The genetics of naturalization: A comparison of morphological variation within and between populations of Agrostis capillaris L as an exotic in New Zealand and as a native in Britain

Previous work in New Zealand has shewn that genetic variation within populations of Agrostis capillaris can be comparable to that between populations, even between populations over a very wide environmental range. To determine whether this reflects the recent advent of A. capillaris in New Zealand, with a small founding gene pool and a short time for ecotypic differentiation, populations from a comparable range of environments were sampled randomly in the same way in Britain. Populations were grown in comparable conditions in the two countries, but to ensure comparability only proportional variation was examined. Characters used in the assessment of within- and between-population variation were step+sheath length, lamina length, lamina width and relative growth rate. Within populations, there were highly significant genotypic differences, especially in the British populations. Differences between populations were rather greater than those within- populations, and for lamina length this was significant in both countries. For both Britain and New Zealand, there were cases where the two genotypes sampled from a population were similar in a particular character. In some cases, populations from comparable habitats in the two countries were similar to each other. For the three morphological characters, total genotypic variation over all populations sampled was greater in Britain than in New Zealand. For some characters this was due to between-site variation, and for some to within-site variation. It is concluded that some of the evidence for non-adaptation in A. capillaris in New Zealand is caused by a more limited gene pool, and insufficient time for sorting of genotypes into habitats.