AGE-RELATED MORPHOLOGICAL-DIFFERENTIATION AMONG POPULATIONS OF DACTYLORHIZA-TRAUNSTEINERI (ORCHIDACEAE) IN EASTERN SWEDEN

Evolution takes time. It is generally believed that for a given species older populations have diversified more than younger ones. To test this hypothesis, two regions in southern Sweden of different age, determined based on land uplift data, were chosen for studying morphological differentiation within the orchid species Dactylorhiza traunsteineri. Individuals from 10 populations in an older region, Gotland, and 11 populations in a younger region, Uppland, were scored for 54 morphological characters. Patterns of morphological variation and the structure of diversity were analyzed using multivariate and simple statistics; the degrees of correspondence among matrices of morphological and environmental factors were calculated. Morphological variation among populations was greater in the older region. This pattern was consistent in all analyses, although more pronounced in the analyses of floral morphology than in analyses of vegetative morphology. Orchid populations on Gotland appear to be relatively old, small and isolated, but genetic drift does not seem to have been important for the differentiation among populations. Other factors, such as habitat heterogeneity, pollinator-mediated selection and accumulation of neutral mutations, were more important. Although populations from Uppland are young, the founder effect does not seem to have been responsible for the low level of diversity among populations. Differentiation appeared to have been limited by low habitat diversity, and a lack of time for genetic drift and for the accumulation of mutations. This study shows that patterns of differentiation within this species are indeed time-dependent.