarse-textured ecotype showed patterns more consistent with a “general
purpose genotype” strategy. Not only did a handful of unique genotypes
make up the majority of wild accessions (Table 1), but these genotypes
showed broad distributions with respect to both geography and
environmental variables. With the exception of one genotype that was
restricted to a 1 km area (coarse_06), the narrowest geographical range
of any coarse-textured clonal genotype was 750 km (coarse_04), and the
three most common genotypes (coarse_01, coarse_02 and coarse_03) all
had ranges >1400 km (Fig. 1; Fig. 2A). Pairwise
environmental distance measures were similarly higher for the
coarse-textured ecotype compared to fine-textured accessions (Fig. 2B);
this indicates that clonal propagules of these widely dispersed
genotypes are not specializing on particular environments in the
locations where they occur.