Two tetraploid subspecies of Dactylis glomerata L.,
subsp. reichenbachii (Hausm.) Stebbins et Zohary and subsp.
glomerata, occur in the French Alps. The former is confined
to dolomitic, south-facing, alpine lawns above
2000 m, whereas the latter occurs in non-dolomitic habitats in
subalpine meadows mainly below 1900 m. Previous
studies of allozyme variation have shown that genetic introgression
between the two subspecies occurs over large
areas. By contrast, morphologically intermediate individuals only
occur in an extremely narrow area, suggesting
that the morphological and physiological differences between the two
subspecies is of adaptive significance. A
reciprocal clone transplant experiment was set up to examine (1)
any genetic differences between subspecies
indicative of ecotypic differentiation in relation to habitat
characteristics and (2) the level of phenotypic plasticity
in the two subspecies. Genetic differentiation was confirmed by a
statistically significant taxon × site interaction
effect in anova for all traits studied. The glomerata
populations produced more tillers, longer leaves and higher
culms in all sites, especially in their home environment. However,
reichenbachii populations produced more seeds
than the glomerata populations in the original
reichenbachii environment, suggesting ecotypic differentiation
between the two subspecies. This result might also explain why
the glomerata subspecies is unable to colonize
dolomitic habitats occupied by the reichenbachii subspecies.
The reichenbachii populations showed less plasticity
than the glomerata populations for leaf length and floriferous
tiller number, a result which is discussed in the
context of the response of plants from productive and non-productive
habitats to environmental variation.